Amprobe ACDC-620T Clamp-On-Multimeter - Manual (Page 53)

non-linear current. This generates odd harmonics of the 5OHz or 60Hz line
frequency. Therefore, the current waveform from the transformer could contain
not only a 60Hz component, but also a 180Hz component, a 30OHz compo-
nent, etc.
The vector addition in a properly balanced power distribution system feeding
non-linear loads may still be quite low. However, the vector addition does not
cancel all the harmonic currents. The odd multiples of the 3rd harmonic (called
the "TRIPLENS") are added together in the neutral. These harmonics can cre-
ate an RMS current in the transformers neutral wire that is 130( of the total
RMS current measured in any individual phase. For example, phase currents
of 80 amperes may cause 104 amperes of harmonic current in the neutral, the
most common harmonic being the 3rd. The electrical designer must consider
the following issues when designing a power distribution system that will con-
tain harmonic current.
1. The AC neutral wires must be of sufficient gauge to
allow for harmonic current.
2. The distribution transformer must have additional cooling to continue opera
tion at its rated capacity. This is because the harmonic current in the sec
ondary neutral wire is circulating in the deltaconnected primary winding.
This circulating harmonic current heats up the transformer.
3. Phase current harmonics are reflected to the primary winding and they
continue back towards the power source, This can cause distortion of the
voltage wave so that any power factor correction capacitors on the line can
be easily overloaded.
We can use this Meter to analyze components such as power distribution
transformers and power factor correction capacitors. An additional feature
allows the measurement of half-cycle peak current by using the 1 ms peak
hold feature. This allows the ability to determine crest factor:
Crest factor + Peak value/True rms value
NOTE: If Crest factor exceeds 1.1 harmonic distortion is present
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