What is it and why is it necessary?
The phrase Load Banking is used in the power generation business to associate the process of applying a substitute electrical load to a generator system. The generator is sized larger than the applied emergency load and critical loads should never be disrupted or put at risk. Because of these factors, building loads are not necessarily the best choice to use in troubleshooting a generator or for full load exercises.
To maintain the Emergency Generator’s health, "load banking" is the best way to certify optimum performance. By utilizing a portable load (e.g. Load Bank) the technician controls the load applied, thereby replicating building loads without disrupting normal business operations. To certify full load capabilities, load is typically applied to 80% of the generators' rating. Load Banking provides a way for the technician to determine that all systems that make up a Generator are fully functional. Examples of these systems are; fuel, cooling, exhaust, intake, turbo charger, lubrication, governor, voltage regulation, just to name a few. This type of testing can be used to commission power systems and should be used annually by everyone responsible for an emergency power system to keep the internals clean and certified.
I am aware of one customer in particular that didn't load bank their generator system. One night during a power outage, the system was put to the ultimate test and it didn't hold up. You see, one cylinder was leaking fuel past the injector, subsequently washing the lubricating oil off the cylinder walls. Catastrophic failure ensued. Had the maintenance people performed a "Load Bank" on a regular basis, they might have found the specific problem long before the malfunction and avoided a costly repair.
To keep an emergency system reliable and to avoid such disasters, the generator should be run weekly, at no load, for a minimum of 15 minutes or until the jacket water temperature stabilizes. On a monthly basis, the building load should be transferred to the Generator(s) for a minimum of thirty minutes. Annually, the system should be certified utilizing a load bank to load the generator system to 80% of its rating, verifying 100% capability with short durations at 100%. This test should be performed for no less than one hour, however, best practice is to run the system for four hours, if possible. Each load bank test should be documented with all values recorded.
Most generator systems are facility specific and unique to each installation. For best results, generator system owners and facility managers should consult with their service provider to develop a maintenance program that is best for their facility.
Bob Piske,
Power Generation Specialist