Electrical Systems: In pictures: Bringing anomalies to light with IR inspection

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.

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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.

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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.

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Figure 12. The left image shows a C-phase thermal overload unit that is cold and carries no load. The right image shows the single-phased motor with internal short.

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Figures 13 and 14. The left image shows a typical thermal pattern of load-generated heat in a circuit breaker panel. The right image shows a load-related heat on a three-phase transformer bank feeding a building.

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Figures 15 and 16. The left image shows a three-phase circuit breaker with an overload condition on the top phase. The right image shows are two contactors and thermal overloads under operating conditions with the right component appearing warmer than the left. A load reading on the right component showed it operating above 80% load capacity.

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Figure 17. Elevated heating on the A-phase fuse was caused by an undersized fuse for the given load.

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Figures 18 and 19. The left image is a three-phase circuit breaker with the B-phase circuit under higher load than the C-phase circuit that is under higher load than the A-phase circuit. An ammeter was used to confirm the uneven load conditions. The right image shows elevated heating on the middle and left windings on a dry-type transformer as compared to the right winding. An ammeter confirmed the load imbalance condition observed with the infrared camera.

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Figures 20 and 21. The right image shows hot windings on a dry-type transformer under balanced loads. When uneven winding temperatures are encountered during an inspection, it’s important to check load conditions to determine the cause of the thermal exception. The right image shows a hot neutral wire under elevated load. Typically, the neutral leg will have a higher load than the hot legs when harmonic problems are present.

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Figure 22. More recent systems have oversized neutral wire mains and, if necessary, harmonic filtering devices installed to counteract the effects of harmonics. An enhanced neutral system (left) is common in a 120/208 V breaker panel. A typical harmonic filter system (center and right) can be installed in-line with the main electrical trunk.

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Figures 23, 24, and 25. The left image shows inductive heating on a corner of a switchgear cabinet. The center image is an example of inductive heating on ferrous metal bolts on main bus supports. The right image is inductive heating resulting from tie-wrapped cables in a 480 V main switchgear cabinet.

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Figures 26 and 27. The left image shows inductive heating on a metal pole located between iso-bus. The right image is an example of inductive heating on transition box.

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Figure 28. Elevated heating pattern on a UPS battery cell, most likely caused by an internal short causing high resistance.

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Figure 29. Elevated heating pattern on a current transformer in a 480 V main switchgear cabinet, most likely caused by an internal short causing high resistance.

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Figure 30. Elevated heating pattern on an impregnated ribbon circuit board in a 13 kV main switchgear relay cabinet — a weak solder connection.

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Figure 31. Elevated heating pattern on lightning arrester in a 13 kV main switchgear relay cabinet.

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Figure 32. A hot cooling fan motor inside a VFD cabinet. Visual inspection showed the fan blades stationary but the motor still operating.

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Figure 33. A hot spot on a metering can. Mostly there is an electrical short causing high contact resistance or a weak connection.

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Figure 34. This image shows the mounting bracket for a stand-off bushing inside a 13 kV load interrupter switch cabinet. This insulator is allowing current to leak to ground.

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