Modelling and simulation of degraded and loss of voltage protection scheme for class 1E bus of a nuclear power plant

Protection of Class 1E bus is fundamental for safe operation of a nuclear power plant. Protection of this bus from under-voltage conditions is done by using a special two level or multi-level protection scheme. In this scheme, if the utility generator power is lost, power to Class 1E bus is supplied from the back up offsite power source. In case the offsite power is also unavailable due to any fault, then power to this bus is supplied from the diesel generator. However, changeover to diesel generator is expensive and any nuisance tripping to the diesel generator must be avoided at any cost. In this paper the authors simulate loss of voltage and degraded voltage protection systems for an automatic bus transfer scheme for Class 1E bus protection of a nuclear power plant.