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Technical description
2 Protection functions
2.4 Relay function dependencies
VM59.EN001
VAMP 24h support phone +358 (0)20 753 3264
49
2.4.
Relay function dependencies
2.4.1.
Current protection function dependencies
The current based protection functions are relative to nominal
current, which is dependent of the application mode. In the
motor protection mode all of the current based functions are
relative to I
MOT
and in the feeder protection mode to I
N
with
following exceptions.
I
2
> (46), I
2
>> (47), I
ST
> (48), N> (66) are always dependent on
I
MOT
and they are only available when application mode is in
the motor protection.
2.5.
Overcurrent protection I> (50/51)
Overcurrent protection is used against short circuit faults and
heavy overloads.
The overcurrent function measures the fundamental frequency
component of the phase currents. The protection is sensitive for
the highest of the three phase currents. Whenever this value
exceeds the user's pick-up setting of a particular stage, this
stage picks up and a start signal is issued. If the fault situation
remains on longer than the user's operation delay setting, a
trip signal is issued.
Three independent stages
There are three separately adjustable overcurrent stages: I>,
I>> and I>>>. The first stage I> can be configured for definite
time (DT) or inverse time operation characteristic (IDMT). The
stages I>> and I>>> have definite time operation
characteristic. By using the definite delay type and setting the
delay to its minimum, an instantaneous (ANSI 50) operation is
obtained.
Figure 2-5 shows a functional block diagram of the I>
overcurrent stage with definite time and inverse time operation
time. Figure 2-6 shows a functional block diagram of the I>>
and I>>> overcurrent stages with definite time operation delay.
Inverse operation time
Inverse delay means that the operation time depends on the
amount the measured current exceeds the pick-up setting. The
bigger the fault current is the faster will be the operation.
Accomplished inverse delays are available for the I> stage. The
inverse delay types are described in chapter 2.14. The device
will show the currently used inverse delay curve graph on the
local panel display.
Содержание VAMP 59
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