In addition to supplying electrical power to the transmission grid, nuclear generating stations rely on the grid to provide power into the facility to support critical equipment during upsets. Although backup power supplies exist, such as diesel generators, the offsite power circuits are considered to be the "preferred power supplies" and must be kept at a high state of readiness. During certain operating conditions, the nuclear unit's generator is utilized to help support the voltage of the nearby high-voltage transmission system. If the offsite power circuits are served from the same high-voltage system, events that would result in tripping of the generator could also cause a depression of voltage on the offsite circuits due to loss of this voltage support. Nuclear operators must ensure that post-trip voltage levels are adequate to support critical equipment, such as emergency pumps and valves, during extreme postulated events, such as the rupture of reactor coolant system piping. Nuclear engineers utilize analytical models of their generating station electrical distribution system to determine the switchyard voltage level needed during various scenarios, but usually rely on outside organizations, such as transmission system operators and planners, to predict the change in switchyard voltage as a result of a nuclear generator trip. These organizations utilize complex models of the transmission system to make this determination. This paper proposes a simplified approach to predicting post-trip switchyard voltage utilizing data that do not rely heavily on outside organizations.
AbstraciA new method was developed by Palo Verde Nuclear Generating Slation (PVNGS) electrical design engineering personncl to updatc the plant auxiliary power system loading, voltage regulation, and short circuit calculations. Innovative techniques were used to model all significant circuit elements and switching arrangements of the AC distribution system from the switchyard to the ter"nals of all three-phase load equipment A computer prowas developed in-housc to interpret the network model. retrieve component data from existing databases, and generate comprchcnsive load flow, voltage, and short circuit results. The program provides a means to quickly and easily run "what if' scenarios to analyze any credible plant event. This method has provided plant engineers with a flexible and readily-available tool which has resulted in a bcttcr understanding of the dismbution system performance and a fully auditable, easy to maintain calculation.
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