How does a static VAR compensator (SVC) work?

Short Answer:

A Static VAR Compensator (SVC) is a power electronic device used in power systems to control reactive power and maintain voltage stability. It works by rapidly adjusting the amount of reactive power (both capacitive and inductive) injected into or absorbed from the system, based on the voltage and load conditions.

SVCs use thyristor-controlled reactors (TCR) and thyristor-switched capacitors (TSC) to provide smooth and fast control of reactive power. By doing so, SVCs help improve power factor, reduce transmission losses, and stabilize voltage during disturbances or load variations.

Detailed Explanation:

Working of static VAR compensator

A Static VAR Compensator (SVC) is part of the Flexible AC Transmission System (FACTS) devices used to improve the performance of electrical power systems. It dynamically manages reactive power compensation, which is essential for maintaining the voltage profile, reducing power losses, and improving system stability.

SVCs are typically installed in high-voltage transmission networks and at large industrial plants where rapid changes in load and voltage can negatively impact system performance. Unlike fixed capacitor banks, SVCs offer real-time and continuously variable reactive power control.

Main Components of an SVC:

  1. Thyristor-Controlled Reactor (TCR):
    • A variable inductor controlled using thyristors.
    • It absorbs inductive reactive power.
    • The conduction angle of thyristors determines the amount of inductive VAR absorbed.
  2. Thyristor-Switched Capacitor (TSC):
    • A capacitor bank switched ON or OFF by thyristors.
    • Supplies capacitive reactive power in steps.
    • Responds rapidly without mechanical switching.
  3. Harmonic Filters:
    • SVCs generate harmonics due to thyristor switching.
    • Filters are installed to remove these unwanted harmonic frequencies.
  4. Control System:
    • Continuously monitors bus voltage and system conditions.
    • Sends signals to adjust thyristor firing angles to maintain desired reactive power levels.

How SVC Operates:

  1. Reactive Power Compensation:
    • If the system voltage is too low, the SVC injects capacitive reactive power using TSC to raise the voltage.
    • If the voltage is too high, the SVC absorbs reactive power using TCR to lower the voltage.
    • It balances the reactive power in the system dynamically and precisely.
  2. Fast Response:
    • Because thyristors are used instead of mechanical switches, SVCs can respond within milliseconds to sudden load changes.
  3. Voltage Control Mode:
    • SVCs often operate in voltage regulation mode, automatically adjusting VAR output to keep voltage within the desired limits.

Benefits of SVC in Power Systems:

  • Maintains voltage stability during fluctuating loads.
  • Improves power factor by supplying or absorbing reactive power.
  • Reduces transmission losses by minimizing excess reactive power flow.
  • Improves system reliability and supports heavy or dynamic loads.
  • Avoids over-voltage or under-voltage conditions during faults or switching.

Applications:

  • High-voltage transmission lines
  • Steel plants, arc furnaces, and cement factories
  • Renewable energy systems (wind and solar farms)
  • Traction substations in electric railways
Conclusion:

A Static VAR Compensator (SVC) works by using thyristor-based control of reactors and capacitors to inject or absorb reactive power as needed. It ensures real-time voltage control, enhances power system stability, and supports efficient transmission. Its fast response and dynamic regulation make it an essential tool in modern electrical power networks, especially where loads are large and rapidly changing.