Static Var Compensator (SVC)
A Static Var Compensator (SVC) is a shunt-connected FACTS (Flexible AC Transmission System) device used to provide fast dynamic reactive power compensation in electrical power systems. It regulates system voltage by rapidly generating or absorbing reactive power (MVAR) through controlled switching of reactors and capacitor banks using thyristors.
SVCs are widely used in high-voltage transmission networks, industrial plants, renewable energy systems, and power quality applications.
1. Working Principle
An SVC controls the reactive power flow by varying its equivalent susceptance:
When the system voltage is low:
·SVC supplies reactive power (capacitive operation)
·Voltage increases
When the system voltage is high:
·SVC absorbs reactive power (inductive operation)
·Voltage decreases
2. Main Components
A.) Thyristor Controlled Reactor (TCR)
Function:
·Provides continuously variable inductive reactive power
Construction:
·Reactor coil
·Anti-parallel thyristor valves
·Control system
Operation:
·Thyristor firing angle controls reactor current.
B.) Thyristor Switched Capacitor (TSC)
Function:
·Provides step-controlled capacitive reactive power
Features:
·Capacitor banks switched by thyristors
·Fast switching response
·No mechanical switching delay
C.) Fixed Capacitor Bank (FC)
Function:
·Provides constant capacitive compensation
D.) Harmonic Filters
Purpose:
·Absorb harmonics generated by thyristor switching
·Improve voltage waveform
Common filter types:
·3rd harmonic filter
·5th harmonic filter
·7th harmonic filter
E.) Control System
Includes:
·Voltage regulator
·Thyristor firing controller
·Protection system
·Measurement circuits
3. Types of SVC Configurations
A.) TCR + Fixed Capacitor (TCR-FC)
Characteristics:
·Variable inductive compensation
·Fixed capacitive output
Applications:
·Transmission voltage control
·Industrial load compensation
B.) TCR + TSC
Characteristics:
·Smooth inductive control
·Step-controlled capacitive switching
Advantages:
·Better voltage regulation
·Reduced harmonic generation
C.) TSC Only
Characteristics:
·Capacitive reactive power support
·Very fast switching
Applications:
·Voltage support systems
4. Operating Modes
Capacitive Mode
SVC supplies reactive power:
·Improves voltage stability
·Supports weak grids
·Corrects low power factor
Inductive Mode
SVC absorbs reactive power:
·Prevents overvoltage
·Controls lightly loaded transmission lines
5. Typical Specifications
·Voltage class: 1 kV – 765 kV
·Capacity: ±10 MVAR to ±1000 MVAR
·Response time: 1–3 cycles
·Frequency: 50/60 Hz
·Connection: Shunt
·Cooling: Air/water cooling
·Control: Thyristor-based
6. Advantages
·Fast voltage regulation: Millisecond-level response
·Improves stability: Supports transmission voltage
·Dynamic reactive compensation: Handles changing loads
·Improves power factor: Reduces reactive power demand
·Increases transmission capacity: Improves power transfer capability
·Reduces voltage flicker: Stabilizes fluctuating loads
7. Applications
Transmission Systems
·Voltage stabilization
·Long transmission line compensation
·Power oscillation damping
·Increased power transfer capability
Renewable Energy Plants
·Wind farms
·Solar farms
·Grid code compliance
Industrial Loads
·Electric arc furnaces
·Rolling mills
·Welding plants
Railway Power Systems
·Voltage balancing
·Flicker reduction
8. SVC in Power Grid Applications
A typical HV SVC installation includes:
Transmission Bus → Circuit Breaker → SVC Transformer → Thyristor Valves → Reactors + Capacitor Banks + Harmonic Filters
It provides:
·Dynamic voltage support
·Reactive power balancing
·Improved grid stability
·Reduced voltage fluctuations
Static Var Compensator summary:
An SVC is a thyristor-controlled reactive power compensation system that dynamically regulates transmission voltage by absorbing or supplying MVARs. It is one of the most widely deployed FACTS devices for voltage stabilization, power quality improvement, and increased transmission system reliability.