The power frequency overvoltage may occur in the network due to contingencies such
as:
• The defective operation of the automatic voltage regulator when the generator is
in isolated operation.
• Operation under manual control with the voltage regulator out of service. A
sudden variation of load, in particular the reactive power component, gives rise to
a substantial change in voltage because of the inherent large voltage regulation of
a typical alternator.
• Sudden loss of load due to the tripping of outgoing feeders, leaving the generator
isolated or feeding a very small load. This causes a sudden rise in the terminal
voltage due to the trapped field flux and overspeed.
If a load sensitive to overvoltage remains connected, it leads to equipment damage.
It is essential to provide power frequency overvoltage protection, in the form of time
delayed element, either IDMT or DT to prevent equipment damage.
4.4.1.7 Signals
Table 412: PHPTOV Input signals
Name
Type Default Description
U_A_AB SIGNAL 0 Phase to earth voltage A or phase to phase voltage
AB
U_B_BC SIGNAL 0 Phase to earth voltage B or phase to phase voltage
BC
U_C_CA SIGNAL 0 Phase to earth voltage C or phase to phase voltage
CA
BLOCK BOOLEAN 0=False Block signal for activating the blocking mode
Table 413: PHPTOV Output signals
Name
Type Description
OPERATE BOOLEAN Operate
START BOOLEAN Start
1MRS758755 A Section 4
Protection functions
REC615 and RER615 411
Technical Manual
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