GL for Power Evacuation

Version 2

STANDARDS/MANUALS/ GUIDELINES FOR SMALL HYDRO DEVELOPMENT

Electro-Mechanical Works – Power Evacuation and Inter Connection With Grid Sponsor: Ministry of New and Renewable Energy Govt. of India

Lead Organization:

Alternate Hydro Energy Center

Indian Institute of Technology Roorkee

May 2011

AGEC/MNRE/SHP Standards/E&M Works – Guidelines for Power Evacuation and Interconnections Page 1 with grid

GUIDELINES FOR POWER EVACUATION AND INTERCONNECTIONS WITH GRID

CONTENTS

1.0 OVERVIEW .................................................................................................................................... 3

1.1 Objective ...................................................................................................................................... 3 2.0 REFERENCES & CODES .............................................................................................................. 3 3.0 VOLTAGE LEVELS ....................................................................................................................... 3

3.1 Generation Voltages .................................................................................................................... 3 3.2 Transmission Voltages ................................................................................................................ 4 3.3 Grid Connection Criteria .............................................................................................................. 5

4.0 GENERAL CONSIDERATION FOR SWITCHING ARRANGEMENTS IN SWITCHYARDS .......................................................................................................................... 11

4.1 Inter Connected Transmission System ...................................................................................... 11 4.2 Voltage Level ............................................................................................................................ 11 4.3 Site Considerations .................................................................................................................... 11 4.4 General Miscellaneous Considerations ..................................................................................... 11

5.0 SWITCHING SCHEMES FOR SWITHYARD ............................................................................ 11 A double bus single breaker scheme .............................................................................................. 11 6.0 POWER EVACUATION AND INTERCONNECTION WITH GRID ........................................ 12

6.1 Power Evacuation Modes .......................................................................................................... 12 6.2 Requirements Power Evacuation ............................................................................................... 12 6.3 Provision in Generating Equipment .......................................................................................... 12 6.4 Isolated Operation Mode ........................................................................................................... 13 6.5 Mini grid Operation (Decentralized distributed generation facilities with local area network) .................................................................................................................................... 14

6.5.1. Government of India of policy 2005 extracts reproduced below. ................................. 14 6.5.2 Synchronization with ELC (with provision of adjustment of reference frequency) ....... 17

6.6 Grid Interconnections ................................................................................................................ 18 6.6.1 Types of Grid inter Connections ............................................................................... 18 6.6.2 System Arrangement ............................................................................................... 18 6.6.3 Voltage Levels for Interconnection ........................................................................... 20 6.6.4 Other Miscellaneous Considerations ......................................................................... 20

7.0 POWER LINES SPECIFICATION (EXAMPLE 33 KV POWER LINE) ................................... 21 7.1 Design Consideration ................................................................................................................ 21

7.1.1 General ................................................................................................................... 21 7.1.2 Relevant IS/IEC: ..................................................................................................... 22 7.1.3 ACSR Conductor ..................................................................................................... 22 7.1.4 Connectors .............................................................................................................. 23 7.1.5 H.T. Insulators ........................................................................................................ 23 7.1.6 String Insulator Hardware (Constructional Features) .................................................. 23 7. 1.7 Steel Tubular Poles .................................................................................................. 23 7.1.8 Hot Dip Galvanized MS Stranded Wire ..................................................................... 24 7.1.9 MS Stay Sets of 20 MM DIA ................................................................................... 24 7.1.10 Structural Work ....................................................................................................... 25 7.1.11 Welding .................................................................................................................. 25 7.1.12 Excavating pits for erection of 410 HT poles ............................................................. 25

7.2 Installation Guidelines ............................................................................................................... 27


7.2.1 General ................................................................................................................... 27 7.2.2 Relevant Standard .................................................................................................... 27 7.2.3 Installation Guidelines: ............................................................................................ 27

ANNEXURE-I ............................................................................................................................................ 31 ANNEXURE-II ........................................................................................................................................... 32 ANNEXURE-III ......................................................................................................................................... 42


GUIDELINES FOR POWER EVACUATION AND INTERCONNECTIONS WITH GRID

1.0 OVERVIEW

Small hydroelectric power plants are mostly located far away from load centers. It becomes, therefore, necessary to step up generation voltage through step up transformers in switchyard located near power plant and connect the same to grid substation through transmission line at a suitable point.

1.1 Objective

The intent of this guideline is to provide guidance for selecting voltage level for power evacuation, bus bar arrangement for connected switchyard, interconnection with isolated load or grid, selection of necessary protection scheme for the selected grid interconnection.. “Central Electricity Authority (Grid Standards) Regulation-2006” has also been annexed for guidance of generation as well as transmission companies.

2.0 REFERENCES & CODES

I. CEB guide for grid connection of embedded generators-2000.

II. Central Board of Irrigation and Power (India) Manuals.

III. IEEE Standard C 37101 – IEEE Guide for generator grounding.

IV. IEEE 37.95 – 2007. IEEE guide for protective reclosing.

V. IEEE Standard 242, 1996 – IEEE recommended practice for protection.

VI. REC Specification 30/1984.

VII. Central Electricity Authority (Grid Standard) Regulation-2006.

VIII. For Power Line reference of relevant ISS are given in section-12.

3.0 VOLTAGE LEVELS

3.1 Generation Voltages

Generation voltages are generally limited to following levels (CBI&P Manual) :

Generation Voltage Level • Upto 750 kVA 415 Volt • 751 to 2500 kVA 3.3 kV • 2501 to 5000 kVA 6.6 kV • Above 5000 kVA 11.0 kV

Generally terminal voltage for large generators is 11 kV in India.

The generation voltage limit of 3.3 kV may be considered for generation capacity of 2 x 750 kVA capacity with one step up transformer only, since it is not convenient to connect 7/6 runs of 3½ core 630/400 Sq. mm cable to LT side of transformer. However generation voltage of 415 V is alright for generation of 2 x 500 kVA capacity with two step up transformer one for each unit.

The size of the cable for connection of generator with generator circuit breaker and generator bus to transformer LT side for different rating is given below based on cable rating factor of 0.6aregiven in following table:


Generation Capacity

Size of Cable Remark Generator Connection to Generator Breaker

Generator Breaker to Transformer LT side

2 x 750 kVA 4 Runs of 630 Sqmm Single core cable.

7 Runs of 3½ core 630 Sqmm cable.

It is not possible to connect 7 No. 630 Sq. mm cable to transformer LT side.

2 x 500 kVA 3 Runs of 400 Sqmm Single core cable


It is not possible to connect 6 No. 400 Sq.mm cable to transformer LT side.

2 x 300 kVA 2 Run of 400 Sqmm Single core cable


It is convenient to connect 4 No. 400 Sq. mm cable to T/f LT side.

2 x 250 kVA 2 Run of 250 Sqmm Single core cable.


It is convenient to connect 4 No. 250 Sq. mm cable to T/f LT side.

3.2 Transmission Voltages

Selection of system voltage.

The selection of highest system voltage to be used at the generating step up substation depends upon the following main consideration.

• Length of transmission line from generating station to receiving substation.

• Conductor required for voltage regulation prescribed in the law of land.

• Voltage level (s) available at the receiving substation and suitability of connectivity.

• Frequency at the generating station and receiving substation.

• Power System Network of the area for stability and future extension works in the vicinity of the generating station.

• Economic consideration as cost of equipment increases with increase of voltage therefore, unit cost of power transmitted is subject to law of diminishing return. The transformers on either side of line also counter the gain, obtained from the higher voltage.

• Provision of line capacitors to increase the economic limit even at lower voltage.

The voltages are therefore selected with complete study of all factors. The transmission voltage is selected from empirical formulae and standard practices in the area, after making a complete study regarding initial and operating cost at various voltages with different size of conductors.

The voltage is selected through following two empirical formulae.

Economical Voltage V = 5.51506.1kVAL

+

Where L = Length of line in Km.

kVA = Power per phase required to be transmitted.


Economical Voltage V = 5.51003

6.1PL

+

Where L = Length of line in Km.

P = Power in kW per phase

The above formulae give an idea of voltage, but final selection is made after detailed studies.

3.3 Grid Connection Criteria

The product of installed capacity in KW and distance in KM of the substation at which the power line is to be terminated is the main criteria for selection of voltage level of power evacuation. For SHP normally following voltage level are selected as per guide lines of REC.

• 415 V

• 11 KV

• 33 KV

• 66 KV

Inter connecting lines are designed for 5 to 9 % voltage regulation both for 11kV and 33kV lines. It is general practice to work out a constant in kW-km on the basis of 1% voltage drop at 60 deg. C at different voltages and conductor size. This helps in calculating the voltage regulation quickly. The constants are tabulated below:

Table- 1 KW-KM FOR 1% VOLTAGE DROP AT 60 Deg. C

Sl. No.

Conductor 1.0 PF. 0.9 PF 0.8PF 0.7 PF 33KV 11KV 415V 33KV 11KV 415V 33KV 11KV 415V 33KV 11KV 415V

1.

Dog (63 sq.mm)

33405 - - 21248 - - 17714 - - 15152 - -

2. Racoon (48 sq.mm)

25150 - - 17500 - - 15000 - - 13091 - -

3.

Squirrel (13 sq.mm)

76 77

1.08 kVA

- 674 0.98 - 640 0.93 - 605 0.88

4.

Weasel (20)sq.mm)

11

1.63 kVA

- 970 1.41 - 900 1.31 - 840 1.25

5.

Rabbit (30sq.mm)

16883 19

2.72 kVA

12975 1490 2.18 11514 1330 1.96 10322 1200 1.78

Thus for33kV line with 48 sq mm ACSR conductor, the maximum limit is135 MW-KM at 9% voltage regulation and 0.8 PF. (Source- AHEC/PFC/Final Report/April2002)


Table-2 For 11KV and L.T. lines, the maximum kW-km at permissible Voltage Regulation are tabulated below

Sl. No.

Conductor size

Voltage KV

Maximum kW-km

% permissible Voltage Reg.

Regulation Constant

1. 13 sq mm ACSR 11 5760 9 6.40 2. 20 sq mm ACSR 11 8100 9 9.00 3. 30 sq mm ACSR 11 11970 9 13.30 4. 13 sq mm ACSR 0.415 5.58 6 5. 20 sq mm ACSR 0.415 7.86 6 6. 30 sq mm ACSR 0.415 11.76 6 7. 16 sq mm ACSR 0.415 6.96 6 8. 30 sq mm 0.415 12.06 6

(Source-AHEC/PFC/Final Report/April2002) TABLE-3 KW-KM FOR ACSR CONDUCTORS FOR 5% REGULATION

Voltage- 11KV 33KV 66KV Power Factor- 0.8 0.9 1.0 0.8 0.9 1.0 0.8 0.9 1.0 Conductor size AWG Or cir. mils

Nearest Conductor

mm

4 8

0 2/0 4/0 266500 336400

6/1/2.11 6/1/2.59

6/1/3.35 6/1/3.66

6/4.72-7/1.57 30/7/2.66 30/7/2.79

3040 4000 5280 6400 8000 10720 11520

3200 4480 6400 7040 9760

12800 14400

3840 5440 8800 10720 16000 23040 28800

27200 36000 48000 56000 72000 96000 104000

28800 40000 56000 64000 88000 115200 129600

35200 49600 80000 96000 144000 208000 256000

110400 144000 192000 224000 288000 384000 416000

114200 140800 160000 198400 224000 320000 256000

384000 352000 576000 460800 832000 518400 1024000

(Source –Bhatia’s Hand Book of Electric Engineering)

However, some State Electricity Boards follow regulation limit as 5% and 8% respectively. The load carrying capability of 33 kV and 11 kV lines is given below:

Sl. No.

Line Voltage Conductor Size

Permissible Voltage Drop

Power Which Can be Transmitted

1. 33 kV Dog 5% 91.2 MW Km 2. 33 kV Racoon 5% 75.2 MW Km

3. 11 kV Rabbit 8% 16.57 MW Km

4. 11 kV Weasel 8% 11.04 MW Km

5. 0.4 kV Rabbit 6% 14.9 HP Km 6. 0.4 kV Weasel 6% 10.2 KP Km


Following figures taken from REC Manual also show the criteria for various voltages levels vis. a vis. type and size of conductor for various PFs:

REC CONSTRUCTION STANDARD

M – 12

CONDUCTOR SIZE

kW – Km for 1% VOLTAGE DROP * 1.0 p.f.

0.9 p.f.

0.8 p.f.

0.7 p.f.

50 mm2 AAAC (7/3.15 mm) 80 mm2 AAAC (7/3.81 mm) 100 mm2 AAAC (7/4.26 mm)

15329

22398

28081

12140

16326

19268

10896

14213

16439

9868

12560

14302



B – 9

CONDUCTOR


0.9 p.f.

0.8 p.f.

0.7 p.f.

7/2.21 mm AAC 7/2.21 mm AAC 7/2.21 mm AAC 7/2.21 mm AAC 7/2.21 mm AAC

1.37

2.69

1.04

1.49

2.42

1.21

2.18

0.94

1.31

1.98

1.14

1.98

0.90

1.22

1.80

1.08

1.81

0.85

1.15

1.65



A – 9

CONDUCTOR


0.9 p.f.

0.8 p.f.

0.7 p.f.

