ABB REL300 Instruction Manual page 63

c. Programmable Reclosing Initiation (Figure 3-19, page 3-41)
Same as for POTT scheme.
d. Carrier Receiving Logic (Figure 3-23, page 3-43)
Same as for POTT scheme.
e. Channel Indicators (Figure 3-23, page 3-43)
Same as for POTT scheme.
3.5.3 Directional Comparison Blocking Scheme (BLK) (See Figure 3-25, page 3-45)
The basic operating concept of a Directional Comparison Blocking system (BLK) are:
1) Pilot relays (PLTP/PLTG) are set to overreach; the Zone 3 relays (Z3P/Z3G) must be set
in the reverse direction to detect the reverse 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
(1)
(2)
For a forward internal fault, the local pilot relay (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 starting. (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, 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 3-5). Pilot trip target would
be the same as for POTT.
For a forward external fault, the local pilot relay (PLTP and/or PLTG) sees the fault,
and operates in the same manner as for the forward internal faults. However, at the
remote terminal, the carriers units ∆I/∆V/ Z3P(R)/Z3G(R)/RDOG also sees this ex-
ternal fault and turns-on the transmitter via OR-41, AND-51, AND-50, OR-18, and
AND-35, sending a blocking signal to the local and remote terminals. The local re-
I.L. 40-385.7
3-19