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Reactive Power Compensation Using Capacitor Banks

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INTRODUCTION In this chapter we are going to discuss about power system in short and about A.P TRANSCO and its role in maintaining power in state from buying and selling the power. 1.1 INTRODUCTION TO POWER SYSTEM Electrical power is a little bit like the air one breathes. One doesn't really think about it until it is missing. Power is just "there," meeting ones daily needs, constantly. It is only during a power failure, when one walks into a dark room and instinctively hits the useless light switch, that one realizes how important power is in our daily life. Without it, life can get somewhat cumbersome. Electric Energy is the most popular form of energy, because it can be transported easily at high efficiency and reasonable cost. The power system of today is a complex interconnected network as shown in fig. 1. 1 Figure 1 Power System interconnected www.final-yearprojects.co.cc | www.troubleshoot4free.com/fyp/
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Page 1: Reactive Power Compensation Using Capacitor Banks

INTRODUCTION

In this chapter we are going to discuss about power system in short and about A.P

TRANSCO and its role in maintaining power in state from buying and selling the power.

1.1 INTRODUCTION TO POWER SYSTEM

Electrical power is a little bit like the air one breathes. One doesn't really think

about it until it is missing. Power is just "there," meeting ones daily needs, constantly. It

is only during a power failure, when one walks into a dark room and instinctively hits the

useless light switch, that one realizes how important power is in our daily life. Without it,

life can get somewhat cumbersome.

Electric Energy is the most popular form of energy, because it can be transported

easily at high efficiency and reasonable cost. The power system of today is a complex

interconnected network as shown in fig. 1.

1Figure 1 Power System interconnected

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Page 2: Reactive Power Compensation Using Capacitor Banks

A Power System can be subdivided into four major parts:

i. Generation.

ii. Transmission and Sub transmission.

iii. Distribution.

iv. Loads.

Power is generated at generating stations, usually located away from the actual

users. The generated voltage is then stepped up to a higher voltage for transmission,

as transmission losses are lower at higher voltages. The transmitted electric power is then

stepped down at grid stations.

The modern distribution system begins as the primary circuit, leaves the sub-

station and ends as the secondary service enters the customer's meter socket. First, the

energy leaves the sub-station in a primary circuit, usually with all three phases.

The most common type of primary is known as a wye configuration.The wye

configuration includes 3 phases and a neutral (represented by the center of the "Y".) The

neutral is grounded both at the substation and at every power pole. The primary and

secondary (low voltage) neutrals are bonded (connected) together to provide a path to

blow the primary fuse if any fault occurs that allows primary voltage to enter the

secondary lines. An example of this type of fault would be a primary phase falling across

the secondary lines. Another example would be some type of fault in the transformer

itself.

The other type of primary configuration is known as delta. This method is older

and less common. In delta there is only a single voltage, between two phases (phase to

phase), while in wye there are two voltages, between two phases and between a phase

and neutral (phase to neutral). Wye primary is safer because if one phase becomes 2

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Page 3: Reactive Power Compensation Using Capacitor Banks

grounded, that is, makes connection to the ground through a person, tree, or other object,

it should trip out the fused cutout similar to a household circuit breaker tripping. In delta,

if a phase makes connection to ground it will continue to function normally. It takes two

or three phases to make connection to ground before the fused cutouts will open the

circuit. The voltage for this configuration is usually 4800 volts.

Transformers are sometimes used to step down from 7200 or 7600 volts to 4800

volts or to step up from 4800 volts to 7200 or 7600 volts. When the voltage is stepped up,

a neutral is created by bonding one leg of the 7200/7600 side to ground. This is

commonly used to power single phase underground services or whole housing

developments that are built in 4800 volt delta distribution areas. Step downs are used in

areas that have been upgraded to a 7200/12500Y or 7600/13200Y and the power

company chooses to leave a section as a 4800 volt setup. Sometimes power companies

choose to leave sections of a distribution grid as 4800 volts because this setup is less

likely to trip fuses or reclosers in heavily wooded areas where trees come into contact

with lines.

For power to be useful in a home or business, it comes off the transmission grid

and is stepped-down to the distribution grid. This may happen in several phases. The

place where the conversion from "transmission" to "distribution" occurs is in a power

substation. A power substation typically does two or three things:

i. It has transformers that step transmission voltages down to distribution voltages

ii. It has a "bus" that can split the distribution power off in multiple directions.

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Page 4: Reactive Power Compensation Using Capacitor Banks

iii. It often has circuit breakers and switches so that the substation can be

disconnected from the transmission grid or separate distribution lines can be

disconnected from the substation when necessary.

It often has circuit breakers and switches so that the substation can be

disconnected from the transmission grid or separate distribution lines can be disconnected

from the substation when necessary. The primary distribution lines are usually in the

range of 4 to 34.5 KV and supply load in well defined geographical area. Some small

industrial customers are served directly by the primary feeders.

1.3 APTRANSCO

Government of Andhra Pradesh enacted the AP Electricity REFORMS ACT in

1998.As a sequel the APSEB was unbundled into Andhra Pradesh Power Generation

Corporation Limited (APGENCO) & Transmission Corporation of Andhra Pradesh

Limited (APTRANSCO) on 01.02.99. APTRANSCO was further unbundled w.e.f.

01.04.2000 into "Transmission Corporation" and four "Distribution Companies"

(DISCOMS).

a.)CURRENT ROLE

From Feb 1999 to June 2005 APTRANSCO remained as Single buyer in the state

-purchasing power from various Generators and selling it to DISCOMs in accordance

with the terms and conditions of the individual PPAs at Bulk Supply Tariff (BST) rates.

Subsequently, in accordance with the Third Transfer Scheme notified by Go AP,

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Page 5: Reactive Power Compensation Using Capacitor Banks

APTRANSCO has ceased to do power trading and has retained with powers of

controlling system operations of Power Transmission.

1.4 CONCLUSION

In this chapter we discussed about the power system and role of A.P TRANSCO

in the state of A.P.

In next chapter we are going to discuss about the salient features of

A.PTRANSCO.

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Page 6: Reactive Power Compensation Using Capacitor Banks

INTRODUCTION

In this chapter, we are going to discuss about the salient feature of A.P

TRANSCO/A.PGENCO/DISCOMS.

The object of reform and restructure of power sector in the state is to create

conditions for sustainable development of the sector through promoting competition,

efficiency, transparency and attracting the much needed private finances into power

sector. The ultimate goal of the reform program is to ensure that power will be supplied

under the most efficient conditions in terms of cost and quantity to support the economic

development of the state and power sector ceases to be a burden on the States budget and

eventually becomes a net generator of resources.

A key element of the reform process is that the government will withdraw from

its earlier role as a regulator of the industry and will be limiting its role to one of policy

formulation and providing directions.

In accordance with Reform Policy, the Government of A.P entacted the A.P

Electricity Reforms Act 1998 and made effective from 1.2.1999. Transmission

Corporation of A.P Ltd (APTRANSCO and APGENCO) were incorporated under

Companies Act, 1956. The assets, liabilities and personnel were allocated to these

companies. Distribution companies have been incorporated under Companies Act as

subsidiaries to distribution to APTRANSCO and the assets, liabilities and personnel have

been allocated to distribution companies through notification of a second transfer scheme

by the Govt. on 31.3.2000.

The Government of A.P established the A.P Electricity Regulatory Commission

(APERC) as per the provision of the act and the Commission started functioning from

3.4.1999. Regular licenses have been issued to APTRANSCO by APERC for

Transmission and Bulk supply and Distribution and Retail supply from 31.1.2000. The

commission has been issuing yearly Tariff orders since then based on Annual Revenue

Requirement (ARR) and tariff proposals of these companies.

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Page 7: Reactive Power Compensation Using Capacitor Banks

2.2 SALIENT FEATURES OF A.P TRANSCO/A.PGENCO/DISCOMS

Table 2.2 (a) features of A.P power system

PARAMETER UNITS 2008-09

(UPTO

MARCH

09)

31.03.09

(PROVL)

2009-10

(UPTO

MARCH

10)

31.03.10

(PROVL)

Energy generated (cumulative) MU - - -

1. Thermal MU - 23325.67 - 24180.38

2. Hydel MU - 7785 - 5510.46

3. Wind MU - - - -

Total MU - 31110.67 - 29690.84

Energy purchased and imported

(includingother’s energy handled)

MU - 36511.56 - 45075.68

Energy available for use (2+3) MU - 67622.23 - 74766.52

Maximum demand during the year

(at generation terminal) MW

ME - 9997

(27-03-

2009)

- 10880

(21-03-2010)

PercpaitaConsumption (includes

captive generation)

KWH - 746 - -

APTRANSCO LINE (EHT) - - - - -400kv CKM 21.44 3008.20 24 3032.79220kv CKM 265.88 1250.25 19068 12693.18132kv CKM 233.02 14938.57 164.88 15103.45

DISCOM’S Lines # - - - - -

33kv Km 1421.78 38628 1230 3985811kv Km 19521.82 248670 10596 259266LT km 10166.53 527852 4212 532064TOTAL - 26630.14 845599.15 6418.17 862017.32

Table 2.2 (b) load generation and sharing of A.P with other state

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Page 8: Reactive Power Compensation Using Capacitor Banks

8

Parameter Units 2008-09

(upto march09)

31.03.09

(Provl)

2009-10

(upto march10)

31.03.10

(Provl)

