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 INTRODUCT INTRODUCTION ION TO POWER POWER SYSTE SYSTEM M 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.

Figure 1 Power System interconnected

1


A Power System System can be subdivided subdivided into four major major parts: i.

Generation.

ii. ii.

Tran Transm smis issi sion on and and Sub Sub tra trans nsmi miss ssio ion. n.

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 substation 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 ph ases. 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 blow the primary primary fuse fuse if any fault fault occurs occurs that allows allows primary primary voltag voltagee to enter 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


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 neutr neutral al is crea create ted d by bondi bonding ng one one leg leg of the the 7200/ 7200/76 7600 00 side side to grou ground nd.. This This is commo commonl nly y used used to powe powerr sing single le phas phasee under undergr groun ound d serv servic ices es or whol wholee housi housing ng developments developments that are built in 4800 volt delta distribution distribution areas. Step downs are used in area areass that that have have been been upgra upgrade ded d to a 7200 7200/1 /125 2500Y 00Y or 7600/ 7600/132 13200Y 00Y and and the the powe power r 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 stepped-down to the distribut distribution ion grid. This may happen in several several phases. The place where the conversion conversion from "transmission" "transmission" to "distribut "distribution" ion" occurs is in a power substation. A power substation typically does two or three things: i. ii.

It has tran transfo sforme rmers rs that that step step trans transmis missi sion on voltag voltages es down down to distri distribut bution ion volta voltages ges It has has a "bus" "bus" that that can spli splitt the the distri distribut bution ion power power off in in multip multiple le direc directio tions. ns.

3


iii.

It often has circuit breakers and switche ches so that the subs ubstation can be discon disconnect nected ed from from the trans transmis missio sion n grid grid or separa separate te distri distribut bution ion lines lines can be disconnected from the substation when necessary. It ofte often n has has circ circui uitt brea breake kers rs and and swit switch ches es so that that the the subst ubstat atio ion n can 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 Corpor Corporati ation on Limite Limited d (APGEN (APGENCO) CO) & Transm Transmiss ission ion Corpor Corporati ation on of Andhra Andhra Prades Pradesh h Limite Limited d (APTR (APTRANS ANSCO) CO) on 01.02.9 01.02.99. 9. APTRAN APTRANSCO SCO was furthe furtherr unbundl unbundled ed w.e.f. w.e.f. 01.04.20 01.04.2000 00 into into "Trans "Transmis missio sion n Corpor Corporati ation" on" and four four "Distr "Distribu ibutio tion n Compani Companies" es" (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. Subseq Subsequent uently, ly, in accord accordance ance with with the Third Third Transf Transfer er Scheme Scheme notifi notified ed by Go AP,

4

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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.

5


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.

6


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

31.03.09

2009-10

(UPTO

(UPTO

MARCH

(PROVL)

09) Energy generated (cumulative)

31.03.10

MARCH

(PROVL)

10)

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

MU

-

36511.56

-

45075.68

(includingother’s energy handled) Energy available for use (2+3)

MU

-

67622.23

-

74766.52

-

9997

-

10880

Maximum demand during the year

ME

(at generation terminal) MW (27-03PercpaitaConsumption

(includes

captive generation) APTRANSCO LINE (EHT) 400kv 220kv 132kv

KWH CKM CKM CKM

DISCOM’S Lines # 33kv 11kv LT TOTAL

21.44 265.88 233.02

2009) 746 3008.20 1250.25 14938.57

-

-

-

1421.78 19521.82 10166.53 26630.14

Km Km km

(21-03-2010)

38628 248670 527852 845599.15

-

-

24 19068 164.88

3032.79 12693.18 15103.45

1230 10596 4212 6418.17

39858 259266 532064 862017.32

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

7

Para aramete meterr

Un Units its

200 2008-0 8-09

31.03.09

2009-10

31.03.10

(upto march09) (Provl) (upto march10) www.final-yearprojects.co.cc www.final-yearpro jects.co.cc | www.troubleshoot4free.com/fyp/ www.troubleshoot4free.com /fyp/

(Provl)

Installed Capacity a)

A.P.GENCO

1.

Thermal

2.

