9
Project 2187 Drawing No. CI-3K51101 Rev 10
DMR 2720 18/07/11
Modbus is a Trademark of Schneider Automation Inc. Other Trademarks or company
names mentioned herein are the property of their respective owners.
limitations of the number format. Internally the count is maintained with greater precision. The reporting
error is less than 1 part per million and is automatically corrected when the count increases.
6.4 Power Factor
The magnitude of Per Phase Power Factor is derived from the per phase active power and per phase
reactive power. The power factor value sign is set to negative for an inductive load and positive for a
capacitive load.
The magnitude of the System Power Factor is derived from the sum of the per phase active power and per
phase reactive power. Individual phases whose apparent power is less than 3% of nominal are not included
in power factor determinations. The system power factor value sign is set to negative for an inductive load
and positive for a capacitive load. The load type, capacitive or inductive, is determined from the signs of the
sums of the relevant active powers and reactive powers. If both signs are the same, then the load is
inductive, if the signs are different then the load is capacitive. The magnitude of the phase angle is the
ArcCos of the power factor. Its sign is taken as the opposite of the VAr's sign.
6.5 Maximum Demand
The maximum power consumption of an installation is provided as power utilities often levy related charges.
Many utilities use a thermal maximum demand indicator (MDI) to measure this peak power consumption. An
MDI averages the power consumed over a number of minutes, reflecting the thermal load that the demand
places on the supply system. The Integra Ci3 digital meter uses a sliding window algorithm to simulate the
characteristics of a thermal MDI instrument, with the demand period being updated every minute. Demand
Integration Times can be set to Off, 5, 8, 15, 20, 30 or 60 minutes. Maximum Demand is the maximum
power or current demand that has occurred since the unit was last reset. This is maintained as a continuous
record of the highest demand value that has been reached. Note: During the initial period when the “sliding
window” does not yet contain a full set of readings (i.e. the elapsed time since the demands were last reset
or the elapsed time since the Integra Ci3 digital meter was switched on is less than the selected demand
integration time) then maximum demands may not be true due to the absence of immediate historical data.
With the Demand Integration Time set to “Off” the “Maximum Demand” values become “Maximum” values as
no averaging is performed on the measured parameters.
6.6 Total Harmonic Distortion
The calculation used for Total Harmonic Distortion is: THD = ((RMS of total waveform – RMS of
fundamental) / RMS of total waveform) x 100. This is often referred to as THD – R, and lies in the range 0 to
100%. THD measurement is subject to the 'range of use' limits. The Integra Ci3 digital meter may give
erratic or incorrect readings where the THD is very high and the fundamental is essentially absent. For low
signal levels the noise contributions from the signal may represent a significant portion of the “RMS of total
waveform” and may thus generate unexpectedly high values of THD. To avoid indicating large figures of
THD for low signal levels the product will produce a display of 0 (zero). Typically, display of THD will only
produce the 0 (zero) value when the THD calculation has been suppressed due to a low signal level being
detected. It should also be noted that spurious signals (for example, switching spikes) may be included in
the “RMS of the total waveform” and will be used in the calculation of THD. The display of THD may be
seen to fluctuate under these conditions.
6.7 Phase Sequence Test
The voltage and current inputs must be above 5% of nominal for the test to operate reliably.
In three phase four wire mode the measurements are referenced from L1.
For the voltage sequence test the phase of L2 relative to L1 must be within the window 240 +/- 48 degrees
and L3 relative to L1 must be within the window 120 +/- 48 degrees to record the sequence V123.
Alternatively, the phase of L2 relative to L1 must be within the window 120 +/- 48 degrees and L3 relative to
L1 must be within the window 240 +/- 48 degrees to record the sequence V132.
For the current sequence test the phase of I1 relative to L1 must be within the window 0 +/- 48 degrees, I2
relative to L1 must be within the window 240 +/- 48 degrees, and I3 relative to L1 must be within the window
120 +/- 48 degrees to record the sequence i123.