Installed Capacity

a) A.P.GENCO

1. Thermal

2. Hydel

3. Wind

Total A.P.GENCO

MW

MW

MW

39.0

39.0

3382.50

3664.36

2.00

7048.86

1000.00

39.00

-

1039.00

4382.50

3703.56

2.00

8087.86

b) Joint Sector

Gas(A.P.G.P.C.L) MW - 272.00 - 272.00

c) Private Sector

Thermal

Gas

Mini Hydel

Wind

Co-generation & Bio mass

projects

Others(IsoGasWells+Wast

e heat +indl .Waste +

Muncipal waste )

TOTAL PRIVATE

SECTOR

MW

MW

MW

MW

MW

MW

MW

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

d) Share from Central

SectorRamagundam STPS

M.A.P.P (madras atomic

power plant)

Neyveli Lignite

corporation

Kaiga nuclear power plant

I &II

Kaiga nuclear power plant

III

Simhadri TPS

Talcher (ph -II) units

-3,4,5,6

Unallocated power from

eastern region

MW

MW

MW

MW

MW

MW

MW

MW

-

-

-

-

-

-

-

-

-

-

-

-

-

-5.65 913.46

-0.25 46.84

-1.94 344.10

-0.98 147.34

5.31 77.67

- 1000

3.77 437.07

85.06

-

-

85.06

-

-

TOTAL SHARE FROM

CENTRAL SECTOR

MW 0.00 2963.22 85.22 3048.54

TOTAL(A.P GENCO

+PRIVATE +CENTRAL )

MW 45.66 12427.25 2114.40 14541.65

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Page 9: Reactive Power Compensation Using Capacitor Banks

2.3 CONCLUSION

In this chapter, we discussed about the salient features of

A.PTRANSCO / A.PGENCO / DISCOMS.

In next chapter we are going to discuss about the need for compensation and types

of compensations used.

3.1 INTRODUCTION

In this chapter, reactive power compensation, mainly in transmission systems

installed at substations is discussed. Reactive power compensation in power systems can

be either shunt or series.

Except in a very few special situations, electrical energy is generated, transmitted,

distributed, and utilized as alternating current (AC). However, alternating current has

several distinct disadvantages. One of these is the necessity of reactive power that needs

to be supplied along with active power. Reactive power can be leading or lagging. While

it is the active power that contributes to the energy consumed, or transmitted, reactive

power does not contribute to the energy. Reactive power is an inherent part of the ‘‘total

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Page 10: Reactive Power Compensation Using Capacitor Banks

power.’’ Reactive power is either generated or consumed in almost every component of

the system, generation, transmission, and distribution and eventually by the loads. The

impedance of a branch of a circuit in an AC system consists of two components,

resistance and reactance. Reactance can be either inductive or capacitive, which

contribute to reactive power in the circuit. Most of the loads are inductive, and must be

supplied with lagging reactive power. It is economical to supply this reactive power

closer to the load in the distribution system.

3.2 TYPES OF COMPENSATION

Shunt and series reactive compensation using capacitors has been 3 widely

recognized and powerful methods to combat the problems of voltage drops, power losses,

and voltage flicker in power distribution networks. The importance of compensation

schemes has gone up in recent years due to the increased awareness on energy

conservation and quality of supply on the part of the Power Utility as well as power

consumers. This amplifies on the advantages that accrue from using shunt and series

capacitor compensation. It also tries to answer the twin questions of how much to

compensate and where to locate the compensation capacitors.

i.) SHUNT CAPACITOR COMPENSATION

Since most loads are inductive and consume lagging reactive power, the

compensation required is usually supplied by leading reactive power. Shunt

compensation of reactive power can be employed either at load level, substation level, or

at transmission level. It can be capacitive (leading) or inductive (lagging) reactive power, 10

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Page 11: Reactive Power Compensation Using Capacitor Banks

although in most cases as explained before, compensation is capacitive. The most

common form of leading reactive power compensation is by connecting shunt capacitors

to the line.

Fig. 3.2(i) represents an A.C generator supplying a load through a line of series

impedance (R+jX) ohms, fig.3.2(ii) shows the phasor diagram when the line is delivering

a complex power of (P+jQ) VA and Fig. 3.2(iii) shows the phasor diagram when the line

is delivering a complex power of (P+jO) VA i.e. with the load fully compensated. A

thorough examination of these phasor diagrams will reveal the following facts which are

higher by a factor of 2

Cos1

φ compared to the minimum power loss attainable in the

system.

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Page 12: Reactive Power Compensation Using Capacitor Banks

Figure 3.2 (i) represents an A.C generator supplying a load through a line of

series.

Figure.3.2 (ii) shows the phasor diagram when the line is delivering a complex

power of (P+jQ)

Figure. 3.2 (iii) shows the phasor diagram when the line is delivering a complex

power of (P+jQ)

The loading on generator, transformers, line etc is decided by the current flow.

i. The higher current flow in the case of uncompensated load necessitated by the

reactive demand results in a tie up of capacity in this equipment by a factor of

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φCos1

i.e. compensating the load to UPF will release a capacity of (load VA

rating X Cosφ ) in all these equipment.

ii. The sending-end voltage to be maintained for a specified receiving-end voltage is

higher in the case of uncompensated load. The line has bad regulation with

uncompensated load.

iii. The sending-end power factor is less in the case of an uncompensated one. This is

due to the higher reactive absorption taking place in the line reactance.

iv. The excitation requirements on the generator are severe in the case of

uncompensated load. Under this condition, the generator is required to maintain a

higher terminal voltage with a greater current flowing in the armature at a lower

lagging power factor compared to the situation with the same load fully

compensated. It is entirely possible that the required excitation is much beyond

the maximum excitation current capacity of the machine and in that case further

voltage drop at receiving-end will take place due to the inability of the generator

to maintain the required sending-end voltage. It is also clear that the increased

excitation requirement results in considerable increase in losses in the excitation

system.

It is abundantly clear from the above that compensating a lagging load by using

shunt capacitors will result in

i. Lesser power loss everywhere upto the location of capacitor and hence a more

efficient system. 13

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Page 14: Reactive Power Compensation Using Capacitor Banks

ii. Releasing of tied-up capacity in all the system equipments thereby enabling a

postponement of the capital intensive capacity enhancement programs to a later

date.

iii. Increased life of equipments due to optimum loading on them.

iv. Lesser voltage drops in the system and better regulation.

v. Less strain on the excitation system of generators and lesser excitation losses.

vi. Increase in the ability of the generators to meet the system peak demand thanks to

the released capacity and lesser power losses.

Shunt capacitive compensation delivers maximum benefit when employed right

across the load. And employing compensation in HT & LT distribution network is the

closest one can get to the load in a power network. However, various considerations like

ease of operation end control, economy achievable by lumping shunt compensation at

EHV stations etc will tend to shift a portion of shunt compensation to EHV & HV

substations. Power utilities in most countries employ about 60% capacitors on feeders,

30% capacitors on the substation buses and the remaining 10% on the transmission

system. Application of capacitors on the LT side is not usually resorted to by the utilities.

Just as a lagging system power factor is detrimental to the system on various

counts, a leading system pf is also undesirable. It tends to result in over-voltages, higher

losses, lesser capacity utilization, and reduced stability margin in the generators. The

reduced stability margin makes a leading power factor operation of the system much

more undesirable than the lagging p.f operation. This fact has to be given due to

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Page 15: Reactive Power Compensation Using Capacitor Banks

consideration in designing shunt compensation in view of changing reactive load levels in

a power network.

Shunt compensation is successful in reducing voltage drop and power loss

problems in the network under steady load conditions. But the voltage dips produced by

DOL starting of large motors, motors driving sharply fluctuating or periodically varying

loads, arc furnaces, welding units etc can not be improved by shunt capacitors since it

would require a rapidly varying compensation level. The voltage dips, especially in the

case of a low short circuit capacity system can result in annoying lamp-flicker, dropping

out of motor contactors due to U/V pick up, stalling of loaded motors etc. and fixed or

switched shunt capacitors are powerless against these voltage dips. But thyristor

controlled Static VAR compensators with a fast response will be able to alleviate the

voltage dip problem effectively.

a.) SHUNT CAPACITORS

Shunt capacitors are employed at substation level for the following reasons:

i. Voltage regulation: The main reason that shunt capacitors are installed at

substations is to control the voltage within required levels. Load varies over the

day, with very low load from midnight to early morning and peak values

occurring in the evening between 4 PM and 7 PM. Shape of the load curve also

varies from weekday to weekend, with weekend load typically low. As the load

varies, voltage at the substation bus and at the load bus varies. Since the load

power factor is always lagging, a shunt connected capacitor bank at the substation

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Page 16: Reactive Power Compensation Using Capacitor Banks

can raise voltage when the load is high. The shunt capacitor banks can be

permanently connected to the bus (fixed capacitor bank) or can be switched as

needed. Switching can be based on time, if load variation is predictable, or can be

based on voltage, power factor, or line current.

ii. Reducing power losses: Compensating the load lagging power factor with the

bus connected shunt capacitor bank improves the power factor and reduces

current flow through the transmission lines, transformers, generators, etc. This

will reduce power losses (I2R losses) in this equipment.

iii. Increased utilization of equipment: Shunt compensation with capacitor banks

reduces KVA loading of lines, transformers, and generators, which means with

compensation they can be used for delivering more power without overloading

the equipment.

Reactive power compensation in a power system is of two types—shunt and series.

