VAMP Ltd Feeder and motor manager
Technical description
VAMP 257
VM257.EN002 VAMP 24h support phone : +358 (0)20 753 3264
65
Measured and recorded values of the overfrequency and
underfrequency stages:
f><, f>><< (81)
Parameter Value Unit Description
Measured
value
f Hz Frequency
SCntr - Start counter (Start) reading
TCntr - Trip counter (Trip) reading
Flt Hz The ma><. fault value
Recorded
values
EDly %
Elapsed time as compared to
the set operating time; 100%
= tripping
2.3.21. Underfrequency protection (81L)
The underfrequency unit consists of two individually adjustable
frequency stages f< and f<<. The protection stages operate with
definite time characteristics. The overfrequency function
measures the frequency based on the measured voltage
depending on the configuration.
The function starts if the actual value for the frequency goes
below the setting value. If the underfrequency situation
continues after the start delay has elapsed, the function trips.
The underfrequency stages are typically used for load shedding
purposes as well. In this case, one stage sheds non-important
load when the frequency starts decreasing. If the frequency still
decreases, another stage sheds more non-important load to gain
balance between the load and the source. By this way, the
important loads remain connected.
Figure 2.3.21-1. Block diagram of the underfrequency stages f< and f<<
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