Gradient Trigger (±Dm/Dt) - Siemens SIMEAS R-PMU Manual

7.2.2.2.1.2 Gradient Trigger (±dM/dt)
A signal gradient describes the level changes within a set time. For the TPR, gradient trigger con-
ditions for alternating signals are met, if the difference of two rms values of the basic oscillation
averaged for t
with the distance of the filter time are compared. The averaging time t
parameterized recording rate of 1 to 5 nominal cycles.
There are two different types of gradients: Rising gradient (+dM/dt, i. e. positive difference) and
falling gradient (-dM/dt, i. e. negative difference). Gradient triggers may be set for the signals
listed in the tables 7-17 and 7-18 (not for symmetrical components). In order to avoid unre-
quested recordings due to short term signal oscillations, the filter time can be set so high that
only signal gradients of a certain level generate a trigger. Figure 7-18 shows a typical measuring
signal.
dt is the filter time, t
Figure 7-18 Effect of the gradient trigger
Filter time
The filter time is indicated in seconds and defines the reference time of the gradient trigger. The
duration of the filter time should be adapted to the recording rate.
The figures 7-19 to 7-21 show the functioning of the filter time for a signal that is normalized to
the nominal frequency.
Note
The longer the selected recording rate, the more signal peaks are no longer detected.
The signal peaks are filtered out during a long recording rate (see Figure 7-21). To ensure that
the trigger event is clearly recorded despite the signal change, the filter time must be
parameterized accordingly low.
Digital Fault Recorder, SIMEAS R-PMU, Manual
E50417-H1076-C360-A5, Release 10.2012
is higher than the parameterized threshold. For DDAUs, the arithmetic means
m
the averaging time.
m
is equivalent to the
m
dt
dM
7
7.2 Fault Recorders
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