test

By Daniel Chavez

April 2018

Maintenance matters

Generator maintenance often includes performing a monthly load bank test at 100 percent load for an extended period. Depending on whether the generator is rated for standby power or continuous prime power, these load bank tests can last 2-12 hours. Load bank testing is a way of ensuring dependable operation of the generator.

Specifically with diesel engine generators, when a unit goes for a long period without running at full capacity, its exhaust system will experience what is called wet stacking. When the generator unit is not running at full operating temperature, wet stacking prevents the fuel from fully combusting, and it leads to the accumulation of unused diesel fuel, moisture, and residue build-up in the exhaust system. This accumulation leads to compromising the service life of the engine generator, preventing the generator from producing full-capacity power, and contributes to increased emission levels.

Technicians also can perform transient-load step testing when conducting load-bank testing. Transient-load step testing involves having a data recorder monitor the load side of the generator, while the load bank is varied at different load steps — 0-25 percent, 0-50 percent, 0-75 percent, 0-100 percent, etc. The data recorder monitors and logs the voltage and frequency response at the different transient steps. This testing allows technicians to confirm that voltage and frequency responses occur according to the manufacturer’s time specifications.

UPS maintenance includes placing the unit in the different operating modes — inverter, battery, and bypass — recording battery cell voltage and conductance readings and monitoring battery cells. Similar to generator maintenance, thermal imaging of conductors, batteries and accessible components is crucial in identifying temperature anomalies within the UPS.

Battery monitoring helps technicians ensure battery cells have adequate capacity and provide important data in order for facilities to decide when to replace the batteries — typically, every three-five years or 7-10 years, depending on the design of the battery cells.