AC Supply System_Std

7/31/2019 AC Supply System_Std

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24 May 2012 PMI Revision 00 1

AC SupplySystem


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Importance of Elect System for Auxiliary

Classification of Auxiliaries

Choice of Voltage for Aux

Aux. Power supply system

Emergency AC Supply

Presentation outline


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Auxiliary Power Supply System

The purpose of an Electrical system is to generate andsupply electrical energy .

The system should be designed and managed to deliverpower with Reliability and Economy.

As these two requirements are quite opposed a balanceis required to have an optimum design of Auxiliary powersupply system

The auxiliaries have Ratings range from a few watts to

few Mega Watts & Located over a large areaWork under varied Operating Conditions


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Auxiliary Power Supply System

Failure of Auxiliaries can cause Outage of Power Plant

Auxiliaries need Reliable Power Supply

System designed to cater to this need

Loads segregated on the basis of

Rating (to decide Voltage)

Location (to decide the

Feeding Point) Change-over schemes & Alternate Power Supply arrangement

to ensure Reliability


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Elements of Aux. Power System

More than 95% of the auxiliaries are driven by Motors

Different Voltage levels are interconnected through

Transformers

Miscellaneous Elements

Incomers

Ties

Diesel Generators


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Voltage Rating of Motors Decided based on kW

Rating Rating 160kW 415V (LV), Contactor

> 160kW & 200kW 415V (LV), Breaker > 200kW & 1500kW 3.3kV (MV), Breaker > 1500kW 11kV (MV), Breaker

Frequent Start / Stop Operations (Coal Conveyor Motors) MV Vacuum Contactor

List of Boards / Feeding Points arrived at based onLocation of Load Centers / Systems

Quantity & Rating of Transformers calculated based on

Load & Operational Requirements Rating of Board Calculated based onthe Operating Load &

Transformer Rating


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Nominal System voltage 6.6kV 11kV 3.3kV

Highest System voltage 7.2 kV 12kV 3.6kV

Rated Frequency 50Hz 50Hz 50Hz

Number of phases/ poles Three Three Three

System Neutral Earthing Earthed through Resistance of 6.35 toLimit E/F Current to 300A

One minute power frequencywithstand voltage

20kV 28kV 10kV

Impulse withstand voltage 60kV (peak) 75kV (peak) 40kV (peak)

Maximum System Fault Level 40kA (rms)

Short time rating of Eqpt. 40kA (rms) for 1 second

Dynamic withstand rating 100kA (peak)


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Nominal System voltage 415V, 10%

Rated Frequency 50Hz

Number of phases Three

System Neutral Earthing Solidly Earthed

Maximum System Fault Level 45kA (rms)

Short time rating of Eqpt. 45kA (rms) for 1 second

Dynamic withstand rating 105kA (peak)


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Sizing of Unit & Station transformer

Start up power

Feeding offsite areas loads

Rating of the Switchgear

Loads

Power Supply arrangement

6.6& 0.415kV System

11 & 3.3 & 0.415kV System


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Commonly used voltage level up to 200 MW unitsize- 6.6kV, 415V

Initially same voltage level (6.6 kv, 415v) were adopted

for 500 MW unit size as well.With 500 MW unit, quantitative and qualitative change

in auxiliaries took place. (11 kv Switchgear)


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Grid Voltage- Normally 400kV for most of the200,500MW units in India except few deviations

Any Intermediate Voltage Available-to providereliable start-up power source and to meet initialcommissioning activities as well as to supply bulk

loads(CW system, make-up water etc.) away fromthe main plants.Generally used Intermediate voltagelevels are 220kV, 132kV, 33kV

Nature of Auxiliaries i.e. ratings, basic

characteristics and location


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G

UAT-A Dyn1

UAT-B16.5 KV

6.6 KV Ynd11

GT

Ynyn0

Station TRF-1

UNIT SWGR--AUNIT SWGR--B

Stn. SWGR-SA SB

UST

A

ESP TRF-AS/Serv.Trf.-B

UST-B ESP TRF-B

USS-A USS-B 415 V Unit EMG SWGR

X

From DG SWGR

XBlr MCC

Turb MCC

BFPID Fan

Air Compr

Trf

X X

X

Stn Serv

Trf-ADMP Serv

Trf

1)SWYServ

Trf-1

2)Ash

Handl T/

1600KV

6.6 KV

B.C.

N.O.

TMCC

Fdr to

Clarif

Water

SWGR


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Transformer feeder Details

To PMCC

MCC/PCCMediumVoltage

MagneticContactor

SFUCB

To ACDB

Motor Feeder

Unit ServiceTransformer

To PMCC

MagneticContactor

SFU

To ACDB

Motor Feeder

Dyn11

C.B.

415 V

6.6 KV


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X X

X X

X XX X

DG-1DG-3

DG-2

DG SWGR-1 DG SWGR-2

UNIT EMER

SWGR-1 UNIT EMER

SWGR-2

UNIT EMER

SWGR-3

UNIT EMER

SWGR-4


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(1) AOP-1 (2) Em. Lighting Trf.

(3) TVDC Reserve Supply (4) UPS Ch.

(5) Scanner Air Fan (6) BVDC Reserve Supply

(7) AC Seal Oil Pump (8) Air Heater Lub Oil Panel

(9) Jacking Oil Pump (10) Stator Water Pump-B

(11) Barring Gear (12) +26 v DC ATRS Ch. B(13) -26V DC ATRS Ch.B(14) 26V DC FSSS Ch. B

(15) 26V DC DDC Ch. A


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(1) BFP-1C (2) BFP-1A

(3) PA Fan-1A (4) ID Fan -1A

(5) UST-1A (6) ESP T/F -1A

(7) FD Fan -1A (8) Coal Mill- 1A, C, E

(9) CEP-1A,C (10) ACW Booster Pump-1A

(11) Bus V.T.


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(1) Unit Em. SWGR (2) Boiler MCC

(3) BVDC A (4) Turb. MCC A

(5) 220V Dc Ch. A (6) +24 DC ATRS Ch. A

(7) -24V DC ATRS Ch.A (8) Turb ACDB A

(9) +24 V DDCMIS Ch. B (10) Gen Control Panel

(11) Boiler ACDB A a) Grav. Feeder A,B, C,D,E,Fb) S/B MCC Feeder-1

c) INC From USS B

(12) MOT Centrifuge


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(1) UPS Ch. (2) +24V FSSS Ch.

(3) TVDC (4) Boiler MCC B

(5) Turb MCC B (6) Turb ACDS B

(7) Boiler ACDB B


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AC Supply System_Std

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