Fundamental Current; Fundamental Voltage - Novatech Bitronics PowerPlex II User Manual

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 100 Amp load with 30% Distortion.
By using TDD, these same two loads would exhibit 0.3% TDD for the 1 Amp load and
30% TDD for the 100 Amp load (if the Denominator was set at 100 Amps). In the PPX
II, Current Demand Distortion is implemented using Equation 3. The TDD equation is
similar to Harmonic Distortion (Equation 2), except that the denominator in the
equation is a user-defined number. This number, I , is meant to represent the average
L
load on the system. The denominator I is different for each phase and neutral, and is
L
set by changing the denominator values within the PPX II.
Note that in Equation 3, if I equals the fundamental, this Equation becomes Equation
L
2 - Harmonic Distortion. In the instrument this can be achieved by setting the
denominator to zero amps, in which case the instrument will substitute the
fundamental, and calculate Current THD.
Note that there is a separate, writeable denominator for each current input channel.
The TDD Denominator Registers are set by the factory to 5 Amps (secondary), which
is the nominal full load of the CT input with a 1:1 CT. These writeable denominators
can be used in conjunction with the distortion measurements to obtain the magnitudes
of harmonics, in other words, convert from percent to amps. This is simply done by
multiplying the percent TDD by the TDD Denominator for that phase, and the result
will be the actual RMS magnitude of the selected harmonic(s). This technique can
also be used if the THD mode (denominator set to zero) is used, by multiplying the
percent THD by the Fundamental Amps for that phase.

5.11.3 Fundamental Current

Fundamental Amps are the nominal component (50/60 Hz) of the waveform. The PPX
II measures the magnitude of the fundamental amps for each phase. These
measurements can be used in conjunction with the distortion measurements to obtain
the magnitudes of harmonics, in other words, convert from percent to amps. As was
mentioned previously, this is simply done by multiplying the percent THD by the
Fundamental Amps for that phase (which is the denominator), and the result will be
the actual RMS magnitude of the selected harmonic.

5.11.4 Fundamental Voltage

Fundamental Volts are the nominal component (50/60Hz) of the waveform. The PPX
II measures the magnitude of the fundamental phase-to-neutral and phase-to-phase
volts. These measurements can be used in conjunction with the distortion
measurements to obtain the magnitudes of harmonics, in other words, convert from
percent to volts. This is simply done by multiplying the percent THD by the
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ML0047 December 1, 2017 Copyright 2017 Bitronics, LLC