ABB RELION REB670, Applications Manual

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applications problems, for the most common busbar protection schemes, are described
in this chapter.
6.1.3.1 General
M12102-3 v4
A busbar protection is a device which protects busbars against short-circuits and
ground-faults. In the early development of electricity systems, no separate protection
device was used for busbar protection. Remote end line protections were used as main
protection for busbar faults. With the increased short-circuit power in the network
separate differential IEDs for busbar protection have to be installed in order to limit the
damage caused by the primary fault currents. At the same time, it is also a must to
secure the network stability, as a delayed tripping for busbar faults can also lead to
network instability, pole slip of near-by generators and even total system collapse.
M12103-3 v3
For bus zone protection applications, it is extremely important to have good security
since an unwanted operation might have severe consequences. The unwanted operation
of the bus differential IED will have the similar effect from the operational point of
view as simultaneous faults on all power system elements connected to the bus. On the
other hand, the IED has to be dependable as well. Failure to operate or even slow
operation of the differential IED, in case of an actual internal fault, can have serious
consequences. Human injuries, power system blackout, transient instability or
considerable damage to the surrounding substation equipment and the close-by
generators are some of the possible outcomes.
Therefore, Busbar differential protection must fulfill the following requirements:
1. Must be absolutely stable during all external faults. External faults are much more
common than internal faults. The magnitude of external faults can be equal to the
stations maximum short circuit capacity. Heavy CT-saturation due to high DC
components and/or remanence at external faults must not lead to maloperation of
the busbar differential protection. The security against misoperation must be
extremely high due to the heavy impact on the overall network service.
2. Must have as short tripping time as possible in order to minimize the damage,
minimize the danger and possible injury to the people who might be working in
the station at the moment of internal fault, and secure the network stability.
3. Must be able to detect and securely operate for internal faults even with heavy CT
saturation. The protection must also be sensitive enough to operate for minimum
fault currents, which sometimes can be lower than the maximum load currents.
4. Must be able to selectively detect faults and trip only the faulty part of the busbar
system.
5. Must be secure against maloperation due to auxiliary contact failure, possible
human mistakes and faults in the secondary circuits and so on.
Section 6
1MRK 505 370-UUS A
Differential protection
110 Busbar protection REB670 2.2 ANSI
Application manual