Understanding Electrical Harmonics - AEMC 721 User Manual

C 4
HAPTER
U
NDERSTANDING
E H
LECTRICAL ARMONICS
Until fairly recently, power quality referred to the ability of the electric
utilities to supply electric power without interruption. Today, the phrase
encompasses any deviation from a perfect sinusoidal waveform. Power
quality now relates to short-term transients as well as steady state distor-
tions. Power system harmonics are a steady state problem with danger-
ous results. Harmonics can be present in current, voltage, or both. Within
the next few years, as many as half of all electrical devices will operate
with nonlinear current draw.
Utility companies invest millions of dollars each year to ensure that voltage
supplied to their customers is as close as possible to a sinusoidal wave-
form. If the power user connects loads to the system which are resistive,
such as an incandescent light bulb, the resulting current waveform will
also be sinusoidal. However, if the loads are nonlinear, which is typically
the case, the current is drawn in short pulses and the current waveform
will be distorted. Total current that is then drawn by the nonlinear load
would be the fundamental as well as all the harmonics.
� �
����������� ������������ ����������������������������
Harmonic distortion can cause serious problems for the users of electric
power, from inadvertent tripping of circuit breakers to dangerous overheat-
ing of transformers and neutral conductors, as well as heating in motors
and capacitor failure. Harmonics can cause problems that are easy to
recognize but difficult to diagnose.
It is becoming increasingly important to understand the fundamentals of
harmonics, and to be able to recognize and monitor the presence of dam-
aging harmonics. Harmonics within an electrical system vary greatly within
different parts of the same distribution system and are not limited simply
14
Harmonic Meter Model 721