rise to a substantial change in voltage because of the large voltage regulation
inherent in a typical alternator.
• Sudden loss of load due to the tripping of outgoing feeders, leaving the
generator isolated or feeding a very small load, can cause 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.
4.5.2.7
Signals
Table 584: PHAPTOV Input signals
Name
Type
Default
Description
U_A_AB
SIGNAL
0
Phase-to-earth volt-
age A or phase-to-
phase voltage AB
BLOCK
BOOLEAN
0=False
Block signal for acti-
vating the blocking
mode
Table 585: PHAPTOV Output signals
Name
Type
Description
OPERATE
BOOLEAN
Operate
START
BOOLEAN
Start
4.5.2.8
Settings
Table 586: PHAPTOV Group settings (Basic)
Parameter
Values (Range)
Unit
Step
Default
Description
Start value
0.05...1.60
xUn
0.01
1.10
Start value
Time multiplier
0.05...15.00
0.01
1.00
Time multiplier
in IEC/ANSI IDMT
curves
Operate delay time 40...300000
ms
10
40
Operate delay time
Operating curve
type
5=ANSI Def. Time
15=IEC Def. Time
17=Inv. Curve A
18=Inv. Curve B
19=Inv. Curve C
20=Programmable
15=IEC Def. Time
Selection of time
delay curve type
1MRS757644 H
Protection functions
620 series
Technical Manual
643
