Throughout the evolution of infrared technology for predictive maintenance applications, electrical system inspections have remained the cornerstone of the industry. Despite being somewhat overshadowed in recent years by building science applications, the demand for infrared inspections of electrical systems remains high. Accurate diagnosis begins with understanding electricity and what causes thermal anomalies. Several types of defects, including those associated with compromised connections, overload conditions, load imbalances, harmonics problems, and inductive heating, may be encountered during an infrared inspection.
|Figure 1. Voltage classes obtain their values by the potential that exists between each phase and between each phase and neutral and/or ground. The same principles apply to other voltage class systems|
|Figure 2. The cross-section view of a conductor under normal load conditions increases in degrees of resistant. As resistant area increases, conductive pathway area decreases and the amount of heat will rise.|
|Figures 3 and 4. When a direct line of sight to the component is available it’s easily recognized. Show typical heating patterns associated with a loose line side conductor connection on a three-pole circuit breaker and a loose bus connection on a two-pole circuit breaker, both showing a direct line of sight to the problem.|
|Figures 5 and 6. The left image shows a centralized heating pattern on a three-phase circuit breaker with an internal contact problem. The right image shows an internal contact problem on the A-phase with a thermal pattern that propagates through the entire breaker.|
|Figures 7 and 8. These show deteriorated connections on an enclosed overhead bus duct. If an overload or load imbalance condition existed here, one would expect to see a warm thermal anomaly along the entire length of the bus.|
|Figures 9 and 10. The left image shows a loose bus connection on a wire harness feeding a circuit breaker inside a motor control bucket. The right image shows a suspected bus/fuse holder connection problem hidden behind the insulation board inside a switchgear cabinet.|
|Figure 11. An infrared inspection at the main lug compartment of the MCC showed the same thermal relationship as observed at the main breaker but also showed a deteriorated connection that no longer was capable of carrying load.|