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ML0047 December 1, 2017 Copyright 2017 Bitronics, LLC
5.0 MEASUREMENTS
Basic measurement quantities are calculated and updated every cycle. 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.
5.1 Changing Transformer Ratios
The PPX II 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 PPX II 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. 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.
5.2 Current
The PPX II has three current inputs, with an internal CT on each channel. 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.
5.2.1 Residual Current
The PPX II 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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