Introduction to Static Var Compensator.pdf

Figure 17 shows a stack of thyristors from a three

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and consist of a number of thyristors stacked on one another. Figure 17 shows a stack of thyristors from a three-phase thyristor valve used in an SVC. Figure 17. Stack of thyristors from a three-phase thyristor valve used in an SVC (photo courtesy of ABB). Each thyristor valve of an SVC controls the current flowing in one phase of the TCR (or the TSC). All thyristors having the same polarity in a thyristor valve are brought to a conducting state by simultaneous application of the proper firing signal to the gate of each of these thyristors. Conversely, all thyristors having the same polarity in a thyristor valve return to a blocking state when the current flowing through these thyristors decreases below the holding current value (of course, the firing signals must be removed from the thyristor gates).
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Main Components of a Static Var Compensator (SVC) Discussion 18 Static Var Compensator (SVC) Figure 18. Light-triggered thyristor (LTT) used in an SVC. The arrows indicate the direction of the light signal in the thyristor (photo courtesy of ABB). The thyristor-switched capacitor (TSC) Equivalent circuit of a TSC Each thyristor-switched capacitor (TSC) in an SVC consists of three capacitors connected to the step-down transformer via three zero-voltage switched (ZVS) solid state relays (SSRs) implemented using thyristors. A TSC is switched in or out by simply turning the corresponding set of ZVS SSRs on or off. The TSCs serve the purpose of supplying reactive power to the system to which the SVC is connected. TSCs also filter out to a certain extent the harmonics generated by the TCR. This is basically due to the fact that the reactance of a TSC decreases with frequency, thereby helping in attenuating harmonics. The circuit diagram of one leg (phase) of a TSC is shown in Figure 19.
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Main Components of a Static Var Compensator (SVC) Discussion Static Var Compensator (SVC) 19 Figure 19. Equivalent circuit of one phase of a thyristor-switched capacitor (TSC) in an SVC. As the above figure shows, an SSR (made of two thyristor valves connected in an inverse parallel configuration) is connected in series with each capacitor of a TSC. Also, a small inductor is connected in series with each capacitor of a TSC to limit the surge in current in case the SSR operates inadequately (e.g., if the ZVS SSR is turned on at an instant when the voltage is not zero). The complete diagram showing all three legs (phases) of a TSC in an SVC is illustrated in Figure 20. As the figure shows, TSCs are generally connected in a 6-wire, delta (6D) configuration, just as for TCRs. Figure 20. Complete diagram of the three legs (phases) of a thyristor-switched capacitor (TSC) in an SVC. ܫ ்ௌ஼ ܧ ்ௌ஼ ܺ ஼,்ௌ஼ ܺ ௅,்ௌ஼ (small) ܺ ஼ଵ,்ௌ஼ ܺ ஼ଶ,்ௌ஼ ܺ ஼ଷ,்ௌ஼ ܳ ܳ ܳ ܳ ܳ ܳ ܧ ்ௌ஼ ܫ ்ௌ஼ ܺ ௅ଵ,்ௌ஼ (small) ܺ ௅ଶ,்ௌ஼ (small) ܺ ௅ଷ,்ௌ஼ (small) To phase A of the SVC step-down transformer To phase C of the SVC step-down transformer To phase B of the SVC step-down transformer To other legs (phases) of the TSC To other legs (phases) of the TSC
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  • One '14
  • Electric power transmission, AC power, TCR, Static VAR compensator

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