Hydel

3.

Wind

MW

Total A.P.GENCO

3382.50

1000.00

4382.50

MW

39.0

3664.36

39.00

3703.56

MW

39.0

2.00

-

2.00

1039.00

8087.86

7048.86

b) b)

Joi Joint Secto ector r

Gas(A.P.G.P.C.L)

MW

-

272.00

-

272.00

Thermal

MW

-

-

-

-

Gas

MW

-

-

-

-

Mini Hydel

MW

-

-

-

-

Wind

MW

Co-generation & Bio mass

MW

-

-

-

-

-

-

-

-

-

-

-

-

c)

Priva rivate te Sector ctor

-

projects Others(IsoGasWells+Wast

MW

-

e heat heat +indl ndl .Wa .Waste ste + Muncipal waste ) TOTAL

-

PRIVATE

SECTOR d) Share

MW from

Central

Sector Ramagundam STPS

MW

-

-

-5.65

913.46

M.A.P. M.A.P.P P (madra (madrass atomic atomic

MW

-

-

-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

-

-

-

-

power plant) Neyveli

LignMW ite

corporation Kaiga nuclear power plant

MW

I &II Kaiga nuclear power plant

MW

III

MW

Simhadri TPS

MW

Talch alcheer

(ph

-II -II)

unit unitss

-3,4,5,6

-

MW -

Unallo Unallocat cated ed power power from from eastern region

8

TOTA TOTAL L SHARE SHARE FROM FROM

MW

0.00

2963.22

85.22

3048.54

CENTRAL SECTOR TOTAL(A. (A.P GENCO NCO

MW

45.66

12427.25

2114.40

14541.65


2.3 CONCLUSION In

thi this

chap chaptter, er,

we disc discus usssed abou aboutt

the sal salient ient feat eatures ures 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 9


power.’’ power.’’ Reactive power is either either generated generated or consumed in almost almost every component component of the system, generation, transmission, and distribution and eventually by the loads. The imped impedan ance ce of a bran branch ch of a circ circui uitt in an AC syst system em cons consis ists ts of two two comp compon onen ents ts,, resi resist stan ance ce and reac reacta tanc nce. e. Reac Reacta tance nce can be eith either er indu induct ctiv ivee or capac capacit itiv ive, e, whic which h 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 Shunt and series series reacti reactive ve compen compensat sation ion using using capacit capacitors ors has been 3 widely 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 schem schemes es has gone gone up in rece recent nt year yearss due due to the the incr increa ease sed d awar awarene eness ss on ener energy gy 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 capacit capacitor or compen compensat sation ion.. It also also tries tries to answer answer the twin questi questions ons of how much much to compensate and where to locate the compensation capacitors.

i.) SHUNT CAPACITOR COMPENSATION Since Since most most load loadss are are indu induct ctiv ivee and and consu consume me lagg laggin ing g reac reacti tive ve power power,, the the comp compen ensa sati tion on requ requir ired ed is usua usuall lly y supp suppli lied ed by lead leadin ing g reac reacti tive ve powe power. r. Shun Shuntt 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


althoug although h in most most cases cases as explai explained ned before before,, compen compensat sation ion is capacit capacitive ive.. The most 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

 1  2  higher by a factor of   compared to the minimum power loss attainable in the  Cos φ  system.

11


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

12


1 Cosφ

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


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 oper ation 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 14


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 15


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:

16


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,

17


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

18


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.

19


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 selfexcitation 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 20


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 21


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

∆Sc

1/ 2   2 2  φ Q Cos QcSin φ c    =  1− + − 1Sc 2 2   Sc Sc   

In general and ∆Sc ≈ Qc Sin φ when QC

∆ Sc

=

<

SC 10

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 = ∆S c x C x i

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

b.) BENEFITS DUE TO REDUCED ENERGY LOSSES:

22


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 I1

+ jI 2 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.

23


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

∆SF =

QC x XSin θ + rCosθ

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:

24


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:

25


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.

26


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

27


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.

