Resistive Load Bank Product

Overview

A resistive load bank is a controlled artificial load: a cabinet of switched resistor groups that converts electrical power directly to heat at unity power factor. It exists because standby power equipment cannot be trusted untested. A diesel generator that has only ever idled will wet-stack and may fail under a real transfer; a UPS battery string shows its true capacity only under a timed discharge. The load bank applies a known, repeatable kilowatt demand so commissioning engineers can verify voltage regulation, frequency stability, transient response, and thermal endurance against specification.

This unit absorbs 500 kW continuously at 400 V three-phase. All power lands in the Resistor Element Bank — 48 helically wound Resistor Elements of iron-chromium-aluminum alloy strung across the cooling duct on Ceramic Insulators. FeCrAl is the standard choice: its resistivity is high and nearly flat with temperature, so the applied load stays within a few percent as the elements heat from ambient to dull-red, and its alumina-forming surface survives years of thermal cycling in open air.

How it works

Load is applied in steps, not continuously. The elements are grouped into branch circuits collected on Element Busbars, and each group is switched by one of twelve Load Step Contactors in the Step Switching assembly. The step sizes are graded — 5, 5, 10, 20 kW then four 50s and four 65s — so combinations resolve any load from 5 to 500 kW in 5 kW increments. The contactors are AC-1 rated devices doing easy resistive duty; each step circuit carries its own Step Fuse. A Control Transformer taps the test source itself to power the fan and controls, so the unit needs no separate auxiliary feed (an external control input is provided for battery-discharge testing where the DC source cannot power the fan).

Cooling is the limiting subsystem. At full load the element bank must reject 500 kW of heat, which the direct-drive Blower Motor axial fan does by forcing roughly 38,000 m³/h of ambient air through the Intake Louver, across the element rows, and out the Exhaust Hood at up to 150 °C above ambient. The Airflow Switch is the critical interlock: a differential-pressure vane that must prove airflow before the controller will close any contactor, and that sheds all load within seconds if the fan stalls. Without moving air the elements would exceed their 800 °C continuous rating in well under a minute.

Control and metering

The Load Controller is built around an Microcontroller that drives the contactor coils, reads three Current Transformers and a fused Voltage Tap, and computes true-RMS volts, amps, kilowatts, and frequency per phase on the LCD Panel. Because the metering is internal, the operator sees exactly what the source under test is delivering — no clamp meters needed at the generator. Automated profiles step the load through standard acceptance sequences (typically 25/50/75/100% holds of 30–60 minutes each per NFPA 110 commissioning practice) and log the results. The tethered Handheld Remote lets the test engineer stand at the generator control panel, watching its gauges while stepping the load.

Protection

Protection is layered in the Protection System assembly. Auto-resetting Overtemperature Thermostats in the exhaust stream drop all steps if discharge air passes roughly 200 °C — the signature of blocked airflow or a failing fan. One-shot Thermal Fuses embedded in the element frame back them up; they open permanently at a higher threshold and force a service visit rather than allow repeat overheating. Branch Fuses protect the control wiring and a pair of Relays implements the trip-and-alarm logic, dropping a dry contact to the test recorder when anything sheds load.

Construction and use

The housing is galvanized, powder-coated Sheet Metal Panel on a channel-steel Base Skid with fork pockets, plus four certified Lifting Eyes for crane handling — these units move between sites constantly. Test cables land on four 400 A Camlock Receptacles for temporary hookups or Main Lugs where a bank is permanently installed beside a generator. Louver Panels ventilate the switching compartment, which is partitioned from the hot duct.

Resistive banks load only real power (kW) at unity power factor. Testing alternator excitation and voltage regulators at rated 0.8 power factor requires adding inductive (reactive) sections, which is why large commissioning jobs pair a resistive bank like this with a separate reactive trailer.