Using hall-effect sensors to add digital recording capability to electromechanical relays

The paper describes the use of Hall-effect sensors for adding digital recording and harmonic analysis capabilities to major substation equipment such as electromechanical relays, circuit breakers, and power transformers. Three case studies are presented describing the use of these sensors as tools for diagnosing problems and identifying root causes of equipment failures. The first case study describes how the sensors were used in a generating plant to identify the cause of a transformer differential relay trip operation. The second study describes how the sensors were used in a switching station to measure harmonic content during capacitor bank switching operations. And, the third case study describes how a potential hazard was inadvertently discovered while using the sensors to capture trip and secondary current signatures in a distribution substation. The paper also describes the unique characteristics of the Hall-effect sensors and the process of preparing them for use in the substation environment. The types of enclosures used and the needed recording requirements are also discussed. The intent of the authors is to present the reader with a novel tool that is truly helpful for identifying problems with major substation equipment.