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Concepts of SVC Voltage Control
Static var compensators (SVCs) are used primarily in power systems for voltage control as either an end in itself or a means of achieving other objectives, such as system stabilization –. This chapter presents a detailed overview of the voltage-control characteristics of SVC and the principles of design of the SVC voltage regulator. The performance of SVC voltage control is critically dependent on several factors, including the inﬂuence of network resonances, transformer saturation, geomagnetic effects, and voltage distortion. When SVCs are applied in series-compensated networks, a different kind of resonance between series capacitors and shunt inductors becomes …ver más…
The slope is usually kept within 1–10%, with a typical value of 3–5%. Although the SVC is expected to regulate bus voltage, that is, maintain a ﬂat voltage-current proﬁle with a zero slope, it becomes desirable to incorporate a ﬁnite slope in the V-I characteristics for reasons described in Section 5.2.3.
When the SVC traverses outside the linear-controllable range on the inductive side, the SVC enters the overload zone, where it behaves like a ﬁxed inductor.
To prevent the thyristor valves from being subjected to excessive thermal stresses, the maximum inductive current in the overload range is constrained to a constant value by an additional control action.
Steady-State Characteristic The steady-state V-I characteristic of the SVC is very similar to the dynamic V-I characteristic except for a deadband in voltage, as depicted in Figs. 5.1(a) and (b). In the absence of this deadband, in the steady state the SVC will tend to drift toward its reactive-power limits to provide voltage regulation. It is not desirable to leave the SVC with very little reactive-power margin for future voltage control or stabilization excursions in the event of a system disturbance. To prevent this drift, a deadband about V ref holds the I SVC at or near zero value, depending on the location of the deadband. Thus the reactive power is kept