Functions
2.4 Load Restoration
SIPROTEC, 7RW80, Manual
C53000-G1140-C233-1, Release date 10.2010
58
You can adjust the trip- and dropout time for every load restoration element. Furthermore, you can adjust the
pickup- and dropout time as a difference to the starting frequency, which together form the threshold of the load
restoration. The frequency must reach this threshold value of the set trip time, before the restoration signal for
the circuit breaker is issued. If the frequency drops below the the set pickup threshold value during the set
dropout time, the time for the pickup will be halted. If the frequency drops to a value below the dropout threshold
value, pickup and dropout time will be reset. This takes into account that the frequency is not restored monot-
onously, but rather is subject to intermittent fluctuations.
The following picture shows the interaction of thresholds and timers.
Figure 2-8 Load Restoration - Sequence
Blocking and Monitoring
The load restoration can be blocked by:
• Binary Input
• Tripping of another protective function of the device, which is not set to „Alarm Only“.
An exception is the underfrequency protection. Tripping of a underfrequency element initiates the load res-
toration.
• Inaccurate or invalid frequency measurements at undervoltage
The blocking condition can be reset by a binary input or disappearing device pickup.
The number of restoration cycles is limited by a parameter. This prevents short-cyclical on- and off switching of
the underfrequency protection and load restoration at major frequency fluctuations. If the number of restoration
cycles exceeds the configured value, the load restoration will be blocked. The restoration cycle is time moni-
tored. The monitoring time of load restoration cycles is configurable.
Pending power system/network faults are kept open during the restoration cycle.
The following graphic shows the operation of the blocking and the monitoring parameters. The overvoltage
function is an example, the same applies to other protection functions except for underfrequency.
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