Communications Channels For Pilot-Aided Schemes - GE L90 Instruction Manual

SINGLE-POLE TRIPPING

10.5.3 Communications channels for pilot-aided schemes

10.5.3.1 Description
In the L90 relay, pilot-aided schemes transmit a code representing the type of fault determined by the local phase selector
according to the scheme logic. At a receiving terminal, the local and remote data are combined to determine the action to
be performed. Schemes can be used with channels that can carry one, two or four bits. Using a one-bit channel, the
schemes at all terminals of the line use their local phase selectors to identify the fault type and initiate appropriate tripping
actions. In single-pole applications however, a three-pole trip can be performed in the event of an in-line single-phase fault
co-incident with a fault on a different phase (cross-country fault) that is within the reach of the local phase selector, which
is considerably longer than the line. This possibility can be reduced by using a two-bit channel, and eliminated by using a
four-bit channel.
Using two-bit channels, the relays can share limited information about their local phase selection, improving considerably
the accuracy of single-pole tripping on cross-country faults. Two-bit channels, however, can only provide four different
messages, one of which must be "no fault has been detected." With only three messages available, it is not possible to
transmit sufficient information to eliminate the use of local phase selector data, so a three-pole operation can occur in a
cross-country fault condition. Using four-bit channels, the relays share enough information about fault types seen from all
the line terminals that local fault selector data can be rejected. In addition, in multiple bit systems the relays do not
respond to non-valid bit combinations, making the protection system more immune to communication problems than in a
single bit system.
Each scheme within the relay has a setting that specifies the number of bits available on the associated communications
channel. This setting defines the input (RX1, RX2, RX3, RX4) and output (TX1, TX2, TX3, TX4 for communications and [Scheme
Abbreviation] TRIP A, TRIP B, TRIP C, TRIP 3P for action) operands used by the scheme, the data codes used to convey fault
data between terminals, and the method of combining information from the local and remote terminals to produce an
output.
10.5.3.2 Single-bit channels
The TX1 and RX1 operands are used, and fault data is coded per the following tables.
Table 10-14: Permissive scheme transmit codes for one-bit channels
Phase selector determination of fault type
AG, BC, BCG, BG, CA, CAG, CG, AB, ABG, 3P
Unrecognized or AR FORCE 3P TRIP
None of the above
Table 10-15: Blocking scheme transmit codes for one-bit channels
Phase selector determination of fault type
AG, BC, BCG, BG, CA, CAG, CG, AB, ABG, 3P
Unrecognized or AR FORCE 3P TRIP
None of the above
Table 10-16: Unblocking scheme transmit codes for one-bit channels
Phase selector determination of fault type
AG, BC, BCG, BG, CA, CAG, CG, AB, ABG, 3P
10
Unrecognized or AR FORCE 3P TRIP
None of the above
10-42
Bit pattern
transmitted
TX1
1
1
0
Bit pattern
transmitted
TX1
0
0
1
Bit pattern
transmitted
TX1
1
1
0
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
CHAPTER 10: THEORY OF OPERATION