PROTECT ION TR I P UNI TS
3/41
RQ Loss of field or reverse reactive power (ANSI 40 or 32RQ) With a constant trip time (t = k) this circuit-breaker trips when the total reactive power absorbed by the generator exceeds the set threshold. It is possible to select a constant threshold (k=0) or a function of the delivered active power of the generator (k≠0).
Q
P
TRIP
OQ Reactive overpower (ANSI 32OF): With a constant trip time (t = k), this trips when the reactive power exceeds the set threshold in the di - rection from the generator to the network.
t
Q27
t27
Q
OP Active overpower (ANSI 32OF): With a constant trip time (t = k), this trips when the active power exceeds the threshold set in the delivering direction from the generator.
t
P26 Q 7
t26 7
P Q
UP Active underpower (ANSI 32LF): With a constant trip time (t = k), this trips when the active power delivered by the generator is lower than the set threshold. It is possible to disable the protection temporarily to manage the start-up phase by set- ting a time window from the closing of the circuit-breaker, by using an electric signal or via incoming com- munication to a relay.
t
P23
t23
P
RQ Second protection against loss of field or reverse reactive power (ANSI 40 or 32R): This functions as the above mentioned RQ protection. These two functions can be active and used at the same time, thus allowing the under-excitation curve of the generator to be accurately followed and avoid- ing unwanted disconnections.
Q
kq kq2
P
Q25
Q24
ROCOF Rate of change of frequency (ANSI 81R) This enables both positive and negative frequency variations to be detected rapidly. The threshold is con- stant and the function trips when the frequency variation in Hz/s is greater than the set threshold. It is possible to set the operating mode to: active, alarm only, or deactivated. The protection enables the iden- tification and disconnection of the area where the fault has occurred while maintaining operation in the rest of the installation.
f(Hz)
frequency after fault
failure
50/60Hz
frequency after fault
Time
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