Novatech Bitronics M87X Series Manual Download Page 57

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ML0021 August 15, 2018

100 Amp load (if the Denominator was set at 100 Amps). In the M87x, 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 load on the system. The

denominator I

is different for each phase and neutral, and is set by changing the four

denominator values within the M87x. Refer to the appropriate protocol manual for specific
information.

Note that in Equation 3, if I

equals the fundamental, this Equation becomes Equation 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. For Odd Harmonic Distortion, the summation only uses harmonics where h
is odd. For Even Harmonic Distortion, the summation only uses harmonics where h is
even. For Individual Harmonic Distortions there is no summation, only one component is
used in the numerator.

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 (primary), 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.

4.8.3 Fundamental Current (1-Cycle Update)

Fundamental Amps are the nominal component (50/60 Hz) of the waveform. The M87x
measures the magnitude of the fundamental amps for each phase and neutral. 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.

4.8.4 Fundamental Neutral Current (M871 Only) (1-Cycle Update)

The M871 measures the magnitude of the Fundamental Neutral Current, which is typically
the magnitude of the nominal component (50/60 Hz) of neutral current. The measurement
is in Amperes, and it is a measure of the load imbalance in a three-phase system.

4.8.5 Fundamental Voltage (1-Cycle Update)

Fundamental Volts are the nominal component (50/60 Hz) of the waveform. The M87x
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 Fundamental Volts for that phase