28


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

Max. Power Voltage Frequency Max. current Internal connection

Application

2GUW

2GUW

Standard 300 kvar 2.4, 4.16, 4.8 kV 50, 60 Hz 75A

Non-standard 500 kvar 4.8 - 13.8 kV 50, 60 Hz 75A

Power

factorPower

CHD

500 kvar up to 20 kV 50, 60 Hz 180 A Delta, but limited star available factorPower

factor

correction for motorscorrection for motorscorrection for motors and load centers.

and load centers.

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 29


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 30


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. 31


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

Rating motor(HP)

of KVAR rating of LT capacitors for various RPM 750RPM

1000RPM

15000RPM

3000RPM

1

3

1

1

1

1

2 3

5 7.5

2 3

2 3

2 3

2 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

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


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 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Name of the rating in KVA of individual welding Capacity of the capacitor in transformer KVAR 1 1 2 2 3 3 4 3 5 4 6 5 7 6 8 6 9 7 10 8 11 9 12 9 13 10 14 11 15 12 16 12 17 13 18 14 19 15 20 15 21 16 22 17 23 18 24 19 25 19 26 20 27 21 28 22 29 22 30 23 31 24 33


32 33 34 35

32 33 34 35

25 25 26 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. 34


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.

35


.

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: 36


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.

37


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: 38


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 39


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.

40


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.

41


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 . 42


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

43

Item . NO

Description

1

Make and Type

2


SHREEM CAPACITOR PVT.LTD. OUTDOOR OIL COOLED,STATIC TYPE

b) Reference 36KV SERIES standards REACTORS FOR CAPACITORS 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)

---

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 i) ii)

length wise (mPa)

cross wise (mPa)

C)percentage elongation

4.3 times (dc)voltage for 1min

--27 to 36 micron --190 200

44


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

45


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

70 KV (rms)/170 KV (peak)

b)Insulation level of winding 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

Yes

a)Harmonics

46

b)Inrush current 24

Material of winding

Aluminium

25

Maximum current density

1.10


c) 36 KV NEUTRAL CAPACITORS

CURRENT

TRANSFORMERS

FOR

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) c) Rated burden(VA)

1 AMP 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

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

OCF 100 for 3 secs ----

Creepage distance a)Total b)Protected

900 mm (approx) 450 mm (approx) 47


12

Insulation level

170 KV (Peak)

a)Impulse with stand test voltage (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

33 KV

b)Secondary

110 V-570 V

48


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

10

a)Protection winding

3P

b)Metering winding

1

Burden a) Protection winding

100 VA

b) Metering winding

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

49


13

14

Creepage distance a)Total

900 mm

b)Protected

450 mm

Fuses a)Secondary side or not

Yes

b)Rating

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


i.

Asia Type

ii.

Shreem Manufacturer

vii.

COOPER Type

iii.

CPS Type

viii.

MEHER Type

iv.

SHAKTI Type

v.

NGF Type

vi.

ix.

CGL Type

ABB Type x.

BHEL Type

51


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

52


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

53


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

54


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

55


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

56


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

57


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

58


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

59


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

60


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

61


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.

62


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. ii. iii.

Improving the voltage profile Reduction of line current resulting in reduction of system losses. 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

63


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 cap acitors.

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.

64


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 65


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 8.28Kms 66


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


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 1

Particulars Line current(in

amps)

feeder with 129

feeder 135

feeder 176

2

capacitor Line current(in

amps)

with 114

118

154

3 4

capacitor Difference in current(in amps) Percentages savings

17 13%

22 13%

15 12%

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 1

Particulars Line current

Feeder 1 without 129

Feeder2 136

Feeder3 176

capacitor 68


2

Line current with capacitor

114

118

154

3

Difference in current

15

17

22

4

Power

factor

with

out 0.65

0.73

0.84

5

capacitor Power factor

with

out 0.87

0.96

0.90

6

capacitor Demand(in KVA)with out 2458

2572

3353

7

capacitor bank Demand(in KVA)with 2171

2248

2934

8

capacitor bank Reduction in demand in 287

324

419

9

KVA % Reduction in demand

11.7%

12.6%

12.5%

10

Feeder loss reduction on 133.59

290.32

490.02

11

11KV side keh per day Savings per day taking 367

798

1348

12

purchase rate of RS.2.75 Total saving /months from 75,390

-----

-----

13

all the three feeder Total cost of capacitors 5x2,12,998=10,64,990 -----

-----

14

banks 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.

