Functions
2.4 Dynamic Cold Load Pickup
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
94
2.4 Dynamic Cold Load Pickup
With the cold load pickup function, pickup and delay settings of directional and non-directional time overcurrent
protection can be changed over dynamically.
Applications
• It may be necessary to dynamically increase the pickup values if, during starting and for a short time there-
after, certain elements of the system have an increased power consumption after a long period of zero
voltage (e.g. air-conditioning systems, heating installations, motors). Thus a raise of pickup thresholds can
be avoided by taking into consideration such starting conditions.
Prerequisites
Note:
Dynamic cold load pickup is not be confused with the changeover option of the 4 setting groups (A to D). It is
an additional feature.
It is possible to change pickup thresholds and delay times.
2.4.1 Description
Effect
There are two methods by which the device can determine if the protected equipment is de-energized:
• Via binary inputs, the device is informed of the position of the circuit breaker (address 1702 Start
Condition = Breaker Contact).
• As a criterion a set current threshold is undershot (address 1702 Start Condition = No Current).
If the device determines that the protected equipment is de-energized via one of the above methods, a time,
CB Open Time, is started and after its expiration the increased thresholds take effect.
Regardless of how parameter 1702 Start Condition is set, the release for cold load pickup can always be
given via binary input „>ACTIVATE CLP“.
Figure 2-25 shows the logic diagram of the dynamic cold load pickup function.
If it is detected via the auxiliary contact or the current criterion that the system is de-energized, i.e. the circuit
breaker is open, the CB Open Time is started. As soon as it has elapsed, the greater thresholds are enabled.
When the protected equipment is re-energized (the device receives this information via the binary inputs or
when threshold BkrClosed I MIN is exceeded), a second time delay referred to as the Active Time is
initiated. Once it elapses, the pickup values of the relay elements return to their normal settings. This time may
be reduced when current values fall below all normal pickup values for a set Stop Time after startup, i.e. after
the circuit breaker has been closed. The starting condition of the fast reset time is made up of an OR-combi-
nation of the configured dropout conditions of all non-directional overcurrent elements. When Stop Time is
set to ∞ or when binary input „>BLK CLP stpTim“ is active, no comparison is made with the "normal" thresh-
olds. The function is inactive and the fast reset time, if applied, is reset.
If overcurrent elements are picked up while time Active Time is running, the fault generally prevails until
pickup drops out, using the dynamic settings. Only then the parameters are set back to "normal".
When the dynamic setting values are activated via binary input „>ACTIVATE CLP“ and this cause drops out,
the "normal" settings are restored immediately even if a pickup is present.
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