23 5.7 Significant Change
power in power factor studies. A revenue meter that doesn’t total negative
power, or doesn’t include the effects of harmonics, may show readings that
differ from this report.
5.7 Significant Change
The Significant Change record type tracks quick fluctuations in the line volt-
age, with single-cycle response, while ignoring gradual changes. Voltage events
are time-stamped to the second, and listed in a report. If the report is empty,
there were no voltage events that exceeded the trigger threshold. This is a
quick way to gauge the voltage power quality, because only voltage fluctua-
tions exceeding the threshold are listed.
5.7.1 Trigger Logic
The Significant Change record type uses a voltage threshold parameter. At the
end of each second during the recording session, the largest and smallest RMS
voltages for that second are compared with the “standard” Significant Change
voltage. This standard voltage starts as the nominal voltage picked by the
Scanner during the two minute countdown (typically 120, 208, 240, 277, or 480
volts). If the difference between the standard voltage and either the maximum
or minimum voltage was more than the threshold, a Significant Change is
recorded. In addition, the voltage (either the max or min) that caused the
trigger becomes the new “standard” until the next Significant Change.
As an example, consider a “standard” voltage of 119 volts, and a threshold
of 2 volts. After 40 seconds, the voltage drops to 118 volts. No Significant
Change is recorded because the 1 volt change is smaller than the 2 volt thresh-
old. After another 35 seconds the voltage increase to 120 volts. The change is
2 volts, from 118 to 120, but no Significant Change occurs because 120 volts is
only 1 volt greater than the “standard” of 119. After another 23 seconds the
voltage increases to 121 volts. A Significant Change is triggered because the
1 volt increase created a 2 volt difference between the 121 maximum voltage
for that second, and the 119 volt standard. The standard voltage is now set
to 121 volts, until the next Significant Change.
Only one Significant Change per second can be recorded per channel. If
both the single-cycle max and min meet the threshold in the same second, the
voltage that is furthest from the standard become the new standard.
