302
D90
PLUS
LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CONTROL ELEMENTS
CHAPTER 7: PROTECTION
Figure 255: Hybrid POTT scheme logic
Directional comparison blocking
The directional comparison blocking scheme compares the direction to a fault at all
terminals of the line. Unlike the permissive schemes, the absence of a blocking signal
permits operation of the scheme. Consequently, the scheme is biased toward
dependability and requires an on-off type of signaling.
By default, the directional comparison blocking scheme uses only a forward-looking over-
reaching zone 2 distance element to identify forward faults. Ground directional
overcurrent functions available in the relay can be used in conjunction with the zone 2
distance element to increase the coverage for high resistance faults. Also by default, only a
Off
AND
AND
Off
AND
RX
Enabled
Enabled
Custom
Custom
Disabled
Disabled
Phase selector
SETTING
= Off
Weak Infeed Condition
SETTING
= Off
Ground Directional OC
Forward
OR
FLEXLOGIC OPERANDS
PH DIST Z2 PKP
GND DIST Z2 PKP
FLEXLOGIC OPERANDS
LINE PICKUP LEO PKP
OPEN POLE OP
LINE PICKUP UV PKP
AND
SETTING
= Enabled
= Disabled
Function
= Off
Block
OR
SETTINGS
= Off
RX1
= Off
RX2
= Off
RX3
= Off
RX4
SETTING
Weak Infeed
OR
SETTING
RX Pickup Delay
T
pickup
0
AND
TIMER
0
100 ms
SETTING
Permissive Echo
SETTING
= Off
Echo Condition
SETTING
= Off
Ground Directional OC
Reverse
FLEXLOGIC OPERANDS
PH DIST Z4 PKP
GND DIST Z4 PKP
PH DIST Z1 PKP
GND DIST Z1 PKP
OR
SETTINGS
T
pickup
T
reset
Transient Block Reset Delay
Transient Block Pickup Delay
AND
SETTINGS
Echo Duration
Echo Lockout
Echo duration and
lockout logic
OR
OR
AND
SETTINGS
0
T
reset
Seal-In Delay
FLEXLOGIC OPERANDS
HYB POTT OP
SETTING
Communication Bits
RUN
Trip table
FLEXLOGIC OPERANDS
HYB POTT TRIP A
HYB POTT TRIP B
HYB POTT TRIP C
HYB POTT TRIP 3P
FLEXLOGIC OPERANDS
AR FORCE 3P TRIP
OPEN POLE OP
AR FORCE 3P TRIP
OPEN POLE OP
AR FORCE 3P TRIP
OPEN POLE OP
870956A5.CDR
Phase selector
SETTING
Communication Bits
RUN
Echo table
RUN
Transmit table
FLEXLOGIC OPERANDS
HYB POTT TX1
HYB POTT TX2
HYB POTT TX3
HYB POTT TX4
AR FORCE 3P TRIP
OPEN POLE OP
AND
RX
Phase
selector
AR FORCE 3P TRIP
OPEN POLE OP