Testing to Evaluate Battery and Battery Charger Short Circuit Current Contributions to a Fault on the DC Distribution System (NUREG/CR-7229)

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Publication Information

Manuscript Completed: November 2016
Date Published: February 2017

Prepared by:
W. Gunther
P. Joshi
Y. Celebi
J. Higgins
R. Weidner
K. Uhlir¹

Brookhaven National Laboratory
Nuclear Science and Technology Department
Upton, New York 11973

¹Standby Power System Consultants, Inc.
Woodridge, IL 60517

M. Gutierrez, NRC Contracting Officer Representative, and
L. Ramadan, NRC Technical Monitor

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

On September 25, 2011, at the Palisades Nuclear Plant, both the battery and the battery charger on one DC Class 1E power division tripped on overcurrent when a fault occurred in a downstream DC panel (see NRC Information Notice 2013-17). The response to a fault on the DC distribution system at a nuclear power plant (NPP) can have a significant impact as seen by this event. Therefore, it is necessary to have proper DC fault calculations to design effective DC system fault protection with coordination that would minimize safety system impacts in a fault event. As a result of the significance, the U.S. Nuclear Regulatory Commission (NRC) contracted with Brookhaven National Laboratory (BNL) to investigate the interactions between a battery and a battery charger under fault conditions at the BNL Battery Test Facility. More specifically, BNL conducted tests to determine whether the individual short-circuit current contributions of a battery and a battery charger are independent of each other in a typical NPP DC system configuration. This information is necessary to ensure understanding of the fault characteristics of batteries and chargers individually and in parallel as described in the Institute of Electrical and Electronic Engineers (IEEE) Standard (Std.) 946-2004, "IEEE Recommended Practice for the Design of DC Auxiliary Power Systems for Generating Stations." The results conducted at BNL provide the empirical data to support improvements to industry standards and to the NRC's oversight of DC distribution systems.

BNL used three sets of Class 1E vented lead acid batteries from three different vendors and two battery chargers: one a Silicon Controlled Rectifier (SCR)-type and one a Controlled Ferroresonant (CF) transformer design. A fault condition was applied to each battery and charger individually and to combinations of each battery in parallel with a battery charger to determine the overall fault responses in these configurations.

This report discusses the potential implications on how protective coordination is approached in NPP DC distribution systems and how a fault on the DC distribution system can impact plant operation. The testing demonstrated that the contribution to a fault from a battery charger and the impedance of the DC system circuit should be considered when establishing the settings for the DC distribution system protective devices. Incorrect settings of these protective devices can lead to undesirable system responses.