Reactive Power Compensation Using Capacitor Banks

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

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

A Power System can be subdivided into four major parts:

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

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

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,

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

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

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

-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

2009)

- 10880

(21-03-2010) PercpaitaConsumption (includes

captive generation)

KWH - 746 -

-APTRANSCO LINE (EHT) - - - -

-400kv CKM 21.44 3008.20 24 3032.79 220kv CKM 265.88 1250.25 19068 12693.18 132kv CKM 233.02 14938.57 164.88 15103.45

-33kv Km 1421.78 38628 1230 39858

11kv Km 19521.82 248670 10596 259266

LT km 10166.53 527852 4212 532064 TOTAL - 26630.14 845599.15 6418.17 862017.32

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

Parameter Units 2008-09

(upto march09)

31.03.09 (Provl)

2009-10 (upto march10)

31.03.10 (Provl) Installed Capacity

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

MW

- - - - -

- - - - -

- - - - -

- - - - -

d) Share from Central

MW MW MW MW

- - - -

- -

5.65 913.46 -0.25 46.84 -1.94 344.10 -0.98 147.34 5.31 77.67

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 MW 45.66 12427.25 2114.40 14541.65

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

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,

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

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

Cos

1

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

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

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

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:

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,

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

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

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

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

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

c 2

c c 2 / 1 2 c

2 2 c

S

Sin Q S

Cos Q 1 S

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

The annual benefit due to the released station capacity = ∆ Sc x C x i

where C= Cost of station & associated apparatus per MVA

b.) BENEFITS DUE TO REDUCED ENERGY LOSSES:

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 I 1 + jI 2 flow through a resistance R The power loss is (Ij2+ I2)R- The power loss due to reactive component is I2 R Compensating the feeder will result in

a change only in I2 Hence the new power loss will be (I2+(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

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

=

∆

rCosXSin

xQ

SF C 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:

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:

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

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

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

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.

2GUWNon-standard

CHD

Voltage 2.4, 4.16, 4.8 kV 4.8 - 13.8 kV up to 20 kV

available

correction for motors and load centers

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

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

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:

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

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

Neon lamps used for advertisements 0.4 to 0.5

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

32 32 25

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,

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

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

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:

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

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