Page 200 - Intro Predictive Maintenance

Thermography 191

Lightning arrester A device used to pass large impulses to
ground.
Mean time between failure (MTBF) A statistical estimate of the time a compo-
nent, subassembly, or operating unit will
operate before failure will occur.

Megahertz (MHz) A term for 1 million hertz (cycles per
second).
Motor alternator A device that consists of an AC generator
mechanically linked to an electric motor,
which is driven by utility power or by bat-
teries. An alternator is an AC generator.
Motor generator A motor generator consists of an AC motor
coupled to a generator. The utility power
energizes the motor to drive the generator,
which powers the critical load. Motor gen-
erators provide protection against noise
and spikes, and, if equipped with a heavy
flywheel, they may also protect against
sags and swells.
Neutral One of the conductors of a three-phase wye
system is the neutral conductor. Sometimes
called the return conductor, it carries the
entire current of a single-phase circuit and
the resultant current in a three-phase
system that is unbalanced. The neutral is
bonded to ground on the output of a three-
phase delta-wye transformer.
Ohm The unit of measurement for electrical
resistance.

Ohm’s law A law of electricity that states the relation-
ship between voltage, amperes, and resis-
tance. It takes a pressure of one volt to
force one ampere of current through one
ohm of resistance. Equation: Volts = am-
peres ¥ ohms (E = I ¥ R).

Radiation RF energy that is emitted or leaks from a
distribution system and travels through
space. These signals often cause interfer-
ence with other communication services.
Rectifier An electrical device containing diodes,
used to convert AC to DC.