Analysis of Open-Phase Conditions in Korean Standard Nuclear Power Plants and Fault Detection Scheme

Abstract

Because of partial losses of power known as “open-phase faults”, controlled reactor shutdown has occurred in nuclear power plants around world. Depending on transformer wiring and loading, such conditions can be difficult to detect, because phase voltage measurements can appear to be normal. Many of the identified events went undetected for several weeks. These findings were sufficient for staff to conclude that an open phase condition is a credible event having safety significance and must be considered in the electric power system design for nuclear power plants. This paper elaborates the processes and results of the open-phase fault studies on the standard nuclear power plants in Korea. The ETAP unbalanced load flow module is used for the system analysis. The analysis described in this paper has been performed to determine the response of unit auxiliary transformers and standby auxiliary transformers during open-phase conditions to aid in the development of system protection schemes designed to detect such conditions.