Electro Industries Shark 200 Installation & Operation Manual page 28

The waveforms shown in Figure 1.12 are not smoothed but do provide an indication of
the impact of combining multiple harmonic frequencies together.
When harmonics are present it is important to remember that these quantities are
operating at higher frequencies. Therefore, they do not always respond in the same
manner as 60 Hz values.
Inductive and capacitive impedance are present in all power systems. We are accus-
tomed to thinking about these impedances as they perform at 60 Hz. However, these
impedances are subject to frequency variation.
X = jL and
L
X = 1/jC
C
At 60 Hz,  = 377; but at 300 Hz (5th harmonic)  = 1,885. As frequency changes
impedance changes and system impedance characteristics that are normal at 60 Hz
may behave entirely differently in the presence of higher order harmonic waveforms.
Traditionally, the most common harmonics have been the low order, odd frequencies,
such as the 3rd, 5th, 7th, and 9th. However newer, non-linear loads are introducing
significant quantities of higher order harmonics.
Since much voltage monitoring and almost all current monitoring is performed using
instrument transformers, the higher order harmonics are often not visible. Instrument
transformers are designed to pass 60 Hz quantities with high accuracy. These devices,
when designed for accuracy at low frequency, do not pass high frequencies with high
accuracy; at frequencies above about 1200 Hz they pass almost no information. So
when instrument transformers are used, they effectively filter out higher frequency
harmonic distortion making it impossible to see.
However, when monitors can be connected directly to the measured circuit (such as
direct connection to a 480 volt bus) the user may often see higher order harmonic
distortion. An important rule in any harmonics study is to evaluate the type of equip-
ment and connections before drawing a conclusion. Not being able to see harmonic
distortion is not the same as not having harmonic distortion.
It is common in advanced meters to perform a function commonly referred to as
waveform capture. Waveform capture is the ability of a meter to capture a present
picture of the voltage or current waveform for viewing and harmonic analysis.
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1: Three-Phase Power Measurement
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Doc E149701 1-16