7/2.11 mm ACSR 7/2.59 mm ACSR 7/3.35 mm ACSR

727

1048

1703

652

902

1356

617

838

1219

585

782

1106


REC CONSTRUCTIONSTANDAD

M – 5

CONDUCTOR SIZE


0.9 p.f.

0.8 p.f.

0.7 p.f.

50 mm2 AAAC (7/3.15 mm) 80 mm2 AAAC (7/4.09 mm) 100 mm2 AAAC (6/4.72 mm + 7/1.57 mm)

15327

22206

28764

11928

15894

19226

10708

13750

16267

9660

12092

14065


4.0 GENERAL CONSIDERATION FOR SWITCHING ARRANGEMENTS IN SWITCHYARDS

Main considerations for selecting a suitable and economical switching arrangement are as follows: • Inter connected transmission system • Voltage level • Site limitations • General & special considerations

4.1 Inter Connected Transmission System

The switching should fit in the planning criteria used to design transmission system. System should remain stable, if a fault occurs on line. However, impact of switching in/off of SHP in grid is insignificant as such studies for system stability are not recommended.

4.2 Voltage Level

Following points must be considered at the time of selection of voltage level for step up. • Power carrying capability of transmission line increases roughly as the square of the voltage.

Accordingly disconnection of higher voltage class equipment from bus bars get increasingly less desirable with increase in voltage level.

• High structures are not desirable in earth quake prone areas. Therefore in order to obtain lower structure and facilitate maintenance it is important to design such switchyards preferably with not more than two levels of bus bars.

4.3 Site Considerations

Practical site consideration at a particular location e.g. lack of adequate flat area of layout of equipment in the switchyard may also influence the choice in such locations. Pollution caused by location near to sea or some other contaminated atmosphere may also effect layouts.

4.4 General Miscellaneous Considerations

Other consideration in the selection of suitable arrangement and layout are given below:

• Repair and maintenance of equipment should be possible without interruption of power supply

• Future expansion of switchyard should be easily possible • In seismic prone zones height of structures should be as low as possible. • The outgoing transmission line should not cross each other.

5.0 SWITCHING SCHEMES FOR SWITHYARD

Following schemes are considered for planning and design of different types of switchyards

A double bus single breaker scheme

• A single bus single breaker scheme - Single & transfer bus - Sectionalized single bus

• A double bus one and half breaker* • Double bus double breaker scheme * • Ring bus*

*These are not considered for SHP and are generally used for EHV transmission.


6.0 POWER EVACUATION AND INTERCONNECTION WITH GRID

6.1 Power Evacuation Modes

(a) Micro hydropower stations up to 100 kW unit size with electronic load controller • Isolated operation • Grid / mini grid connected operation (provision of manual flow control is required)

(b) Mini and small hydropower plant (unit size 0.1 to 5 MW) with integrated governor and plant control with conventional manual facility/ SCADA • Isolated operation • Grid / mini grid connection

(c) Small hydropower plant (SHP) unit size 5 MW to 25 MW size having PLC based unit governor and plant control with SCADA • Grid connected operation only

6.2 Requirements Power Evacuation

• Step up voltage at generating station is to be fixed in accordance with para 3 above. • Interconnected transmission and switching scheme to be designed in accordance with

para 5 above. • Transmission line protection to be provided in accordance with prevalent schemes for

different voltage levels. The high voltage transmission lines i.e. 66 KV and above, must be disconnected both at receiving end as well as sending end by carrier or other communication signals.

• Provide for no voltage closing for receiving end breakers and synchronizing check relay closing at sending end breaker.

• It is normal practice to provide synchronizing facilities at sending end breaker of transmission line.

6.3 Provision in Generating Equipment

• Isolated and islanding operation will require adequate flywheel for stable operation for commercial load changes. This may be checked by full load rejection. The speed rise should not be more than 35% or even lower in case of special (large motor) load characteristics.

• In case isolated operation is not required flywheel effect could be reduced and the criteria of speed rise on full load rejection can be increased upto 55% - 60%.

• Excitation system for generator should have a provision for power factor control in grid connected mode. Voltage control is required for isolated mode operation as well grid connected mode operation. Before synchronizing machine with the grid voltage control mode is required and after synchronizing change over from voltage control mode to power factor control mode is required. In case of micro-hydels manual excitation control with excitation limit could be provided.

• The transformers for micro hydels for interconnection with the grid should be cast dry outdoor type as per REC specifications 30 / 1984 which corresponds to IEC 726. The transformers are suitable for harsh conditions and require less rigid maintenance schedule.

• The transformers should be connected with grounded star on low voltage side and delta on high voltage side, so that grounded neutral is provided for local load in case the SHP is shut down

The HV (33 kV) side is grounded from sending end side. HV side is protected by HV breaker installed at receiving end transformer grid substation for ground fault.

• The generator breaker and bus bar at generator voltage be provided for islanding operation.


• For 33 kV and above line side breakers should be electrically operated circuit breakers. • For islanding operations synchronizing arrangement should be made from generator

breakers as well from interconnecting LV/MV grid breaker. • Reclosing on receiving end grid breaker should be prevented/ blocked.

6.4 Isolated Operation Mode

• Isolated power supply systems using renewable technologies are emerging as technically reliable and economical option for power supply to remote and secluded places.

• For electrification of remote and secluded rural areas there are two general methods; grid extension and diesel generators. In remote areas both options are extremely costly as such renewable resource such as river based or stream based micro, mini or small hydropower plant with isolated operation mode provide low cost alternative.

For such systems following provisions in generating equipment are essential:

• Adequate fly wheel affect for stable operation for commercial load changes on full load rejection speed rise should be less than 35%

• Excitation system for generator should have provision of voltage control. In case of micro hydel manual excitation control with excitation limit can be considered.

• Electronic load controller or Induction Generator controller can be used for load variations. Fig 8 & 9 shows standard connection for isolated operation.

T I.G.

WATER SUPPLY INPUT

INDUCTION GEN.

LOAD

LEGEND:IGC - INDUCTION GENERATOR CONTROLLER

TURBINE

IGC

BREAKER

CAPACITOR BANK

FIG. 9 INDUCTION GENERATOR IN ISOLATED MODES


6.5 Mini grid Operation (Decentralized distributed generation facilities with local area network)

Micro hydels for electrification of remote rural areas should conform to following.

6.5.1. Government of India of policy 2005 extracts reproduced below.

6.5.1.1 Rural Electrification by Small & Micro Hydel Projects

The development objective of the power sector in the country is supply of electricity to all areas including rural areas as per Indian Electricity Act.

Reliable rural electrification systems with small and micro hydel projects especially in Northern states which aim at creating the following are required.

(a) Rural Electrification backbone (REDB) with at least one 33/11 kV (or 66/11 kV) substation in every block and more if required as per load, networked and connected appropriately to the state transmission system.

(b) Emanating from REDB would be supply feeders and one distribution transformer at least in every village settlement.

(c) Household Electrification from distribution transformer to connect every household on demand.

6.5.1.2 Accordingly it is suggested that as follows :

i) That 11 kV substation be provided for electrifying each village.

ii) That mini grid for micro hydels should be at 11 kV. The mini grid may be connected to REDB 33/11 kV (or 66/11 kV) substation which is if not existing may be identified for the block and the grid should be with reference to the proposed REDB.

iii) Adequate protection for successful mini grid operation be provided.

iv) In view of Govt. of India policy following provisions should also be incorporated

a) All micro hydels be provided with 415V/11kV transformer so that village electrification by 11 kV substations is feasible.

b) A 11 kV mini grid interconnecting the micro hydels should be formed so that a spare capacity are reduced and reliability of power supply is increased.

c) The 11 kV mini grid could be connected to the rural electrification backbone (REDB) in every block envisaged in the Government policy. If the REDB does not exist it could be identified and mini grid form with reference to be REDB.

d) Provision be made for grid/mini grid operation in generators, excitation system and electronic load controller for successful grid/ minigrid operation.

Special Requirements

Technical specifications have been grouped in 3 different sizes

i. Category A - 10kW;

ii. Category B –above 10 to 50kW and


iii. Category C – above 50 to 100 kW

Micro hydro for power generation category B & C should have the following provisions:-

Parallel operation in local grids whenever available.

Parallel operation with main grid whenever extended.

Micro hydropower generating station category B & C having more than 1 unit shall have following additional provisions:-

Parallel operation between units at the station

The Governor/Load Controller, AVR should have adequate provision for adjusting the Speed Droop and

Voltage Droop for facilitating the Parallel Operation of the Units.

Micro Hydel Mini Grid

i) 11 kV sub station be provided for electrifying each village.

ii) Mini grid for micro hydels should be at 11 kV. The mini grid may be connected to REDB 33/11 kV (or 66/11 kV) sub station which is if not existing may be identified for the block and the grid should be with reference to the proposed REDB.

iii) Adequate protection for successful mini grid operation be provided.

11 kV Equipment

11 kV equipment should meet Rural Electrification Corporation (REC) standards as follows.

i) 11 kV Air Break Switches as REC spec. 43/1987; IS: 9920.

ii) Sectionalizing switches be 200A/400A capacity with HRC fuses as per REC Standard F-9.

Fig 10a shows a typical metering, relaying and interconnection with mini grid

And Fig.10b shows a micro hydel minigrid single line diagram.


SEE NOTE-1

BALLSATLOADELC

Vs

F

V

As A

32

5927

81L/H

TO SYNCH.

TO MINI GRID

A.B.

ISOLATED SUPPLYFEEDER

81-L FREQ. RELAY (LOW)81-H FREQ. RELAY (HIGH)27 UNDER VOLTAGE RELAY32 REVERSE POWER RELAY

A AMMETERF FREQUENCY METERV VOLTMETERLA LIGHTNING ARRESTORkWh KILO WATT HOUR METERMCCB MOULDED CASE CIRCUIT BREAKERMCB MINIATURE CIRCUIT BREAKERA.B. LOAD BREAK SWITCH

LEGEND

NOTES

1.

2.

LA

ELC ELECTRONIC LOAD CONTROLLER

MCCB WITH SERIES OVERLOAD, INSTANTANEOUSAND RESIDUAL CURRENT PROTECTIONIN CASE OF MULTIPLE UNITS PROVIDEADDITIONAL SYNCHRONISING FACILITY FORSYNCHRONISING WITH 415 VOLT BUS

ELC SHOULD HAVE PROVISION FOR ADJUSTMNET OFREFERENCE FREQUENCY FOR OPERATION IN GRID

3.

GENERATORS SHOULD HAVE AUTOMATIC VOLTAGEREGULATOR WITH MANUAL EXCITATION CONTROL WITHEXCITATION LIMIT FOR MINI GRID OPERATION

4.

MICRO HYDEL GENERATING EQUIPMENT SHOULD BE ASPER AHEC MICRO HYDEL STANDARDS 16511.

5.

ALL 11kV EQUIPMENT SHOULD BE AS PER REC STANDARDS6.

R

OVER LOPAD

INSTANTANEOUS PROTECTION

SC

LA

MCCB(SEE NOTE-1)

A As

MCCB

SSB

kWh As AkW

Vs V

TOSYNCHROSCOPE

(SEE NOTE-1)MCCB

CURRENTTRANSFORMER

POTENTIALTRANSFORMER

MCCB/MCB

Fig 10a- A typical metering, relaying and interconnection with mini grid


415V/11kVT/F

BALLSATLOADELC

R

AB

TO VILLAGE TO VILLAGE

415V/11kVT/F

BALLSATLOADELC

R

AB

MHP-1MHP-2

L.A. L.A. L.A. L.A.

AB AB

33/11kV

RURAL ELECTRIFICATION DISTRIBUTION BACKBONE

G1G2

NOTES

MICRO HYDEL AS PER SINGLELINE DIAGRAM FIGURE1

11kV AIR BREAK SWITCHES ABAS REC SPEC. 43/1987; IS: 9920

SECTIONALIZING AIR BREAKSWITCHESREQUIRED CAPACITY WITH RECWITH HRC FUSES AS PER REC STANDARDS.

1.

2.

3.

REDB (FUTURE)

415V/11kV TRANSFORMER BE DRYTYPE AS PER REC SPEC. 30/1984

4.

L.A. L.A.L.A.

ABABABAB

MCCB

MCCB

SSB

MCCB

SSB

MCCB

11kV FEEDERS

LINEISOLATORS

11kVBUSBAR

CIRCUIT BREAKER

Fig. 10b- Micro hydel minigrid single line diagram

6.5.2 Synchronization with ELC (with provision of adjustment of reference frequency)

6.5.2.1 Procedure

• Run up turbine

• ELC regulates speed/ frequency

• Mini grid and hydro side protection sets,

• Auto synchronizer than controls ELC to bring generator and put mini grid in synchronism.

• When synchronization occurs main contactor/ breaker is closed and system is connected to grid.

6.5.2.2 Advantages of synchronization with ELC

• Provides smooth synchronization

• No need of fine control of water flow to turbine

• It is possible to synchronize at low power output in order to use small ELC e.g. 1 MW system can be synchronized at 50 to 100 kW output only.


6.6 Grid Interconnections

6.6.1 Types of Grid inter Connections

There are mainly following type of grid connections of SHP.

6.6.1.1 Power plants with substantial local load

These power plants will regularly operate in parallel with connected grid, but supply the requirements of localized industrial or other facility. The power plant and load when considered together may either be a net importer or net exporter of electrical energy from grid.

