Coupling of discharge currents between conductors of electrical machines owing to laminated steel core

Over the past few years, a number of techniques have evolved for detecting discharges in the insulation systems of electrical machines by measuring the discharge currents flowing at the machine terminals. The propagation of these currents through the winding, from the discharge site to the terminals, is influenced by the capacitive and inductive coupling between the conductors of the winding. The paper is concerned solely with the inductive component of that coupling, through the laminated steel stator core of the machine. It describes how this coupling makes a significant contribution to the equivalent circuit for the propagation of discharge currents containing frequencies from 20 kHz to 20 MHz.