Evaluating the transient performance of emergency diesel generator units by computer modeling

Diesel generator units applied as standby power supplies for nuclear power generating stations are required to start, accelerate, and accept engineered safeguards loads within a specified time period. In addition, voltage and frequency at the generator terminals must be maintained within limits during normal and transient conditions, including transients caused by load application and removal. Traditionally, factory tests, site acceptance, and periodic test have been used to demonstrate the capability of diesel generator units. For the factory tests, equivalent loads are used to approximate the dynamic characteristics of the engineered safeguards loads. For site tests, it is difficult to obtain the actual loading that could occur during plant emergency conditions. Also, plant modifications to meet the ongoing regulatory process may require that existing diesel generator units supply more equipment. However, before changes are made to the loading of an existing diesel generator unit, it is necessary to analyze the effect of additional loads on its transient performance. Alternate loading sequences may have to be considered, and it may be necessary to consider replacing the governor or the voltage regulator to accommodate the load increases. The Electromagnetic Transient Analysis Program (EMTP) has recently been used to analyze the transient performance of existing and newly purchased diesel generator units at a nuclear power generating station. A model was developed to represent the dynamics of the diesel engine, governor, generator, exciter/regulator, motors with driven equipment, and other loads