6.6.1.2 Power plants with minimal local loads

These power plants are built to harness a source of energy. These power plants are typically connected to grid through a dedicated line. Typically there will be no other customer load between the grid substation and power plant. The generators of these power plants will always operate in parallel with the grid.

There are several plant presently in operation with minimal local load which supplies the requirement of generating pant and associated residential colonies and drinking water system.

6.6.2 System Arrangement

Typical arrangement of grid connection and local feeders is shown in fig.-11.


FIG. 11


6.6.3 Voltage Levels for Interconnection

The voltage at the point of supply from the small hydropower plant shall be determined as follows:

6.6.3.1 Micro HPs with installed generation capacity upto and including 250 kVA shall be inter connected at LV distribution voltage level, if the nominal voltage of generator is 415 V line to line, three phase or 240 V line to neutral, three phase.

6.6.3.2 SHPs with an installed generating capacity exceeding 1000 kVA shall be interconnected at 11 kV or 33 kV.

For installed capacities between 250 kVA to 1000 kVA, it can be decided on case by case basis, depending on the capacity of transformer sub-station.

6.6.3.3 SHPs with an installed capacity exceeding 5000 kVA shall be interconnected at 66 kV or 132 kV depending on voltage level of nearest grid sub-station.

6.6.4 Other Miscellaneous Considerations

6.6.4.1 Voltage rise

The voltage rise due to generation at grid sub-station bus bar must be within operational limits. Generator voltage variation as per IS, IEC should be within +/-5%.

6.6.4.2 Earthing

For earthing provisions of Indian Standards IS: 2309, IS: 3043, IEEE: 80, Indian Electricity Rules and Indian Electricity (supply) Act are to be followed.

6.6.4.3 Protections

Protections and islanding based on IEEE C 37.95 are recommended for these guidelines. A typical simple scheme of interconnection for an SHP with 33 kV grid with local 415 volts feeder is shown in Fig. 11.

Minimum protection relays to ensure adequate protection of both generator as well as interconnection are shown in the figure.

The transformer is connected grounded star on low voltage side so that grounded neutral system is provided for local load in case SHP is shut down. HV (33 kV) side is grounded from sending end side. HV side is protected by HV breaker installed at receiving end transformer grid sub-station for ground fault.

(i) Transformer Protection

Fig 11shows transformer protected by transformer differential (87T), Buccholz relay (63) and high voltage side over current (50/51) and ground fault (51G) relays. In case of smaller Hydro electric plants bus differential relays could be replaced by11 KV side fuses and over current relays (50/51) on the LV side.

(ii) Transformer low voltage side bus and feeder protection

Bus differential (87B) provided can be removed and common bus & transformer differential can be provided if the local feeder load is beyond the capacity of local generation.

Back up protection for both the transformer and the feeders is provided by transformer over current relays(50/51) and (51G).The setting of these back up relays should be coordinated with the over current relay which protects the feeder(50/51)and (50N/51N)


(iii) Protection of inter connecting line

Reverse power relay (32) which can detect when SHP is not able to supply power to the grid and will operate the grid supply HV side breaker. In normal cases over voltage (59), under voltage (27) and under/over frequency (81) relay will isolate the grid from SHP in case of line outage.

Ground fault protection on the HV line should be provided by over voltage relay (59G) in open delta. A time delay can be provided to clear temporary faults.

(iv) Synchronising

Suitable inter locks, check relay, and operating procedure should be designed for following conditions.

Planned or inadvertent outage of the plant

Grid failure or disturbances

For example refer fig. 11:

Breakers 52-3 and 52-4should have facility to synchronise the

SHP to system

Dead line and synchronise check in relay should be used on

breaker 52-1&52-2

Provision of these will permit following operating procedure.

Breaker 52-1 &52-2 tripped for any fault on inter connecting line.

Breaker 52-1 should close only when it is confirmed that inter connecting line is energized.

Breaker 52-2 should close breaker 52-3 is open

If SHP is in operation and bus 1 is energized then 52-3 may be synchronized and closed.

If bus 1 is de-energised and breaker 52-4 is open, breaker 52-3 may be closed

7.0 POWER LINES SPECIFICATION (EXAMPLE 33 KV POWER LINE)

7.1 Design Consideration

7.1.1 General

i. All electrical installation shall confirm to the Indian Electricity Act, IE Rules and Regulation in force, in the state, by electrical inspectorate.

ii. Before charging the line/equipment, contractor shall submit the completion report for each part/equipment indicating rectifications/modifications carried out during erection, site test certificates with observations, rectifications carried out. Contractor shall also indicate the correctness of operational and safety interlocks. Site test certificates shall also indicate the corresponding values obtained in the factory test.

iii. The conductor/jumpers shall be correctly and effectively connected to the terminals of equipment. The connection shall be flexible to withstand stresses during switching operation.


7.1.2 Relevant IS/IEC:

1. Aluminium Conductor for overhead Transmission Purposes (ACSR/AAAC)

IS 398

2. Conductor and earth wire accessories for overhead power line IS 2121 3. Design and construction of foundation for transmission line poles IS 4091 4. Hot-dip galvanizing coatings on round steel wires IS 4826 5. Hot-dip galvanizing coatings on structural steel & allied products IS 4759 6. Porcelain insulators for overhead power lines with a nominal voltage

greater than 1000 V. IS 731

7. Solid core insulators IS 2544 IS 5350 IS 13134

8. Electric power connectors IS 5561 9. Method of testing weights, thickness & uniformity on H.D.G. articles IS 2633 10. Recommended practices for hot dip galvanizing of iron & steel IS 2629 11. Insulator fitting for overhead power lines with a normal voltage

greater than 1000 V IS 2486

12. Use of structural steel in overhead transmission lines IS 802 13. Rolled steel beams, channels and Angle sections IS 808 14. Nuts & threaded fasteners IS 1367 15. High tension structural steel IS 961 16. Hexagonal bolts & steel structure IS 6639 17. Washers Spring-

Plain-IS 2016 Heavy-IS 6610

IS 3063

18. Terminal connectors IS 5561

7.1.3 ACSR Conductor

Construction

Conforming to IS 398 (Part-II), 1996.

i. Aluminium wire made from at least 99.5% pure electrolytic aluminium rods of EC grade with copper content less than 0.04%.

ii. Steel wires uniformly coated with electrolytic high grade, 99.95% pure zinc.

iii. Steel strand hot dip galvanized with minimum coating of 250 gm/sq.m. after standing.

iv. No joints permitted in the individual aluminium wires and steel core of the conductor.

Standard length of conductor shall be 2500 meter with a tolerance of + 5%

. Material – The materials in common use for conductor and connections are ACSR conductors. The following sizes are commonly used.

72.5 kV; 30 x 2.79 + 7 x 2.79 ACSR

145 kV; 30 x 4.27 + 7 x 4.27 ACSR

245 kV; 54 x 3.53 + 7 x 3.53 ACSR

or

42 x 4.13 + 7 x 2.30 ACSR


7.1.4 Connectors

Bi-metallic connectors shall be used for connecting equipment terminals made of copper or brass, bolts, nuts and washers for connector shall be made of mild steel and shall be electro-galvanized and passivated to make them corrosion resistant conforming to requirements of BS 1706.

7.1.5 H.T. Insulators

String insulators (Constructional Features)

Suspension and tension insulators shall be wet process porcelain with ball and socket connections. Insulators shall be interchangeable and shall be suitable for forming either suspension or strain strings.

The insulator shall be such that stresses due to expansion and contraction in any part of the insulator shall not lead to deterioration. All ferrous parts shall be hot dip galvanized, the zinc used for galvanizing shall be grade Zinc 99.5% a per IS: 209. The zinc coating shall be uniform, adherent, smooth, reasonably bright, continuous and free from imperfections such as rust stains, bulky white deposits and blisters.

7.1.6 String Insulator Hardware (Constructional Features)

Insulator hardware shall be of forged steel. The surface of hardware must be clean, smooth, without cuts, abrasion or projections. No part shall be subjected to excessive localized pressure. The metal parts shall not produce any noise generating corona under operating condition.

Insulator tension string hardware assembly shall be designed with electromechanical strength of 11500 kg.

Tension string assembly shall be supplied along with suitable turn buckle (one turn buckle per string).

All hardware shall be bolted type. The tension/suspension clamp shall be Aluminium alloy.

7. 1.7 Steel Tubular Poles

The Swaged Type Steel Tubular Poles Shall conform to IS: 2713 Part-I to Part-III (1980) including subsequent amendments thereof in every respect. Poles shall be made of steel tubes having minimum tensile strength as 42 kg/mm2 and minimum percentage elongation as specified in IS: 1161 (1979).

Technical Parameters Sl. No.

Description Type of Pole SP-21 SP-23 SP-33 SP-45 SP-55

1. Total length in Met. 8.5 8.5 9.0 10.0 11.0 2. Outside Diameter & Thickness of section in mm Bottom 139.7 x

5.4 165.1 x

4.85 165.1 x 5.4 165.1 x 5.4 193.7 x

4.85 Middle 114.3 x

4.5 139.7 x 4.5 139.7 x 4.5 139.7 x 4.5 165.1 x 4.5

Top 88.9 x 3.25

114.3 x 3.65

114.3 x 3.65

114.3 x 3.65

139.7 x 4.5

3. Min. weight of Pole in kg 129.0 148.0 164.0 178.0 227.0 4. Breaking load in kgf 462.0 596.0 >=612.0 >=580.0 650.0 5. Crippling load kgf 328.0 423.0 >=435.0 >=412.0 462.0 6. Max. permissible

working load F.O.S. of 1.5 m crippling load with

218.0 282.0 >=290.0 >275.0 308.0


point of application of load at 0.3 M from top of the Poles in kgf

7.1.8 Hot Dip Galvanized MS Stranded Wire

The hot dip galvanized MS stranded wire of sizes 7/8, 7/10 and 7/16 mm etc. SWG shall conform to the following specifications:

1. Material

a) MS Wire: Used for each strands shall have the chemical composition maximum Sulphur & Phosphor – 0.055%, Carbon-0.25%.

b) Zinc shall conform to grade Zn 98 specified as per IS: 209-1966 and IS: 4926-1979 with up-to-date amendments.

2. Zinc Coating: Shall be in accordance with IS: 4826-1979 (heavily coated hard quality grade 4 as per table-1).

3. Galvanizing: Shall be as per IS: 2629-1966, IS: 4826-1979 with up-to-date amendments.

4. Uniformity of Zinc Coating: Shall be as per IS: 2633-1972 (Col. 4.2.1 to 4.2.3) with up-to-date amendments.

5. Tensile Properties: Of each strand ensuring MS wire, mechanical properties as per IS: 280-1972 Cl. 8.1 to 8.3 and after galvanizing each wire shall be of tensile strength minimum 700 N/mm2 (71 kg/mm2).

Tensile strength breaking load and elongation of each wire and full stand shall conform to IS: 2141-1968, IS: 2141-1979 in the tensile grade given above.

6. Construction: Shall be as per IS: 2141-1968.

7. Test on Wire before manufacture: As per IS: 2141-1979 (Cl. 7.1 to 7.2.2).

8. Test on Complete Strand: Test shall be conducted in accordance to IS: 2141-1979.

9. Packing: Each coil shall be between 50-100 kg packed as per IS: 2141-1968 (Cl. 9.10 6594-1979) and 2141-1979 (Cl. 11).

10. Marking: As per IS: 2141-1968 (Col. 8.1 and 8.1.1), IS: 2141-1979 Cl. 10 and 10.1).

11. Danger board for 33 kV voltage and danger mark conforming to IS: 2551-1963 shall be fixed on each location.

7.1.9 MS Stay Sets of 20 MM DIA

7.1.9.1 GS Stay Sets For Ht Lines (Galvanized Non-Painted) (20x 1800 MM)

a) Anchor Rod with one washer and nuts :-

Overall length of rod should be 1800 mm to be made out of 20mm dia MS Rod end threaded upon 40 mm length with a pitch of 5 threads per cm and provided with one square MS washer of size 40 x 40 x 1.6mm and one MS hexagonal nut conforming to IS: 1367 - 1967 and IS : 1363 :1967, and as per latest version. Both washer and nut to suit threaded rod of 20mm dia. The other end of the rod shall be made into a round eye having an inner dia of 40mm with best quality welding.

b) Anchor Plate size 200 x 200 x 6mm :

To be made out of MS plate of 6mm thickness. The anchor plate shall have at its centre 18mm dia hole.


c) Turn Buckle:

i) Eye bolt with 2 nuts : To be made of 20mm dia MS rod having overall length of 450mm, one end of the rod to the threaded upto 300mm length with a pitch of 5 threads per cm and provided with two MS Hexagonal nuts of suitable size conforming to IS : 1363 - 1967 and IS : 1367 - 1967. The other end of rod shall be rounded into a circular eye of 40mm inner dia with proper and good quality welding.

ii) Bow with welded angle: To be made out of 20mm dia rod. The finished bow shall have an overall length of 995mm and height of 450mm. The apex or top of the bow shall be bent at an angle of 10R. The other end shall be welded with proper and good quality welding to a MS angle 180mm long having a dimension for 50 x 50 x 6mm. The angle shall have 3 holes of 22mm dia each.

d) Thimble:

To be made of 1.5mm thick MS sheet into a size of 75 x 22 x 40mm shape.

e) Entire stay set shall be hot dip galvanized as per relevant IS.

f) Using stay wire of 7/10 SWG GS grade.

