Novatech Bitronics M87X Series, Manual

Page: 49 / 184

ML0021 August 15, 2018
33
Copyright 2018 Bitronics, LLC
4.0 MEASUREMENTS
Basic measurement quantities are calculated and updated every 1/4 cycle. These
quantities include RMS Amperes and RMS Volts. Watts, VARs, VAs, Power Factor, all
harmonic-based measurements (such as fundamental-only quantities), Energy,
Frequency, and Phase Angle are updated every cycle.
Note: For all of the following measurements, it is important to keep in mind that the
specific protocol used to access the data may affect the data that is available, or the format
of that data. No attempt is made here to describe the method of accessing measurements
- always check the appropriate protocol manual for details.
4.1 Current (1/4-Cycle Update)
The current signals are transformer coupled, providing a true differential current signal.
Additionally, a continuous DC removal is performed on all current inputs. Instrument
transformer ratios can be entered for each current input, as described in the Signal Input
Module section (Section 7). This can be accomplished via a network and protocol (refer to
the specific protocol manual for details) or by using the 70 Series Configurator.
When used on 2-element systems, if there are only 2 currents available to measure, a "0"
can be written to the CT Ratio for the missing phase current. This will cause the M87x to
fabricate the missing phase current from the sum of the other 2 phase currents. This
feature is not recommended for WYE connected systems.
The average of the 3 current phases ((Ia + Ib + Ic)/3) is also available. The Average 3-
phase Amps for bus 1 and bus 2 (M872) are calculated and made available on a per cycle
basis.
4.1.1 Neutral and Residual Current (1/4-Cycle Update)
M871 Signal Input Modules have a separate input for neutral current. This channel is
measured just like any of the other current channels, and the result presented as Neutral
Current. Additionally, all M87x units calculate the vector sum of the three phase currents,
which is known as the Residual Current. The Residual Current is equivalent to routing the
common current return wire through the neutral current input on systems without separate
current returns for each phase, with the exception that individual Harmonics are not
measured on Residual Current.
On systems without a Neutral CT, the Residual Current measurement can be used as a
substitute for Neutral Current. This allows the Neutral Current input on the M871 to be
used to measure any extra currents in the system.
4.2 Voltage Channels (1/4-Cycle Update)
The M87x uses a unique voltage connection method, which is combined with simultaneous
sampling to provide an extremely flexible voltage measurement system. All voltage inputs
are measured relative to a common reference level (essentially panel ground). See Figure
9 (pg. 89-96) and Section 7 for input connection information. Because all phase signals