Maintenance (load bank testing)

Load bank testing of standby gensets is a preventive maintenance practice for an emergency power supply system (EPSS). The testing is primarily meant for diesel-powered gensets. The main purpose of this testing is to help ensure the genset’s reliable operation during utility power failure. If this testing is performed regularly, it can extend the genset’s life.

When conducting load bank testing, plant engineers run gensets under a full load for an extended period of time–typically, two to four hours. However, providing such a load for this testing from the existing facility load may not be practical because of the risk of power interruption to critical computer, life safety, or communication equipment in the facility. Any interruption of power to these loads may cause a loss of data, operations, or may jeopardize personal safety.

The main reason for load bank testing is to raise the operating temperature (i.e. combustion temperature) of the gensets. In order to achieve this full operating temperature, diesel engines must operate with sufficient load for an extended period. If the engine can’t operate at sufficient load for an extended period, some fuel remains unburned; carbon builds up in the stack, and wet stacking results. Wet stacking is a common problem for diesel generators that are operated for extended periods with light or no loads applied. The unburned fuel accumulates in the exhaust system, thereby rendering the fuel injectors, engine valves, and exhaust system, foul. Wet stacking not only reduces the operating performance of the gensets, it also creates a significant fire hazard.

A generator needs to run under full load for several hours to reach the full operating temperature. This operation “burns out” the accumulation of unburned fuel and helps to get the engine and exhaust system back in shape. When the exhaust stack smoke is nearly invisible, the system has been cleaned of excess oil, fuel, and hydrocarbon buildup.

The main requirement of such testing is a load bank, an artificial electrical load that can bring the engine up to full operating temperature. The purpose of a load bank is to accurately mimic the operational or “real- load” that a genset will experience in actual application. However, unlike the “real- load”, which is unpredictable and random in value, a load bank provides a contained and controlled load. This load bank may be a portable unit that is designed to be rolled up to the generator being tested or it may be trailer mounted for generator sets in the 1-3 MW range. The load bank also includes control and accessory devices required for its operation. The three most common types of load banks are resistive load banks, reactive load banks, and capacitive load banks.

Load banking of the genset tests the engine’s ability to produce the full-rated KW output and the generator’s ability to produce the KVA output. It confirms the generator’s ability to come up to full load and to provide continuous power without overheating or possibly shutting down. Testing also evaluates other critical system readings, such as oil and fuel pressure, to make sure the engine is well lubricated and is getting enough fuel to produce the power the generator requires. Power system specialists recommend testing the generator systems once a year at full load with a load bank.

The National Fire Protection Association’s NFPA Code 110 – Standard for Emergency and Standby Power Systems, 2005 Edition, specifies load bank testing for EPSS as a requirement by law where life safety electrical needs are involved. Section 8.4.2.3 of this code states the generator must be run at a supplemental load of 25% of nameplate rating for 30 minutes, followed by 50% of nameplate rating for 30 minutes, followed by 75% of nameplate rating for 60 minutes, for a total of two continuous hours.

How Prime Power can help you in load bank testing
Prime Power has the expertise and the equipment to ensure your generator systems operate efficiently when you need them. We provide experienced technical support and trained personnel to oversee load bank testing.

Prime Power has load banks that can handle wet stacking, diagnostics, and troubleshooting. We supply the load bank, cables and an experienced test engineer who will conduct the test safely. The test engineer has the ability to assess the performance of the equipment throughout the test.

Prime Power monitors critical engine parameters such as oil pressure, engine temperature or fuel pressure. We record these readings to ensure that once the unit reaches full-rated load, it runs at normal operating temperatures and pressures. We deliver a full report of the readings to show your equipment’s activity including generator output readings such as voltage, amperage, KW amount, etc.

Prime Power backs up each test with complete written reports detailing any unusual occurrences, recommended remedial work, or suggested improvements. We include a quote for any recommended work.