7.1.10 Structural Work

Design and fabrication of structural parts shall conform to the applicable provisions of the DIN standards, including DIN 19704, Hydraulic steel structures: criteria for design and calculations and DIN 4114, Stability of steel structures, unless otherwise prescribed elsewhere in these Specifications. All embedded metal shall be at least 12 mm thick and all other metal shall be at least 10 mm thick. Dimensions without tolerances shall be according to DIN 7168, Deviations for dimensions without tolerances, class "mittel", unless otherwise specified.

7.1.11 Welding

The minimum strength of welding provided on various components of 16mm dia stay sets shall be 3100 kg. Minimum 6mm filter weld or its equivalent weld area shall be deposited in all positions of the job i.e. at any point of the weld length.

The welding shall be conforming to relevant IS: 823/1964 or its latest amendment.

7.1.12 Excavating pits for erection of 410 HT poles

i. After the pit locations are finalized and peg marked on the ground, the pole pit of size 750 x 750 x 1500/1850mm be dug (9/11 Mtr. pole). The base padding of 200mm thick with 1:4:8 cement concrete shall be done before erection of pole. The earthing coil shall also be grounded 800mm below ground level by digging a separate pit minimum 4 mtr away from pole and filling the pit with soil. The pole in the pole pit shall be erected in truly vertical position and the pit is filled with 1:3:6 cement concrete mixture for size 600 x 600 x 1500/1850 mm and muffing be provided on pole upto 400 x 400 x 400mm above ground level of 1:2:4 RCC.

ii. Painting of pole with on one coat of red oxide and two coats of approved aluminium paints on portion above ground level shall be applied.

iii. For the portion buried under ground, additional two coats of Bitumen paints shall be applied.

iv. Each pole shall be earthed with MS earth rod 2500x20mm below the 800mm below ground level including fixing of 6 SWG Gl wire between rod and pole. At 60cm height above ground level by putting hole in pole and bolting with 16mm size nuts and bolts. The earth coil shall be grounded 800mm below ground level by digging separate pit and filling the pit with soil. All materials are included in tenderer's scope, as part of erection work.

7.1.12.1 Fixing cross arm, top clamps, channels etc. on the poles


The fitting such as V cross arm, top clamps, channel etc. shall be fixed on poles as per standard practice. The fabrication of above fittings shall also be done as per approved standard drawing submitted by tenderer. The general specifications of steel sections are given below :

i) V cross arm shall be made of MS angle of size 125 x 65 mm.

ii) Top clamp shall be made of MS flat of size 50 x 8, mm.

iii) Double Cross arm shall be made out of the MS channel of size 100 x 50 x 6mm.

iv) Other special fittings if required may be got fabricated as per the standard drawings of utility. The clamps for holdings the fittings shall be fabricated out of MS flat 65 x 8mm size.

All nuts and bolts used shall be of MS with combination of plain and spring washer and machine made.

7.1.12.2 Clamps and Connectors (Constructional Features)

The clamps and connectors shall be made of materials listed below:

For connecting ACSR Conductors destination

Aluminium alloy casting conforming to destination. A6 of IS: 617 and shall be tested for all test as per IS: 617.

For connecting equipment terminals made of copper with ACSR conductors

Bimetallic connectors made from aluminium conforming to destination A6 of IS: 617.

For connecting G.I. Shield wire Galvanized mild steel. Bolts, nuts and plain washers Hot dipped galvanized mild steel except for sizes

below M12 for which electro-galvanized ones shall be used.

Spring washers for items ‘a’ to ‘c’ Electro galvanized mild steel as per service conditions at least 3 of IS: 1573.

All casting shall be free from blow holes, surface blisters, cracks and cavities. All sharp edges and corners shall be blurred and rounded off. No current carrying part of a clamp or connector shall be less than 12 mm thick.

All ferrous parts shall be hot dip galvanized conforming to IS: 2629-1966.

For bimetallic clamps and connectors, bimetallic strip shall be used.

Flexible connectors, braids or laminated straps shall be made from tinned copper sheets or aluminium laminates depending on the clamp. The terminal clamps for bus posts shall be suitable for both expansion as well as fixed / sliding connection as required. Fixed / sliding feature shall be possible just by reversing the top gripper without the necessity of any additional components.

Code number for the clamp / connector shall be indelibly marked on each component of the clamp / connector, except on the hardware.

Clamp shall be designed to carry the same current as the conductor and the temperature rise shall be equal or less than that of the conductor at the specified ambient temperature. The rated current for which the clamp / connector is designed with respect to the specified reference ambient temperature, shall also be indelibly marked on each component of the clamp / connector, except on the hardware.

All current carrying parts shall be designed and manufactured to have minimum contact resistance.

Clamps and connectors shall be designed corona controlled.


The welding sleeve for the aluminium tube shall match with that of the aluminium tube to avoid unnecessary work at site after the dispatch. The length of the sleeve shall be minimum seven times the OD of the main aluminium tube.

Sleeves along with distancing pins (4 nos. per sleeve) shall be supplied

7.1.12.3 Fixing of insulators and Connected Hardware

i. Insulator shall be handled carefully in all stages of loading and individually checked for cracks, damages, loss of glaze etc. before assembling and erection at site.

ii. The 33kV galvanized steel pins made by process of forging suitable for 33kV pin insulators having maximum failing load of 10KN with small steel head as per fig. IB of IS: 2486 -1974 shall be used. The pin shall be provided with nut (hot-dip galvanized) one plain washer and one spring washer (electro galvanized).

iii. The disc insulators shall be fitted with 33kV Hardware for tensioning the conductor 33kV hardware should be fixed in the disc insulators as per the standard practice and in the correct position to bear the tension of conductor. The 33kV strain hardware fitted of aluminium alloy suitable for required conductor (ACSR) shall be used conforming to IS: 2486 (Part-II) 1989.

7.2 Installation Guidelines

7.2.1 General

The Power Line work includes Survey, Profiling, Alignment each including preparation of schedule of material, check survey profiling etc., manufacture/ procurement of electrical equipment, shop testing, packing, transportation, loading & unloading, delivery, storage at site, handling, erection, Laying Stringing & Sagging of 3 phase ACSR (Required) conductor with 7/16 SWG GI earth wire including the hosting of Disc insulator, Disc Fitting & jumpering of line by fixing of PG clamp and erection of poles pre-commissioning test and commissioning of all equipment/ system including preliminary acceptance test, performance guarantee and post commissioning services.

7.2.2 Relevant Standard

I.S CODE NO. TITLE

IS: 3043-198 Installation of Grouting/Earthing of Power Line.

IS: 2551-1963 Installation of Danger Board

IS: 398 (Part II) 1996 Stringing of Conductor

IS: 2486 (Part II) 1989 Stringing of Conductor

IS: 209 Installation of Insulators




IS: 2713 (Part I to III (1980) Installation of Steel Tubular Pole

IS: 2062-1992 Structural Steel (fusion welding quality)

7.2.3 Installation Guidelines:

7.2.3.1 Excavating pits for erection of poles

• After the pit locations are finalized and peg marked on the ground, the pole pit of size 600 x 900 x 2250mm be dug. The base padding of 200mm thick with 1:3:6/1:2:4/1:11/4:2 as per design


cement concrete shall be done before erection of pole. The earthing coil shall also be grounded 800mm below ground level by digging a separate pit and filling the pit with soil. The pole in the pole pit shall be erected in truly vertical position and the pit is filled with 1:3:6/1:2:4/1:11/£:2 cement concrete mixture for size 450 x 600 x 2050mm and muffing be provided on pole upto 400 x 400 x 400mm above ground level.

• The poles shall be erected normally with a span of 80 to 90 meters or as per standard design.

• Painting of pole with two coats of red oxide and two coats of aluminium paints on portion above ground level shall be applied.

• For the portion buried under ground, additional two coats of Bitumen paints shall be applied.

• Each pole shall be earthed with Gl pipe electrode of 50mm dia / 115 turns of 4mm dia Gl wire at 60cm height above ground level by putting 18mm hole in rail/pole and bolting with 16mm size nuts and bolts. The earth coil shall be grounded 800mm below ground level by digging separate pit and filling the pit with soil.

7.2.3.2 Fixing cross arm, top clamps, channels etc. on the poles

• The fitting such as V cross arm, top clamps, channel etc. shall be fixed on poles as per standard practice. The fabrication of above fittings shall also be done as per standard drawing. The general specification of steel sections are given below:

i) V cross arm shall be made of MS angle of size 75 x 75 x 6mm.

ii) Top clamp shall be made of MS angle of size 75 x 75 x 6mm.

iii) Double Cross arm shall be made out of the MS channel of size 100x50x6mm.

• All nuts and bolts used shall be of MS with combination of plain and spring washer and machine made.

7.2.3.3 Fixing of insulators and Connected Hardware

• Insulator shall be handled carefully in all stages of loading and individually checked for cracks, damages, loss of glaze etc. before assembling and erection at site.

• The 33kV galvanized steel pins made by process of forging suitable for 33kV pin insulators having maximum failing load of 10KN with small steel head as per fig. IB of IS: 2486 -1974 shall be used. The pin shall be provided with nut (hot dip galvanized) one plain washer and one spring washer (electro galvanized).

• The disc insulators shall be fitted with 33kV Hardware for tensioning the conductor 33kV hardware should be fixed in the disc insulators as per the standard practice and in the correct position to bear the tension o£ conductor. The 33kV strain hardware fitted of aluminium alloy suitable for Dog conductor (ACSR) shall be used conforming to IS: 2486 (Part -11)1989.

• The pit 0.4 x 0.6 x 1.6 meter shall be excavated and anchor plate with stay rod shall be suitably aligned in such a manner that the stay wire when bonded with - anchor rod and stay clamp at pole, the same shall make on angle of 30o to 45o from the pole. Cement concrete mix of 1:3:6/1:2:4/1:1½:2 shall be poured in the pit, rammed adequately and cured properly.

• The conductor shall be laid out in such a way that there is no damage to conductor/ Reels of conductor shall be handled carefully so that no damage to conductor strands occurs.

7.2.3.4 Stringing of Conductor

• Conductor shall be laid out from rotating wheel supported on jacks for easy unwinding of the conductor. Snatch blocks shall be used for stringing the conductor and shall have


grooves of a shape and size to allow early flow of conductor and ensure damage free operation. Clamps shall be used to grip the conductor at the time of stringing.

7.2.3.5 Sagging of conductor

• All conductors sagging shall be in accordance with the sag and tension tables as per relevant Indian Standards. After the conductors have been pulled to the required sag, inter mediate spans shall be checked to determine the correct sag. The conductor shall be installed on insulators secured to it by means of 6 SWG aluminium binding wire. The jumpers at the tension locations shall also be bound by 6 SWG aluminium binding wire. Before fixing the conductor on insulator and strain hardware, aluminium tape shall be wrapped on the conductor.

7.2.3.6 Guarding

• The 33kV cross arm fitted on the pole guarding line with 6SWG GI wire guard wire and 8 SWG G I wire for lacing. Guarding cross made of 75 x 75 x 6mm angle, 8 feet long shall be claimed at 300mm below the bottom arm of V cross arm.

7.2.3.7 Anti Climbing Devices

• Barbed wire weighing 35kg per pole shall be wrapped at a height of 3000mm above ground level stretching in 900mm length. Both ends of barbed wire shall be clamped suitably to avoid coming down from its location.

7.2.3.8 Danger Board

• Danger board for 33kV voltage and danger mark conforming to IS: 2551 - 1963 shall be fixed on each location.

7.2.3.9 Survey and Markings for Construction of Overhead lines

i. The preliminary survey of the line shall be done and plotted on the map.

ii. During preliminary survey, crossings / proximity to buildings and to all categories of power lines as well as telecom lines under P&T Department shall be clearly indicated in the route map.

iii. The detailed survey shall be undertaken only after finalizing the route alignment

iv. The pit marking shall then be done at the locations. Any likely discrepancy in respect of ground / building clearance shall be sorted out first, and then the work shall be started.

v. Some sites are under forest department, safety of forest property, for which forest clearance from Government, shall be got approved.

7.2.3.10 Construction:

• ACSR Conductor

Conforming to IS 398 (Part-II), 1996.

i. No joints permitted in the individual aluminium wires and steel core of the conductor.

ii. Standard length of conductor shall be 2500 mtr. with a tolerance of ± 5% shall be used.

• Clearances:

The net clearance in air for conductor, bus bars, Jumpers etc. shall not be less than as per Indian Electricity Act 200


Voltage class Ground clearance (meters)

Sectional clearance ( meters)

Not exceeding 11 kV 2.75 2.6 Not exceeding 33 kV 3.7 2.8 Not exceeding 66 kV 4.0 3.0 Not exceeding 132 kV 4.6 3.5

7.2.3.11 String insulators (Constructional Features) :

• Suspension and tension insulators shall be wet process porcelain with ball and socket connections. Insulators shall be interchangeable and shall be suitable for forming either suspension or strain strings. Rated strength of each insulator shall be printed on the porcelain before firing. Polymeric insulators may be used as per the guidelines of the Engineer in charge.

7.2.3.12 String insulator hardware (Constructional Features)

• Insulator hardware shall be of forged steel. The surface of hardware must be clean, smooth, without cuts, abrasion or projections. No part shall be subjected to excessive localized pressure. The metal parts shall not produce any noise generating corona under operating condition.

• Insulator tension string hardware assembly shall be designed with electromechanical strength of 11500 kg.

