SVG Reactive Current Compensation Explained

SVG reactive current compensation is the controlled injection or absorption of current that corrects the reactive component seen by a plant source. Instead of switching fixed capacitor steps, a static var generator measures the electrical system, calculates the required current and uses power electronics to produce a continuously adjustable response. This makes SVGs useful where load changes quickly, inductive and capacitive conditions alternate, or harmonics and unbalance must be considered alongside power factor.

The CNBYG SVG ürün sayfası is the product reference for this article. Exact current, voltage, topology, control modes and installation limits must come from the selected model’s documentation and the site’s measured one-line.

The compensation point must be stated before any calculation. “Improve the plant power factor” is incomplete unless the drawing identifies the bus, feeder or load group being measured. The same SVG can make the incomer look better while leaving a downstream motor group unchanged if the CTs are placed elsewhere. Treat the boundary, sign convention and priority mode as part of the equipment specification.

What the SVG is correcting

In a three-phase system, apparent power contains active power and reactive power. Motors, transformers and reactors normally draw inductive reactive current; cables, lightly loaded transformers and capacitors can create a capacitive component. The source current is the vector sum of active and reactive components. If the reactive component is reduced at the correct measurement point, source current and apparent power fall for the same useful kW.

An SVG does not create active energy. It changes the phase relationship and waveform of current so that the source supplies less unwanted reactive current. The controller can target a power factor, a reactive-current value, a voltage-support objective or a coordinated combination, depending on the model and approved settings.

How the control loop works

The exact algorithm is model-specific, but a commissioning engineer should be able to identify these functional stages:

1. Voltage and current sensors establish phase, magnitude, frequency and measurement direction.
2. The controller separates active, reactive, harmonic and unbalanced components according to the enabled mode.
3. A reference current is generated for the selected compensation target.
4. The converter produces a current that tracks the reference within its voltage, current and thermal limits.
5. Feedback verifies the result and reduces or limits output when protection or capacity boundaries are reached.

The measurement point matters. A CT at the feeder incomer produces a different target from a CT downstream of one motor group. A reversed CT, wrong ratio or wrong phase mapping can make a correctly functioning SVG appear to worsen the power factor. The SVG troubleshooting guide shows how to separate measurement faults from sizing faults.

Reactive-current compensation modes

Use the table as a planning aid. It describes common objectives, not a promise that every model supports every mode simultaneously.

Sizing the required current

Start with measured kW, kvar and voltage at the intended compensation point. If the target is a power factor, convert the target and measured active power into a reactive requirement, then add margin for load variation and measurement uncertainty. If harmonics or unbalance are also required, reserve current for those functions instead of adding their numbers blindly.

At a fixed voltage, a larger kvar demand means more reactive current. At a lower voltage, the same kvar needs more current. That is why the article on how grid voltage affects SVG output capacity should be reviewed before selecting a model. The selected current rating must also fit the feeder, breaker, cable, transformer and cabinet thermal limits.

Build margin from measured duty rather than from connected motor nameplate power. A motor may run lightly for much of the day, while a short production step creates the highest reactive demand. Conversely, a transformer may draw magnetizing current even when the process load is low. Record the worst normal state, the expected voltage at that state and the current already reserved for harmonic or unbalance compensation. If the plant has a generator transfer, include the generator voltage and short-circuit conditions as a separate case. The result should state both the continuous current requirement and any permitted short-time duty, with the protection response documented for each.

Measurement and CT checks

Verify CT ratio, polarity, phase assignment, location, burden, shorting arrangement and the controller input range. Confirm voltage sensing uses the same phase reference as the current measurement. Do not assume that a label on a drawing matches the installed conductor; trace each phase and record the result.

Compare the SVG display with an independent analyzer while the load is stable. Use the same sign convention and define whether leading kvar is positive or negative. A display that looks numerically plausible can still be reversed by one phase or one CT. Correct the measurement chain before changing compensation gain.

Interaction with capacitor banks and generators

An SVG can operate alongside a capacitor bank, but the control objectives must be coordinated. A fixed capacitor can create leading current at light load; the SVG may need to absorb it or reduce inductive support. APFC steps can hunt if both controllers respond to the same error with similar timing. A generator, UPS or active front end can change the voltage stiffness and harmonic spectrum.

Define ownership of the target. Decide which device controls base reactive power, which device handles fast variation and which device is allowed to operate near its limit. Record minimum-load rules and interlocks. The SVG vs SVC comparison provides broader application context, while the site control narrative should govern actual settings.

Commissioning sequence

Commissioning should move from safe inspection to controlled energization:

1. Confirm the approved one-line, phase sequence, CT schedule, voltage range and protection settings.
2. Inspect mounting, cable entry, clearances, ventilation and isolation points.
3. Energize control power and confirm no alarm before enabling compensation.
4. Verify measured voltage, current direction, phase assignment and frequency.
5. Enable one compensation objective at a conservative target and compare analyzer readings.
6. Apply representative load steps and observe current tracking, overshoot and recovery.
7. Enable additional objectives only after confirming the current allocation and priorities.
8. Record as-left settings, traces, alarms, ambient, load and acceptance signatures.

The SVG commissioning test checklist can be used to structure that evidence. A commissioning result should state what was enabled and what was intentionally left disabled; otherwise later teams may mistake a limited test for a full performance guarantee.

When the plant uses a central controller, document which signal has priority over the local SVG target and what happens when communication is lost. A safe fallback should be defined before the first load step. The record should also identify whether the measured kvar is signed at the source or load side, because reversing that convention can make a correct response look incorrect during review.

Reading the result

Evaluate both the source and the load side. A better SVG display value is not sufficient if the incomer still sees unexpected kvar. Compare source current, voltage, kW, kvar, PF, harmonic current, SVG output and any other compensator output at the same timestamps. Look for saturation, clipping, repeated alarm states or a change in the measurement boundary.

Do not judge a fast controller from one screenshot. Use a time trace that includes load changes. A stable result at one operating point may hide poor coordination at light load or during a generator transfer. Save raw files, not only a final average.

Sık sorulan sorular

Does reactive-current compensation reduce the plant’s kW consumption?

It normally reduces source current and apparent power, not the useful active power consumed by the load. Any kW change must be measured and attributed separately.

Can an SVG replace every capacitor bank?

Not automatically. Compare voltage, load variation, harmonic environment, required speed, cost, redundancy and operating strategy. A coordinated hybrid system may be more appropriate.

Why can the SVG show output while the incomer power factor stays poor?

The CT boundary may be wrong, another device may be creating reactive current, the unit may be undersized, or the display and incomer use different sign conventions. Compare synchronized measurements.

What should be included in the handover pack?

Include the one-line, CT and voltage schedule, settings, firmware, protection values, traces, alarm history, test instruments, load states, limitations and signed acceptance record.

Sonuç

SVG reactive current compensation is a measurement-and-control function, not simply a box that adds kvar. Define the compensation boundary, verify CTs and voltage references, size the shared current budget, coordinate other devices and prove the result with synchronized traces. That process turns a nominal product rating into a defensible plant performance record.

Neutral video: active-filter control background

The IIT Roorkee lecture below gives neutral background on shunt active-filter operation. It is educational context, not a model-specific SVG setting procedure.