Planning For Success
The primary purpose of many generator sets is to provide emergency power during a power outage. If a situation like this should occur, you need your generator to work as planned to ensure uninterrupted power delivery. However, backup generators can sit for extended periods of time without being used, resulting in a variety of operational problems.
Regularly scheduled load bank testing of generators will help you avoid reduced performance or even a critical failure by verifying system capabilities, identifying preventative maintenance concerns, and ensuring compliance with National Fire Protection Association (NFPA) standards.
What Is a Generator Load Bank Test?
The load bank test applies artificial loads on a generator to attain its maximum kilowatt (kW) output rating and full operating temperature. This contrasts with no load testing which briefly turns on a generator but does little else. In fact, excessive no load testing can lead to wet stacking, a condition where unburned fuel builds up in the exhaust system, reducing engine efficiency and lifespan.
Requiring a portable load bank, this assessment is timed as the kW load is gradually stepped up to monitor the engine’s performance in handling increased power demands over a predetermined period of time. Contractor generators must be run for 8 hours, continuous-duty generators 24 hours, and large, industrial generators should run with a full load for a week.
How to Conduct a Load Bank Test
No matter the length of the test, there are typically six steps to complete.
1. Check generator fluid levels.
Make sure the fuel tank is full and check other fluid levels such as oil and coolant.
2. Start the generator.
Let the generator run until the water temperature stabilizes. Pay close attention for any mechanical issues which may occur. If any do, stop the test to take care of those issues.
3. Connect the loads.
Step load the generator, initially with a 220-volt load followed by incremental 110 loads attached to each leg until peak load is attained.
4. Record the amperage.
Using an ammeter set to measure AC volts, record the amperage of each leg after every load increase. For a single-phase generator, the amount of current measured for each leg should be half the rated output divided by the voltage.
5. Monitor the generator.
As load is increased, continue to look out for issues such as overheating or mechanical failure. If this occurs, immediately end the test to perform repairs/maintenance.
6. Reduce loads gradually.
At the test’s conclusion, remove the load leads gradually. After that, allow the generator to run a light/no load for at least one hour, depending on the length of the test. Before powering down the generator, make sure all loads and cables have been detached at least ten minutes.
Generator Load Bank Test Benefits: Why Do It?
While no load testing – essentially just making sure a generator will start – is a common practice, there are additional benefits from load bank testing:
- Equipment Capability: Confirms generator set can produce peak kW output, and cooling systems operate efficiently under load.
- Preventative Maintenance: Burns off excess fuel buildup to avoid wet stacking from light/no loading, and identifies potential problems to be maintenance before more expensive or catastrophic failures occur.
- NFPA 110 – Standard for Emergency and Standby Power Systems Compliance: NFPA 110 details testing specifications for an emergency power supply system (EPSS) including monthly testing of diesel generators at operating temperature for 30 minutes and every 3 years with a minimum 30% kW load for 4 hours.
Every generator represents a significant investment, and the last thing you want, thanks to infrequent equipment use, is preventable problems. It’s never too early to formulate a maintenance schedule including load bank testing.
Depco Power Systems’ testing center is equipped with two generator load banks, 750kW and 2MW, to test generator sets as well as a dyno facility to evaluate all engines via our critical testing process.