SVG for

Reactive Power Compensation in Industrial Plants

A shovel line that punished the capacitor bank

A copper mine in Chile ran an 800 kW electric shovel with 1.2 MW peaks on a 690 V bus. Voltage flicker (Pst) measured 1.6 against the 1.0 limit, and the contactor-switched capacitor bank cycled more than 200 times per day. Contactors failed every seven months, and the site paid a reactive power penalty in eleven of the last twelve months.

The load swings from motoring to regenerative in seconds, and reactive demand follows it. A capacitor bank steps in fixed 50 kvar increments behind a 100 ms contactor delay; it cannot track the swing. An SVG for reactive power compensation can — continuously, in both directions, within milliseconds.

What a reactive power swing costs in the field

Reactive power penalties are the visible cost. Utilities in most industrial markets bill below a set power factor, typically 0.90–0.95, and every month under the threshold adds a surcharge.

The hidden costs exceed the penalty. Contactor-switched banks wear mechanically: at 200 operations per day, a contactor rated for 100,000 cycles fails in under two years. Capacitors in frequently switched banks see repeated inrush currents of 10–20 times rated, which accelerates dielectric aging. Voltage dips during load steps force motor restarts, weld rework, and lighting flicker that operators notice within one shift.

SVG for reactive power compensation versus capacitor banks

An SVG is a voltage-source converter: an IGBT bridge connected to the bus through a coupling inductor, with SPWM modulation controlling the output current. It injects leading current (capacitive) or lagging current (inductive) at any amplitude, and it changes output continuously rather than in steps.

The response difference is the engineering decision. A contactor bank needs 100–500 ms to switch one group; a thyristor-switched bank (TSC) needs 20–40 ms. An SVG reaches a new operating point in under 5 ms, which is fast enough to hold bus voltage stable while a shovel motor reaccelerates.

Control is closed-loop: the unit computes the reactive reference from measured bus voltage and current, and the inner current loop tracks it every switching cycle. This is what makes the output continuously variable — no discrete step exists anywhere in the chain.

Table A — Contactor capacitor bank vs SVG

Sizing: measure the reactive power curve, not the nameplate

The common mistake is sizing from the transformer kVA rating. The correct input is the reactive power curve — a seven-day recording of Q(t) at the PCC, captured with a power quality analyzer over a full production cycle.

Size the SVG to the largest instantaneous reactive deficit, not the average. A plant with a 0.6 average power factor but 0.3–1.0 Mvar swings needs an SVG rated for the 1.0 Mvar peak. Add margin for 45 °C ambient operation, dust loading, and confirmed production growth, and verify the unit's harmonic capability if THDi at the bus already exceeds 8 %.

Set the regulation point to the contract target, typically 0.95–0.99, not to maximum output. The SVG holds power factor at the setpoint and stops there, which prevents overcompensation during light-load night shifts.

Table B — SVG capacity matching matrix

Above roughly 1 Mvar, or on 3.3–35 kV buses, the economic boundary shifts to an MV STATCOM in cascaded H-bridge topology. The control principle is identical; the packaging and insulation class change. On LV buses, a single SVG cabinet covers most ratings up to 600 kvar, and multiple units parallel for larger requirements.

Installation without shutdown

An SVG connects in parallel with the bus through a molded-case breaker, exactly like the capacitor bank it replaces. CTs mount on the line side of the load, the unit energizes, and commissioning verifies phase sequence, CT polarity, and the regulation setpoint. Typical commissioning takes one day, with production running.

The SVG coexists with an existing capacitor bank when the site keeps one. The bank supplies the steady reactive base, the SVG absorbs the dynamic portion, and the two do not fight: the SVG regulates against the measured bus power factor, not against the bank.

The payback calculation

Return to the Chilean mine. The reactive penalty averaged USD 1,100 per month. Contactors and capacitors cost USD 3,200 per replacement cycle — roughly two cycles per year. Motor restarts after voltage dips cost production time that the maintenance log could not fully quantify.

An 800 kvar SVG removed the penalty and the replacement cycle, and Pst dropped from 1.6 to 0.7 after commissioning. The site reported payback at 15 months. Dynamic-load plants typically land between 12 and 18 months, before counting production improvements.

FAQ

Q1: How do I calculate the SVG capacity my plant needs? Record the reactive power curve at the PCC for at least seven days and find the largest instantaneous deficit against your target power factor. That peak, not the average, sets the rating. Verify the selected unit delivers full output at your ambient temperature, and add 10–15 % margin for load growth.

Q2: Can an SVG replace my existing capacitor bank or work alongside it? Both. A common retrofit keeps the capacitor bank for the steady reactive base and adds an SVG for the dynamic part, which minimizes capex. Where the load is almost entirely dynamic, the SVG replaces the bank entirely. The SVG does not resonate with capacitors because it regulates against the measured power factor rather than switching into the bus.

Q3: Do SVG units need regular maintenance? Less than the equipment they replace. Quarterly cleaning of cooling fans and filters in dusty environments, annual torque checks, and DC-link capacitor replacement on its lifetime schedule (roughly five to ten years). There are no contactors to wear and no capacitor groups to re-tune.

Q4: What is the difference between an SVG and an active harmonic filter — and can I install both? An SVG controls reactive power: power factor, voltage stability, and flicker. An AHF controls harmonic current: THDi. Dynamic loads often present both problems, and the two units run in parallel on the same bus without interaction. For sites with both issues, YT Electric supplies combined SVG+AHF cabinets sized from a single measurement report.

Conclusion: match the compensation speed to the load

A capacitor bank fails on dynamic loads not because it is old, but because it cannot move fast enough. An SVG for reactive power compensation tracks the load in milliseconds, regulates in both directions, and removes the penalty, the wear, and the flicker in one installation. Measure the reactive power curve first, size to the peak deficit, and expect payback in 12–18 months — YT Electric's engineering team provides the measurement report and the SVG rating based on your recorded load data.