Challenges In Designing A 10 kV Skin Effect Trace Heating System

A risk assessment for operating a skin effect trace heating system at 10 kVac in hazardous locations was conducted. The primary risk identified was the possible occurrence of electrostatic and partial discharges containing sufficient energy to trigger an explosion. Several skin effect insulated conductor (cable) designs were assessed against this risk by performing partial discharge measurements and ignition proof testing as a function of voltage and temperature. Certification according to the IECEx product scheme for increased safety “eb” was carried out by using I EC 60079-33 to allow incorporation of the type tests in IEEE Std 844.1-2017/CSA C22.2 No. 293.1-17 and by including the ignition tests from IEC 60079-7. It was found that the transferred charge could be substantially reduced by incorporating a semi-conductive shield around the insulation layer in the skin effect insulated conductor. With this shielded configuration, ignition in an explosive atmosphere did not occur up to the test voltages required for a 10 kVac rating.