ABB REL-300 Instruction Leaflet page 57

I.L. 40-385.1B
c. Programmable Reclosing Initiation (Figure 3-19)
Same as for POTT scheme.
d. Carrier Receiving Logic (Figure 3-23)
Same as for POTT scheme.
e. Channel Indicators (Figure 3-23)
Same as for POTT scheme.
3.5.3 Directional Comparison Blocking Scheme
(BLK)
The basic operating concept of a Directional Com-
parison Blocking system (BLK) are:
(1) Pilot relays (PLTP/PLTG) are set to over-
reach; the Zone 3 relays (Z3P/Z3G) must be
set in the reverse direction to detect the re-
verse external faults and for carrier start.
(2) Pilot channel is an "ON-OFF" type power line
carrier. Transmitter frequency at each termi-
nal can be the same. Channel is normally
OFF until the carrier start relay senses the
fault and starts the transmitter.
(3) Pilot trip is performed when the pilot relay(s)
operate(s) and a carrier blocking signal is not
received.
The BLK system, as shown in Figure 3-25, includes
the following logic (functional display "STYP" should
be set at the BLK position):
a. Tripping Logic (Figure 3-25)
(1) For a forward internal fault, the local pilot re-
lay (PLTP and/or PLTG) sees the fault;
output signal of OR-40 disables and stops
the carrier start circuit (the ∆I and ∆V starts
the carrier before the distance unit picks up),
via OR-16, S.Q. Timer (0/150 ms) and AND-
50, to prevent the local transmitter from start-
ing. (The receiver receives the signal from
both local and remote transmitters.) At the
same time, output of OR-40 will satisfy one
input of AND-48 and also starts the channel
coordination timer (BLKT), range 0 to 98, in
2 ms steps. (See Segment 5.1.8e for BLKT
setting.) After the preset time of the channel
coordination timer, logic AND-47 will satisfy
AND-48, if there is no received carrier signal
from either remote or local on internal faults,
3-12
and if the local transient block circuit (TBM)
does not setup. Then AND-48 output will sat-
isfy AND-52 and will produce pilot trip via
OR-2 (Figure 3-24). Pilot trip target would be
the same as for POTT.
(2) For a forward external fault, the local pilot re-
lay (PLTP and/or PLTG) sees the fault, and
operates in the same manner as for the
forward internal faults. However, at the re-
mote terminal, the carriers units ∆I/∆V/
Z3P(R)/Z3G(R)/RDOG also sees this exter-
nal fault and turns-on the transmitter via OR-
41, AND-51, AND-50, OR-18, and AND-35,
sending a blocking signal to the other termi-
nals. The local receiver receives the blocking
signal, disables the operation of AND-47;
therefore, AND-48 will produce no carrier trip
signal for AND-52.
b. Carrier Keying Logic
(1) Reverse fault keying (Figure 3-25)
For a reverse fault, the ∆I and ∆V as well as
the local reverse-looking relay Z3P(R)/
Z3G(R) or RDOG sees the fault, operates
the CARSND relay and starts the transmitter,
sending a blocking signal to the other
terminals.
NOTE: The use of ∆I and ∆V for carrier
start provides more security to the
blocking scheme.
This keying circuit includes logic OR-50A,
AND-50, AND-173, OR-41, AND-51, OR-18
and AND-35. The logic of AND -50B and the
32/0 ms timer circuit stops the internal fault
"SEND" on a weakfeed condition. The signal
of 52b to OR-16 is for disabling the "SEND"
circuit when the breaker is open and line side
potential is used.
Since the present keying practice on BLK
system uses either the contact open (nega-
tive or positive removal keying) or contact
close (positive keying) approach, a form-C
dry contact output for keying is provided in
MDAR.
(2) Signal continuation and TBM logic
(5/92)