The earthquake and subsequent tsunami that hit the Fukushima Dai-ichi nuclear power plant on March 11, 2011 precipitated a loss of offsite power (LOOP) event, which was followed by a loss of all AC power sources otherwise known as a station blackout (SBO). The tsunami caused all but one of the on-site emergency diesel generators (EDG) to fail resulting in an inability to restore operation of the reactor cooling systems. The inability to restore power in time to support critical cooling systems lead to meltdowns in units 1, 2 and 3 and overheating of the unit 4 spent fuel pool. This event has certainly raised awareness of the critical need for reliable backup power in the event of a LOOP event. While no control system could have ensured operation of the emergency diesel generators due to the utter devastation of the EDG equipment and their fuel supplies; this event and the subsequent failures of the reactor and fuel storage pool coolant systems have raised public and operator awareness of the importance of backup power systems. This paper discusses the design and implementation of both a digital automatic voltage regulator (AVR) and digital engine speed controller (ESC) that are designed to meet the stringent requirements of a Class IE safety related nuclear power plant application. These controllers in conjunction with a digital IE PLuS 32~? Distributed Control System provide reliable control and monitoring of an EDG to ensure safe and continuous operation of the critical power plant systems if a LOOP event should occur.
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