NUREG/CR-7148 BNL-NUREG-98563-2012 Confirmatory Battery Testing: The Use of Float Current Monitoring to Determine Battery State-of-Charge Office of Nuclear Regulatory Research AVAILABILITY OF REFERENCE MATERIALS IN NRC PUBLICATIONS NRC Reference Material Non-NRC Reference Material As of November 1999, you may electronically access Documents available from public and special technical NUREG-series publications and other NRC records at libraries include all open literature items, such as books, NRC’s Public Electronic Reading Room at journal articles, transactions, Federal Register notices, http://www.nrc.gov/reading-rm.html. 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DISCLAIMER: This report was prepared as an account of work sponsored by an agency of the U.S. Government. Neither the U.S. Government nor any agency thereof, nor any employee, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party’s use, or the results of such use, of any information, apparatus, product, or process disclosed in this publication, or represents that its use by such third party would not infringe privately owned rights. NUREG/CR-7148 BNL-NUREG-98563-2012 Confirmatory Battery Testing: The Use of Float Current Monitoring to Determine Battery State-of-Charge Manuscript Completed: October 2012 Date Published: November 2012 Prepared by: W. Gunther, G. Greene, M. Villaran, Y. Celebi, and J. Higgins Brookhaven National Laboratory Nuclear Science and Technology Department Systems Engineering Group Upton, NY 11973-5000 Liliana Ramadan, NRC Project Manager NRC Job Code N6542 Office of Nuclear Regulatory Research ABSTRACT In February 2007, the U.S. Nuclear Regulatory Commission (NRC) issued Regulatory Guide (RG) 1.129 Rev. 2, “Maintenance, Testing, and Replacement of Vented Lead-Acid Storage Batteries for Nuclear Power Plants." In this RG, the NRC staff endorsed the Institute of Electrical and Electronics Engineers (IEEE) Standard 450-2002, “Recommended Practice for Maintenance, Testing, and Replacement of Vented Lead-Acid Batteries for Stationary Applications." This standard provides the recommended practices, test schedules, and testing procedures including recommended methods for determining a battery’s state-of-charge to maintain permanently installed vented lead-acid storage batteries (typically of the lead-calcium type) for their standby power applications. Previous versions of this standard suggested that either float current or specific gravity could be used for determining the battery’s state-of-charge. The NRC sponsored the research project described herein to validate the use of float charging current as a measure of a battery’s state-of-charge for batteries that are used in the nuclear industry. This report describes the approach taken, the specific activities performed to achieve the objectives of this research effort, and the results achieved. It provides analysis of the data and offers observations and recommendations for use by the NRC and its licensees. iii TABLE OF CONTENTS Section Page ABSTRACT ................................................................................................................................ iii TABLE OF CONTENTS .............................................................................................................. v LIST OF FIGURES ................................................................................................................... vii LIST OF TABLES ....................................................................................................................... ix EXECUTIVE SUMMARY ........................................................................................................... xi ACKNOWLEDGMENTS ........................................................................................................... xiii 1. Introduction .................................................................................................................... 1 1.1. Background ......................................................................................................... 1 1.2. Program Objectives ............................................................................................ 1 1.3. Research Approach ............................................................................................ 1 2. Testing Protocols ............................................................................................................ 7 2.1. Introduction ......................................................................................................... 7 2.2. Battery String Configuration ................................................................................ 8 2.3. Test Equipment Used ......................................................................................... 9 2.4. Test Cycle Description .......................................................................................10 2.5. Testing Process: Evaluation of Charging Current as a Monitoring Technique ...12 3. Test Results ..................................................................................................................15 3.1. Performance Tests by Battery (Cycles 1-10) ......................................................15 3.2. Float Current Responses on Recharge ..............................................................23 3.3. Specific Gravity Measurements and Response ..................................................30 3.4. Comparison of Float Current and Specific Gravity Responses ...........................39 3.5. Conductance and Connection Resistance Data .................................................40 3.6. Temperature Monitoring Data ............................................................................42 3.7. Summary ...........................................................................................................45 4. Analysis of Test Results ................................................................................................47 4.1. An Assessment of Float Current as a Measure of State-of-Charge ....................47 4.2. Specific Gravity as a Measure of State-of-Charge ..............................................50 4.3. Analysis of Battery Capacity Trends and Capacity Recovery (Test Cycle 11) ....52 4.4. Use of Conductance for Monitoring Battery Condition ........................................57 4.5. Analysis of Temperature Measurements ............................................................59 4.6. “Return-to-service” Tests