Page 191 - Intro Predictive Maintenance

182 An Introduction to Predictive Maintenance

Capacitors

A capacitor has two conductive surfaces, which are separated by a dielectric barrier.
Capacitors usually function as power factor correctors. When energized, all units
should have the same temperature if the size is the same. A high uniform temperature
is normal. A cold capacitor usually indicates a blown fuse or bad cell. Isolated
spots showing a high temperature on a surface of the capacitor may indicate a bad
capacitor.

High-Voltage Switchgear

Scan lighting arresters, insulators, cables, cables connections, bussing, circuit break-
ers, and disconnect switches.

Load Break Switches

In the switch, two metal surfaces act as conductors when they are brought into contact.
Usually, problems are restricted to the contact surface. Poor contacts usually show up
as hot spots.

Fuses
A fuse is a metal conductor, which is deliberately melted when an overload of current
is forced on it. Major problems affected are loose mechanical stab clips that cause hot
spots, corroded or oxidized external contact surfaces, and/or poor internal connec-
tions, which are bolted or soldered.

Circuit Breakers
Circuit breakers serve the same function as a fuse. It is a switching device that breaks
an electrical circuit automatically. Problem areas are caused by corroded or oxidized
contact surfaces, poor internal connections, poor control circuitry, and/or defective
bushings.

Conductors
The melting points and current-carrying capacity of conductors are determined by the
size and base material of the conductors. During a survey, compare between phases
and between conductors and connections. An unbalanced load will account for some
differences between conductors. Use metering devices already installed to check the
differences.

The type of load will affect whether the load is balanced. Three-phase motor loads
should be balanced; lighting and single-phase loads may be unbalanced.