When required for interlocking of non-urgent tripping applications, the threshold setting of the low forward power
protection f
unction should be less than 50% of the power level that could result in a dangerous overspeed
condition on loss of electrical loading.
When required for loss of load applications, the threshold setting of the low forward power protection function, is
system dependent, however, it is typically set to 10 - 20% below the minimum load. The operating mode should be
set to Reverse for this application.
For interlocking non-urgent trip applications the time delay associated with the low forward power protection
function could be set to zero. However, some delay is desirable so that permission for a non-urgent electrical trip is
not given in the event of power fluctuations arising from sudden steam valve/throttle closure. A typical time delay
is 2 seconds.
For loss of load applications the pick-up time delay is application dependent but is normally set in excess of the
time between motor starting and the load being established. Where rated power cannot be reached during
starting (for example where the motor is started with no load connected) and the required protection operating
time is less than the time for load to be established then it will be necessary to inhibit the power protection during
this period. This can be done in the PSL using AND logic and a pulse timer triggered from the motor starting to
block the power protection for the required time.
When required for loss of mains or loss of grid applications where the distributed generator is not allowed to
export power to the system, the threshold setting of the reverse power protection function, should be set to a
sensitive value, typically <2% of the rated power.
The low forward power protection function should be time-delayed to prevent false trips or alarms being given
during power system disturbances or following synchronisation. A time delay setting, of 5 s should be applied
typically.
The delay on the reset timers would normally be set to zero.
To prevent unwanted alarms and flags, the protection element can be disabled when the circuit breaker is open
via Pole Dead logic.
P14x Chapter 12 - Power Protection Functions
P14xEd1-TM-EN-1 265
To Next Page
Loading...
Need help?
General
