Calculating Settings For Step 4; Calculating Settings For Two Step Residual Overvoltage Protection Lv-Side, Rov2Ptov - ABB Relion 650 Series Applications Manual

1MRK 504 124-UEN B
The minimum residual current to detect works out as 3I
2. Set
Characteristic2 : ANSI Def.Time
The delay of
s). 0.8 s is proposed.
3.1.8.4

Calculating settings for step 4

1. Set
The current setting of step 4 should be chosen according to standard procedure in the
grid. From experience it can be concluded that the setting down to about 100 A can be
used. This setting is however highly dependent on the line configuration, manly if the line
is transposed or not.
The delay of
protection of the lines.
2. Set
Characteristic4 : RD type
3. Set
4. Select
If definite time delay is used there is some risk of unselective tip at high resistive earth-
faults or series faults. If dependent time delay (inverse time) is used some degree of
selectivity can be achieved.
Here, inverse time delay of type RD is selected: logarithmic
3.1.9 Calculating settings for two step residual overvoltage
protection LV-side, ROV2PTOV
The residual overvoltage protection is fed from the open delta connected voltage transformer
at the 22 kV side of the transformer.
The residual overvoltage protection has the following purpose:
• Back-up protection for earth-faults on the 22 kV feeders out from the substation.
• Main protection for earth-faults on the 22 kV busbar
• Main protection for earth-faults on the 22 kV transformer winding
The residual voltage protection has two steps. In this application step 1 should trip the 22 kV
circuit breaker and if the earth-fault is situated in the transformer 22 kV winding or between
the transformer and the 22 kV breaker the 145 kV breaker is tripped from step 2.
The voltage setting of the protection is depending on the required sensitivity and the system
earthing. The 22 kV system has earthing with a Petersen coil (connected to the system via a
separate earthing transformer) and a parallel neutral point resistor. The Petersen coil is tuned
to compensate for the capacitive earth-fault current in the 22 kV system. The neutral point
resistor gives 10 A earth-fault current at zero resistance earth-fault. This means that the
resistance is
22000
=
R
N
GUID-4ECDF824-B17E-436D-A668-ACA06BB375F7 V2 EN-US
The total zero sequence impedance of the 22 kV system is
Transformer protection RET650
Application manual
t2 to 0.8 s
IN2> should be set longer than the distance protection zone 2 (normally 0,4
IN4> to 42 % of IBase , corresponding to 100 A
IN4> should be set larger than the delay of sensitive residual current
k4 to 0.3
t4Min to 1.2 s
inverse time delay of type RD to logarithmic
/ 3
W
=
1270
10
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RET650 setting examples
= 1.0 kA.
0AB,min
GUID-0369BC86-B1BB-4981-BEA8-A8922D2557A3 v2
GUID-ED62BA1A-F715-4631-8298-B5A9713EEECE v2
(Equation 22)
Section 3
49