308 D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS CHAPTER 7: PROTECTION
Ground Directional OC Forward
Range: any FlexLogic operand
Default: OFF
This setting selects the FlexLogic operand (if any) of a protection element used in
addition to zone 2 for identifying faults on the protected line, and thus, for initiating
operation of the scheme. Good directional integrity is the key requirement for an over-
reaching forward-looking protection element used for this feature.
Even though any operand can be used, enabling the user to combine responses of
various protection elements or to apply extra conditions through FlexLogic equations,
this extra signal is primarily meant to be the output operand from either the negative-
sequence directional or neutral directional overcurrent elements. Both these elements
have separate forward and reverse output operands.
Use the forward indication (that is, NEG SEQ DIR OC1 FWD or NEUTRAL DIR OC1 FWD).
Coordinate the selected protection element (or elements in combination) with this
setting. For all the forward external faults seen by an element selected by the
Ground
Directional OC Forward
setting at one end of the line, the reverse-looking element
selected by the
Ground Directional OC Reverse setting at the other end picks up and
provides a blocking signal.
Ground Directional OC Reverse
Range: any FlexLogic operand
Default: OFF
This setting selects the FlexLogic operand (if any) of a protection element that is used in
addition to zone 4 for identifying reverse faults, and thus, for initiating the blocking
signal. Either reverse-looking directional or non-directional overcurrent protection
element can be used for this feature.
Even though any operand can be used, enabling the user to combine responses of
various protection elements or to apply extra conditions through FlexLogic equations,
this extra signal is meant to be the output operand from either the negative-sequence
directional, neutral directional, or a non-directional instantaneous overcurrent element.
Coordinate the selected protection element (or elements in combination) with the
selection of the
Ground Directional OC Forward setting. For all the forward external faults
seen by an element selected by the
Ground Directional OC Forward setting at one end of
the line, the reverse-looking element selected by the
Ground Directional OC Reverse
setting at the other end picks up and provides a blocking signal.
Communication Bits
Range: 1, 2, 4
Default: 1
This setting specifies the number of bits of the communications channel available for the
directional comparison blocking scheme. With only one bit available, the scheme sends
the blocking signal by asserting the 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 DIR BLOCK TX1 FlexLogic operand.
For tripping, the directional comparison blocking scheme responds to lack of the
blocking signal on bit 1 (selected by the
RX1 setting). The scheme uses only local fault
type identification provided by the phase selector to assert the DIR BLOCK TRIP A, DIR
BLOCK TRIP B, DIR BLOCK TRIP C, and DIR BLOCK TRIP 3P output operands.
To take advantage of the four-bit blocking scheme, initiate the blocking signals from a
disturbance detector. This can be accomplished by using both 50DD and the DIR BLOCK
TX INIT operand to assert the blocking signal. Subsequently, specific bits are de-asserted
by the scheme based on the phase selection providing the peer device with more
information on the fault type. Otherwise, the peer device issues a three-pole trip upon
receiving the [0, 0, 0, 0] bit pattern.
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