ML0042 October 15, 2019 - 91 - Copyright 2019 Bitronics, LLC
6.0 MEASUREMENTS
Basic measurement quantities are calculated and updated every 100 ms. These
quantities include RMS Amperes and RMS Volts, Watts, VARs, VAs, Power Factor, all
harmonic-based measurements (such as fundamental-only quantities), Energy, and
Frequency, and Phase Angle.
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.
6.1 Changing Transformer Ratios
The M66X has the capability to store values for Current Transformer (CT) and
Potential Transformer (VT) turns ratios. The VT and CT values are factory set to 1:1
CT and 1:1 VT. These values can be entered into the M66X over the network or via
front display buttons or web page, and will be stored in internal non-volatile memory.
All measurements are presented in primary units, based on these ratios. Please note
that the value entered via the front display should be the result of the division of the
primary value by 5. For example, for a ratio of 6000:5, you would enter a value of
1200 through the front display. The web interface allows you to choose either 1A or
5A for the denominator, and the primary value is entered directly. The PT ratio is to 1
when entering through the front display. The web allows other denominators (110,
115, or 120) to be used. Refer to the appropriate protocol manual for more
information on changing transformer ratios.
6.2 Current
The M66X has three current inputs, with an internal CT on each channel except in the
case where external split-core CTs are used. These inputs can read to 2x nominal
(2A
RMS
for 1A input, 10A
RMS
for 5A input (symmetrical)) under all temperature and input
frequency conditions. No range switching is used, allowing a high dynamic range.
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 above.
The average of the 3 current phases ((Ia + Ib + Ic)/3) is also available on a per cycle
basis.
6.2.1 Residual Current
The M66X calculates 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.
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