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The minimum number of waveform cycles that can be recorded during a disturbance
is 16. The PM295 will record a disturbance as it lasts, so the maximum duration of
a disturbance the instrument can record is limited by only the amount of memory
allocated by the user for waveform recording.
4.16.2 Monitoring Disturbances
Monitoring disturbances allows the user to trigger a setpoint in the event the
instrument detects deviation in voltage waveshape on any phase exceeding the
predefined threshold.
Monitoring disturbances is based on continuous testing of the sampled voltage
waveforms for a non-stationary waveshape. In a 3-wire open delta wiring mode, the
instrument tests the two line-to-line voltages (L12 and L23), and in other wiring
configurations - the three line-to-neutral voltages. In the event the instrument detects
a waveshape deviation that exceeds operating threshold, the disturbance trigger is
operated. The instrument can detect disturbances with a minimum duration of 1 ms.
Operate limit for the voltage disturbance trigger specifies the voltage deviation
allowed in percentage of nominal (full scale) voltage. The reference nominal voltage
is 120V RMS (170V amplitude) for instruments with the 120V input option, and
380V RMS (537V amplitude) for instruments with the 660V input option. For
example, a 5% disturbance threshold for the instrument with the 120V input option
specifies an 8.5V allowed deviation in voltage amplitude.
4.16.3 Recording Disturbances
To record disturbed waveforms, the high-speed (32 ×16) waveform logging action
should be specified when programming a setpoint.
A total of 16 cycles of each sampled waveform, both voltage and current, on all
three phases can be recorded simultaneously on a disturbance trigger. The user can
specify the number of pre-event cycles to be recorded from 1 to 8. The number of
post-event data will be adjusted automatically up to a full 16 -cycle waveform.
In the event that disturbance lasts for more time than the number of post-event
cycles the user specified, the disturbance recorder will continue storing waveforms
while the voltage waveshape is still non-stationary. The recorder may run until the
disturbance end, or until the non-wrap memory partition is filled up - whichever
occurs first. In the event of the wrap-around partition, the long-duration disturbance
may be written over the oldest records.
Operation Techniques
83
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