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Operational Events in Off-Site Power System

| 2016:323 | Mikael Wämundson
This report presents several international events where disturbances in the off-site power system have had impact on the on-site power system and jeopardized the nuclear safety of the plant. A number of experiences from four Nordic NPPs are presented together with the mitigating actions taken to prevent further events.
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Four possible tools are presented in the report that could be further investigated and applied to minimize future incidents and events related to loss of off-site power.

The first tool is a method to detect loss-of-phase, which is presented since this phenomenon was accentuated by the event in Forsmark on May 30, 2013. The method presented utilizes existing IEDs for step-up and start-up transformers.

The second tool addresses the issue of keeping the nuclear units connected to the grid in case of close-up faults in the network in combination with a non-functioning faultclearing system (circuit-breaker). By reducing the fault-clearing time the ability for the NPP to stay synchronized to the grid is increased. The tool presented is double circuitbreakers in series.

The third and fourth tools do not address specific technical problems but are higher level concepts to prevent future incidents and possible events of station blackout. The tools are the concept of “withstand or isolate” and duplicated analyses.