Detection And Measurement - AEMC 721 User Manual

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Please note that our %DF is not the same value as the Distortion Factor
as expressed in the IEEE standard 519-1992 (in which Distortion Factor
is same as THD).
4.1

Detection and Measurement

Harmonic analysis is the first step in alleviating the many problems that
can be encountered. Field measurements are performed to identify fre-
quency and magnitude. An important factor to remember is that most
distribution systems are designed specifically to carry 60 Hz. To begin
identifying a possible harmonics problem, take an inventory of equipment
that may generate harmonic currents (e.g. electronic equipment, fluores-
cent lighting fixtures with electronic ballasts, variable speed motors, etc).
List the nonlinear loads which are on each branch circuit. The electrical
panel is the point at which most nonlinear harmonic problems can be
detected. Excessive current flow on the neutral can be detected with a
True RMS current meter, but may also be indicated by a resonant buzzing
sound or even visually with discolored connections on the neutral buss.
Beginning at the service entrance panel, measure and record the True
RMS current in each phase, as well as the neutral of the distribution trans-
former secondary. Compare this measured neutral current to the antici-
pated current due to phase imbalance. If the phase currents are equal, the
vector sum of the neutral currents will add to zero. If excessive amounts
of triplen harmonics are present in the neutral, neutral current may exceed
phase current. Consult the NEC
the conductors that have been tested.
20
Distortion Factor
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for the maximum ampacity for each of
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Harmonic Meter Model 721