Shunt compensation can be installed near the load, in a distribution substation, along the

distribution feeder, or in a transmission substation. Each application has different

purposes. Shunt reactive compensation can be inductive or capacitive. At load level, at

the distribution substation, and along the distribution feeder, compensation is usually

capacitive. In a transmission substation, both inductive and capacitve reactive

compensation are installed.

b.) SHUNT CAPACITOR INSTALLATION TYPES:

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Page 17: Reactive Power Compensation Using Capacitor Banks

The capacitor installation types and types of control for switched capacitor are

best understood by considering a long feeder supplying a concentrated load at feeder end.

This is usually a valid approximation for some of the city feeders, which emanate from

substations, located 4 to 8 Kms away from the heart of the city.

Absolute minimum power loss in this case will result when the concentrated load

is compensated to up by locating capacitors across the load or nearby on the feeder. But

the optimum value of compensation can be arrived at only by considering a cost benefit

analysis.

Figure 3.2 (iv) long distribution feeder supplying a concentrated load

It is evident from fig. 3.2 (v) that it will require a continuously variable capacitor

to keep the compensation at economically optimum level throughout the day. However,

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Page 18: Reactive Power Compensation Using Capacitor Banks

this can only be approximated by switched capacitor banks. Usually one fixed capacitor

and two or three switched units will be employed to match the compensation to the

reactive demand of the load over a day. The value of fixed capacitor is decided by

minimum reactive demand as shown in Fig 3.2 (v)

Figure. 3.2 (v) reactive demand

Automatic control of switching is required for capacitors located at the load end

or on the feeder. Automatic switching is done usually by a time switch or voltage

controlled switch as shown in Fig 3.2(v). The time switch is used to switch on the

capacitor bank required to meet the day time reactive load and another capacitor bank

switched on by a low voltage signal during evening peak along with the other two banks

will maintain the required compensation during night peak hours.

ii) SERIES CAPACITOR COMPENSATION

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Page 19: Reactive Power Compensation Using Capacitor Banks

Shunt compensation essentially reduces the current flow everywhere upto the

point where capacitors are located and all other advantages follow from this fact. But

series compensation acts directly on the series reactance of the line. It reduces the transfer

reactance between supply point and the load and thereby reduces the voltage drop. Series

capacitor can be thought of as a voltage regulator, which adds a voltage proportional to

the load current and there by improves the load voltage.

Figure 3.2 (vi) Aerial view of 500-kV series capacitor installation

Series compensation is employed in EHV lines to

i. Improve the power transfer capability

ii. Improve voltage regulation

iii. Improve the load sharing between parallel lines.

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Page 20: Reactive Power Compensation Using Capacitor Banks

Economic factors along with the possible occurrence of sub-synchronous

resonance in the system will decide the extent of compensation employed.

Series capacitors, with their inherent ability to add a voltage proportional to load

current, will be the ideal solution for handling the voltage dip problem brought about by

motor starting, arc furnaces, welders etc. And, usually the application of series

compensation in distribution system is limited to this due to the complex protection

required for the capacitors and the consequent high cost. Also, some problems like self-

excitation of motors during starting, ferro resonance, steady hunting of synchronous

motors etc discourages wide spread use of series compensation in distribution systems.

3.3 ECONOMIC JUSTIFICATION FOR USE OF CAPACITORS:

Increase in benefits for 1KVAR of additional compensation decrease rapidly as

the system power factor reaches close to unity. This fact prompts an economic analysis to

arrive at the optimum compensation level. Different economic criteria can be used for

this purpose. The annual financial benefit obtained by using capacitors can be compared

against the annual equivalent of the total cost involved in the capacitor installation. The

decision also can be based on the number of years it will take to recover the cost involved

in the Capacitor installation. A more sophisticated method would be able to calculate the

present value of future benefits and compare it against the present cost of capacitor

installation.

When reactive power is provided only by generators, each system component

(generators, transformers, transmission and distribution lines, switch gear and protective

equipment etc) has to be increased in size accordingly. Capacitors reduce losses and

loading in all these equipments, thereby effecting savings through powerless reduction

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Page 21: Reactive Power Compensation Using Capacitor Banks

and increase in generator, line and substation capacity for additional load. Depending on

the initial power factor, capacitor installations can release at least 30% additional

capacity in generators, lines and transformers. Also they can increase the distribution

feeder load capability by about 30% in the case of feeders which were limited by voltage

drop considerations earlier. Improvement in system voltage profile will usually result in

increased power consumption thereby enhancing the revenue from energy sales.

Thus, the following benefits are to be considered in an economic analysis of

compensation requirements.

a) Benefits due to released generation capacity.

b) Benefits due to released transmission capacity.

c) Benefits due to released distribution substation capacity.

d) Benefits due to reduced energy loss.

e) Benefits due to reduced voltage drop.

f) Benefits due to released feeder capacity.

g) Financial Benefits due to voltage improvement.

Capacitors in distribution system will indeed release generation and transmission

capacities. But when individual distribution feeder compensation is in question, the value

of released capacities in generation and transmission system is likely to be too small to

warrant inclusion in economic analysis. Moreover, due to the tightly inter-connected

nature of the system, the exact benefit due to capacity release in these areas is quite

difficult to compute. Capacity release in generation and transmission system is probably

more relevant in compensation studies at transmission and sub-transmission levels and

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Page 22: Reactive Power Compensation Using Capacitor Banks

hence are left out from the economic analysis of capacitor application in distribution

systems.

a.) BENEFITS DUE TO RELEASED DISTRIBUTION SUBSTATION

CAPACITY:

The released distribution substation capacity due to installation of capacitors

which deliver Qc MVARs of compensation at peak load conditions may be shown to be

equal to

c2c

c2/1

2c

22c

c S1S

SinQ

S

CosQ1S

−φ+

φ−=∆

In general and φ≈∆ SinQS cc when 10S

Q CC <

∆ Sc = Released station capacity beyond maximum station capacity at original

power factor

SC = Station Capacity

Cosφ = The P.F at the station before compensation:

The annual benefit due to the released station capacity = ixCxSc∆

where C= Cost of station & associated apparatus per MVA.

b.) BENEFITS DUE TO REDUCED ENERGY LOSSES:

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Page 23: Reactive Power Compensation Using Capacitor Banks

Annual energy losses are reduced as a result of decreasing copper loss due to

installation of capacitors. Information on type of capacitor installation, location of

installation nature of feeder loading etc. are needed to calculate.. The calculation can

proceed as follows.

Let a current 21 jII + flow through a resistance R. The power loss is (Ij2+ I22)R-

The power loss due to reactive component is I22 R. Compensating the feeder will result in

a change only in I2. Hence the new power loss will be (I22+(I2-IC) 2) R where Ic is the

compensating current. Hence the decrease in power loss due to compensating part of

reactive current is (2 I2Ic-Ic2) R.

Now, if I2 is varying (it will be varying according to reactive demand curve) the

average decrease in power loss over a period of T hours will be equal to (2 I2Ic FR-Ic2) R

where I2 stands for peak reactive current during T hours through the feeder section of

resistance R, Ic is compensation current flowing through the same section for the same

period and FR is reactive load factor for T hours in the same section. Thus total energy

savings in this section of feeder for T hours will be 3(2I2IcFR-Ic2) RT.

One day can be divided in to many such periods depending on the number of

fixed and switched capacitors and the sequence of operation of switched capacitors. Also,

the feeder can be modeled by uniformly distributed load or discrete loading and total

energy savings can be found out for each period over the entire period by mathematical

integration or discrete summation. The daily and hence the annual energy savings for the

entire feeder can be worked by an aggregation over the time periods.

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Let ∆ E this value if total energy savings per year. Annual benefits due to

conserved energy will be ∆ E cost of energy.

c.) BENEFITS DUE TO RELEASED FEEDER CAPACITY:

In general feeder capacity is restricted by voltage regulation considerations rather

than thermal limits. Shunt compensation improves voltage regulation and there by

enhances feeder capacity. This additional feeder capacity can be calculated as

θ+θ=∆

rCosXSinxQ

S CF where Qc is compensation (MVAR)employed, X and R are

feeder reactance & resistance respectively and Cos θ is the P.F before compensation.

The annual benefits due to this will be ∆ SF X C x i where C is the cost of the installed

feeder per MVA and / is the annual fixed charge rate applicable.

d.) FINANCIAL BENEFITS DUE TO VOLTAGE IMPROVEMENT:

Energy consumption increases with improved voltage. Exact value of the

increased consumption can be worked out from a knowledge of elasticity of loads of the

concerned feeders with respect to voltage, Let it be ∆ EC. Annual revenue increase due to

this will be ∆ Ecx cost of energy.

e.) ANNUAL EQUIVALENT OF TOTAL COST OF THE

INSTALLED CAPACITORS:

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This will be equal to Qc*C*i where Qc is total capacitive MVAR to be installed,

C is cost of capacitors per MVAR and i is the annual fixed charge applicable.

The total annual benefits should be compared against the annual equivalent of

total cost of capacitors to arrive at optimum compensation levels.

3.4 CONCULSION

In this chapter, we discussed about reactive power compensation, mainly in

transmission systems and the types of compensations of which shunt and series are the

main compensation techniques.

In next chapter we are going to discuss about the different types of capacitor

banks and their ratings.

4.1 INTRODUCTION:

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In this chapter we are going to discus about the different types of capacitor banks

and their ratings.

A capacitor consists of two electrodes or plates, each of which stores an opposite

charge. These two plates are conductive and are separated by an insulator or dielectric.

