Page 189 - Intro Predictive Maintenance

180 An Introduction to Predictive Maintenance

8.8.1 Mechanical Looseness

Mechanical looseness occurs most often. A loose connection will result in thermal
stress fatigue from overuse. Fuse clips are a good example because the constant heat-
up and cooldown creates a poor connection. An accurate temperature measurement,
or use of an isotherm, will identify a loose condition. When the isotherm is brought
down to a single pixel, or temperature, it will identify the source of the loose
condition.

8.8.2 Component Failure
Understanding the nomenclature of the problem can identify component failure.
Specifically, the actual component will be the heat source. For example, a heat-stressed
fuse in a three-phase assembly will appear hotter than the other two fusses.

8.8.3 Common Problems Found and What to Scan
Following are examples of what to scan while performing an infrared survey to easily
detect common problems.

Motor Control and Distribution Centers
Have the switchgear panel covers opened or removed by qualified personnel before
inspection. Scan cable, cable connections, fuse holders, fuse circuit breakers, and bus.

Main Secondary Switchgear

Have the switchgear panel covers opened or removed by qualified personnel before
inspection. Scan cables, cables connections, circuit breakers (front and back), and bus.

Circuit Breaker Distribution Panels
Covers on small circuit breaker panels do not have to be removed for scanning. Circuit
breakers and conductors are very close to the metal covers. Defective components are
usually detectable by the heating of the cover in the area of the problem. If a problem
exists, remove the panel cover to locate the problem. Only remove panel covers that
can safely be removed.

Bus Duct
Electrical conductors are very close to the metal “skin” of the duct. Defective joints
are usually detectable by the heating of the cover in the vicinity of the problem.

Motors
Do not scan motors less than 25 horsepower unless they are critical to production. On
motors greater than 25 horsepower, scan the “T” boxes, visible conductors, connec-