EMI Shielding as a Dielectric Test Medium
A customer requested a solution that could utilize a reusable EMI Shielding cloth to create a 50,000 volt differential for testing molded-Polyethylene utility pole crane buckets.
PROBLEM:
A customer requested a solution that could utilize a reusable EMI Shielding cloth to create a 50,000 volt differential for testing molded-Polyethylene utility pole crane buckets. The existing test method involved using water to fill the buckets as a conductive medium. However, this method was logistically problematic, very time consuming and created post-test water disposal problems.
REQUIREMENTS:
A suitable material would have to be electrically conductive, withstand a 50Kv voltage differential between the inner and outer bucket liners as well as to incorporate a design feature to keep the voltage from arcing over the bucket lip to the outer layer. The material had to be flame retardant so as to not burn if a bucket liner failed and voltage arced through the bucket to the outside layer. Any acceptable solution had to yield a conductive cloth inner and outer sleeve that would fit each bucket shape without any gaps greater than 1/2 inch. The finished bucket liners had to be collapsible so they could be packed into a duffle bag kit. Each kit had to include a repair patch feature that would allow easy field repair of any arc-through holes that occurred during testing.
SOLUTION:
The Zippertubing Company utilized its flame-retardant, Nickel-over-Copper-plated Modacryl shield fabric known as Z-5080-CN. The outer sleeve was fitted to the Polyethylene bucket liner and held in place near the bucket lip using a 2-inch wide elastic band. The inner sleeve included multiple sewn-in, small-diameter pockets made from Zippertubing’s PVL-10 (PVC impregnated Polyester cloth). The pockets allowed ¼” diameter collapsible tent poles to be inserted, which held the inner sleeve tight against the inner bucket liner corners and walls. The top of the conductive inner sleeve had an open, elastic, nonmetallic mesh material attached that stretched up and over the bucket liner lip and was held in place using a 2-inch wide elastic band. The open elastic mesh created enough space between the inner and outer conductive sleeves to eliminate any arc-over during testing. Both the inner and outer sleeves included color coded power supply attachment tabs for easy test equipment hookup.
The solution above was tested by the customer’s test personnel at The Zippertubing Company manufacturing facility and proved that the system could replace the existing water-based test methodology. Portable test kits were fabricated, including tent poles, pole spacer blocks and conductive material repair patches. These kits made it possible to conduct the test in the field at the bucket location. It eliminated the shipping time delay involved with sending buckets to and from the test facility. It also eliminated the need for the disposal of large amounts of test water that the EPA considered hazardous. If you have what seems to be an impossible design problem, contact Zippertubing for an innovative solution!