The charge is stored at the surface of the plates, at the boundary with the dielectric.

Because each plate stores an equal but opposite charge, the total charge in the capacitor is

always zero.

Figure. 4.1 (a) showing plate separation

When electric charge accumulates on the plates, an electric field is created in the

region between the plates that is proportional to the amount of accumulated charge. This

electric field creates a potential difference V = E·d between the plates of this simple

parallel-plate capacitor.

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Page 27: Reactive Power Compensation Using Capacitor Banks

Figure.4.1 (b) showing polarized molecules

The electrons in the molecules move or rotate the molecule toward the positively

charged left plate. This process creates an opposing electric field that partially annuls the

field created by the plates. (The air gap is shown for clarity; in a real capacitor, the

dielectric is in direct contact with the plates.)

a.) CAPACITANCE:

The capacitor's capacitance (C) is a measure of the amount of charge (Q) stored

on each plate for a given potential difference or voltage (V) which appears between the

plates:

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge

causes a potential difference of one volt across the plates. Since the farad is a very large

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unit, values of capacitors are usually expressed in microfarads (µF), nano farads (n F) or

pico farads (p F).

The capacitance is proportional to the surface area of the conducting plate and

inversely proportional to the distance between the plates. It is also proportional to the

permittivity of the dielectric (that is, non-conducting) substance that separates the plates.

b.) STORED ENERGY:

As opposite charges accumulate on the plates of a capacitor due to the separation

of charge, a voltage develops across the capacitor owing to the electric field of these

charges. Ever increasing work must be done against this ever increasing electric field as

more charge is separated. The energy (measured in joules, in SI) stored in a capacitor is

equal to the amount of work required to establish the voltage across the capacitor, and

therefore the electric field. The energy stored is given by:

where V is the voltage across the capacitor.

4.2 RATINGS OF CAPACITORS:

The three-phase capacitors are characterized by negligible losses and high

reliability. The capacitor consists of thin dielectric polypropylene film wound together

with electrodes of aluminum foil. Discharge resistors are built-in.

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A bio-degradable hydrocarbon compound with excellent electrical properties is

used as the impregnation fluid. The container is of surface-treated high-quality steel and

the bushings and terminals are of the highest quality and reliability.

a.) RATINGS:

The ratings of the capacitor depends upon the power to be delivered, voltage

regulation, frequency and also the internal connections as tabulated below.

Table 4.1 ratings of capacitor

2GUW

Standard

2GUW

Non-standard

CHD

Max. Power 300 kvar 500 kvar 500 kvarVoltage 2.4, 4.16, 4.8 kV 4.8 - 13.8 kV up to 20 kVFrequency 50, 60 Hz 50, 60 Hz 50, 60 HzMax. current 75A 75A 180 AInternal connection Delta, but limited star

availableApplication Power factor

correction for motors

and load centers.

Power factor

correction for motors

and load centers.

Power factor

correction for motors

and load centers.b.) BANK ASSEMBLY:

Depending on the total output requirement more then 1 capacitor might be

needed.2GUE bank assembly are available.

All 2GUE assemblies include:

i. 1 to 4 Three-Phase Capacitor Units type 2GUW

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Page 30: Reactive Power Compensation Using Capacitor Banks

ii. Direct stud-mounted current limiting fuses (1⁄2" UNC); 1 per phase

iii. Bushing enclosure and cover

iv. Dust-proof and weatherproof.

Three Phase High voltage; Capacitors 50 Hz / 60 Hz; From 2.4 kV To 20.70 kV

i. Maximum voltage 20.70 kV

ii. Maximum output 750 KVAR

iii. All Polypropylene (APP) film dielectric

iv. Ultra Low Losses

v. Indoor or Outdoor

vi. application up to 96 kV BIL

vii. Superior electrical performance

viii. Improved tank rupture characteristics

Calculation for Capacitor Bank requirement for a power distribution system

calculation and selection of required capacitor rating

Qc = P * {tan [acos (pf1)] - tan [ acos (pf2)]}

Qc = required capacitor output (kVAr)

pf1 = actual power factor

pf2 = target power factor

P = real power (kW)

The table below shows the values for typical power factors in accordance with the above

formula

Actual Power Factor

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0.7;0.75;0.8;0.85;0.9;0.92;0.94;0.96;0.98;1

--------------------------------------------------------

0.40--- 1.27; 1.41;1.54;1.67;1.81;1.87; 1.93;2; 2.09;2.29

0.45--- 0.96;1.1;1.23;1.36;1.5;1.56;1.62;1.69;1.78;1.98

0.5---- 0.71;0.85;0.98; 1.11;1.25;1.31; 1.37; 1.44; 1.53; 1.73

0.55--- 0.5; 0.64; 0.77; 0.9; 1.03; 1.09; 1.16; 1.23; 1.32; 1.52

0.60--- 0.31; 0.45; 0.58; 0.71; 0.85; 0.91; 0.97; 1.04; 1.13; 1.33

0.65--- 0.15; 0.29; 0.42; 0.55; 0.68; 0.74; 0.81; 0.88; 0.97; 1.17

0.70--- 0; 0.14; 0.27; 0.4; 0.54; 0.59; 0.66; 0.73; 0.82; 1.02

0.75--- 0; 0.13; 0.26; 0.4; 0.46; 0.52; 0.59; 0.68; 0.88

The required capacitor output may be calculated as follows:

select the factor (matching point of actual and target power factor) k

calculate the required capacitor rating with the formula:

Qc = k * P

Example:

actual power factor = 0.70, target power factor = 0.96, real power = P = 500kW,

Qc = k * P = 0.73 * 500kW = 365 KVAR

4.3 INSTALLATION OF CAPACITORS:

In the case of induction motors, power factor is low and it is the responsibility of

industrial and agricultural consumers to improve the power factor to the prescribed limit.

for this consumers have to use capacitors.

The table below shows the capacity of capacitors required for various loads.

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Table 4.3(a) shows the capacity of capacitors required for various loads

Power factors of some of the common types of loads are given below.

The table 4.3(b) shows the Power factors of some of the common types of loads.

Incandescent lamps 1

Arc lamps used in cinemas 0.3to0.7

Neon lamps used for advertisements 0.4 to 0.5

Fluorescent lamps 0.6 to0.8

Fans 0.9

Electrical drills 1

Resistance heaters 0.85

32

SLNO Rating of motor(HP)

KVAR rating of LT capacitors for various RPM

750RPM 1000RPM 15000RPM 3000RPM

1 3 1 1 1 1

2 5 2 2 2 23 7.5 3 3 3 3

4 10 4 4 4 3

5 15 6 5 5 4

6 20 8 7 6 5

7 25 9 8 7 6

8 30 10 9 8 7

9 40 13 11 9 9

10 50 15 15 10 10

11 60 20 20 12 14

12 75 24 23 16 16

13 100 30 30 19 20

14 125 39 38 24 26

15 150 45 45 31 30

16 200 60 60 48 40

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Arc furnaces 0.85

Induction furnaces 0.6

Arc welders 0.3to0.4

Resistance welders 0.65

Induction motors 0.4 to 0.8

Capacity of Capacitors required for welding transformers

The table 4.3(c) shows Capacity of Capacitors required for welding transformers.

SLNO Name of the rating in KVA of individual welding transformer

Capacity of the capacitor in KVAR

1 1 1 2 2 23 3 34 4 35 5 46 6 57 7 68 8 69 9 710 10 811 11 912 12 913 13 1014 14 1115 15 1216 16 1217 17 1318 18 1419 19 1520 20 1521 21 1622 22 1723 23 1824 24 1925 25 1926 26 2027 27 2128 28 2229 29 2230 30 2331 31 24

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32 32 2533 33 2534 34 2635 35 27

4.4 LOCATION OF CAPACITOR BANKS:

Depending upon specific factors such as cost, requirement of area for

installation and load, the location of capacitor banks is divided into three types. They are,

a. Central compensation

b. Group compensation

c. Individual compensation

a) CENTRAL COMPENSATION:

When the main purpose is to reduce reactive power purchase due to power

supplier’s tariffs, central compensation is preferable. Reactive loading conditions within a

plant are not affected if compensation is made on the high voltage side. When made on

the low voltage side, the transformer is relieved. Cost of installation on the high voltage

and low voltage sides respectively determine where to install the capacitor.

b) GROUP COMPENSATION:

Group compensation is preferable to central compensation if sufficiently large

capacitors can be utilized. In addition to what is obtained at central compensation, load

on cables is reduced and losses decrease. Reduced losses often make group compensation

more profitable than central compensation. Because of large available group

compensation is suitable for harmonic filters.

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Page 35: Reactive Power Compensation Using Capacitor Banks

c) INDIVIDUAL COMPENSATION:

The advantage with individual compensation is that existing switching and

protective devices for the machine to be compensated can also be utilized for switching

and protection of capacitors. The costs are there by limited solely to purchasing the

capacitors. Another advantage is gained by the capacitor being automatically switched in

and out with the load. However this signifies that individual compensation is solely

motivated for apparatus and machines which have a very good load factor.

Usually, in a long feeder, receiving end voltage bucks considerably due to drop

and consumers at this is affected. Therefore, it is essential to install the switched

capacitor nearer to the receiving end of the feeder where the load concentration is more.

Subsequently, the improvement in power factor and voltage will be experienced by

consumers who are connected after the tapping point of switched capacitor in the system.

However prior to the installation of the switched capacitor at set location, the power

factor, the peak demand and off peak demand load current should be noted carefully.

