PROTECT ION TR I P UNI TS
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n linear mode (restrained mode, two voltage limits are selected within which the protection is tripped at the set threshold (I20) reduced by the factor K corresponding to the measured voltage. The variation of the factor K is proportional to the voltage, and for voltages greater than the upper threshold (Uh), the thresh- old I20 applies, and for voltages below the lower threshold (UI), the minimum threshold (I20 * Ks) applies.
K
1
Ks
V
UI
Uh
Residual overvoltage (RV – ANSI 59N) : with constant trip time (t = k), helps protect against insulation loss in systems with insulated neutral or with grounded neutral with impedance.
2
V23
V12
α α
1
3
V31
Loss of field or reverse reactive power (RQ – ANSI 40 or 32RQ) : with constant trip time (t = k), the circuit breaker tripped when the total reactive power absorbed by the generator exceeds the set threshold. The constant threshold (k=0) or a function of the delivered active power of the generator (k≠0) can be selected.
Q
P
TRIP
Reactive overpower (OQ – ANSI 32OF) : with constant trip time (t = k), the function is tripped when reactive power exceeds the set threshold in the generator to network direction.
t
Q27
t27
Q
Active overpower (OP – ANSI 32OF) : with constant trip time (t = k), the function is tripped when the active power exceeds the threshold set in the delivering direction of the generator.
t
P26
t26
P
Active underpower (UP – ANSI 32LF ): with constant trip time (t = k), the function is tripped when the active power delivered by the generator is lower than the set threshold. The protection can be temporarily dis- abled in order to manage the start-up phase, by setting a time window from the closing of the circuit breaker, by using an electrical signal or via incoming communication to a relay.
t
P23
t23
P
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