Detection of High Resistance Contacts in the Electrical Distribution System during the Induction Motor Starting Transient

High resistance electrical contacts due to loose, corroded, or contaminated connections are one of the main factors that cause degradation in efficiency and reliability of the electrical distribution system. Detection of such defects currently relies on off-line or walk-around type on-line tests, which require access to the contacts exposing the maintenance personnel to safety hazards. A remote and automated method for identifying poor contacts is desirable for efficient, reliable, and safe operation of the industrial facility. In this work, a simple method for detecting high resistance contacts during the starting transient of mains-fed induction motors from voltage and current measurements available in the system, is proposed. It is shown that the starting transient provides the most favorable condition for detecting the defect with high sensitivity. Experimental testing on 380 V and 6.6 kV induction motors in the lab and field show that the existence, severity, and location of high resistance contacts can be identified.