IR Thermography in Predictive Maintenance

Fig. 1 Infrared inspections have proven their value over the past 30 years when performed on electrical distribution equipment, as part of a comprehensive predictive maintenance program. The image to the left (Fig. 1) quickly and clearly reveals the isolated-resistance-rise (IRR) caused by a poor connection on Phase A of this single-phase, fused disconnect.

In combination with conventional vibration analysis, infrared imaging of moving parts, such as in the motor-coupling-compressor assembly to the right (Fig. 2), greatly enhances the maintenance testing of mechanical equipment. The infrared image identifies a progressing failure mode arising from deteriorated bearings on the motor. In this case a follow-up vibration test may be performed to aid in analysis of the problem.   Fig. 2

Fig. 3 What's wrong with this picture?(Fig.3) The hot spot does not seem to be originating from the energised conductors. Instead, the highest temperatures are seen on the cabinet adjacent to the bushing and a gradient is formed outward from that area. In this situation a ferrous bushing was used on this cabinet at the egress point of a 3 phase meter cabinet. Normally, this would not pose an inductive problem as all 3 phase conductors are exiting the same opening and the 120 degree current phase angle difference between them would cause their individual magnetic fields to cancel each other out. However, the infrared image shows clearly that the 3-phase loads are not balanced and some magnetic coupling is taking place, inducing a voltage that is responsible for eddy-currents within the cabinet. The resulting temperature rise betrays their existence to the infrared camera.