Static VAR Compensator (SVC)

Overview

• Purpose: Provides fast-acting reactive power on high voltage electricity transmission networks.
• Category: Part of the Flexible AC Transmission System (FACTS) device family.
• Functions: Regulates voltage, power factor, harmonics, and stabilizes the system.
• Comparison: Unlike synchronous condensers (rotating machines), SVCs have no significant moving parts other than internal switchgear.

Historical Context

• Before SVCs, power factor compensation was achieved with large rotating machines such as synchronous condensers or switched capacitor banks.

Design and Operation

• Automated Device: Designed to bring the system closer to unity power factor.
• Key Components: Thyristor-controlled reactors, switched capacitor banks.
• Adjustment: Impedance matching to manage reactive power.

Applications

Transmission

• Purpose: Regulates grid voltage.
• Capacitive Load: Uses thyristor-controlled reactors to consume VARs and lower system voltage.
• Inductive Load: Uses capacitor banks to provide a higher system voltage.
• Combination: Continuously variable leading or lagging power by coupling thyristor-controlled reactors with capacitor banks.

Industrial

• Purpose: Improves power quality near large industrial loads (e.g., arc furnaces).
• Effect: Smoothes flicker voltage.

Components and Mechanisms

• Thyristor-Controlled Reactor (TCR): Reactor may be air or iron-cored.
• Thyristor-Switched Capacitor (TSC): Capacitors controlled by thyristors.
• Harmonic Filters: Smooth out waveform; they are capacitive and export VARs.
• Mechanically-Switched Capacitors or Reactors: Activated by circuit breakers for coarse voltage control.
• Cooling: Deionized water commonly used to cool thyristors.

Harmonics and Filtering

• Issue: Injecting reactive load leads to undesirable odd-order harmonics.
• Solution: High power filters are used to smooth the waveform.

Control and Regulation

• Voltage Regulation: Achieved through closed-loop controllers; can also be manually adjusted.
• Remote Control: Supervisory control for remote adjustment.

Advantages of SVCs

• Response Time: Near-instantaneous response to system voltage changes.
• Operational Point: Often operated close to zero point for rapid correction capability.
• Cost and Performance: Cheaper, higher capacity, faster, and more reliable than dynamic compensation schemes (synchronous condensers).

Disadvantages

• Cost: More expensive than mechanically switched capacitors.
• Integration: Often used in combination with mechanically switched capacitors for steady-state VARs.