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3.3 Cold load pick-up and inrush
current detection
3 Supporting functions
Technical description
110
VAMP 24h support phone +358 (0)20 753 3264
VM59.EN001
3.3.
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 more coarse
setting group for over-current 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 2
nd
harmonic ratio to fundamental frequency, I
f2
/I
f1
, of
at 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
f2
/I
f1
to zero, the inrush
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 more coarse setting group for the appropriate
overcurrent 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.
Содержание VAMP 59
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