Operation: CP1SD/T/L Version
80
CENTRON® Polyphase Meter Technical Reference Guide
The next step is to graphically plot the above information into a phasor diagram as shown in
the figure below.
Figure 33: Phasor Diagram
By comparing the phasor diagram drawn from the information found in the snapshot versus
the typical phasor diagram, it becomes clear that the C phase current is out of the user-
defined envelope. The correct phasor should be around 240.0°, not the 297.0° where the
phasor currently is. This is not a problem with the meter or a wiring problem at the site, but
it does indicate a poor load power factor condition which may need to be corrected. Also
note that diagnostic counter d4 has incremented to “001”.
SiteScan Diagnostic #5
The purpose of this diagnostic is to check for the presence of DC on any of the current
phases. If DC is present on a phase, depending on the amount, this can adversely affect the
metering of power on that phase. The DC has the affect of distorting the waveform seen on
the secondary side of the CT.
A DC index is calculated for every current phase present for a given service. This index is
compared against a threshold that was established through extensive data analysis applying
different loads to the CTs and evaluating the DC Index. If a DC Index is found above the
threshold, then this is a single failure. As with the other diagnostics, there must be failures
on three consecutive checks before a failure is registered.