• Tension string assembly shall be supplied along with suitable turn buckle (one turn buckle per string).

• All hardware shall be bolted type. The tension / suspension clamp shall be Aluminium alloy.

• Each Insulator string shall comprise of 4 nos. disc insulator for 33kV to meet the required creepage / dry arc distance requirements.


ANNEXURE-I

No. Dia No. Dia mm. mm2

Mole 12 6.45 0.010 6 1.5 1 1.5 4.50 10.58 12.35 410 2.7050 29.0 13.8 42.8 2455 105Squirrel 8 12.90 0.020 6 2.11 1 2.11 6.33 20.95 24.44 770 1.3660 57.5 27.2 84.7 2500 212Gopher 7 16.13 0.025 6 2.36 1 2.36 7.08 26.30 30.68 955 1.0890 71.9 34.1 106.0 2000 212Weasel 6 19.35 0.030 6 2.59 1 2.59 7.77 31.63 36.90 1135 0.9047 86.6 41.1 127.7 1650 211

Fox 6 22.58 0.035 6 2.79 1 2.79 8.38 36.79 42.92 1310 0.7780 100.6 47.9 147.5 1410 210Ferret 5 25.81 0.040 6 3.00 1 3.00 9.00 42.35 49.41 1500 0.6760 116.2 55.1 171.3 1220 209Rabbit 3 32.26 0.050 6 3.35 1 3.35 10.05 52.95 61.78 1860 0.5404 144.8 68.8 213.6 1960 419Mink 2 38.71 0.060 6 3.66 1 3.66 10.98 63.06 73.57 2205 0.4540 172.9 82.1 255.0 1600 408

Beaver 1 45.16 0.070 6 3.99 1 3.99 11.97 74.97 87.42 2615 0.3820 205.5 97.5 303.0 1350 409Raccoon 1 48.39 0.075 6 4.09 1 4.09 12.27 78.84 91.94 2745 0.3632 215.9 102.5 318.4 1280 408

Otter 1 51.61 0.080 6 4.22 1 4.22 12.66 83.74 97.74 2915 0.3418 229.9 109.1 339.0 1200 407Cat 1/0 58.06 0.090 6 4.50 1 4.50 13.50 95.29 111.20 3315 0.3005 261.4 124.0 385.4 1060 409

Hare 2/0 64.52 0.100 6 4.72 1 4.72 14.16 105.20 122.70 3660 0.2722 287.6 136.7 424.3 960 408Dog 2/0 64.52 0.100 6 4.72 7 1.57 14.15 105.20 118.80 3310 0.2722 287.6 106.4 394.0 1110 438

Leopard 3/0 80.65 0.125 6 5.28 7 1.75 15.81 131.60 148.50 4120 0.2177 359.8 133.8 493.6 885 437Coyote 3/0 80.65 0.125 26 2.54 7 1.91 15.89 131.70 151.70 4645 0.2198 365.1 155.8 520.9 2020 1053

Tiger 3/0 80.65 0.125 30 2.36 7 2.36 16.52 131.50 162.10 5790 0.2203 363.4 240.4 603.8 1960 1184Wolf 5/0 96.77 0.150 30 2.59 7 2.59 18.13 158.10 195.00 6875 0.1831 437.8 289.6 727.4 1640 1193Lynx 6/0 112.99 0.175 30 2.79 7 2.79 19.53 183.90 226.80 7945 0.1575 508.1 336.1 844.2 1410 1191

Panther 252,000 129.00 0.200 30 3.00 7 3.00 21.00 211.70 261.20 9095 0.1368 587.4 388.6 976.0 1225 1196

Lion 283,000 145.20 0.225 30 3.18 7 3.18 22.26 237.50 292.90 10160 0.1219 660.0 436.6 1096.6 1090 1196Bear 314,000 161.30 0.250 30 3.35 7 3.35 23.45 264.80 326.60 11320 0.1093 732.2 484.5 1216.7 975 1187Goat 400,000 193.50 0.300 30 3.71 7 3.71 25.97 324.00 399.60 13765 0.08935 898.2 594.2 1492.4 1550 2314

Sheep 440,000 225.80 0.350 30 3.99 7 3.99 27.93 374.70 462.10 15900 0.07730 1039.0 687.3 1726.3 1335 2305

Antelope 440,000 225.80 0.350 54 2.97 7 2.97 26.73 374.50 423.10 11885 0.07606 1037.0 381.0 1418.0 1240 1759Deer 503,000 258.10 0.400 30 4.27 7 4.27 29.89 429.10 529.20 18190 0.06748 1190.0 787.2 1977.2 1165 2304Zebra 503,000 258.10 0.400 54 3.18 7 3.18 28.62 427.50 482.90 13245 0.06723 1184.0 435.0 1619.0 1090 1765Elk 566,000 290.30 0.450 30 4.50 7 4.50 31.50 476.30 587.50 20185 0.06079 1321.5 874.2 2195.7 1050 2306

Camel 566,000 290.30 0.450 54 3.35 7 3.35 30.15 476.60 538.40 14740 0.06076 1320.0 485.0 1805.0 975 1760Moose 629,000 322.60 0.500 54 3.53 7 3.53 31.77 528.50 597.00 16280 0.05480 1463.6 537.9 2001.5 880 1762

ALUMINIUM CONDUCTORS STEEL REINFORCED (ACSR)-BAREBRITISH STANDARD SIZES (METRIC) CONFORMING TO BS 215 : 1956

Equivalent to nearest copper ACSR Gross area

of aluminium

Gross area of

complete cable mm2

Approx-imate

ultimate strength

kg.

Approxi-mate

resistance at 20°C

ohms per km.

Approximate weight in kg. per km.

Approx. wt. of

standard length of cable kg.

Code Name

Dia of complete

cableStranding No. and wire dia. Mm.

Aluminium Steel

Standard Nominal copper

area (sq. in)

Aluminium SteelComplete

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Standard length of

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Area mm2SWG OR

CM


ANNEXURE-II CENTRAL ELECTRICITY AUTHORITY (GRID STANDARDS)

REGULATIONS - 2006 1. Short Title, Commencement and Interpretation

1) These regulations may be called the Central Electricity Authority (Grid Standards) Regulations, 2006 framed as per provisions under section 34, Section 73(d) and section 177(2) (a) of the Electricity Act, 2003.

2) These regulations shall come into force on the date of their publication in the official Gazette.

3) Grid Standards for Operation and Maintenance of Transmission Lines as prescribed by the Authority are given in the "Schedule" appended to these Regulations.

4) These regulations shall be reviewed by the Authority in consultation with all the stake holders as and when considered necessary.

2. Definitions

In these Regulations, unless the context otherwise requires;

1) "Act" means the Electricity Act, 2003.

2) “Appropriate Load Despatch Centre" means the National Load Despatch Centre (NLDC), Regional Load Despatch Centre (RLDC) or State Load Despatch Centre (SLDC) or Area Load Despatch Centre as the case may be.

3) “Area Load Despatch Centre" means the centre as established by the state for load despatch & control in a particular area of the state.

4) “Bulk consumer" means a consumer who avails supply at voltage of 33 kV or above.

5) Disaster management is the mitigation of the impact of a major breakdown on the system and bringing about restoration in the shortest possible time.

6) “Emergency Restoration System" A system comprising transmission towers/ structures of modular construction complete with associated components viz. insulators, hardware fittings, accessories, foundation plates, guys, anchors, installation tools etc. to facilitate quick restoration of damaged/failed transmission line towers/ sections.

7) “Islanding Scheme" is a scheme for separation of the grid into two or more independent systems as a last resort with a view to save healthy portion of the grid at the time of the grid disturbance.

8) “Standards" means "Grid Standards for Operation and Maintenance of Transmission Lines" set forth in the Schedule appended to these Regulations.

9) “Transient stability" means the ability of all the elements in the network to remain in synchronism following abrupt change in operating conditions like tripping of a feeder, tripping of generating unit, sudden application of a load and network switching etc.

10) “User" means a person such as a Generating Company including captive generating plant or Transmission Licensee other than the Central Transmission Utility (CTU) and State Transmission Utility (STU), Distribution Licensee or Bulk Consumer whose electrical plant is connected to the Grid at voltage level 33kV and above.

11) "Voltage Unbalance" is defined as the deviation between highest and lowest line voltage divided by Average line Voltage of the three phases.


The words and expressions used and not defined in these Regulations but defined in the Electricity Act, 2003 shall have the meaning assigned to them in the said Act.

3. Applicability of the Regulations

These Regulations shall be applicable to the Transmission Licensees including Central Transmission Utility (CTU) and State Transmission Utilities (STUs), Users, Appropriate Load Despatch Centres, and, Regional Power Committees (RPCs).

4. Objectives

The aim of the regulation is:

1. To ensure safe operation, security, integrity and reliability of the grid.

2. To have a coordinated operation and maintenance of transmission lines and generators.

5. Standards

All Transmission Licensee, Users, Load Despatch Centres, Central Transmission Utility (CTU) and State Transmission Utilities (STUs) and Regional Power Committees (RPCs) shall abide by the provisions of the Standards for Operation and Maintenance of Transmission Lines set forth in the Schedule appended to these Regulations.

6. Operation Planning

The Regional Power Committee shall periodically review the performance of the grid for the past period and plan stable operation of the grid for the future, considering various parameters and occurrences such as frequency deviations, voltage profile, line loadings, grid incidents, performance of system protection schemes, protection coordination.

7. Maintenance Planning

1. The annual maintenance plan for generating stations in a region and the inter-State transmission lines shall be prepared by the concerned RPCs, keeping in view the demand pattern and maintenance schedule of the generating units and diversity in demand of the States before the commencement of the financial year. The annual maintenance plan for Inter-Regional transmission lines shall be coordinated between the concerned RPCs. The coordinated generation and transmission line maintenance plan shall be reviewed and revised, if necessary on a quarterly basis and also in the monthly Operating Committee Meetings of the RPCs.

2. The annual maintenance plan of Intra-State transmission lines shall be coordinated by the concerned SLDC in consultation with the concerned intra-state transmission licensee taking into account the annual maintenance plan of generating units and inter-state transmission system decided by the concerned RFC. Concerned SLDC will also review and coordinate the maintenance plan of intra-state transmission lines for the next month, taking into account the monthly plan of generating units and inter-state transmission lines by the concerned RPC for the next month.

3. The monthly maintenance plan for generating unit & transmission line shall be implemented with the consent of the SLDC or RLDC, as the case may be.

8. Coordination in Operations

1. No element of the grid shall be introduced or taken out of the grid without the concurrence of the appropriate load dispatch centre. Only in case of imminent risk of safety of plant and personnel, can the concerned equipment be taken out without concurrence of the Appropriate


Load Despatch Centre. However the Appropriate Load Despatch Centre must be intimated of the same at the earliest along with the reasons.

2. RLDC shall inform all affected parties in case it affects their system.

9. Written Operating Instructions

1. Written operating instructions for each equipment and operating procedure for sequence of operations of power system equipment shall be available at each sub-station and switchyard.

2. The operating procedures followed shall not be inconsistent with the manufacturer's instructions regarding particular items of equipment.

3. All operators shall be aware of all the operating instructions and procedures and be capable of operating the equipment skillfully.

4. These operating instructions and procedures shall be revised whenever required.

10. Instructions by RLDCs and SLDCs

All operational instructions given by RLDCs and SLDCs through telephone, Fax, e-mail, etc shall be coded. Voice recorder shall be provided at every RLDC and SLDC for recording and reproduction of conversation with time tag/stamp. Archives may be kept at least for one month.

11. Automatic under frequency Relay

All Regional constituents shall set their under frequency (UF) and rate of change of frequency with time (df/dt). Relays in their respective .systems as per plan finalized by RPC to provide adequate relief for grid security. They shall ensure healthiness and operation of these relays at the set frequencies.

12. Islanding Schemes

Islanding schemes for separation of systems with a view to save healthy system from total collapse in case of grid disturbance if considered necessary shall be finalized by the RPCs.

13. Restoration of grid following disturbance

Regional Load Despatch Centre in consultation with Regional Power Committee and Regional Constituents shall develop procedures following grid disturbance, partial grid collapse or blackouts for enabling restoration and normalization of the grid at the earliest. State Load Despatch Centre shall also develop procedures accordingly for restoration of intra-state system. The operating procedures shall be reviewed following any addition of generating station or transmission line or at least once in two years, and revised, if considered necessary by RLDC and SLDC as the case may be. The above procedure shall be available to and followed by all concerned Users.

14. Reporting of Events Affecting Grid Operation

Any tripping of generating unit or transmission element shall be promptly reported by the respective user to the Appropriate Load Despatch Centre. Details of the respective relay indications in case of tripping shall also be furnished within two (2) hours.

15. Reporting of Grid Disturbance

All the incidents of grid disturbance shall be reported by the Appropriate RLDC to the concerned RFC and the Authority immediately.

16. Operational Data during normal operation and during grid disturbances

All real time operational data as required by the appropriate Load Despatch Center shall be furnished by the users. All data required by RPC Secretariat in discharge of the responsibilities assigned to it, shall be furnished by Regional Load Despatch Centre (RLDC). All operational


data, including Disturbance Recorder and Event Logger reports, for analyzing the grid disturbance should be furnished by ail the users within 24 hours to the RLDC and concerned RPC. All equipments such as Disturbance Recorders and Event Loggers should be kept in healthy condition, so that under no condition such important data is lost. Any other data which in its view can be of help for analyzing grid disturbance but not demanded by the RLDC or RPC, shall also be furnished by the user.

