Study of Arc Track
Properties of Plastic Materials When Subjected to DC Voltages Ranging from
12 volt DC – 150 volt DC
Download Summary
Download Final Report - December 15, 2003
Download
Final Report Addendum - October 15, 2004
Download Technical Presentation
Contractor: Underwriters Laboratories
Funding: Jointly Funded by USCAR (45%) and MVFRI (55%)
Purpose:
The automotive industry is evolving automobile designs using greater
electrification of systems and components previously mechanically operated
(e.g. air conditioning, water pumps, oil pumps, heating, and solenoid
operated engine valves). The resulting demands on electrical systems require
upgrading from the traditional 12 volt DC battery supply to a 36 volt DC
battery supply with a nominal 42 volt DC charging circuit.
A potential fire hazard from failures of polymeric materials used for
automotive switches, electrical connectors, etc. has been identified as a
concern when operating at increased DC voltage levels. One specific concern
is the DC arc ignition properties of polymeric materials. A DC electrical
arc, once struck may be more readily sustained than an AC arc due to the
inherent stability of its uni-polarity. In a DC arc, the arc voltage and arc
current do not experience a zero crossover and once DC arcing is established
the arc tends to be self-sustaining. This project has been developed to
document the potential fire hazard associated with the increased DC voltages
and to study ignition properties of polymeric materials when exposed to a DC
high-current arc ignition source. An existing method for evaluating arc
ignition performance of polymeric materials is the High Current Arc Ignition
Test (HAI) using the apparatus described in UL 746A Polymeric Materials –
Short Term Property Evaluations. Under certain normal or abnormal operation
of electric equipment, insulating materials might be in proximity to
electrical arcing. Depending upon the intensity and duration of the arcing,
the insulating material may ignite. The HAI test is intended to simulate
such a condition.
In order to develop a meaningful test to evaluate polymeric materials for
automotive use, modifications to an AC tester will be necessary to operate
at DC voltages. The Research will be conducted in three phases. Exploratory
Research and Equipment Development will be conducted as part of Phase 1.
Phase 2 will Conduct Testing on Automotive Specific Polymeric Materials.
Phase 3 will complete the validation of the DC test procedure through a
series of round robin tests. The work tasks associated with each phase are
as follows:
Phase 1 - Exploratory Research
- Task 1 – Situation Analysis
Literature, standards developed by others, and previous research work
will be reviewed for relevant information concerning the proposed DC-CTI
test.
- Task 2 – Equipment Development
The equipment used for AC-HAI testing will be modified to permit DC-HAI
testing. Testing with the following modifications will be explored:
- Replacing AC voltage supply with a DC power supply.
- Testing with the current that the power supply is capable of
delivering.
- Experimentation to determine the influence of electrode separation
rate and dwell time.
- Experimentation to optimize the withdrawal rate and dwell time at
the maximum electrode separation.
- The use of permanent magnets on either side of the polymeric
material
- Experimentation to verify the effects of electrode polarity on the
movable and stationary electrodes.
- Each test will be conducted at a rate of 40 arcs/minute for a
maximum of 200 arcs or ignition of the test specimen, whichever occurs
first.
- A rationale for each modification will be developed and the relative
influence considered.
- Task 3 – Preliminary Materials Testing
A maximum of 10 polymeric materials will be subjected to preliminary
testing to assure that the developed DC-HAI test protocol incorporates
sufficient control and precision to produce repetitive test results that
would allow the test to be used to establish a polymeric material
performance hierarchy when automotive material are tested as part of Phase
2
Following completion of the above testing, the data will be reviewed to
determine if further areas of exploratory research testing may be
required.
- Tasks 5, 6, & 7 – Draft & Final Report and Presentation Review
From the information obtained in the above tasks, a summary report will
be prepared for Phase 1. This includes draft and final reports along with
a presentation reviewing the results.
Phase 2 – Automotive Testing
- Task 8 – Automotive Materials Testing
A maximum of seventy-Five (75) polymeric materials will be identified
by USCAR/MVFRI for testing by manufacturer and grade designation. These
materials will be taken from 4 groups as follows:
- Group A (25 Materials) – This group will consist of the identical
thermoplastic materials being evaluated as part of the DC-CTI testing.
- Group B (18 Materials) – This group will be the identical materials
used in the Southwest Research Institute cone calorimeter test and will
consist primarily of exterior body materials.
- Group C (25 Materials) – This group of materials will consist
largely of interior materials (e.g. dash material, seat cushion
material, floor carpeting, etc.).
- Group D Fluids (7 Fluids) – This group will consist of under hood
fluids (e.g. power steering fluid, automatic transmission fluid,
windshield washer fluid, motor oil, radiator anti-freeze, brake fluid
and clutch fluid)
For each material, the DC HAI test will be performed for a maximum of
200 arcs or flaming ignition of the test specimen, whichever occurs first.
For each test, the number of arcs and the elapsed time to cause ignition
will be recorded. The voltage and current will be recorded at a sampling
rate of 25 kHz for each test.
Following completion of the above testing, the data will be analyzed
and summarized. This analysis will include a determination of the minimum
total arc energy to cause ignition (up to a maximum of 200 arcs) of each
material tested. Where possible, the performance of the materials on the
DC test will be compared to the performance of the same materials on the
AC test, if previously tested.
- Tasks 10, 11, & 12 – Draft & Final Report and Presentation Review
From the information obtained in the above tasks, a summary report will
be prepared for Phase 2. This includes draft and final reports along with
a presentation reviewing the results.
Phase 3 – Validation of Test Procedure
- Task 13 – Testing Expanded Sample Base
A total of 40-50 polymeric materials will be solicited from 5-10
different suppliers giving specific attention to selecting polymeric
materials typically used in automobiles.
- Task 14 – DC-HAI Test Equipment
Three HAI testers (modified to test using DC voltages) will be obtained
from an outside equipment supplier. These new testers will incorporate all
necessary modifications and safety upgrades to permit DC-HAI testing of
polymeric materials on a routine basis. One of these testers will be
located at each of three different UL domestic test locations.
- Task 15 – Round Robin Testing
A series of round robin tests will be performed to validate the DC-HAI
test procedure. Identical materials will be tested at each of the selected
test locations and the test results obtained compared.
- Tasks 16 – Analysis of Data and Relationships
Following completion of the DC-HAI testing, the data will be analyzed.
The test methodology and results will be subjected to scrutiny for
repeatability, reproducibility, and the ability to represent likely
operation or failure modes.
Following completion of the activities associated with Phase 3, a final
report will be prepared.
|