Calculating Settings For Step 4 - ABB REC650 Applications Manual

1MRK 511 286-UUS A
3.1.6.4
3.1.7
Application manual

Calculating settings for step 4

1. Set Pickup4 to 42 % of IBase, corresponding to 100 A
The current setting of step 4 should be chosen according to standard procedure in the
grid. From experience it can be concluded that a setting down to about 100 A can be
used. This setting is however highly dependent on the line configuration, mainly if
the line is transposed or not.
The delay of Pickup4 should be set larger than the delay of the sensitive residual
current protection of the lines.
2. Set TD4 to 0.3
Characterist4: RD type
3. Set t4Min to 1.2 s
4. Set inverse time delay of type RD to logarithmic
If definite time delay is used there is some risk of unselective trip during high
resistive ground-faults or series faults. If a dependent time delay (inverse time) is
used some degree of selectivity can be achieved.
Here an inverse time delay of the RD type is selected: logarithmic
Calculating settings for two step residual overvoltage protection
LV-side, ROV2PTOV (59N)
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 ground-faults on the 22 kV feeders out from the substation.
• Main protection for ground-faults on the 22 kV busbar
• Main protection for ground-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 ground-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 dependent on the required sensitivity and the
system grounding. The 22 kV system has grounding through a Petersen coil (connected to
the system via a separate grounding transformer) and a parallel neutral point resistor. The
Petersen coil is tuned to compensate for the capacitive ground-fault current in the 22 kV
Section 3
REC650 setting examples
55