Dynamic Cold Load Pickup; Description - Siemens SIPROTEC 7SJ61 Manual

2.3

Dynamic Cold Load Pickup

With the cold load pickup function, pickup and delay settings of 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.
• As a further option the pickup thresholds may be modified by an automatic reclosure function in accordance
with its ready or not ready state.
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.
2.3.1

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.
In addition, switching between parameters can be triggered by two further events:
• by signal "79M Auto Reclosing ready" of the internal automatic reclosure function (address 1702 Start
Condition = 79 ready). Thus the protection thresholds and the tripping times can be changed if auto-
matic reclosure is ready for reclosing (see also Section 2.11).
• Irrespective of the setting of parameter 1702 Start Condition, the release of cold load pickup may
always be selected via the binary input „>ACTIVATE CLP".
Figure 2-18 shows the logic diagram for 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.
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
Functions
2.3 Dynamic Cold Load Pickup
77