Choice Of Operating Mode; Choice Of Transfer Tripping Scheme - ABB RELION REB500 Technical Manual

1MRK 505 406-UEN B
This supplementary logic interlocks the distance protection receive signal at the end of the
ground fault function's basic time or when it picks up in the backwards direction. To this end,
the signal RecveInh is connected to the distance protection input ExtBlkHF. Thus the
communication channel is initially available for use by the distance protection and only made
available to the ground fault protection at the end of the basic time. The basic time setting
must allow adequate time for the distance protection to detect and clear a fault if it can.
Independent directional ground fault protection
The ground fault function can also be applied as a stand-alone function, but only in MV and HV
systems.
The coordination of ground fault and distance protections in this case is achieved by
appropriately setting the parameter t
If this time is too short, there is a likelihood that the ground fault protection will issue a three-
phase trip before the circuit-breaker has opened for faults that have been correctly detected
by the distance protection.
The basic time of the ground fault protection must therefore be long enough to ensure that
the distance protection can trip phase-selectively.
No facility is provided for using the distance relay starters to achieve phase-selective tripping
by the directional ground fault function.
An independent directional ground fault function requires its own communication channel,
which must be entirely independent of the distance protection.
5.9.6.2

Choice of operating mode

It is assumed that the ground fault protection settings at both ends of the protected line are
the same. This applies especially to the basic time, the blocking time, the transfer tripping
scheme in use and options.
5.9.6.3

Choice of transfer tripping scheme

In the case of a permissive directional comparison scheme, the amount of fault resistance,
which can be detected, reduces towards the remote end of the line, because the enabling
current must be exceeded at both ends. Without additional precautions, the use of a
permissive scheme would be limited on lines with a weak infeed at one end.
It was possible to eliminate this disadvantage by providing the directional ground fault
protection with its own echo logic for weak infeeds, which can be switched in and out as
required.
On the other hand, a directional comparison scheme using a blocking signal is able to detect
high-resistance ground faults along the whole length of the line, because the protection at the
strong infeed end is always able to trip although the current at the weak infeed end does not
reach the enabling level.
Permissive directional comparison scheme
In this scheme, each of the protection functions has to receive a signal from the opposite end
of line in order to be able to trip. A protection function sends a permissive signal when its
Bay protection functions REB500
Technical manual
Basic
The protection only operates in a comparison mode during the comparison
time (1 s) and is blocked at the end of this time. The comparison time starts at
the end of the basic time. information icon alerts the reader of important facts
and conditions.
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Section 5
Bay protection functions
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