ABB RELION 620 Series Technical Manual page 637

1MRS757644 F
4.5.1.7
620 series
Technical Manual
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.
Signals
Table 573: PHPTOV Input signals
Name Type
U_A_AB SIGNAL
U_B_BC SIGNAL
U_C_CA SIGNAL
BLOCK BOOLEAN
Table 574: PHPTOV Output signals
Name Type
OPERATE BOOLEAN
START BOOLEAN
Protection functions
Default Description
0 Phase to earth voltage A or phase to phase voltage
AB
0 Phase to earth voltage B or phase to phase voltage
BC
0 Phase to earth voltage C or phase to phase voltage
CA
0=False Block signal for activating the blocking mode
Description
Operate
Start
Section 4
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