Dynamic Cold Load Pickup; Description - Siemens SIPROTEC 4 User Manual

2.4

Dynamic Cold Load Pickup

With the cold load pickup function, pickup and delay settings of directional and non-directional time overcur-
rent 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
thereafter, 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 thresh-
olds 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 accord-
ance with its ready or not ready state.
NOTE
i i
Dynamic cold load pickup must 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.
In addition, switching between parameters can be triggered by two other 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
•
Irrespective of the setting of parameter 1702 Start Condition, the release of cold load pickup may
always be selected via the binary input
Figure 2-39 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-
combination of the configured dropout conditions of all directional and non-directional overcurrent elements.
When Stop Time is set to ∞ or when binary input
the "normal" thresholds. 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".
If the dynamic setting values were activated via the binary input
Reclosing ready" and this cause drops out, the "normal" settings are restored immediately, even if a pickup is
the result.
SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016
2.16 Automatic Reclosing System
>ACTIVATE CLP .
>BLK CLP stpTim is active, no comparison is made with
>ACTIVATE CLP or the signal "79M Auto
Functions
2.4 Dynamic Cold Load Pickup
79).
111