VAMP Ltd
Feeder and motor manager
Technical description
VAMP 257
VM257.EN002
VAMP 24h support phone : +358 (0)20 753 3264
61
2.3.18.
Undervoltage protection (27)
The three-phase undervoltage function consists of three separa-
tely adjustable undervoltage stages (stage U<, U<< and U<<<).
The undervoltage function measures the positive sequence
component of the line voltages. The protection stages operate
with definite time characteristics.
The function starts if a positive sequence component exceeds
the setting value. If the undervoltage situation continues after
the start delay has elapsed, the function trips.
The undervoltage stage U< has a settable release delay, which
enables detecting instantaneous faults. This means that the
time counter of the protection function does not reset immedia-
tely after the fault is cleared, but resets only after the release
delay has elapsed. If the fault appears again before the delay
time has elapsed, the trip counter continues from the previous
fault value. This means that the function trips after a certain
number of instantaneous faults.
The undervoltage function can be blocked with an external
digital signal for example if the secondary voltage of the
measuring transformers disappears (e.g. fuse failure). The
undervoltage function can also be blocked with an internal
blocking signal, which is defined during the parameterisation.
Further, the function can be blocked with a separate NoCmp
setting. With this setting, all the protection stages are blocked
even when the actual values for all the phases fall below the set
value.
Figure 2.3.18-1. Block diagram of the three-phase undervoltage stages U<,
U<< and U<<<