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COMPARISON BETWEEN STATCOM AND SVC

Comparison Between STATCOM and SVC — Which One Fits Your System?

Author: Engr. Aneel Kumar

STATCOM vs SVC comparison infographic — FACTS devices for reactive power compensation
Figure 1: Infographic comparing STATCOM and SVC — technology, operation, and applications.

Introduction

In modern AC power systems, dynamic reactive power control is essential for voltage stability, power quality, and efficient transmission. Two prominent technologies deliver shunt reactive power compensation: STATCOM (Static Synchronous Compensator) and SVC (Static Var Compensator). Both belong to the FACTS (Flexible AC Transmission Systems) family, but they differ in topology, dynamic performance, cost profile, harmonic behavior, and typical applications. This article provides a practical, technical comparison to help engineers, planners, and grid operators choose the right solution.

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Basics: What are SVC and STATCOM?

What is SVC?

A Static Var Compensator (SVC) is a shunt-connected device that uses thyristor-switched capacitors (TSC), thyristor-controlled reactors (TCR), or combinations to absorb or supply reactive power. An SVC is essentially a set of switched passive elements controlled by thyristors to regulate bus voltage and improve stability.

What is STATCOM?

A Static Synchronous Compensator (STATCOM) is a voltage-source converter (VSC)-based FACTS device. It uses power-electronic converters (IGBTs, MOSFETs, or similar) to synthesize a controlled AC voltage behind a coupling transformer; by controlling converter output voltage magnitude and phase, it exchanges reactive power with the grid rapidly and continuously.

Working Principle

SVC operation (technical)

SVCs control reactive power by switching or firing thyristors to change the net susceptance seen by the grid. A TCR modulates inductive reactance by varying firing angle; TSC banks are switched for step changes in capacitance. The net effect is a variable current that leads or lags voltage, controlling bus voltage magnitude.

STATCOM operation (technical)

STATCOMs use a PWM-based VSC to produce a controllable AC voltage. When the STATCOM’s generated voltage magnitude is higher than system voltage, it injects reactive current (capacitive); when lower, it absorbs reactive current (inductive). The response is continuous and near-instantaneous because the converter can vary output without discrete switching of capacitor banks.

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Key technical differences (side-by-side)

Below is a compact comparison that engineers usually consult when selecting between STATCOM and SVC.

Feature SVC (Thyristor-based) STATCOM (VSC-based)
TechnologyThyristor-switched capacitors/reactors (passive elements)Voltage-source converter (IGBTs/IGCTs) with coupling transformer
Response timeFast (tens to hundreds of ms)Very fast (ms level)
Reactive power at low voltageCapability reduces at very low system voltageMaintains capability even at low voltages
Control granularityStepwise + continuous (coarser)Continuous and precise
HarmonicsNeeds filtersPWM easier to filter
CostLower CAPEXHigher CAPEX (but falling)
ApplicationsBulk reactive power, substationsRenewables, weak grids, HVDC
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Advantages and disadvantages

STATCOM — Advantages

  • High-speed response
  • Works at low bus voltages
  • Continuous, precise control

STATCOM — Disadvantages

  • Higher cost
  • More complex maintenance

SVC — Advantages

  • Lower cost
  • Proven, robust technology

SVC — Disadvantages

  • Slower under deep dips
  • Stepwise control limitations

Conclusion

STATCOM is ideal when high-speed, precise dynamic voltage support is required, especially for renewable integration or weak grids. SVC remains cost-effective for steady-state VAR compensation and substation applications. The choice depends on performance needs, cost, and grid strength.

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