ABB RELION 670 Series Applications Manual page 101

1MRK 505 337-UUS A
6.1.2.2 Meshed corner application and T-connection application
The REB670 general differential function is suitable for application on mesh-corner arrangements.
Mesh corners might have four or even up to six CT inputs and are basically simple single busbar
arrangements. A similar application will occur when a T-protection is required for breaker-and-a-
half or ring busbar arrangements.
ANSI11000237 V1 EN-US
Figure 39: Example of REB670 application on T-connection
6.1.3 Busbar protection applications
6.1.3.1 General
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. In 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.
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
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ANSI11000237-1-en.vsd
Section 6
Differential protection
M12098-3 v4
SEMOD127456-1 v1
M12102-3 v3
M12103-3 v3
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