Calculating Settings For Four Step Phase Overcurrent Protection - ABB REL650 Applications Manual

Section 3
REL650 setting examples
3.1.9
66
Default value
5. Set UVPickup to 70 % of VBase
Default value that must be lower than the voltage at normal operation
6. Set tDuration to 0.020 s
Default value for time delay of UI detection
7. Set tSOTF to 1.0 s
Default value for drop off delay of SOTF function
8. Set tDLD to 0.2 s
Default value for drop off delay of Dead Line Detection
The switch onto fault logic is aimed to give fast trip of faults energized by switching
in of the line circuit breaker. There are two different modes for operation:
• Impedance: meaning that ZCVPSOF is released by a non-directional start
signal from the distance protection function (normally zone 2).
• VILevel: meaning that ZCVPSOF is released by a combination of low voltage
(lower than settingUVPickup) and current higher than a set value (IphPickup).
It is possible to set the mode of operation to the combination: Impedance and
VILevel.
The function can be initiated by a binary input signal BC: (closing of the circuit
breaker). If this signal is not available there can be an automatic initiation based on
the voltage and current measurement.

Calculating settings for four step phase overcurrent protection

3-phase output OC4PTOC 51_67
The phase overcurrent protection is more difficult to set as the short circuit current is
highly dependent of the switching state in the power system as well as of the fault type. In
order to achieve setting that assure selective fault clearance a large number of calculations
have to be made with different fault locations, different switching states in the system and
different fault types. Below one example of setting of phase overcurrent protection for a
line in a meshed solidly grounded system is given.
The phase overcurrent protection has the following purpose:
• Backup protection for short circuits on the line in case the distance protection is
unavailable (after fuse failure blocking)
• Backup protection for short circuits on the adjacent busbar in case the distance
protection is unavailable (after fuse failure blocking)
• Backup protection for short circuits on the local busbar
• Protection for short circuits between the line circuit breaker and the line current
transformer
1MRK 506 334-UUS A
Application manual