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Cold Load Pick-up
and Inrush Current
Detection
Cold Load Pick-up
A situation is regarded as cold load when all the three phase
currents have been less than a given idle value and then at least
one of the currents exceeds a given pick-up level within 80 ms.
In such case the cold load detection signal is activated for a
given time. This signal is available for output matrix and
blocking matrix. Using virtual outputs of the output matrix
setting group control is possible.
Application for Cold Load Detection
Right after closing a circuit breaker a given amount of overload
can be allowed for a given limited time to take care of concurrent
thermostat controlled loads. Cold load pick-up function does this
for example by selecting a coarser setting group for overcurrent
stage(s). It is also possible to use the cold load detection signal to
block any set of protection stages for a given time.
Inrush Current Detection
Inrush current detection is quite similar with the cold load
detection but it does also include a condition for second
harmonic relative content of the currents. When all phase
currents have been less than a given idle value and then at least
one of them exceeds a given pick-up level within 80 ms and the
nd
ratio 2
harmonic ratio to fundamental frequency, I
least one phase exceeds the given setting, the inrush detection
signal is activated. This signal is available for output matrix and
blocking matrix. Using virtual outputs of the output matrix
setting group control is possible.
By setting the Pickupf2 parameter for I
signal will behave equally with the cold load pick-up signal.
Application for Inrush Current Detection
The inrush current of transformers usually exceeds the pick-up
setting of sensitive overcurrent stages and contains a lot of even
harmonics. Right after closing a circuit breaker the pick-up and
tripping of sensitive overcurrent stages can be avoided by
selecting a coarser setting group for the appropriate over-current
stage with inrush detect signal. It is also possible to use the
detection signal to block any set of protection stages for a given
time.
Supporting Functions
/I
, of at
f2
f1
/I
to zero, the inrush
f2
f1
857-UM001A-EN-P – July 2009
4-5
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