GE L90 Instruction Manual page 615

CHAPTER 5: SETTINGS CONTROL ELEMENTS
Consider the selected protection element (or elements in combination) with the selection of . For all the
GND DIR O/C FWD
forward external faults seen by an element used as at one end of the line, the reverse-looking element
GND DIR O/C FWD
used as at the other end should picks up and provides a blocking signal. For greater security and to
GND DIR O/C REV
overcome spurious directional element operation during transients, adding a pickup delay greater than the pilot channel
delay to the reverse directional element is recommended.
— This setting specifies the number of bits of the communications channel available for
BLOCK SCHEME NO OF COMM BITS
the scheme. With only one bit available, the scheme sends the blocking signal by asserting the FlexLogic
DIR BLOCK TX INIT
operand. Use this operand to start the channel (set the blocking signal). On internal faults, the scheme removes the
blocking signal by asserting the FlexLogic operand.
DIR BLOCK TX1
For tripping the scheme responds to lack of the blocking signal on bit 1 ( setting). The scheme uses only
BLOCK SCHEME RX1
local fault type identification provided by the phase selector to assert the output operands A, B, C, and 3P.
DIR BLOCK TRIP
To take advantage of the four-bit blocking scheme, initiate the blocking signals from a disturbance detector. This can be
accomplished by using both and to assert the blocking signal. Subsequently, specific bits are de-
50DD DIR BLOCK TX INIT
asserted by the scheme based on the phase selection providing the peer relay with more information on the fault type.
Otherwise, the peer relay issues a three-pole trip upon receiving the bit pattern (0, 0, 0, 0).
through — These settings allow the user to select the FlexLogic operands that
BLOCK SCHEME RX1 BLOCK SCHEME RX4
represent the receive signals for the scheme. Typically input contacts interfacing with a signaling system are used. In
single-bit applications, must be used. In two-bit applications, and
BLOCK SCHEME RX1 BLOCK SCHEME RX1 BLOCK SCHEME RX2
must be used. In four-bit applications, , , , and
BLOCK SCHEME RX1 BLOCK SCHEME RX2 BLOCK SCHEME RX3 BLOCK SCHEME RX4
must be used.
Figure 5-221: Directional blocking scheme logic
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L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 5-391