Testing backup power systems with Load Banks

What are load banks?

Load banks are resistive devices that are used to simulate electrical loads for testing generators and other backup power systems. They allow technicians to test the full load capacity and performance of generators without actually connecting the generator to facility equipment. By drawing various load levels on the generator, load banks help identify any issues with the generator's power output or help ensure it can handle peak loads before an actual power outage occurs.

Load bank components

Load Bank consists of several types of resistive elements that can be switched or adjusted to provide different amounts of resistance. The most common elements are banks of steel and alloy grids or coils that act as heat sinks to dissipate excess power drawn from the generator. Air-cooled or liquid-cooled elements are available depending on the required load capacity. Load banks also contain circuit breakers, contactors, control panels and instrumentation to safely test generators at various load levels.

Load bank testing benefits

Generator load testing identifies potential electrical or mechanical problems that may only appear under full load conditions. It also verifies the generator's rated capacity matches its actual output capacity to meet facility power needs during outages. Regular load bank testing guarantees the generator can reliably handle momentary peak loads and allow for load shedding from the facility if needed. The testing also helps comply with maintenance requirements for backup power systems.

Load bank testing process

The testing process involves connecting the generator's output leads to the load bank through appropriate cable sizes based on the generator rating. The generator is then started and allowed to stabilize before switching on the required load levels on the load bank. For diesel generators, a full load test simulates normal running conditions for the generator. Instrumentation monitors the generator's output voltage, current, and other parameters at each load level. Any abnormalities or failure to maintain rated outputs indicate issues requiring further inspection and maintenance. Documentation of all test results helps establish performance baselines and compliance.

Load level selection

Proper selection of load levels is important for effective testing. Typical levels include 25%, 50%, 75% and 100% of the generator's rated capacity applied in steps while monitoring generator parameters. Additional overloads up to 110-125% of rating stress test the generator's surge capacity for essential backup applications. Short duration tests at different loads can be scheduled to simulate varied building load profiles on the generator. Load banks can also simulate loss of a large building load to verify generator load shedding capability.

Resistive load bank types

Several resistor configurations are used in load banks depending on test requirements:

- Low profile, self-contained units mount directly on generator sets for portable testing.

- Cabinet style load banks house resistors, controls and can test multiple generators in central plants.

- Separate resistor cabinets connect to control cabinets for testing larger generators.

- Modular cabinets allow increasing load in increments as generators are paralleled during commissioning.

- Digital load banks provide programming flexibility with microprocessor controls and metering.

- AC load banks test asynchronous generators by simulating induction motor loads.

- DC load banks test engine starters and systems operating on direct current.

Choosing the right load bank type depends on the generator rating, test goals and site accessibility factors. Proper sizing ensures safe testing without overloading generators or load bank components.

Load bank maintenance

With heavy dissipation of wasted generator power, load banks also require periodic maintenance. This includes:

- Cleaning air-cooled resistor elements of dust buildup
- Checking bus bar and electrical connections for corrosion or overheating
- Calibrating instrumentation and control functions
- Testing circuit breakers and contactors by periodic load cycling
- Inspecting resistor grids/wire coils for damage or melting
- Replacing fans/blowers in liquid-cooled systems as needed.

Proper load bank maintenance ensures reliable performance during generator testing programs essential for backup power system compliance and safety.

In the load bank testing plays a key role in verifying generator and backup power system performance before outages. Selecting the right load bank type and load levels along with periodic maintenance helps deliver accurate, repeatable test results to diagnose issues early and certify system reliability.

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