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.