A real time display of the grid position shall also be made available to the RPC.

17. Operational Data Records

Operational data including equipment and system parameters (both manually and electronically logged) shall be preserved for at least three years. Logbooks shall be maintained by every sub-station. All operations conducted shall be recorded in chronological order. The time of each operation and occurrence of each event shall be recorded. There shall not be any overwriting. No words shall be erased from the logbook. Observations made during inspection shall be recorded in the logbooks. Important parameters and deviation of parameters outside permissible tolerances shall also be recorded in the logbook. All entries must be made in' the logbooks without any time lag. Automatic recording of operational parameters shall be encouraged. A compendium of grid disturbances shall be maintained by the appropriate Regional Power Committee.

18. Communication facilities

The communication facilities installed by the Transmission Licensees shall be as per Central Electricity Authority (Technical Standards for Connectivity to the Grid) Regulations 2006 and shall be maintained in good operating condition.

19. Safety

a) CEA (Supply and Safety) Regulations, 2006 shall be complied with.

b) Contingency procedures shall be prepared and kept handy for use of operators at each sub-station and switchyard.

c) All staff members shall be trained in safety procedures at regular intervals. The entities shall require their personnel to follow the safety rules during operation and maintenance.

d) Safety Rules shall be displayed prominently.

e) The fire fighting equipment shall be made available at all substations, switchyards and converter stations and shall be checked periodically for its upkeep. Mock exercises in fire fighting shall be carried out periodically.

20. Maintenance of Tools and Equipment

The maintenance staff of the transmission licensee must be made aware of the list of tools, devices and equipment for various maintenance and rectification works on transmission lines, sub-stations and converter stations. The tools must be readily available and certified for usage.

21. Maintenance Procedures

Maintenance procedures for each equipment shall be prepared in line with the manufacturer's recommendations and prudent utility practices.

22. Hot Line Methods

Where feasible, hot line techniques for maintenance of critical transmission lines and sub-stations shall be adopted e.g. washing, and replacement of Insulators, replacement of damaged section of conductor, replacement of hardware components. Only trained staff shall be used for such techniques. The hot line tools employed shall have necessary certification from a national or international accredited laboratory before usage.


23. Emergency Restoration System

Each transmission licensee shall have an arrangement for restoration of transmission lines of 400 kV and above and strategic 220 kV lines through the use of Emergency Restoration System (ERS) in order to minimize the outage time of the transmission lines in case of tower failures.

24. Inspection and Patrolling

1) All essential parameters which indicates the healthiness of the equipment, shall be inspected by the shift engineer once in each shift and once daily by the officer in-charge.

2) Overhead lines shall be patrolled at periodicity decided by the transmission licensee. Different patrolling schedules shall be implemented by the transmission licensees for normal terrain, vulnerable terrain and most vulnerable terrain. Patrolling schedules for ground inspection of live lines and tower top inspection of de-energized lines shall be separately issued by the licensees. Important lines shall be inspected by senior engineers after patrolling by junior staff. Maintenance works such as tree cutting and replacement of damaged insulators shall be carried out immediately after patrolling wherever required. Preventive maintenance of transmission lines shall be carried out at least once before onset of summer and once before onset of winter.

25. Maintenance Schedules

1) Traditional Time Based Maintenance (TBM) need to be replaced by Condition Based Maintenance(CBM) or Reliability Based Maintenance (RBM) as far as possible, based on criticality of equipment in order to save on the expenditure on maintenance of equipment. The periodicity of maintenance of lines shall be fixed based on whether they are passing through normal area or polluted area or coastal area. The transmission lines and sub-stations in polluted areas should be maintained more frequently. The maintenance of lines passing through all such areas should be completed once before onset of winter so as to minimize tripping under conditions of fog or due to salt deposit on insulator discs in coastal areas and once before onset of summer.

2) Maintenance and cleaning of various equipment fittings, accessories, primary instruments and sensors shall be carried out when they are de-energized during the shut-down of main equipment although the maintenance on these additional items is not due.

3) Where defects are observed through condition monitoring as given below or during patrolling and inspection, the maintenance work on various items of equipment may be proponed with reference to general periodicity schedules depending on the condition of the equipment.

26. Use of Diagnostic Techniques for Condition Monitoring of Equipment

The diagnostic methods of maintenance shall be preferred over traditional time based maintenance. For this purpose, the following, but not limited to, devices / methods shall be used.

a) Hot line puncture detection of insulators

b) Vibration measurement of the line

c) Pollution measurement of the equipment

d) Dissolved Gas Analysis of Transformer oil

e) Frequency response analysis of transformers/reactors

f) Tan 5 and capacitance measurement

g) Circuit breaker operational analyzer

h) Dynamic contact resistance measurements of breakers


i) Third harmonic resistive current measurements of surge arresters

j) Recovery voltage measurements of transformers/reactors

k) Vibration measurements of the reactors

l) Steady state and Dynamic testing of protective relays

m) Signature Analysis

n) Partial Discharge measurement for transformers/Gas insulated Switchgear

o) Static resistance meter for circuit breakers, isolators, bus bar joint, earth switches etc.

p) Ground tester for measurement of resistivity of soil and ground resistance

q) Battery impedance test equipment

r) Insulator tester

s) SF6 gas leakage detector

t) Power quality Analyzer

u) Fibre optic cable testing devices

27. Thermo - Vision Scanning

Thermo-vision scanning for hot spots on overhead lines and sub-station equipment shall be carried out at least once before onset of summer and once before onset of winter for all 400 kV lines and equipment and important 220 kV lines and equipment.

28. Failure Analysis

All cases of major equipment failure at voltage level of 220 kV and above and tower collapse shall be investigated and analysed by an expert or group of experts appointed by the Authority. Representatives of manufacturers may be invited to participate in the analysis if considered necessary. All relevant data which would help the experts or group of experts in analysing the failures shall be furnished by the owner of the equipment. The recommendations of the expert or group of experts shall be submitted to the Authority. The recommendations accepted by the Authority shall be implemented to prevent recurrence of similar failures.

29. Inventory Control and Spare Part Management

1) The required spare parts shall be kept in stock, so that at no time is the maintenance of the equipment held up for non-availability of spare parts.

2) All spare parts would be divided into 3 categories i.e. vital, essential and desirable. ABC analysis may be carried out in each category of the equipment.

3) Computerized material management system would be developed by the users to optimize inventory.

30. Maintenance Audit

1) An internal committee may be- established by the users to verify whether actual maintenance works are carried out at site in compliance of the schedules, procedures and the policy of the transmission company.

2) The observations of the Committee shall be put up to the management of the user for perusal and taking corrective action, if any.

31. Residual Life Assessment


Residual life assessment shall be carried out for all major equipments such as transformers, reactors, breakers, after the equipment has completed 80% of the life specified by the manufacturer. Accordingly, decisions may be taken by the management of the user in consultation with experts whether to replace or repair or refurbish the same.

32. Disaster Management

The maintenance staff shall be trained in disaster management. Detailed procedure for the same shall be developed. Mock exercises shall be carried out periodically. Disaster Input procedure shall be reviewed periodically. These procedures should be displayed prominently. The staff shall be trained in emergency restoration procedures for managing major failures and breakdowns. Equipment such as vehicles, diesel generating sets and fire fighting equipment and Emergency Restoration System for transmission lines shall be kept available at sub-station or at appropriate location for disaster management.

33. Maintenance Records

Records of all maintenance carried out for each equipment shall be kept. The table and formats may be so devised that the next due dates for maintenance of each item of work is clearly seen.

34. Use of New Technologies

Use of new technologies which would result in efficient and effective maintenance shall be encouraged.

35. Training

1) Every person involved in operation and maintenance of transmission lines shall be trained at the induction level and at least once in a year.

2) The shift staff shall be trained so that they are thorough in carrying out operations at each station. Every person concerned with real time operation shall be adequately trained. Every grid operator shall undergo training in real time digital simulator and a refresher course at least once in two years.

3) The maintenance personnel of every entity shall also be trained in preventive and breakdown maintenance for restoration after breakdowns of various items of equipment. The personnel must be trained in various detailed maintenance procedures.

4) Induction training and refreshment training shall be arranged as per the CEA (Safety) Regulations.


Schedule Grid Standards for Operation and Maintenance of

Transmission Lines

1. FREQUENCY

The standard frequency of system operation is 50 Hz and all efforts shall be made to operate at frequency close to nominal as possible. The frequency shall not be allowed to go beyond the range 49.0 to 50.5 Hz, except during the transient period accompanying tripping or connection of load.

2. VOLTAGE

(1) The steady state voltage shall be maintained within/the, limits given below:

Nominal System Voltage kV rms Voltage Variation 765 +/- 3% 400 +/- 3% 220 +/- 5%

132 and below +/- 10%

(2) Temporary over voltage due to sudden load rejection shall be within the limits specified below:

Nominal System Voltage kVrms Phase to Neutral Voltage kV peak 765 914 400 514 220 283 132 170

(3) For the voltage level below 132 kV, the voltage variation limits as given in (2) above shall be decided by the State Commission in the respective State Grid Code.

3. Voltage Unbalance

(1) The maximum permissible values of voltage unbalance shall be as under:

Nominal System Voltage kVrms Voltage Unbalance % 765 and 400 1.5%

220 2% 132 3%

(2) Bulk consumers shall ensure balanced load during operation.

(3) Low Voltage Single phase loads shall be balanced periodically at the distribution transformer by Distribution licensees..

4. Protection Standards

(1) The Transmission Licensee and Users shall provide standard protection systems having the required reliability, selectivity, speed and sensitivity to isolate the faulty equipment and protect all components from any type of faults, within the specified fault clearance time. Protection coordination shall be done by the RFC.


(2) Fault Clearance Time:

The maximum fault clearance times are as given below:

Nominal System Voltage kVrms Maximum Time ( in milliseconds) 765 and 400 100 220 and 132 160

(3) In the event of non clearance of the fault by a circuit breaker within the time limit prescribed in 4 (ii) above the Breaker Fail Protection shall initiate tripping of all other breakers in the concerned bus-section to clear the fault in next 200 milliseconds.

5. Criteria for System Security

The following minimum security criterion shall be followed for operation and maintenance planning of the elements of the grid:

The Grid System shall be capable of withstanding one of the following contingencies without experiencing loss of stability:

(a) Outage of one single largest generating unit of the system or

(b) Outage of a 132 kV Double circuit line or

(c) Outage of a 220 kV Double circuit line or

(d) Outage of a 400 kV Single circuit line or

(e) Outage of a 400 kV Single circuit line with series compensation or

(f) Outage of 765 kV Single circuit line without series compensation or

(g) Outage of one pole of HVDC Bipolar line or

(h) Outage of an Interconnecting Transformer

6. Transient Stability

Under any one of the following contingencies the system shall remain stable and sustain integrity (i.e., no generator shall lose synchronism and no part shall get isolated from the rest of the system):

a) Tripping of a single largest generating unit or

b) Transient ground fault in one phase of a 765 kV Single Circuit Line close to the bus or

c) A sustained single phase to ground fault in 400 kV single circuit line followed by 3 pole opening of the faulted line or

d) A sustained fault in one circuit of a 400 kV Double Circuit Line when both circuits were in service in the pre-contingency period or

e) A transient single phase to ground fault in one circuit of a 400 kV Double Circuit Line when the second circuit is already under outage or

f) A three-phase sustained fault in a 220 kV or 132 kV or

g) A sustained fault in one pole of HVDC bipolar in a HVDC Converter Station.

7. Harmonics

The voltage wave-form quality shall be maintained at all points in the Grid.

(1) In this Standard Harmonic Content limits are stipulated as follows:-

Total Harmonic Distortion = VTHD (expressed as percentage)


100xVVn

V2

1

240n

2nTHD ∑

=

=

=

'I1 refers to fundamental frequency (50 Hz)

'n' refers to the harmonic of n*1 order (corresponding frequency is 50 x

nHz)

(2) Maximum Limits of total Harmonic Distortion

System Voltage Total Harmonic

Distortion Individual Harmonic of any particular

Frequency kVrms % %

765 1.5 1.0 400 2.0 1.5 220 2.5 2.0 132 3.0 2.0

This Standard shall come into force not later than five years from the date of the publication in the official Gazette.


ANNEXURE-III

GUIDELINES FOR DESIGN AND INSTALLATION OF GROUNDING SYSTEM OF SHP up to 3 MW

Prof. O.D. Thapar, AHEC, IIT, Roorkee

1. Grounding system for Generating Stations and Step up Sub Station

1.1 Introduction

These small powerhouses are generally connected to the grid at 33 kV and below. The grounding system may be designed for the generating station and step-up sub-station as per following guidelines for the generating station and step-up sub stations. Site soil resistivity measurements, Indian Electricity Rules and design codes for safety etc. are the basis of the design. For hydropower stations connected to step up voltages for grid connections higher than 33 kV or higher than 5 MW may be designed by detailed design procedures.

