Dynamic Cold Load Pickup; Description - Siemens siprotec SJ62 User Manual

2 Functions
2.4

Dynamic Cold Load Pickup

Applications
Prerequisites
2.4.1

Description

Effect
117
With the cold load pickup function, pickup and delay settings of directional and non-
directional time overcurrent protection can be changed over dynamically.
• It may be necessary to dynamically increase the pickup values if, during starting
and for a short time thereafter, certain elements of the system have an increased
power consumption after a long period of zero voltage (e.g. air-conditioning sys-
tems, 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 reclo-
sure function in accordance with its ready or not ready state.
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.
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 (ad-
dress 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 in-
creased 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 automatic reclosure is ready for reclosing
(see also Section 2.14).
• 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 2-34 shows the logic diagram for dynamic cold load pickup function.
When the auxiliary contact or current criterion detects that the system is de-energized,
i.e. the circuit breaker is open, the CB open time CB Open Time is started. As soon
as it times out, the greater thresholds are enabled. When the protected equipment is
re-energized (the device receives this information via the binary inputs or when thresh-
old 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. The time may be reduced when current values after startup, i.e.
after the circuit breaker is closed, fall below all normal pickup values for a set time,
Stop Time. 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 time overcurrent ele-
ments. When Stop Time is set to ∞ or when binary input „>BLK CLP stpTim" is
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015