When Using Generator Power, The Harmonic Filter Capacitor Must Be Disconnected

Industrial power systems often require a robust harmonic filter to maintain power quality. However, operating these systems on backup generator power introduces a severe risk. When a generator powers a circuit with connected capacitors, it can trigger a dangerous phenomenon known as self-excitation, leading to destructive overvoltages.

The Danger of Generator Self-Excitation

Why does generator self-excitation occur? When a backup generator connects to harmonic filtering equipment, the leading power factor caused by the capacitors opposes the generator's magnetic field. This forces the internal voltage to rise rapidly beyond safe operational limits, threatening the insulation of the entire electrical network.

To prevent generator self-excitation overvoltage, operators must isolate capacitors or switch off the automatic harmonic filter before transferring the load to a backup generator. When the generator operates, the leading reactive power from capacitors destabilizes the generator's voltage regulation, resulting in severe voltage spikes that damage connected industrial components.

Mitigation Protocol

Preventing electrical failure during generator operation requires strict adherence to power isolation procedures. Engineers utilize specific mitigation steps to protect their infrastructure:

1. Isolate the Filter: Disconnect all shunt capacitors before switching the transfer switch to generator power.

2. Monitor Power Factor: Ensure the load remains slightly lagging to maintain generator stability.

3. Deploy Smart Filtering: Utilize an ahf harmonic filter that dynamically adjusts mitigation without fixed capacitive banks.

Selecting Safe Mitigation Systems

Fixed vs. Dynamic Solutions

Fixed capacitor banks present the highest risk during islanded generator operation. Implementing an automatic harmonic filter can mitigate this risk by automatically disconnecting capacitive elements during low-load or backup power scenarios, preventing voltage amplification.

Cost and ROI of Active Mitigation

While traditional passive systems present self-excitation risks, active solutions offer a safer alternative. Evaluating the active harmonic filter cost against potential generator damage reveals long-term financial benefits. Active systems inject compensating current precisely, eliminating the dangerous capacitive spikes associated with traditional passive networks