2. Standards, Codes and Rules – (Latest Amended)

a) Indian Electricity Rules

b) National Electricity Code – ISI

c) IS: 3043-2001 Code of Practice for Earthing

d) IEEE std. 665 – 1995 – 2001 IEEE Guide for Generating Station Grounding

e) IEEE std. 80 – 2000 IEEE Guide for Safety in AC substation Grounding

f) UPSEB – 1978 Substation Construction Manual for substation 11/0.415 kV and

33/11 kV

3. Site Soil Resistivity Measurements and Installation

Site soil resistivity measurements may be carried out by 4 probe method to determine average resistivity as detailed in standardisation instruction attached as annexure-1.

4. Grounding System for powerhouse & Sub Station

4.1 General requirements of earthing system for generating station sand sub station

The requirements as per national electric codes issued by Indian standards institutions are summaries as follows:

a) Earthing shall be carried out in accordance with the requirements of Indian electricity Rules (Extracts at Annexure-6).

b) All medium voltage equipment shall be earthed by two separate and distinct connections with earth through an earth electrode. In the case of high and extra high voltages the neutral points shall be earthed by not less than two separate and distinct connections with each having its own electrode at the generating station or substation and may be earthed at any other point provided no interference is caused by such earthing.

c) Earth electrode shall be provided at generating stations, sub-stations and consumer premises in accordance with the requirements.

d) Each earth system shall be devised that the testing of individual earth electrode is possible. It is recommended that the value of any earth system resistance shall not be more than 5 ohm, unless otherwise specified.


4.2 Current Carrying Capacity

Any conductor, electrode or connection used in a grounding system should be large enough to carry the following currents without excessive heating:

a) Fault currents of magnitude and duration such as to produce maximum heating effect.

b) The current caused by a direct lightning stroke, or introduced by a lightning stroke may be relatively high but are usually of short duration and, therefore, generally present no problem for grounds that meet the other electrical and mechanical requirements.

c) The current that may expected to flow in the grounding system as a result of sustained neutral currents.

4.3 Control of Ground Potentials and Gradients

The grounding system should within reasonable limits, provide a low impedance path to ground for fault currents, neutral currents and lightning discharges, with uniform or near-uniform potentials of earth surfaces in the area under consideration. This result should be accomplished without the occurrence of hazardous potential differences between any surface on which a person may be standing and any surrounding structures or objects within his reach; and also without the imposition of dangerous difference of potential on equipment and circuits.

In situation where the impedance is such that potentials in the vicinity cannot be kept reasonable safe, special arrangements of grounding system should be devised.

4.4 Mechanical Reliability

The design and installation of conductors, electrodes and connections of a grounding system should be adequate to minimize the possibility of mechanical injury in order to maintain the reliability and continuity of the grounding system.

4.5 Electrical Reliability

The design and installation of the grounding system should be such as to maintain permanently the performance requirements of stated above. This point is of particular significance with regard to electrical connections.

4.6 Resistance to Corrosion

The design and installation should be suitable for preventing deterioration from corrosion. For this purpose, the installation should be compatible with the surrounding soil, atmosphere and adjacent underground plants.

4.7 Low Impedance for System Operation

The impedance of the grounding system should be sufficiently low to stabilize system potentials with respect to ground; to provide positive operation of overcurrent devices; to improve voltage regulation and to restrict neutral potentials to suitably low values in those circuits where the grounding system is required to carry portion of the neutral current.

4.8 Provision for test and Inspection

It is important that the condition of the grounding system at each installation may be known at any time. Therefore, the design of the grounding systems should be such as to permit adequate testing and inspection.

5. Grounding Material

Steel grounding material is used with provision for corrosion. Size of conductors for earthing system is given in table 4.1


Table 4.1

Equipment Buried conductor

Conductor above ground & in trenches

Main station grid 25 mm dia & 2.5 m long MS rod; 50 x 6 MS flat

50x6 mm GS flat

Switchgear/MCC -- 50x6 mm GS flat

415 V distribution boards -- 50x6 mm GS flat

HT motors -- 50x6 mm GS flat

LT motors above 125 kW -- 50x6 mm GS flat

LT motors - 25 to 125 kW -- 25x6 mm GS flat

LT motors - 1 to 25 kW -- 25x3 mm GS flat

Fractional HP LT motors -- 8 SWG GS wire

Control panel & control desk -- 25x3 mm GS flat

Push button stn. & Junction box -- 8 SWG GS wire

Cable trays, cols. & structures -- 50x6 mm GS flat

Bus duct enclosures -- 50x6 mm GS flat

Rails & other metal parts -- 25x6 mm GS flat

Eqpt. earthing for switchyard equipment

-- 50x6 mm GS flat and 50x6 mm GS flat

6. Generating Station Grounding

6.1 Design objective in generating station grounding are as follows:

a) Provide safety ground for protecting personal from injury.

b) Equipment ground to trip faulted circuit for protection and alarm

c) Neutral ground to provide ground reference of electrical system

d) Minimum noise interference in control and instrumentation system

e) Lightning protection

6.2 Ground Grid Design

Difference between substation and generating station grounding grid design are as follows :

Persons inside the power house are not exposed to many of the step and touch voltage condition of sub-stations. IEEE guide 665 recommended that separate grid for step and touch voltage criteria is not required in generating station.

Outer grid conductor comprising the largest rectangle enclosing the power house should be provided.


High voltage sub-station, if located on the generating station site, the sub-station ground mat should be interconnected with generating station grounding grid.

6.3 Design of grounding System for Generating Stations at Medium Voltage with 11 kV substation

As per IS Medium voltage (415 vlots) generators require earthing by 2 separate and distinct connections with earth. Further neautral ground is to be provided for reference of elertcrical system. Normally neutral is grounded through resistance and ground fauklt current is limited by the resistance. Therefore three electrodes are sufficient.

Further step up substation if at 11 kV also requires three electrodes for earthing and lightning arrestor.

6.4 Generating Stations at high voltage with step up voltage at 33 kV

a) Provide outer grid conductor comprising largest rectangle enclosing powerhouse

b) Provide interconnection with step up station

6.5 Generating Stations Grounding Recommended

For purposes of uniformity design as per Para 6.4 may be adopted for all generating stations. A typical example is shown as Annexure 2 (a). Grounding design for Belsar Power Station which have two units of 415 volts is shown in Enclosure 2 (b).

7. Design of Grounding System of sub station

7.1 General

The modern practice of earthing of substation is by means of ground mat. Earth strips of recommended size are laid horizontally and inter-connected to form a mesh or mat. The mat is buried below the ground. The equipment to be earthed are directly joined to mat. The mat itself is earthed by earthing electrodes which are driven vertically into the ground.

7.2 Allowable Values of resistance of Grounding System

It is recommended that earth resistance of grounding system for 33/11 kV substations should not be more than 2 ohms and that for 11 kV sub stations and power house not more than 5 ohms.

7.3 Earthing of Substation at 11 kV

11 kV substation may be earthed as per CBI & P Guidelines enclosed as Enclosure 3 and 4 (c). 33 kV substation may be earthed as per UPSEB guidelines as Enclosure 4 a, b, c, and d.

8. Installation of Grounding System

Installation of Grounding System shall be as per Guidelines enclosed as Annexure 5.

9. Testing of Earth Resistance

Earthing should be tested once in a year in the month of May/June and proper record of the same should be maintained.


Enclosure -1

SOIL RESISTIVITY MEASUREMENTS 1. Soil Resistivity Measurements

1.1 Period of Tests: Estimates based on soil classification permits only a crude approximation of the resistivity. Therefore for obtaining an accurate data on the soil resistivity, field tests at the site are very essential. Further in order to know the effects of temperature and moisture content, the tests may be performed in the hottest month of June before rains; then sometime in the month of September and again in the coldest months of December/January.

1.2 Test Locations: The area at the station site should be covered adequately by conducting resistivity measurements at several positions as shown in Fig. 1.1; and with different probe spacings to get an indication of any important variations of resistivity with location or depth.

1.3 Extent of Probe - Spacings: It can be shown that the portion of the earth, which has an influence on the station ground resistance, extend down to a depth roughly equal to the station equivalent radius “r” (the radius of a circle, having the same area as the station grounding net-work). This means that to establish the nature of the soil at a given site for grounding design; the resistivity tests should be performed, as far as practicable, with probe spacings upto the station equivalent radius.

1.4 Formulae for equal probe spacing: Resistivity measurements should be done by the conventional 4-probe method described by Dr. F. Wenner of the U.S. Bureau of Standards. This consists of driving two current probes and two intermediate potential probes into the earth at equal distance apart and in a straight line, to a depth, as shown in Figure 1.2. An earth tester circulates a current I between the outer two probes. Due to this current, a potential difference is established between the two potential electrodes equal to I x R where R is the resistance of the earth between the potential electrodes. The ratio IR/1 i.e., the resistance of the portion of the earth between two inner electrodes is indicated directly on the earth tester. Using this value of the resistance, the resistivity of the soil is found out from the equation.

2222 44

2

4

211

4

ZS

S

ZS

SSR

+−

+

++

=πρ …… (1)

Where,

ρ = resistivity of soil in ohm-meters.

R = resistance measured on the instrument in ohms.

S = Probe spacing in meters.

Z = depth to which probes are driven, in meters.

(ii) When Z is less than 1/15th of the probe spacing; the foregoing equation can be further simplified to

SRπρ 2= …… (2)

(iii) For very large probe spacings equal to station radius “R”, which might easily be several hundred feet, 4-electrode method with equal probe spacings of that order is hardly practicable. Further, One short-coming of this method has been the rapid decrease in magnitude of potential between the two inner probes, when probe spacing is increased to relatively large values. This has often resulted in inadequate sensitivity and inability to


obtain low resistivity readings at wide probe spacings because of the range of limitations of test instruments.

1.5 Formulae for unequal probe spacings

(i) A method of expanding the range of measurement and thus improving sensitivity, is by increasing the potential probe spacing as described by L.S. Palmer and A.L. Kinyon. The spacing is increased equally in each direction, keeping each potential probe a like distance from its adjacent, current probe as shown in Fig. 1.3 and the resistivity is calculated from the formulae.

QSSR +

=2

πρ …… (3)

Where,

ρ = the measured resistivity of soil in ohm-meter

S = distance from C1 to P1 and C2 to P2 in meters

Q = distance from P1 to P2 in meters

R = instrument reading in ohms

(ii) The above equation cal also be written in the following form.

aR.2

1 2

ααρ −

= …… (4)

Where,

α = ratio of distance between potential electrodes to that between current electrodes

A = one-half distance between current probes

1.6 Testing Kit

A soil resistivity testing “Kit” should consist of

i) 4-terminal Megger Earth Tester range 0-2; 10;100;1000;10000 ohms 1 No.

ii) Electrodes, about one meter long …… 10 Nos.

Note : The electrodes should have cross-bars welded near the top of the rod of facilitation their extraction from the ground.

Leads, P.M.C./ insulated; 2.5 mm2 (1/1.80 Al.)

150 meters reel …. 1 No.

75 meters reel …. 2 Nos.

iii) Short instrument leads.

iv) Sledge hammer, 5 to 8 lbs. 2 Nos.

v) Measuring tape 100 ft… 1 No.

vi) Tools-pliers, wrenches, clips etc.

Note : For test connections; test procedure and correction factors if any; reference should always be made to the instruction booklet supplied with the instrument.


1.7 Earth Resistivity Curves

For a homogeneous soil, the value of resistivity thus obtained will be independent of the probe spacing. In actual fact, the ground is never homogeneous. There may be wide horizontal changes and significant vertical variations in the soil structure. However, as the lateral changes in the composition of soil are usually small and gradual, compared with vertical ones; the soil resistivity is normally considered as a function of depth only.

Further in a 4-probe method, the penetration of current and hence the resistance is roughly limited to a depth corresponding to the probe spacing. Thus more frequently than not, the resistivity as measured by the 4-probe method will vary with probe spacing. This variation usually indicates, a soil resistivity, which varies with depth. A plot of the measured resistivity should therefore be drawn against the probe spacing known as “Earth Resistivity Curve”. At a particular site, a number of such curves are drawn for different locations as shown in Fig. 1.4 and an average curve is evolved. This average resistivity curve is then analysed.

Resistivity measurement records should include temperature data and information as to the dry ;or moist condition of the soil at the time the resistivity is measured. Metallic objects (like rails, pipes, wires etc.) buried, or in contact with the soil can invalidate readings made by the method described above, if they are close enough to alter the test current flow pattern appreciably. All date available on burried conductors known or suspected to be in the area studied should therefore be recorded and tests should be done at such locations twice, with probes in two mutually perpendicular directions.

1.8 Uniform (Homogeneous) Soil

If the variation in the resistivity is less than 30%; ;the soil in the vicinity of test location can be considered homogeneous and an average value determined from the resistivity curve is adopted for design purposes. If the variation is more than 30%, the soil cannot be treated as uniform and the analysis of the curve is needed.

1.9 Non-Uniform Soil

In the non-uniform soil, where the soil resistivity varies markedly with probe spacing, a designer would like to know the value of apparent soil resistivity “ρa” that he should adopt for the design purposes; so that the calculated resistance of the grounding system approximately equals the measured resistance after the installation of the grounding system. This may be done in accordance with C.B.I.P. (Central Board of Irrigation Power) manual No.

