Operation: CP1SD/T/L Version
CENTRON® Polyphase Meter Technical Reference Guide
81
Current Waveform Distortion Check
Diagnostic #5 detects DC on a per-phase basis using what is know as a comb filter method.
Rectified loads produce even harmonics which are typically in phase with the voltage signal.
The algorithm works by summing current samples, which occur 90° after every zero
crossing of the voltage waveform. This information is accumulated for a sample interval.
These sample points should represent peak current values. If no DC is present on any of the
phases, the current waveforms will be symmetrical and the accumulation of the current
samples will be near zero. If DC is present on a phase, the current waveform is offset
vertically and the accumulation of the current samples will be significantly higher.
Diagnostic #5 will trigger when the level of DC present is such that the accuracy of the
CENTRON Polyphase meter could be affected. This level varies for different installations
based on the per-phase load conditions. When DC current is present, the CENTRON
Polyphase meter can be programmed to display the Diagnostic #5 error code (i.e. lock,
scroll, ignore). The number of times DC was present is available through meter
communications on a per-phase basis. The number of times that DC was present on all
phases is available by accessing the Toolbox Mode and viewing the Diagnostic #5 counter
or through meter communications.
SiteScan Diagnostic #6
The purpose of this diagnostic is to check for the presence of harmonic distortion.
Unlike the other diagnostics, Diagnostic #6 has a programmable minimum duration before
the condition is triggered. The minimum duration may be programmed from 5 to 3600
seconds in increments of 5 seconds.
The check is performed every 5 seconds. It compares the instantaneous %THD V for each
phase against a configured threshold and it compares the instantaneous %TDD I for each
phase against a configured threshold. The %THD V threshold and the %TDD I threshold
may both be configured from 1.0 to 35.0.
Once the condition occurs, the check must pass twice in a row for the condition to clear.
Diagnostic #6 Error Example
The following is the information from the SiteScan snapshot when the Diagnostic #6 error is
triggered.
Phase A Display
(Left Element)
Phase B Display
(Center Element)
Phase C Display
(Right Element)
Voltage Phase
Angles
0.00 119.20
239.20
Phase Voltage
120.875
120.000
120.150
Current Phase
Angles
359.10 118.40 237.50
Phase Current
5.8
6.0
5.9
%THD V
0.330
7.730
0.280