4.5 CONCLUSION

In this chapter we discussed about the different types of capacitor banks and their

ratings.

In next chapter we are going to discuss about latest technology involved in

reactive power compensation.

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Page 36: Reactive Power Compensation Using Capacitor Banks

.

5.1 INTRODUCTION

In this chapter we are going study about latest technology involved in reactive

power compensation.

5.2 STATIC VAR CONTROL (SVC):

Static VAR compensators, commonly known as SVCs, are shunt connected

devices; vary the reactive power output by controlling or switching the reactive

impedance components by means of power electronics. This category includes the

following equipment:

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Page 37: Reactive Power Compensation Using Capacitor Banks

i. Thyristor controlled reactors (TCR) with fixed capacitors (FC)

ii. Thyristor switched capacitors (TSC)

iii. Thyristor controlled reactors in combination with mechanically or Thyristor

switched capacitors

SVCs are installed to solve a variety of power system problems:

i. Voltage regulation

ii. Reduce voltage flicker caused by varying loads like arc furnace, etc.

iii. Increase power transfer capacity of transmission systems

iv. Increase transient stability limits of a power system

v. Increase damping of power oscillations

vi. Reduce temporary over voltages

vii. Damp sub-synchronous oscillations

A view of an SVC installation is shown in Fig.5.1.

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Figure 5.1 View of static VAR compensator (SVC) installation.

5.3 DESCRIPTION OF SVC:

Figure5.2 shows three basic versions of SVC. Figure 5.2a shows configuration of

TCR with fixed capacitor banks. The main components of a SVC are thyristor valves,

reactors, the control system, and the step-down transformer.

5.4 WORKING OF AN SVC:

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As the load varies in a distribution system, a variable voltage drop will occur in

the system impedance, which is mainly reactive. Assuming the generator voltage remains

constant, the voltage at the load bus will vary. The voltage drop is a function of the

reactive component of the load current, and system and transformer reactance. When the

loads change very rapidly, or fluctuate frequently, it may cause ‘‘voltage flicker’’ at the

customers’ loads. Voltage flicker can be annoying and irritating to customers because of

the ‘‘lamp flicker’’ it causes. Some loads can also be sensitive to these rapid voltage

fluctuations.

An SVC can compensate voltage drop for load variations and maintain constant

voltage by controlling the duration of current flow in each cycle through the reactor.

Current flow in the reactor can be controlled by controlling the gating of thyristors that

control the conduction period of the thyristor in each cycle, from zero conduction (gate

signal off) to full-cycle conduction. In Fig. 2a, for example, assume the MVA of the fixed

capacitor bank is equal to the MVA of the reactor when the reactor branch is conducting

for full cycle. Hence, when the reactor branch is conducting full cycle, the net reactive

power drawn by the SVC (combination of capacitor bank and thyristor controlled reactor)

will be zero. When the load reactive power (which is usually inductive) varies, the SVC

reactive power will be varied to match the load reactive power by controlling the duration

of the conduction of current in the thyristor controlled reactive power branch. Figure.3

shows current waveforms for three conduction levels, 60, 120 and 1808. It is possible to

vary the net reactive power of the SVC from 0 to the full capacitive VAR only. This is

sufficient for most applications of voltage regulation, as in most cases only capacitive

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Page 40: Reactive Power Compensation Using Capacitor Banks

VARs are required to compensate the inductive VARs of the load. If the capacitor can be

switched on and off, the MVAR can be varied from full inductive to full capacitive,up to

the rating of the inductive and capacitive branches.

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Page 41: Reactive Power Compensation Using Capacitor Banks

Figure 5.2 Three versions of SVC.

(a) TCR with fixed capacitor bank;

(b) TCR with switched capacitor banks; and

(c) Thyristor switched capacitor compensator breakers.

5.5 CONCLUSION:

In this chapter we studied about latest technology involved in reactive power

compensation.

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Page 42: Reactive Power Compensation Using Capacitor Banks

In next chapter we are going to study about the technical specifications of

associated equipment of capacitor bank units and different types of manufacturing

designs.

6.1 INTRODUCTION:

In this chapter we are going to study about the various types of capacitor and

their technical specification and different types of .

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6.2 TECHNICAL PARTICULARS FOR CAPACITOR BANK UNIT:

The technical information or the technical particulars for the associated

equipment of the capacitor bank unit is tabulated as shown below.

a.) Guaranteed technical particulars for spare capacitor units

TABLE NO 6.1(a) Guaranteed technical particulars for spare capacitor units

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b) 36KV SERIES REACTORS FOR CAPACITORS

44

Item .NO

Description

1 Make and Type SHREEM CAPACITOR PVT.LTD. OUTDOOR OIL COOLED,STATIC TYPE

2 Reference standards IS :13925/1988(PART-I)

3 Rated voltage for each capacitor units KV 21.9 11.24 7.32 7.3 7.32 193.5 6.93 11 10.4 10.44

4 Rated frequency 50hz

5 KVAR(at rated voltage and frequency of each unit)

400 400 26606 200 200 200.5 166 150 125 11

6 No. of bushing Two

7 Type of bushing terminals BRASS

8 Maximum permissible over voltage and duration 110%brass rated voltage for 12 hrs in a day

9 Maximum permissible current ---

a) Continuous 130% rated current

b) Short term-duration in secs 130% rated current

10 Maximum permissible operating over voltage ---

11 Residual voltage 100% of rated voltage

12 Discharge time 50volts

13 Minimum time interval required between denergisation and re-energisation of the bank

10 min or 5 min

14 Temperature rise under 10 min or 5 min

15 Limiting ambient temperature 50deg c

16 Capacitance variation due to 50 deg c

17 Loss per KVAR(maximum) Negliglible

18 Voltage withstand tests (capacitor units) 0.13 watts/Kvar (max)

a) Terminal to terminal 50c/s 1min.dry KV (RMS)

---

b)terminal to case 50c/s1min.dry KV(RMS) 4.3 times (dc)voltage for 1min

19 impulse withstand voltage KV 70 38 28 28 28 50 28 38 38 38

20 Individual fuse rating 170 95 75 75 75 125 75 95 95 95

21 Physical and electrical properties of capacitors ---

a) Nominal thickness of polypronviene ---

b) Tensile strength 27 to 36 micron

i) length wise (mPa) ---

ii) cross wise (mPa) 190

C)percentage elongation 200

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TABLE NO 6.1(b) Guaranteed technical particulars for 36 kv series reactors

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46

ITEM NO

DESCRIPTION 14.4 KVAR

1 Make and type Shrihans /Quality power

2 Reference standard IS: 5553-Part –III-1990

3 a)Insulation level with post insulators

b)Insulation level of winding

70 KV (rms)/170 KV (peak)

4 Rated KVAR 2.4

5 Rated current and voltage 54.69 A,33KV

6 Rated Reactance/Phase (ohms) 0.802

7 Rated frequency 50 HZ

8 Over current factor 130 of rated current

9 Compensation percent of series reactors 0.20%

10 Maximum temperatures rise of coil over ambient specified for which reactor is designed

105 Deg C

11 Number of phases Single

12 Dimensions (overall)approx 600 * 430 * 900

13 Total weight/weight of coil and assembly unit(approx) 32 kg

14 Rated short time circuit 0.911

15 Duration of short circuit 2

16 Type of cooling Air cooled

17 Losses at rated current and frequency at 75 Deg.C(Watts) 325

18 Winding resistance (Cold/Hot) 0.098

19 Voltage and Rating of reactor bushing/support insulator ---

20 Terminal arrangement ---

i) Incoming 2 * 24 KV

ii) Outgoing Suitable for bus bar connection

21 Maximum system voltage for which reactor is designed. 36

22 Choke voltage per phase at rated current 44

23 Whether reactor designed for

a)Harmonics

b)Inrush current

Yes

24 Material of winding Aluminium

25 Maximum current density 1.10

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c) 36 KV NEUTRAL CURRENT TRANSFORMERS FOR CAPACITORS

TABLE NO 6.1(c) Guaranteed technical particulars for 36 kv neutral current transformer

ITEM NO

DESCRIPTION

1 Make and type Gyro/Instrument /SVEI

2 Reference IS:2705/1992

3 Rated terminal Voltage/Highest voltage (kv) 33 KV/36 KV

4 Rated primary current (Amps) 10-5 A

5 Secondary core details ----

6 a)No. of secondary cores Two

b)Rated secondary current (A) 1 AMP

c) Rated burden(VA) Core -1:-15VA

Core- 2:-15VA

d) Accuracy class 5P 5P

e) Accuracy limit factor 10 10

f)Knee point voltage (Volts) ----

g) Excitation current (mA) ----

h) Secondary resistance at 75 deg.C (ohms) ----

7 Instrument security factor ----

8 Short time thermal current and its duration kA.Secs OCF 100 for 3 secs

9 Rate dynamic current (peak) kA ----

10 a)Rate continuous thermal current (A) 120% of rated current

b) Temperature rise over ambient deg.C 30 Deg.C, above ambient temperature of 40Deg.C

11 Creepage distance

a)Total 900 mm (approx)

b)Protected 450 mm (approx)

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12 Insulation level

a)Impulse with stand test voltage (kV peak )

170 KV (Peak)

b)One minute power frequency withstand test voltage of primary (kV rms )

70 KV rms

c)One minute power frequency withstand test voltage of secondary (kV rms)

3 KV rms

13 Quantity of insulating oil (litres) 25 Ltrs

14 Total weight including oil (kg) 76 kg.(approx)

15 Magnetization curve of CT cores NA

16 Mounting details 340 mm * 250mm

17 Live part to ground clearance (mm) 530 mm (approx)

18 Material of primary winding Copper

19 Current transformer design (live tank or dead tank) Live tank

20 Whether all ferrous parts are hot dip galvanized No, not hot dip galvanized. All ferrous parts exposed to atmosphere are duly painted.