Conductor for earthing mat and work steel flats with proper allowance for corrosion are used. – Standard sizes of conductor for earth mats as per IS 1730-1989 as follows:

i) 10 x 6 mm2 ii) 20 x 6 mm2

iii) 30 x 6 mm2 iv) 40 x 6 mm2

v) 50 x 6 mm2 vi) 60 x 6 mm2

vii) 50 x 8 mm2 vii) 65 x 8 mm2

ix) 75 x 12 mm2


Fig. 1.1 Resistivity Test Locations

Fig. 1.2 Measuring Earth Resistivity with Equal Probe Spacing


Fig. 1.3 Measuring Earth Resistivity with Unequal Probe Spacing


Fig. 1.4 Resistivity test Curves for the Month of June


Enclosure -2 (a)

11kV SWITCHGEAR PANEL ROOM

LA LA

TFR TFRRISER TOGTTB-1 RISER TO

GTTB-1

RISERTO GN-1

RISERTO GN-1

RISERSTO GN-2

GROUND ROD(SEE NOTE-7)


RISER TOGTTB-2

TRC

25200

3000 3000 3000 3000 3000 3000 3000 3000600

800

6000

4000

600

8800

830015003000

4000

4000

4000

4000

500

500

4000 4000 4000 4000

750 750

LALALA

250

A A

RISER TOGTTB-2


GROUND MAT & NETWORK

CL

NOTE

PENSTOCK PIPES BE BONDED WITHGROUNDING GRID

GROUND ROD

FALT (EMBEDDED)

BONDING BY 50 x 6 MM STRIP

PENSTOCK PIPES


Enclosure - 2(b)


Enclosure - 3

Fig. 1: 11 kV/433-250 V, Distribution Sub Station Location of Earthpits and Connections (Modern Trends and Practices in Power Sub-Transmission and Distribution Systems)

Fig. 2: Grounding Arrangement for 11 kV Sub Station


Enclosure -4 Sub-Station Earth Mat for 33 kV Sub Station (UPSEB Practice) For 33 kV Substation having capacity upto 10 MVA the earth mat be designed as per drawings given below (UPSEB Guidelines):

Sl. No. Soil resistivity Size of Earth Mat Drawing No.

1. 20 to 70 ohm-meters 22 M x 24 M 4 (a) 2. - DO - 16 M X 32 M 4 (b) 3. Upto 250 ohm-meters 21 M X 42 M 4 (c) 4. Earthing Arrangements as per

CBI & P 33/11 kV Sub station 4 (d)

Except in the hill regions, the soil resistivity generally varies from 20 to 70 ohm-meters. Thus the actual resistance of sub-station earth mat will be even less than 2 ohms. At each substation soil resistivity should be measured by 4 electrodes method. Where it is within the range, the proposed earth mat may be laid. However, it is more than 70 ohm-meters the earthing system will have to be designed separately.


Fig. 4 (a) : Grounding Arrangement for 33 kV S/S with feeders at Right Angle to Busbars (for layout of S/S)


Fig. 4 (b): Grounding Arrangement of 33/11 kV Sub-Station with Two Feeders


(parallel to bus bar) in opposite Direction

Fig.4 (c) : Grounding Arrangement for 33/11 kV S/S with Earth Resistivity 250 ohm-meter

Fig. 4 (d) : Earthing Arrangement in 33/11 kV Substation (CBI & P -Construction Practices – Sub Station)

AHEC/MNRE/SHP Standards/E&M Works – Guidelines for Power Evacuation & Interconnections with Grid 59

Enclosure -5 INSTALLATION INSTRUCTION

1.1 Introduction

This instruction lays down the method of grounding system including layout of grounding system in small and large hydro stations. These instructions primarily pertain to the grounding system with steel grounding strips as the main conductor. The instruction outlined herein are issued to:

i. Assist the work of designer by avoiding repetition of grounding details of layout drawings, as these details can be better referred to in here, with considerable saving in time.

ii. Assist the field authorities to arrive at on the spot decisions necessary during installation.

1.2 Code Applicable

The grounding shall generally be carried out in accordance with the requirements of Indian Electricity Rules as amended upto-date & in accordance with I.S. 3043-1987 as far as practicable.

1.3 Installation of Grounding System

1.3.1 General:

i. Grounding conductors shall consist of mild steel strips for ground net-work and mild steel rounds for ground rods.

ii. Grounding strips used for end connections to the equipment are galvanised.

iii. Connectors like bolts, nuts, etc. used for grounding the equipment are galvanised.

1.3.2 Ground Mats and Test Terminal Boxes

i. All grounding strips in the ground mats are laid in position as per typical methods shown in Annexure-I figure 7&8, unless otherwise stated. When the grounding strips have been laid in trench, it shall be covered with excavated base material mixed with clay if possible and filled upto half the depth of the trench. The remaining half of the trench shall be filled with lean concrete so that the strip remains securely in position. A thick coat of bitumen may be applied over it if necessary so that it does not bond with the concrete which may be placed over it.

ii. The ground rod are fixed in position first by drilling a vertical hole of about 70 mm dia into the ground, then placing the rod centrally inside. Drilled base material mixed with clay, if available, are then poured into the hole all around by little and compacted at short intervals by ramming with a suitable dia hollow C.I. pipe having a socket at the lower end. In locations where there is clay or soft soil, the ground rods can be driven in the ground by an augur (figure 6).

iii. In the installation of grounding strip the field authorities are in a better position than the designer to judge whether the mat is adequately anchored. They should feel free to add additional anchors but should never use less than those indicated on the drawings.

iv. For rust protection, welded joints in the soil shall be thoroughly brushed, provided with a coat of shalimastic H.D. paint and wrapped with asphalt saturated cotton fabric tape/hessian cloth impregnated with shalimastic H.D. Paint followed by another coat of shalimastic H.D. paint.

Alternatively welded joints may be protected by grouting concrete of not less than 40 mm thickness.


1.3.3 Grounding Net-Works

i. Installation of grounding strips are carried out in accordance with the grounding system network drawings, but field may deviate to clear possible obstructions keeping in view the technical requirements.

ii. The route of embedded grounding strips between two connected points are by the shortest distance.

iii. Main grounding strips inside the power plant building are laid surface embedded on the walls as per Figure 13 so that these can be tapped easily later on for connection to the individual equipment, which may or may not have been covered in the net work drawings.

iv. Embedded equipment such as frames for lighting distribution boards, power outlets, misc. raceases etc., are grounded by electricity welding the grounding strip to such equipment. For all other equipment, which is to be installed at a later stage, grounding strip stub of at least 3000 mm length is provided near such equipment for grounding. For equipment fixed on the wall, stubbing should be from the wall and not from the floor or the tapping for this purpose shall be taken from the surface embedded grounding strip on the walls by an exposed grounding strip. It means that any tapping for grounding purpose taken only from grounding ring laid surface embedded on the walls.

v. Cable racks on the walls and in cable trenches is welded directly to the grounding strips provided for the purpose. Cable racks installed on the floor and fixed under the ceiling is grounded at two points. ( preferably entrance ends) and the different sections of the racks is bonded separately by a grounding .. to ground the entire cable rack effectively.

1.4 Jointing of Grounding Strips

All joints between grounding strips and between grounding strips and ground rods shall be by electrical welding. At the time of welding, the jointing surface is cleaned by sand blasting or by other convenient means. The joint is clamped tightly to ensure that a good surface contact exists. Typical details of welded joints are shown in figure 1, 2, 3, 5 & 8.

1.5 Connections To Equipment

i. Exposed surface of all electrical equipment must be grounded and non-electrical items like mat hand-rails, hauch cover frames. Cable rack support etc., should be grounding. In reinforced concrete structure most structural elements such as windows, frames, grills and louvers need not be grounded. Economy does not permit grounding of metal parts.

ii. The frame of every generator, motor, circuit breaker and the metallic parts (not intended as conductors) of all transformers, and regulating or control apparatus connected with the supply shall be grounded by two separate and distinct connections.

iii. The metal conduits, armour and/or sheath of a cable may be used as ground conductor and should be earthed at one point only (preferably at the source end) in the following cases : -

a. Conduit, armour and/or lead sheath of single phase cable.

b. In long runs, insulating sleeves are occasionally installed in the lead sheath, thus breaking up long sections and reducting sheath potentials. Each section of the lead sheath should be grounded. Grounding the same lead sheath of a single phase cable at both ends intentionally or accidentally may over heat the cable and should be avoided.


iv. Three phase cables shall have the lead sheaths grounded at both ends in all cases.

v. Metallic junction or pull boxes not containing protective equipment, and in which conduits are installed with a socket and metallic bush are not considered a break, when the voltage is below 240 volts to ground, but shall be so considered for higher voltages.

vi. All junction and pull boxes in the runs of non-metallic conduits as well as these containing overload protective devices are individually grounded.

vii. All paint, enamel, and scale is removed from the point of contact on metal surfaces before making ground connections.

viii. In switchyard any items of equipment not covered by grounding system layout drawings and which are so located that there is some chance of a high-tension conductor flashing to or coming in contact with them must also be grounded with individual connections.

ix. Where some arrangement for grounding is already provided on the equipment by manufacturers, that arrangement should be used for grounding if suitable for the size of grounding strips specified in the net-work drawing concerned. The mode of connection may not be the same as shown in typical equipment connections.

x. The bases of lightning arrestors are directly connected to the grounding test terminal box (G.T.T.B.) of SYSTEM by grounding strips as short and straight as practicable to ensure minimum impedance.

xi. For lightning arrestors mounted near the transformers, grounding strips are located clear of the cable and coolers in order to avoid possible leakage caused by arcing.

xii. Typical grounding strips connections to various equipment are shown in Figure 4, 9, 10 & 11.

1.6 Precautions

i. Grounding strips should never be run through a steel conduit or through an opening in the floor or walls of magnetic material. It may be run in either fiber conduit or conduit of non-magnetic material.

ii. Grounding strips should never be laid close to or parallel to generator single-phase main-leads or single core power leads and the distance or separation should not be less than 300 mm. This will be shown on the drawings concerned.

iii. Current transformer secondary circuit should never be grounded at more than one point.

1.7 Ground Mat Resistance

After the grounding system is laid, actual measurement shall be taken and remedial measures if any required will be devised by the field to bring down the resultant grounding resistance within safe limits.

1.8 Installation/Details (Figure 1 to 14)

NOTES

1. All dimensions are in mm unless otherwise stated

2. All joints between ground strips and ground rod should be made electrical welding. at the time of welding the jointing surface should be cleaned by sand blasting or by other convenient means. The joint should be clamped tightly so that a good surface contact exists.

3. For straight joints between ground strips an overlapping not less than twice the width of plate should be made for welding typical angle joints and t-joints are shown in


figure-3 and figure-4 respectively. Typical welded connection between ground rod and ground strip is shown in figure-9.

4. Main grounding strips ring in side the power plant building should be laid surface embedded on the wall as shown in fig-14. So that these can be tapped easily later on for connection to individual equipments, which may or may not have been covered in the network drawing.

5. The frame of every generator, motor, control panels and the metallic parts of all transformer connected with the supply should be grounded by two separate and distinct connections.

6. Any tapping for grounding purpose shall be taken only from grounding ring surface embedded on the walls.

Fig. 1 - Welding Detail of Straight Joint (Typical)


Fig. 2 - Welding Detail of Angle Joint (Typical)

Fig. 3 - Welding Detail of Tee Joint (Typical)


Fig. 4 - Welding Connection to Exposed Cabinet


Fig. 5 - Welding Detail of Cross Joint (Typical)


Fig. 6 – Installation of ground Rod (scale 1: 25)


Fig. 7 – Installation of Ground Strip of Ground Mat (scale 1: 5)


Fig. 8 – Welding Detail of Connection Between Ground Rod and Grounding Strips (typical)

Fig. 9 – Welded Connection to Recess Frame


Fig. 10 – Bolted Connection to Extention Leg

Fig. 11 – Bolted Connection to Base Plate


Fig. 12 – Details GTTB


Figure 13


Figure 14


Enclosure-6

Provision of Indian Electricity Rules 1956 – Regarding earthing for medium voltage Generators (extracts)

Connection with Earth

1. The following provisions shall apply to the connection with earth of systems at low voltage in cases where the voltage normally exceeds 125 volts and of systems at medium voltage:-

a) Neutral conductor of a 3 phase, 4 wire system and the middle conductor of a 2 phase, 3-wire system shall be earthed by not less than two separate and distinct connections with a minimum of two different earth electrodes or such large number as may be necessary to bring the earth resistance to a satisfactory value both at the generating station and at the sub-station. The earth electrodes so provided, may be inter-connected to reduce earth resistance. It may also be earthed at one or more points along the distribution system or service line in addition to any connection with earth which may be at the consumer' s premises.

b) In the case of a system comprising electric supply lines having concentric cables, the external conductor of such cables shall be earthed by two separate and distinct connections with earth.

c) The connection with earth may include a link by means of which the connection may be temporarily interrupted for the purpose of testing or for locating a fault.

2. The frame of every generator, stationary motor, portable motor, and the metallic parts (not intended as conductors) of all transformers and any other apparatus used for regulating or controlling energy and all medium voltage energy consuming apparatus shall be earthed by the owner by two separate and distinct connections with earth.

3. All metal casings or metallic coverings containing or protecting any electric supply-line or apparatus shall be connected with earth and shall be so joined and connected across all junction boxes and other openings as to make good mechanical and electrical connection throughout their whole length. Provided that where the supply is at low voltage, this sub-rule shall not apply to wall tubes or to brackets, switches, ceiling fans or other fittings(other than portable hand lamps and portable and transportable apparatus)unless provided with earth terminal and to class-II apparatus/appliances.

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