Power-Integrated Circuit Active Leakage Current Detector

Most of the failures of induction motors become insulation faults, causing a permanent damage. Using differential current transformers, a system capable of insulation fault detection was developed, based on the differential relay protection scheme. Both signal injection and fault detection circuitry were integrated in a single chip. The proposed scheme is faster than other existing protection and not restricted to protect induction motors, but several other devices (such as IGBTs) and systems. This paper explains the principle of operation of fault protection scheme and analyzes an integrated implementation through simulations and experimental results. A power-integrated circuit (PIC) implementation is presented. 1. Introduction Nowadays, induction motors are the most frequently used drives for motion control systems in industrial applications [1]. The industry is particularly concerned about the failure of these devices since it could cause significant economical losses due to the stop of production for long time spans and the risk to the personal safety of the operators. Statistics show that annual down times of 0.5% to 4% may be expected [2]. The main causes of motor failure are the variation of the feeding phase voltages, mechanical overloads, and problems produced by inadequate or faulted electrical installations [3–5]. Other causes may include the aging of the motor or eventual adverse environmental conditions. Most of these events lead to an increase of the current and to a subsequent rise of motor temperature. An unacceptable overheating of the motor damages the insulation of the windings and puts the motor out of service [4–7]. High dv/dt, characteristic of PWM variable speed drives, is a source of further stress and deterioration of the insulation. The objective of motor protection is to keep the mechanical and thermal conditions within the acceptable limits while ensuring the highest fault detection sensitivity. In order to fulfill this objective, several protection and monitoring systems are introduced in the bibliography with a clear tendency to integrate them in the variable speed drives. The purpose of monitoring systems is to detect a failure in an early stage of its development, by checking some parameters such as parasitic capacitances and resistance or the dissipation factor, without letting the fault to cause irreversible damage to the machine or its driving devices. On the other hand, most protection methods detect a fault when it becomes severe. Monitoring can be classified as online or offline depending on whether the motor can be