69


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 e d o . N o N g . n i B d n e S

e d o N g n i v i e c e R

SENDING Injecting Real Power P (Pu)

Injecting Reactive Power Q (Pu)

Receivin g end Voltage

Real Power Losses (Kw)

Reactiv e Losses (KVAR)

Power Factor

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 70


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

71


e d o . N o N g . n i B d n e S


Injecting Real Power P (Pu)





Power Factor

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]=0.0636 6

Q[10]=0.0911 1

0.84939

0.1961

0.0648

0.5728

11

11

12

P[11]=0.0564 8

Q[11]=0.0862 7

0.84777

0.3383

0.1119

0.5477

12

12

13

P[12]=0.0517 8

Q[12]=0.0832 1

0.84488

1.1667

0.9180

0.5284

13

13

14

P[13]=0.0454 4

Q[13]=0.0795 9

0.82938

0.3759

0.4947

0.4958

14

14

15

P[14]=0.0382 8

Q[14]=0.0751 8

0.82198

0.2992

0.2663

0.4537

15

15

16

P[15]=0.0259 0

Q[15]=0.0666 8

0.81692

0.3192

0.2331

0.3621

16

16

17

P[16]=0.0196 0

Q[16]=0.0624 1

0.81200

0.4600

0.6141

0.2996

17

17

18

P[17]=0.0122 8

Q[17]=0.0581 8

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]=0.0362 1

Q[19]=0.0364 5

0.99426

0.2149

0.1937

0.7048

20

20

21

P[20]=0.0271 8

Q[20]=0.0314 2

0.98732

0.0330

0.0385

0.6542

21

21

22

P[21]=0.0179 6

Q[21]=0.0252 2

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]=0.0739 1

Q[23]=0.0747 5

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

72


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]=0.0885 9

Q[26]=0.0874 8

0.91412

0.2516

0.1281

0.7116

27

27

28

P[27]=0.0823 3

Q[27]=0.0623 5

0.91119

0.7527

0.6636

0.7972

28

28

29

P[28]=0.0760 8

Q[28]=0.0522 2

0.89946

0.4784

0.4168

0.8245

29

29

30

P[29]=0.0693 3

Q[29]=0.0465 6

0.89134

0.2094

0.1066

0.8302

30

30

31

P[30]=0.0568 5

Q[30]=0.0391 4

0.88773

0.2775

0.2743

0.8237

31

31

32

P[31]=0.0466 4

Q[31]=0.0330 3

0.88054

0.0315

0.0367

0.8161

32

32

33

P[32]=0.0313 7

Q[32]=0.0127 6

0.87919

0.0039

0.0061

0.9263


Power Factor

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

e d o . N o N g . i n B d n e S


SENDING





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 73


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 e d o . N o N g . i n B d n e S


1

1

2

P[1]=0.12765

Q[1]=0.12478

1.00000

2

2

3

P[2]=0.12740

Q[2]=0.12451

3

3

4

P[3]=0.11503

4

4

5

5

5

6

SENDING Reacti ve Losses (KVAR)

Power Facto r

0.3658

1.2111

0.7351

0.99680

0.7354

1.1434

0.7352

Q[3]=0.11530

0.98848

0.6312

0.4609

0.7063

P[4]=0.07065

Q[4]=0.07240

0.98077

0.6625

0.5841

0.6984

6

P[5]=0.05801

Q[5]=0.06394

0.97057

0.6069

0.8296

0.6719

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

Receivi ng end Voltage


xeq=0.14530p.u

c.)COMPARISION OF TEST SYSTEMS: Voltage comparison of a 12 Bus system

74


Table no.7.2 (e) Readings of Voltage comparison Voltage before compensation

Voltage after 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 factor before compensation

Power factor after 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

0.495 75


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

Voltage before compensation

Voltage after 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

76


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 factor before compensation

Power factor after 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 77


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

0.9263

8.1 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:

78


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. 79


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 80


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. 81

Reactive Power Compensation Using Capacitor Banks

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