21 Details of terminal connectors ---

d) GUARANTEED TECHNICAL PARTICULARS FOR 36 KV RESIDUAL VOLTAGE TRANSFORMERS

TABLE NO 6.1(d) Guaranteed technical particulars for 36 kv residual voltage transformers

ITEM NO

DESCRIPTION

1 Make and type Gyro/Instrument/SVEI

2 Reference STANDARD IS:3156

3 Rated terminal voltage /Highest voltage (KV)

a)Primary

b)Secondary

33 KV

110 V-570 V

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4 Rated current (Amps)

a)Primary

b)Secondary

---

---

5 Connection Star/Star –Open Delta

6 Secondary core details ---

a) No. of secondary cores ---

b)Rated secondary burden (VA) ---

c) Accuracy class ---

d) Accuracy limit factor ---

e) Knee point voltage ---

f) Secondary resistance at 75 deg.C (ohms) ---

7 Instrument security factor ---

8 Voltage factor 1.2 Cont & 1.9 for 30 secs

9 Accuracy class

a)Protection winding

b)Metering winding

3P

1

10 Burden

a) Protection winding

b) Metering winding

100 VA

100 VA

11 Frequency 50 HZ

12 Insulation level

a) Impulse with stand voltage (kV peak)b) Power frequency with stand voltage (kV rms)

170

70

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13 Creepage distance

a)Total

b)Protected

900 mm

450 mm

14 Fuses

a)Secondary side or not

b)Rating

Yes

2 Amps

15 Quantity of insulating oil (litres) 80 Ltrs (approx)

16 Total weight including oil (kg) 275 kgs (approx)

17 Magnetization curve of RVT cores ---

18 Mounting details 500 mm * 300 mm

19 Live part to ground clearance (mm) 475 mm(approx)

20 Material of primary winding Copper

21 Whether all ferrous parts are hot dip galvanized No, not hot dip galvanized. All ferrous parts exposed to atmosphere are duly painted

22 Details of terminal connectors ---

6.3 DESIGN OF DIFFERENT MANUFACTURERS OF THE

CAPACITOR:

There are several manufacturing companies that designed the capacitors with

specific dimensions which are approximate. These dimensions indicated are designed in

such a way that due to design improvements they do not effect the functional parameters.

The designs of different manufacturing companies are shown below and the different

companies are,50

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i. Asia Type vi. CGL Type

ii. Shreem Manufacturer vii. COOPER Type

iii. CPS Type viii. MEHER Type

iv. SHAKTI Type ix. ABB Type

v. NGF Type x. BHEL Type

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Figure 6.1(a) showing external fuse capacitor of Asia type .

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Figure 6.1( b) showing internal fuse capacitor of Shreem manufacturer .

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Figure 6.1( c) showing external fuse capacitor of CPS type .

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Figure 6.1( d) showing external fuse capacitor of CGL type .

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Figure 6.1(e) showing external fuse capacitor of COOPER type .

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Figure 6.1(f) showing external fuse capacitor of MEHAR type .

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Figure 6.1(g) showing external fuse capacitor of SHAKTI type .

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Figure 6.1(h) showing external fuse capacitor of NGF type .

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Figure 6.1(i) showing external fuse capacitor of ABB type .

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Figure 6.1(j) showing internal fuse capacitor of BHEL type .

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6.2 CONCLUSION:

In this chapter we have studied about technical particulars of associated equipment

of capacitor bank units and design of capacitors of different manufacturers and capacitors

installed in APTRANSCO.

In the next chapter we are going to discuss about the various case studies at different

substations.

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7.1 CASE STUDY - 1

a.) INTRODUCTION:

Most of the electrical equipments connected to a power supply not only require

active power but also certain amount of reactive power. Magnetic fields in Motors and

Transformers are maintained by reactive current. Also series inductance in transmission

lines implies consumption of reactive power. Hence it is imperative that in an electrical

system, the feeder lines cater considerable amount of reactive power in addition to the

active power carried by them. Shunt capacitors are employed to compensate the reactive

power generated in the system to alleviate the ill effects of reactive components and will

benefit the system in:-

i. Improving the voltage profile

ii. Reduction of line current resulting in reduction of system losses.

iii. Increased line efficiency resulting in optimum utilization of designed capacity.

b.) IMPLEMENTATION:

Out of the existing 56 feeders 32 feeders were selected for installation of

capacitors, 19 of which are rural feeders, one industrial feeder and one feeder catering to

combined urban as well as rural loads. Work was carried out through turnkey contract at

a total cost of 146.16 lakhs which is 6.32% below the DPR cost. The work was

completed in 3 months time Single pole mounted Capacitor Bank at project site Close up

view of Capacitor Bank at project site 5

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Three feeders were selected for conducting the sample study. The feeders are DF 2

and DF 6 of D Cross sub-station and KF 8 of KIADB sub-station. The data of the feeders

for nine months was obtained. The period covers three months prior to the installation of

capacitors and six month after commissioning of capacitors.

Location: DODDABALLAPUR SUB-STATION

The study of installation of switched capacitors on 11 KV feeders

Site address: DODDABALLAPUR subdivision,

BANGALORE Electricity Supply Company Limited.

Period of study: January 2009 to April 2009.

The three feeders DF2, DF6 and KF8 at Doddaballapur of different lengths with

different usage of conductors are mentioned below and the current and power (MW) are

noted down in the morning peak and in the evening peak.The corresponding power

factors that is average power factor for the taken readings is calculated and tabulated as

shown below. From these readings, we calculate the average peak load for certain

durations and further we calculate the reduction in peak current which can be used for

improving the power factor towards unity.

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Feeder: DF 2

Feeder Length: 21.46 Kms

Distance of Location from SS: 6 Km

Conductor: Rabbit

Table no.7.1(a) results of DF2 feeder

Feeder: DF 6

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Feeder Length: 6.48 Kms

Distance of Location from “D”Cross SS: 1.5 Km

Conductor: Rabbit

Table no.7.1 (b) results of DF6 feeder

Feeder: KF 8

Feeder Length 8.28Kms66

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Distance Conductor: Rabbit

Location from KIADB SS 2.5&3.8 Km

Table no.7.1 (c) results of KF8 feeder

A sample study was also conducted on the above three feeders by taking the

instantaneous readings. The individual readings were taken with the capacitors ON &

OFF the circuit. These instantaneous readings are considered for calculation of cost

benefits as they reflect the correct savings of energy, whereas average values provided 67

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above will have many other factors viz., seasonal fluctuations, temporary change over of

loads etc, influencing the results.

Table no.7.1 (d) calculation of cost benefits

Sl.no Particulars feeder feeder feeder1 Line current(in amps) with

capacitor

129 135 176

2 Line current(in amps) with

capacitor

114 118 154

3 Difference in current(in amps) 15 17 224 Percentages savings 12% 13% 13%

Reduction in line current is of order of 12-13 percent and so is the reduction in

demand. This has also resulted in improvement of tail end voltages by 2 to 3%.

c.) COST BENEFIT ANALYSIS:

The benefit from installation of capacitors will be in the form of reduction in loading

of transmission and distribution network. This in turn results in reduction in energy

losses. The pay back period has been worked out by considering the savings in terms

power purchase cost to Bescom, which works out to 8.5 months. The benefits available

from the transmission system are not considered as the same are in the KPTCL preview.

Detailed calculations are furnished below:-

Table no.7.1 (e) cost benefit analysis

Sl.no Particulars Feeder 1 Feeder2 Feeder31 Line current without

capacitor

129 136 176

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2 Line current with capacitor 114 118 154

3 Difference in current 15 17 22

4 Power factor with out

capacitor

0.65 0.73 0.84

5 Power factor with out

capacitor

0.87 0.96 0.90

6 Demand(in KVA)with out

capacitor bank

2458 2572 3353

7 Demand(in KVA)with

capacitor bank

2171 2248 2934

8 Reduction in demand in

KVA

287 324 419

9 % Reduction in demand 11.7% 12.6% 12.5%

10 Feeder loss reduction on

11KV side keh per day

133.59 290.32 490.02

11 Savings per day taking

purchase rate of RS.2.75

367 798 1348

12 Total saving /months from

all the three feeder

75,390 ----- -----

13 Total cost of capacitors

banks

5x2,12,998=10,64,990 ----- -----

14 Pay back period 14 months ----- -----

Installation of Capacitor Bank to 11KV Feeders at D.B PUR.

For the calculation of feeders losses

a) resistance of rabbit conductor is considered.

b) line length of 4.5 KMs is considered.

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c) Capacitor bank is assumed to work our 5 hours in a day.

d.) GUIDELINES FOR REPEATABILITY IN OTHER

DISTRIBUTED AREAS:

Since this is a simple devise and does not require any special skill or effort for

execution and requires only a minimum shutdown of lines, the APTRANSCO can reap

considerable benefit by executing such projects. By installing 63 capacitors banks on 31

feeders, the subdivision is benefited in terms of reduction losses and improved quality of

power supply.

