detecting the risk of loss of synchronism than, for example, the lowest phase-to-phase
voltage.
Analyzing the loss of synchronism of a generator is rather complicated and requires a
model of the generator with its prime mover and controllers. The generator can be able
to operate synchronously even if the voltage drops by a few tens of percent for some
hundreds of milliseconds. The setting of PSPTUV is thus determined by the need to
protect the power station from the risks of the islanding conditions since that requires
a higher setting value.
The loss of synchronism of a generator means that the generator is unable to operate
as a generator with the network frequency but enters into an unstable condition in
which it operates by turns as a generator and a motor. Such a condition stresses the
generator thermally and mechanically. This kind of loss of synchronism should not be
mixed with the one between an island and the utility network. In the islanding
situation, the condition of the generator itself is normal but the phase angle and the
frequency of the phase-to-phase voltage can be different from the corresponding
voltage in the rest of the network. The island can have a frequency of its own relatively
fast when fed by a small power station with a low inertia.
PSPTUV complements other loss-of-grid protection principles based on the
frequency and voltage operation.
Motor stalling and failure to start can lead to a continuous undervoltage. The positive-
sequence undervoltage is used as a backup protection against the motor stall
condition.
4.4.5.6 Signals
Table 448: PSPTUV Input signals
Name
Type Default Description
U
1
SIGNAL 0 Positive phase sequence voltage
BLOCK BOOLEAN 0=False Block signal for activating the blocking mode
Table 449: PSPTUV Output signals
Name
Type Description
OPERATE BOOLEAN Operate
START BOOLEAN Start
4.4.5.7 Settings
Table 450: PSPTUV Group settings (Basic)
Parameter
Values (Range) Unit Step Default Description
Start value 0.010...1.200 xUn 0.001 0.500 Start value
Operate delay time 40...120000 ms 10 40 Operate delay time
1MRS758755 A Section 4
Protection functions
REC615 and RER615 433
Technical Manual
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