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.

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.

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)
Technology	Thyristor-switched capacitors/reactors (passive elements)	Voltage-source converter (IGBTs/IGCTs) with coupling transformer
Response time	Fast (tens to hundreds of ms)	Very fast (ms level)
Reactive power at low voltage	Capability reduces at very low system voltage	Maintains capability even at low voltages
Control granularity	Stepwise + continuous (coarser)	Continuous and precise
Harmonics	Needs filters	PWM easier to filter
Cost	Lower CAPEX	Higher CAPEX (but falling)
Applications	Bulk reactive power, substations	Renewables, weak grids, HVDC

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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