A technical reference for electrical engineers and maintenance teams covering how a static var generator works, installation safety precautions, common fault codes, maintenance intervals, and when to repair versus replace an SVG unit.

What Is a Static Var Generator?

A Static Var Generator (SVG), also called a STATCOM (static synchronous compensator), is a power-electronics device that supplies or absorbs reactive power continuously. Typical low-voltage SVGs operate at 0.4 kV and range from 100 kvar to several hundred kvar per cubicle, with response time under 10 ms. They are used in industrial plants, data centers, commercial buildings and renewable-energy installations where load fluctuation, harmonic distortion or unbalanced three-phase loads require fast reactive compensation.

How an SVG Works

The SVG measures load current through current transformers (CTs) and calculates the required reactive power. The control board sends PWM signals to an IGBT-based voltage source converter, which generates a three-phase AC voltage at the point of common coupling. By adjusting the amplitude and phase of this voltage relative to the grid, the SVG either absorbs or supplies reactive current — continuous and stepless, with no step changes.

The DC side uses a DC-link capacitor bank to maintain a stable DC voltage. After shutdown, these capacitors hold a residual charge and must be discharged before any internal work begins.

SVG vs Traditional Capacitor Bank

Safety Precautions During SVG Installation

● Lock out and tag out (LOTO) — isolate the upstream feeder and verify zero voltage at the unit terminals before opening the cabinet.

● Wait for DC discharge — wait at least the manufacturer-specified time (typically 5–15 minutes) for the built-in discharge circuit to bring the DC bus to a safe level, then verify with a meter before touching internal parts.

● Verify CT polarity and wiring — reversed CT polarity causes the SVG to compensate in the wrong direction and can trip the unit on over-current.

● Check the coupling reactor — confirm mounting torque, insulation resistance and air gap per the installation drawing.

● Ground the cabinet properly — protective earth must be connected before power-up; ground resistance should meet local electrical code.

● Set control parameters before energizing — configure the rated voltage, CT ratio, control mode (voltage regulation or power factor) and protection thresholds.

● Perform a no-load test first — energize the unit without connecting load and verify DC bus voltage, fan operation and communication before closing the output contactor.

Troubleshooting Static Var Generator Faults

When to Replace Rather Than Repair an SVG

Minor faults fan failure, communication issues, loose terminals, firmware updates are repaired on site. Consider replacing the unit or a major subassembly when:

● IGBT module failure in a unit past its design life — repair cost often exceeds half the replacement cost.

● DC-link capacitor degradation — capacitance drops below 90% of rated value, or bulge/leakage appears on multiple capacitors.

● Repeated trips on multiple fault codes — suggests a control-board or main-board failure rather than a single component.

● Cooling system corrosion from a humid or chemically aggressive environment that cannot be cleaned.

● Parts are no longer available — older SVG models may have obsolete IGBTs or control boards; a modern replacement is more reliable than searching for spares.

● Measured losses exceed manufacturer specifications — indicates wear across multiple components.

Maintenance Schedule

● Every 6 months — clean air filters, inspect cabinet seals, check terminal torque.

● Every 12 months — inspect cooling fans, measure DC-link capacitance, verify insulation resistance, inspect CT and PT wiring.

● Every 3–5 years — replace cooling fans as preventive maintenance, regardless of running status.

● Every 5–8 years — evaluate DC-link capacitor bank; plan replacement if capacitance has drifted.

● Firmware — check with the manufacturer for control-board updates that improve performance or fix known faults.

Frequently Asked Questions

Q: What is the difference between an SVG and a capacitor bank?

A: An SVG supplies reactive power continuously within 10 ms with no resonance risk. A capacitor bank supplies reactive power in switched steps and can be prone to harmonic resonance. See the comparison table above for details.

Q: Can an SVG work at low grid voltage?

A: Yes. Because the converter actively regulates its own output voltage, SVG output is less dependent on grid voltage than a capacitor bank. This is one reason SVGs are preferred in weak or unstable grids.

Q: How long does the DC-link capacitor last?

A: Typical design life is 50,000–100,000 hours at rated temperature. Annual capacitance measurement shows whether the bank is drifting toward end of life.

Q: Is a discharge resistor required?

A: Yes. Most units include a built-in discharge circuit; always wait the specified time and verify residual voltage with a meter before opening the cabinet for internal work.

Conclusion

An SVG provides fast, stepless reactive compensation without the resonance risk of a capacitor bank. Most faults are fan, communication or sensor related and can be repaired on site; major IGBT or DC-capacitor failures in an aged unit usually justify replacement rather than repair.