7.2 CASE STUDY – 2:

The case studies regarding Shahpurnagar and Kalyan nagar substations are

discussed below. The corresponding results and conclusions before and after the

compensation are tabulated below.

a.) RESULTS OF CASE STUDY –KALYAN NAGAR:

BEFORE COMPENSATION

Table no.7.2 (a) readings before compensation at Kalyan nagar

B.N

o.

Sen

din

g N

od

e

Receiv

ing

Nod

e SENDING

Receiving end

Voltage

Real Power Losses(Kw)

Reactive

Losses (KVAR)

Power Factor

Injecting Real Power

P (Pu)

Injecting Reactive Power Q

(Pu)

1 1 2 P[1]=0.45458 Q[1]=0.43743 1.00000 2.9958 1.5271 0.7206

2 2 3 P[2]=0.45400 Q[2]=0.43713 0.99484 12.4262 6.3290 0.7204

3 3 4 P[3]=0.40479 Q[3]=0.39496 0.97006 19.2551 2.5611 0.7157

4 4 5 P[4]=0.30956 Q[4]=0.31159 0.95547 40.4721 9.1239 0.7048

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5 5 6 P[5]=0.27830 Q[5]=0.30746 0.94115 9.0420 7.8055 0.6711

6 6 7 P[6]=0.23183 Q[6]=0.29755 0.90603 0.8717 2.8815 0.6146

7 7 8 P[7]=0.12894 Q[7]=0.19929 0.89259 7.2121 5.2049 0.5432

8 8 9 P[8]=0.10807 Q[8]=0.19514 0.85335 3.9541 2.8408 0.4845

9 9 10 P[9]=0.08086 Q[9]=0.18865 0.83187 3.6644 2.5974 0.3939

10 10 11 P[10]=0.06090 Q[10]=0.18239 0.81227 0.6720 0.2222 0.3167

11 11 12 P[11]=0.05124 Q[11]=0.17901 0.81007 1.2558 0.4153 0.2752

12 12 13 P[12]=0.04607 Q[12]=0.17820 0.80608 4.8358 3.8047 0.2503

13 13 14 P[13]=0.03881 Q[13]=0.17750 0.77953 1.7573 2.3132 0.2136

14 14 15 P[14]=0.02798 Q[14]=0.17341 0.76486 1.8524 1.6487 0.1593

15 15 16 P[15]=0.01422 Q[15]=0.16953 0.75438 2.3082 1.6856 0.0836

16 16 17 P[16]=0.00637 Q[16]=0.16710 0.74400 3.9737 5.3055 0.0381

17 17 18 P[17]=0.00294 Q[17]=0.16517 0.71326 0.0358 0.0342 0.0178

18 2 19 P[2]=0.01292 Q[2]=0.15908 0.70392 0.0363 0.0347 0.0809

19 19 20 P[19]=0.03621 Q[19]=0.03701 0.99387 0.2607 0.2349 0.6993

20 20 21 P[20]=0.02717 Q[20]=0.03680 0.98632 0.0542 0.0633 0.5940

21 21 22 P[21]=0.01791 Q[21]=0.03539 0.98429 0.0786 0.1040 0.4516

22 3 23 P[3]=0.00886 Q[3]=0.03515 0.98100 0.4235 0.2893 0.2444

23 23 24 P[23]=0.07381 Q[23]=0.07687 0.96520 0.7479 0.5906 0.6926

24 24 25 P[24]=0.06438 Q[24]=0.07640 0.95561 0.5043 0.3946 0.6444

25 6 26 P[6]=0.03164 Q[6]=0.07497 0.94863 0.2644 0.1347 0.3888

26 26 27 P[26]=0.08785 Q[26]=0.08967 0.90356 0.2653 0.1351 0.6998

27 27 28 P[27]=0.08158 Q[27]=0.06775 0.90054 0.8286 0.7305 0.7693

28 28 29 P[28]=0.07532 Q[28]=0.06083 0.88801 0.5558 0.4842 0.7780

29 29 30 P[29]=0.06849 Q[29]=0.05832 0.87908 0.2824 0.1438 0.7614

30 30 31 P[30]=0.05593 Q[30]=0.05727 0.87502 0.4496 0.4443 0.6987

31 31 32 P[31]=0.04565 Q[31]=0.05648 0.86568 0.0789 0.0920 0.6286

32 32 33 P[32]=0.03020 Q[32]=0.04408 0.86326 0.0460 0.0715 0.5652

AFTER COMPENSATION

Table no.7.2 (b) readings after compensation at Kalyan nagar

SENDING

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B.N

o.

Sen

din

g N

od

e

Receiv

ing

Nod

e

Receiving end

Voltage

Real Power Losses (Kw)

Reactive

Losses (KVAR)

Power Factor

Injecting Real Power

P (Pu)

Injecting Reactive Power Q

(Pu)

1 1 2 P[1]=0.43214 Q[1]=0.38253 1.00000 2.5093 1.2792 0.7488

2 2 3 P[2]=0.43164 Q[2]=0.38228 0.99523 10.1106 5.1496 0.7486

3 3 4 P[3]=0.38292 Q[3]=0.33555 0.97257 14.7593 1.9631 0.7521

4 4 5 P[4]=0.28990 Q[4]=0.25065 0.95959 30.4874 6.8730 0.7565

5 5 6 P[5]=0.26314 Q[5]=0.24068 0.94694 6.6732 5.7607 0.7379

6 6 7 P[6]=0.22666 Q[6]=0.22981 0.91656 0.5151 1.7028 0.7022

7 7 8 P[7]=0.12539 Q[7]=0.13257 0.90706 3.6168 2.6102 0.6872

8 8 9 P[8]=0.10487 Q[8]=0.11887 0.87735 1.6001 1.1496 0.6616

9 9 10 P[9]=0.08126 Q[9]=0.10426 0.86221 1.1801 0.8365 0.6147

10 10 11 P[10]=0.06366

Q[10]=0.09111

0.84939 0.1961 0.0648 0.5728

11 11 12 P[11]=0.05648

Q[11]=0.08627

0.84777 0.3383 0.1119 0.5477

12 12 13 P[12]=0.05178

Q[12]=0.08321

0.84488 1.1667 0.9180 0.5284

13 13 14 P[13]=0.04544

Q[13]=0.07959

0.82938 0.3759 0.4947 0.4958

14 14 15 P[14]=0.03828

Q[14]=0.07518

0.82198 0.2992 0.2663 0.4537

15 15 16 P[15]=0.02590

Q[15]=0.06668

0.81692 0.3192 0.2331 0.3621

16 16 17 P[16]=0.01960

Q[16]=0.06241

0.81200 0.4600 0.6141 0.2996

17 17 18 P[17]=0.01228

Q[17]=0.05818

0.80022 0.0357 0.0340 0.2065

18 2 19 P[2]=0.00582 Q[2]=0.05357 0.79661 0.0358 0.0341 0.1080

19 19 20 P[19]=0.03621

Q[19]=0.03645

0.99426 0.2149 0.1937 0.7048

20 20 21 P[20]=0.02718

Q[20]=0.03142

0.98732 0.0330 0.0385 0.6542

21 21 22 P[21]=0.01796

Q[21]=0.02522

0.98570 0.0291 0.0385 0.5801

22 3 23 P[3]=0.00893 Q[3]=0.02018 0.98358 0.4120 0.2815 0.4046

23 23 24 P[23]=0.07391

Q[23]=0.07475

0.96778 0.6731 0.5315 0.7031

24 24 25 P[24]=0.0644 Q[24]=0.0694 0.95863 0.2745 0.2148 0.6804

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9 7

25 6 26 P[6]=0.03182 Q[6]=0.05094 0.95309 0.2601 0.1325 0.5298

26 26 27 P[26]=0.08859

Q[26]=0.08748

0.91412 0.2516 0.1281 0.7116

27 27 28 P[27]=0.08233

Q[27]=0.06235

0.91119 0.7527 0.6636 0.7972

28 28 29 P[28]=0.07608

Q[28]=0.05222

0.89946 0.4784 0.4168 0.8245

29 29 30 P[29]=0.06933

Q[29]=0.04656

0.89134 0.2094 0.1066 0.8302

30 30 31 P[30]=0.05685

Q[30]=0.03914

0.88773 0.2775 0.2743 0.8237

31 31 32 P[31]=0.04664

Q[31]=0.03303

0.88054 0.0315 0.0367 0.8161

32 32 33 P[32]=0.03137

Q[32]=0.01276

0.87919 0.0039 0.0061 0.9263

req=0.11229p.u xeq=0.14530p.u

b.)RESULTS OF CASE STUDY – SHAHPURNAGAR:

BEFORE COMPENSATION

Table no.7.2(c) readings before compensation at Shahpur nagar

B.N

o.

