DOT HS 811 553 March 2012

Hydrogen Fuel Cell Vehicle Fuel System Integrity Research

Electrical Isolation Test Procedure Development and Verification

DISCLAIMER

This publication is distributed by the U.S. Department of Transportation, National Highway Traffic Safety Administration, in the interest of information exchange. The opinions, findings, and conclusions expressed in this publication are those of the authors and not necessarily those of the Department of Transportation or the National Highway Traffic Safety Administration. The United States Government assumes no liability for its contents or use thereof. If trade names, manufacturersnames, or specific products are mentioned, it is because they are considered essential to the object of the publication and should not be construed as an endorsement. The United States Government does not endorse products or manufacturers.

Project Report

TABLE OF CONTENTS Page

EXECUTIVE SUMMARY ......................................................................................................... iii

PROJECT REPORT SCOPE.......................................................................................................v

1.0 INTRODUCTION..............................................................................................................1

2.0 TEST PROCEDURE DEVELOPMENT .........................................................................2 2.1 Purpose Statement................................................................................................... 2 2.2 Standards and Regulations Review......................................................................... 2

2.2.1 Summary of Results .................................................................................... 3 2.2.2 Standards and Regulations.......................................................................... 6

2.3 Acceptance Criteria............................................................................................... 21 2.4 Test Instrumentation ............................................................................................. 22 2.5 Test Sequence Development................................................................................. 30 2.6 Data Sheets............................................................................................................ 34 2.7 Final Test Procedure ............................................................................................. 35

3.0 TEST PROCEDURE VERIFICATION ........................................................................36

4.0 ADDITIONAL ANALYSIS ............................................................................................38 4.1 High Voltage Bus Measurement Discrepancies ................................................... 38 4.2 Fuel Cell Coolant Conductivity Testing ............................................................... 41

5.0 CONCLUSION ................................................................................................................47

6.0 RECOMMENDATION FOR FUTURE WORK..........................................................48

REFERENCES.............................................................................................................................49

List of Appendices

APPENDIX A: TEST PROCEDURE

APPENDIX B: TEST PROCEDURE DATASHEETS

APPENDIX C: TEST PROCEDURE VERIFICATION REPORT

Electrical Isolation Test Procedure Development and Verification i

Project Report

TABLE OF CONTENTS (CONTINUED) Page

List of Tables

Table 1. Literature used for HFCV test procedure development. .................................................. 3 Table 2. Megohmmeter market survey results. ............................................................................ 26 Table 3. Procedure verification results. ....................................................................................... 37

List of Figures

Figure 1. Test procedure development diagram. ........................................................................ 1 Figure 2. Conventional time/current zones of effects of DC currents on persons for a

longitudinal upward current path (IEC TS 60479-1: 2005-07) with 100 ohms/volt and 125 ohms/volt references added. .......................................................................... 8

Figure 3. Three expressions representing Ohm's law. .............................................................. 22 Figure 4. Voltage (V), current (I), and resistance (R) of a conductor. ..................................... 22 Figure 5. Insulation breakdown. ............................................................................................... 24 Figure 6. QuadTech 1855 ......................................................................................................... 27 Figure 7. QuadTech Guardian 500 VA..................................................................................... 29 Figure 8. General block diagram for an HFCV with test points and disconnects. ................... 31 Figure 9. Simplified HFCV power system diagram. ................................................................ 31 Figure 10. Potential shock hazard from fuel cell and coolant loop. ........................................... 32 Figure 11. Test points for source without disconnects. .............................................................. 33 Figure 12. Test points for source with disconnects. ................................................................... 33 Figure 13. GM Chevrolet Equinox test point locations. ............................................................. 36 Figure 14. DC to DC converter block diagram........................................................................... 38 Figure 15. Input power filter....................................................................................................... 39 Figure 16. Input power filter DC equivalent circuit. .................................................................. 40 Figure 17. Input power filter AC equivalent circuit. .................................................................. 40 Figure 18. Temperature conductivity test setup. ......................................................................... 42 Figure 19. Glass electrode for megohmmeter. ............................................................................ 42 Figure 20. Glysantin megohmmeter results at increasing temperatures. .................................... 43 Figure 21. New Glysantin sample from Ford results at increasing temperatures. ...................... 44 Figure 22. Aged Glysantin sample from Ford results at increasing temperatures. ..................... 44 Figure 23. Aged Glysantin sample from General Motors results at increasing temperatures. ... 45

Electrical Isolation Test Procedure Development and Verification ii

Project Report

EXECUTIVE SUMMARY The Federal Motor Vehicle Safety Standards (FMVSS) establish minimum levels for vehicle safety, and manufacturers of motor vehicle and equipment items must comply with these standards. The National Highway Traffic Safety Administration (NHTSA) contracted Battelle to develop a procedure for testing electrical isolation on hydrogen fuel cell vehicles (HFCVs) when crash testing without hydrogen. FMVSS 305, Electric Powered Vehicles: Electrolyte Spillage and Electrical Shock Protection, requires electrical isolation as the basis for defining electrical safety and for establishing a criterion for the prevention of electrical shock. Enhancement is required to address electrical safety of hydrogen vehicles, particularly when testing without hydrogen onboard the vehicle.

The current electrical isolation test procedure described in FMVSS TP-305-01, Laboratory Test Procedure for Electric Powered Vehicles: Electrolyte Spillage and Electrical Shock Protection, uses an active onboard high-voltage power system to determine the electrical safety of the vehicle. FMVSS TP-305-01 is written specifically to require full engagement of the test vehicles propulsion system before the crash test. Due to safety concerns, however, some automobile manufacturers and international regulatory bodies are proposing to conduct crash testing of compressed hydrogen vehicles using an inert gas substitute, such as helium. Unlike electric and hybrid electric vehicles, the absence of hydrogen in a hydrogen-fueled vehicle renders the fuel cell inactive, prohibiting the generation of high voltage and preventing the propulsion system from being fully engaged. Consequently, another method for verifying electrical isolation between the high-voltage source(s) and potential human contact points is needed for hydrogen-fueled vehicles if the propulsion system is not engaged fully.

Task Order 4 developed and verified an alternative electrical isolation test procedure for HFCVs with an inactive fuel cell using a megohmmeter or Megger, a piece of test equipment that supplies high voltage and measures the resulting leakage current to the vehicles chassis as necessary to verify the isolation. A systematic approach was used to develop the procedure and was initiated with a test requirements review. The review examined the latest standards and literature from industry and regulatory bodies to solidify the requirements for the final test procedure. In addition to current documentation, Battelle received technical insight and guidance from General Motors Corporation (GMC) and Ford Motor Company. The information was compiled and evaluated on the applicability to electrical safety of postcrash HFCV with an inert gas. The test procedure was written to test electrical isolation of an inactive high-voltage sour