25 5.8 Event Change
detailed disturbance information on a cycle basis is required, use the Event
Change report. Event Change gives much more detail, but is more compli-
cated to examine. The timestamp of a Significant Change event can be used
to find the same disturbance in the Event Change report for further analysis.
For even more detail, Waveform Capture can be used (if available). If the
disturbance triggered Waveform Capture, the raw waveforms of each voltage
and current channel can be displayed. Again, the Significant timestamp is
used to find the waveform in the list of captured waveforms.
5.8 Event Change
The Event Change report provides detailed cycle-level information about each
voltage disturbance. This is the most detailed report available short of actually
looking at raw waveforms with Waveform Capture. An event is triggered when
the voltage moves past any of a series of trip points. Max and min voltages
and currents during the event, the event duration (in cycles), and the current
before and after the event are all recorded.
5.8.1 Trigger Logic
Event Change triggering involves three parameters. The first, the Nominal
voltage, sets a baseline voltage level. This is not the same nominal voltage
selected by the Abnormal Voltage record type during the two minute count-
down. The Event Change Nominal voltage is specified by the user, and is
not picked by the Scanner. The second parameter is the Threshold, in volts.
The Threshold is added and subtracted to the Nominal to form voltage trip
points. These trip points are created all the way down to zero volts and up
to the maximum Scanner voltage by using multiples of the Threshold. For
example, a Nominal of 120 and a Threshold of 6 would create trip points at
120 ƒ 6 = 114; 126; 120 ƒ 2 ‡ 6 = 108; 132; 120 ƒ 3 ‡ 6 = 102; 138; etc.
The voltage region around the Nominal, but before any trip points (115
to 125 volts in the above example) is the Nominal Band. If the voltage moves
from the Nominal Band to cross a trip point, an Event Change is triggered.
This Event Change continues until the voltage either returns back into the
Nominal Band, or moves past another trip point. Each time the voltage
moves past another trip point, the existing Event Change ends and a new
Event Change is triggered. The trip points can be visualized as a grid (every
6 volts in the above example) from zero volts to the maximum Scanner voltage,
and any time the line voltage crosses a grid line, an Event Change is triggered.
There is one exception to the previous paragraph. The third setting, Hold-
off Time, specifies in cycles how long to wait before allowing a new Event
