Can Electrical Insulation and Conductor Performance Be Predicted?

Long power cables and large machines require different application techniques from most electrical wiring. The first topic discussed is a new technique for evaluation of insulation for continued use. The second area is a different method for selection of conductor size considering temperature and voltage drop. The hi-pot evaluation is primarily a maintenance function, while the voltage drop procedure is primarily a design practice. For the first topic, high potential (hi-pot) tests are often conducted on power cables and large machines. However, there has been no standardized method of determining if the insulation is acceptable. Various methods have tried to compare leakage current between conductors, use a fixed limit on leakage current, or compare with previous tests. Each has its advantages and limitations. From empirical data and diverse experience, we have developed a numeric technique that will indicate impending failure. The procedure is mathematically rigorous but can be practically applied. It is very applicable to computer controlled hi-pot systems as well as manual systems. The second topic is the voltage drop for long conductors. We have applied numerous considerations to develop a simple relationship that can be readily applied. It incorporates wire diameter, length, current, number of phases, and temperature correction, with permissible voltage drop.