Resistive vs RLC load banks: what genset and UPS testing actually needs

What a resistive load actually tests

A resistive load bank loads at unity power factor and mainly proves the prime mover: output power, governor behaviour and heat rejection. It is the most common and lowest-cost form of loading, and it is adequate for routine load runs and cooling verification.

What it does not exercise is the excitation system, the automatic voltage regulator (AVR) and, for a UPS, the inverter stage — because the reactive current is close to zero.

Why inductive loading matters

Real grid loads sit around 0.8 power factor lagging. Loading at 0.8 PF forces the alternator to deliver the full current associated with its rated apparent power, which is the only condition under which the excitation system and AVR operate at their design point. The voltage regulation, transient voltage dip and recovery-time requirements in ISO 8528 and GB/T 2820 are only meaningful with reactive load applied.

Capacitive loading and modern power electronics

IT loads in data and computing centres are typically capacitive, and PV inverters and storage PCS can operate at leading power factor. Capacitive loading drives an alternator toward under-excitation, which can trip loss-of-field protection or cause voltage oscillation. Commissioning tests for computing-centre power systems increasingly require load banks with capacitive capability for exactly this reason.

Form factor: rack, wall-mounted or containerised

Rack-mounted banks suit permanent installation in a test hall or data centre and are easy to parallel for more capacity. Wall-mounted units fit sites with limited floor space. Containerised units are for high-power, transportable field testing, with their own airflow path and weather protection. LANDI's RLC load banks cover AC 400V to 13.8kV up to 10,000kW per unit in all three form factors, with remote network control and parallel operation.

A workable test plan

A complete genset acceptance test normally includes 25% / 50% / 75% / 100% step loading, a steady-state run at rated load and 0.8 PF, transient voltage and frequency checks on load acceptance and rejection, and a continuous full-load temperature-rise run of at least several hours. Where the plant supplies a computing centre, add a stability check under capacitive load.