Novatech Bitronics M660 - 6.11 Harmonic Measurements

ML0042 October 15, 2019 - 99 - Copyright 2019 Bitronics, LLC
6.10.5 Demand Interval
The M66X uses 900 seconds (15 minutes) as the default demand interval for current.
The default for average volts and average power measurements is 60 seconds. Three
separate, independent demand intervals may be set for current, voltage, and power.
The range of demand intervals is 10 to 9999 seconds. These settings can be
accomplished by using the front display or web server setup.
6.11 Harmonic Measurements
All harmonic and harmonic related measurements are calculated every 100 ms. In
the following sections, Harmonic 0 indicates DC, Harmonic 1 indicates the
fundamental, and Harmonic N is the nth multiple of the fundamental.
6.11.1 Voltage Distortion (THD)
Voltage Harmonic Distortion is measured by phase in
several different ways. The equation for Total Harmonic
Distortion (THD) is given in Equation 1. Note the
denominator is the fundamental magnitude.
6.11.2 Current Distortion (THD and TDD)
Current Harmonic Distortion is measured by phase in
several different ways. The first method is Total Harmonic
Distortion (THD). The equation for THD is given in Equation
2. Note the denominator is the fundamental magnitude.
Alternatively, Current Harmonic Distortion can be
measured as Demand Distortion, as defined by
IEEE-519/519A. Demand Distortion differs from
traditional Harmonic Distortion in that the denominator
of the distortion equation is a fixed value. This fixed
denominator value is defined as the average monthly
peak demand. By creating a measurement that is
based on a fixed value, TDD is a "better" measure of distortion problems. Traditional
THD is determined on the ratio of harmonics to the fundamental. While this is
acceptable for voltage measurements, where the fundamental only varies slightly, it is
ineffective for current measurements since the fundamental varies over a wide range.
Using traditional THD, 30% THD may mean a 1 Amp load with 30% Distortion, or a
63
2
2
1
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h
h
I
THD
I
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63
2
2
1
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h
h
V
THD
V
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2
2
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h
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I
TDD
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Equation 1 - Voltage THD
Equation 2 - Current THD
Equation 3 - Current TDD