Svc and Applications

8/13/2019 Svc and Applications

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STATIC VARCOMPENSATOR (SVC)&APPLICATION

DINESH K AP/EEE


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VOLTAGE CONTROL

Objective:Static Var Compensators (SVCs) are usedprimarily in power systems for voltage controlSystem Stabilization


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VI Characteristics of the SVC


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Dynamic Characteristics

Reference voltage, VrefLinear range of SVC controlSlope or Current DroopOverload rangeOvercurrent Limit


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Reference Voltage, Vref

The voltage at the terminals of the SVC duringfloating condition, that is, when the SVC isneither absorbing nor generating any reactive

power.The reference voltage can be varied betweenthe maximum and minimum limits- Vref maxand Vref min either by the SVC controlsystem, in case of thyristor controlledcompensators, or by the taps of the couplingtransformer, in the case of the saturated

reactor compensators.


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Reference Voltage, Vref

Typical values of Vref max and Vref min are1.05 pu and 0.95 pu


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Linear range of SVC control

This is the control range over which SVCterminal voltage varies linearly with SVCcurrent or reactive power, as the latter is varied

over its entire capacitive-to-inductive range.


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Slope or current Droop(intentionalloss)

The ratio of voltage-magnitude change tocurrent-magnitude change over the linear-controlled range of the compensator.

Thus slope of K SL is given by,

The per unit value of the slope is obtained as, I

V K

SL

%100.)(

r

r r SL V

orQatI V K

pu

V orQatI V

K r

r r SL .

)(


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Slope or current Droop(intentionalloss)

The slope is often expressed as an equivalentreactance : XFL=KSL in pu the slope is usually kept within 1 10%, with atypical value of 3-5%


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Overload Range

When the SVC traverses outside the linear-controllable range on the inductive side, theSVC enters the overload zone, where it

behaves like a fixed inductor.


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Overcurrent Limit

To prevent the thyristor valves from beingsubjected to excessive thermal stresses, themaximum inductive current in the overload

range is constrained to a constant value by anadditional control action.


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Steady state Characteristic

The Steady state VI charactersitic of the SVCis very similar to the dynamic V-I characteristicexcept for a deadband in voltage.


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Voltage control by the SVC


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Advantages of the slope in theSVC Dynamic characteristic

Substantially reduces the reactive-powerrating of the SVC for achieving nearly thesame control objectives.

Prevents the SVC from reaching its reactive-power limits too frequently;Facilitates the sharing of reactive power

among multiple compensators operating inparallel


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1. Reduction of the SVC rating


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2. Prevention of frequent operationat reactive-power limits


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3. Load Sharing between parallel-connected SVCs

Svc and Applications

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