VAMP 257 - Page 101

VAMP Ltd Feeder and motor manager
Technical description
VAMP 257
VM257.EN002 VAMP 24h support phone : +358 (0)20 753 3264
59
The U> stage has a settable release delay, which enables
detecting instantaneous faults. This means that the time
counter of the protection function does not reset immediately
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 delay counter continues from the previous
value. This means that the function trips after a certain
number of instantaneous faults.
Another application for an extended release delay is to
disconnect a small generator from the network during the dead
time of an auto-reclose (see Figure 2.3.17-2). In a fault
situation, the breaker 1Q0 starts the auto-reclose sequence and
opens. The voltage function at 2Q0 will also pick up any under-
voltage or residual overvoltage fault. If the voltage fault
remains, the 2Q0 will also trip and the reclosing cycle can
continue.
However, if opening the 1Q0 clears the fault, the 2Q0 will not
trip since the voltage relay at 2Q0 has a long start release time.
In most cases, the isolated load is too much for the generator to
maintain the frequency during this release time. Then the 2Q0
will be tripped by a frequency stage and the possible past
voltage fault. A frequency fault or a voltage fault in the
network alone will not trip the 2Q0. An asynchronised
connection of breaker 1Q0 to the network is blocked with a
synchro-check relay.
During a short circuit or an earth fault, the breaker 1Q0
performs an auto-reclose. The breaker 2Q0 has to be tripped
before the auto-reclose of the breaker 1Q0 in order to ensure
that the generator does not continue to feed the fault.
110 kV
Auto
reclosing
with
synchro-
check
U< ands Uo> stages have a
release delay of 10 seconds.
110kV/10kV
GENERATOR
LOAD
LOAD
G
VAMP257
U<
f<
U>
0
f>
UUU
L1 L2 L3
+
LossOfMains257
START
START
TRIP
TRIP
1Q0
2Q0
Figure 2.3.17-2. Disconnection of a generator from the network during the
dead time of an auto-reclose cycle (Loss of mains application).