Date Code 20011026 Specifications 2-11
SEL-321/321-1 Instruction Manual
Directional Comparison Blocking (DCB) Logic
This logic performs the following tasks:
• Provides the individual carrier coordination timers for the Zone 2 and Level 2 elements to
allow time for the block trip signal to arrive from the remote terminal.
• Instantaneously keys the communications equipment to transmit block trip for reverse
faults and extends this signal for a settable time following the dropout of all Zone 3 and
Level 3 elements.
• Latches block trip send condition by the phase distance elements following a close-in
zero-voltage three-phase fault where the polarizing memory expires. Latch is removed
when the polarizing memory voltage returns or current is removed.
• Extends the received block trip signal by a settable time.
External Input
Received Block
Trip Signal BT Assign BT to a programmable input. Drive with
block trip receive output.
Timer Settings
Zone 3 Dropout
Extension Delay Z3XD Current reversal guard timer.
Block Receive
Extension Delay BTXD Sets reset time of block trip received condition after
the reset of block trip input.
Zone 2 Phase 21 (M2P)
Carrier Coord. Delay Z2PSD Delays M2P element output.
Zone 2 Ground 21 (Z2G)
Carrier Coord. Delay Z2GSD Delays Z2G element output.
67N2 Carrier
Coordination Delay 67N2SD Delays 67N2 element output.
67Q2 Carrier
Coordination Delay 67Q2SD Delays 67Q2 element output.
Logic Outputs
Stop carrier STOP Program to an output contact to stop carrier.
Start carrier START Program to an output contact to start carrier.
Includes current reversal guard logic.
Block Trip Extension BTX Block trip receive signal extended by BTXD timer.
Supporting Drawings: Figure 2.33 and Figure 2.34.
For further information, request Application Guide 93-06: Applying the SEL-321 Relay to
Directional Comparison Blocking (DCB) Schemes from your representative or the factory.
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