Sen

din

g N

od

e

Receiv

ing

Nod

e SENDING

Receiving end

Voltage

Real Power Losses (Kw)

Reactive

Losses (KVAR)

Power FactorInjecting Real

Power P (Pu)

Injecting Reactive

Power Q (Pu)

1 1 2 P[1]=0.12752 Q[1]=0.12979 1.00000 0.3602 1.1926 0.7288

2 2 3 P[2]=0.12728 Q[2]=0.12953 0.99584 0.7441 1.1570 0.7289

3 3 4 P[3]=0.11492 Q[3]=0.11677 0.98846 0.6723 0.4909 0.7014

4 4 5 P[4]=0.07059 Q[4]=0.07692 0.98055 0.7965 0.7022 0.6761

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5 5 6 P[5]=0.05792 Q[5]=0.07486 0.96950 0.8258 1.1289 0.6119

6 6 7 P[6]=0.04812 Q[6]=0.07298 0.95363 0.3460 0.3080 0.5504

7 7 8 P[7]=0.03929 Q[7]=0.07114 0.94837 0.0591 0.0301 0.4835

8 3 9 P[3]=0.01895 Q[3]=0.06956 0.93810 0.1195 0.0609 0.2628

9 9 10 P[9]=0.03759 Q[9]=0.03791 0.98605 0.0729 0.0373 0.7041

10 10 11 P[10]=0.01947 Q[10]=0.03750 0.98446 0.0977 0.0739 0.4608

11 11 12 P[11]=0.01340 Q[11]=0.03668 0.98180 0.0234 0.0119 0.3431

AFTER COMPENSATION

Table no.7.2(d) readings after compensation at Shahpur nagar

B.N

o.

Sen

din

g N

od

e

Receiv

ing

Nod

e SENDING

Receiving end Voltage

Real Power Losses (Kw)

Reactive

Losses (KVAR)

Power Facto

r

Injecting Real Power

P (Pu)

Injecting Reactive Power Q

(Pu)

1 1 2 P[1]=0.12765 Q[1]=0.12478 1.00000 0.3658 1.2111 0.7351

2 2 3 P[2]=0.12740 Q[2]=0.12451 0.99680 0.7354 1.1434 0.7352

3 3 4 P[3]=0.11503 Q[3]=0.11530 0.98848 0.6312 0.4609 0.7063

4 4 5 P[4]=0.07065 Q[4]=0.07240 0.98077 0.6625 0.5841 0.6984

5 5 6 P[5]=0.05801 Q[5]=0.06394 0.97057 0.6069 0.8296 0.6719

6 6 7 P[6]=0.04835 Q[6]=0.05736 0.95698 0.2204 0.1961 0.6445

7 7 8 P[7]=0.03974 Q[7]=0.05153 0.95261 0.1190 0.0606 0.6107

8 3 9 P[3]=0.01952 Q[3]=0.03933 0.94550 0.1192 0.0607 0.4446

9 9 10 P[9]=0.03765 Q[9]=0.03775 0.98607 0.0469 0.0240 0.7061

10 10 11 P[10]=0.01953 Q[10]=0.02769 0.98468 0.0475 0.0360 0.5764

11 11 12 P[11]=0.01348 Q[11]=0.02367 0.98265 0.0086 0.0044 0.4950

req=0.11229p.u xeq=0.14530p.u

c.)COMPARISION OF TEST SYSTEMS:

Voltage comparison of a 12 Bus system

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Table no.7.2 (e) Readings of Voltage comparison

Voltagebefore compensation

Voltageafter compensation

1 1

0.99584 0.9968

0.98846 0.98848

0.98055 0.98077

0.9695 0.97057

0.95363 0.95698

0.94837 0.95261

0.9381 0.9455

0.98605 0.98607

0.98446 0.98468

0.9818 0.98625

Power factor comparison of a 12 Bus system

Table no.7.2 (d) Readings Power factor comparison

Power factorbefore compensation

Power factorafter compensation

0.7288 0.7351

0.7289 0.7352

0.7014 0.7063

0.6761 0.6984

0.6119 0.6719

0.5504 0.6445

0.4835 0.6107

0.2628 0.4446

0.7041 0.7061

0.4608 0.5764

0.3431 0.49575

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Voltage comparison of a 33 Bus system

Table no.7.2 (e) Voltage comparison of a 33 Bus system

Voltagebefore compensation

Voltageafter compensation

1 1

0.99484 0.99523

0.97006 0.97257

0.95547 0.95959

0.94115 0.94694

0.90603 0.91656

0.89259 0.90706

0.85335 0.87735

0.83187 0.86221

0.81227 0.84939

0.81007 0.84777

0.80608 0.84488

0.77953 0.82938

0.76486 0.82198

0.75438 0.81692

0.744 0.812

0.71326 0.80022

0.70392 0.79661

0.99387 0.99426

0.98632 0.98732

0.98429 0.9857

0.981 0.98358

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0.9652 0.96778

0.95561 0.95863

0.94863 0.95309

0.90356 0.91412

0.90054 0.91119

0.88801 0.89946

0.87908 0.89134

0.87502 0.88773

0.86568 0.88054

0.86326 0.87919

Power factor compensation of a 33 Bus system

Table no.7.2 (f) Power factor compensation of a 33 Bus system

Power factorbefore compensation

Power factorafter compensation

0.7206 0.7488

0.7204 0.7486

0.6711 0.7379

0.6146 0.7022

0.5432 0.6872

0.4845 0.6616

0.3939 0.6147

0.3167 0.5728

0.2136 0.4958

0.0381 0.2996

0.0178 0.2065

0.0809 0.108

0.6993 0.7048

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0.594 0.6542

0.4516 0.5801

0.2444 0.4046

0.6926 0.7031

0.6444 0.6804

0.7614 0.8302

0.6987 0.8237

0.6286 0.8161

0.5652 0.92638.1 CONCLUSION

The power factor of a power system is the major of its economy. So, the design

Engineers always attempts to make this power factor as close as to unity. Power factor

decreases due to the increased usage of inductive loads .Therefore the power distribution

companies always sets up a mandatory minimum power factor at the premises of

consumers. In our state the mandatory power factor is 0.9 described by the Andhra

Pradesh Transmission Corporation. The decrease in power factor below this reference

is compensated by the consumer based on their maximum demand and the no. of units

consumed.

Hence, to compensate for this decrease in power factor shunt capacitor method

can be used as its advantages are already described in Chapter 3. Proper analysis design

and implementation of this capacitor banks with appropriate mounting and protecting

devices will not only reduce the bill charges but also make the profit on long term.

8.2 Future trends of the project:

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The electricity consumption depends upon the infrastructure, instruments and

different loads. Hyderabad area is going to consume more loads in future with increase in

population. Practical implementation of the capacitor placement technique requires

further cost-benefit analysis which in turns depends on the costs of capacitor bank and

energy saving.

1. Technical Reference Book - A.P.TRANSCO.

2. A.S. PABLA, “Electrical Power Distribution” fifth edition TATA Mc.

Graw-Hill Publication Company Limited, New Delhi – 20

3. TURAN GONEN, “Electrical Power Distribution System

Engineering”, TATA Mc GRAW-HILL, book Company, New York.

4. Suresh Kumar “Application of Capacitors”.

5. B.R. GUPTA “Power System Analysis & Design” 3rd Edition, wheeler

Publishers.

6. C.L.Wadhwa, Power Systems,4th Edition, New Age International (P)

Limited,Publishers-1998

7. L.Elgerd Olle, An Introduction To Energy Systems, 2nd edition, Tata Mac

Graw Hill, Inc Edition.

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Page 80: Reactive Power Compensation Using Capacitor Banks

APPENDIX-I

The Karnataka Power Transmission Corporation Limited, also known as KPTCL

is the sole electricity transmission and distribution company in state of Karnataka of India

(Bharath ). Its origin was in Karnataka Electricity Board ( K.E.B ) which was earlier sole

distributor of grid electricity in state of Karnataka. This electricity transmission and

distribution entity was corporatised to provide efficient and reliable electric power supply

to the people of Karnatak state.The KPTCL has transmission lines along with Substation to

transfer electricity from one place to another in the state.

KPTCL buys power from power generating companies like Karnataka Power

Corporation Limited (KPCL) and other IPPs (Independent Power Producers) like GMR,

Jindal, etc., and sell them to their respective ESCOMS.The electric generating power

stations previously under the control of K.E.B has now transferred to a separate company

called Visweshraiah Vidyut Nigama Limited or VVNL.

Zones and Circles

The KPTCL is further divided into Zones and Circles are also known as Electric

Supply Companies popularly known as ESCOM's. Each of these zones look after

distribution of electricity in a particular region of Karnataka consisting of few districts of

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Page 81: Reactive Power Compensation Using Capacitor Banks

the state. Whereas KPTCL looks after transmission. The KPTCL has five zones at

present, names of which is as below.

i. Bangalore Electricity Supply Company.

ii. Mangalore Electricity Supply Company ( Mescom ).

iii. Hubli Electricity Supply Company

iv. Gulbarga Electricity Supply Company

v. Chamundeshwari Electricity Supply Company

APPENDIX - II

• Average load: Average of the load occurring on the power station in a given

period is known as average load.

• Capacity factor: It is the ratio of actual energy produced to maximum possible

energy that could have been produced during a given period.

• Connected load: It is the sum of continuous rating of all the equipment connected

to supply system.

• Demand factor: It is the ratio of maximum demand on power station to its

connected load.

• Depreciation: The decrease in the value of the power plant equipment and

building due to constant use is known as depreciation.

• Diversity factor: The ratio of sum of individual maximum demands to the

maximum demand on power station.

• Fixed cost: It is the cost which is independent of maximum demand and unit

generated.

• Interest: The cost of use of money is known as interest.

• Load curve: The curve showing the variation of the load on the power station

with reference to time is known as load curve.

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Page 82: Reactive Power Compensation Using Capacitor Banks

• Load factor: The ratio of average load to maximum demand during a given

period.

• Maximum demand: It is the greatest demand of load on power station during a

given period.

• Payback period: The time between which capital cost is compensated from the

day of installation is known as payback period.

• Running cost: It is the cost which depends only upon the number of unit

generated.

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