The time scale of transient voltage stability due to static VAR compensator is

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Explanation: The transient voltage stability of a power system utilizing Static VAR Compensators (SVCs) is typically characterized by a time scale of approximately 1 second. This duration corresponds to the response time required for the SVC's automatic voltage regulator (AVR) to effectively modulate reactive power and stabilize the bus voltage following a disturbance.

Working Principle: An SVC operates as a shunt-connected reactive power compensation device consisting of a Thyristor-Controlled Reactor (TCR) and a Thyristor-Switched Capacitor (TSC). Upon sensing a voltage deviation, the control system calculates the necessary reactive compensation and triggers the thyristors to adjust the firing angles. Because the SVC lacks energy storage elements like rotating inertia, the transient recovery depends solely on the speed of the control loop and thyristor switching, which is fast but constrained by the system's fundamental frequency control cycle.

Key Formulas: $Q_{svc} = V^2 \cdot B_{svc}$ — Reactive power output provided by the SVC susceptance; $\Delta t \approx \frac{1}{f}$ — Typical control response cycle based on system frequency

Key Points: SVCs provide dynamic voltage control by adjusting the susceptance ($B_{svc}$) in response to grid voltage fluctuations.; The 1-second time scale is the standard industry benchmark for transient voltage stability analysis in SVC-compensated systems.; Fast control response is achieved through thyristor switching, which operates within sub-cycle intervals, but the overall system stabilization includes the coupling of lines and loads.

Advantages: Near-instantaneous reactive power support; Effective damping of power oscillations; Improved steady-state and dynamic voltage regulation

Disadvantages: Generates harmonics requiring passive or active filters; Limited capacity for real power support; Susceptibility to resonance conditions

Applications: Transmission voltage stabilization; Flicker mitigation in industrial loads; Power factor correction in heavy load centers

Additional Info: The time scale of 1 second is significantly faster than traditional tap-changing transformers (5-30s) but slower than sub-cycle relay protection.. Options B, C, and D represent values outside the standard design range for the primary transient recovery period of SVC controllers in high-voltage networks.

Answer: A is correct — The transient voltage stability of an SVC-compensated system typically manifests within a 1-second time scale following a disturbance.

Exam Tip: Always distinguish between transient stability (usually

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