Directional Comparison Blocking - ABB REL 301 Instruction Leaflet

I.L. 40-386.4
2.5.1.3 Directional Comparison Blocking (Figure 2-24)
If a directional comparison blocking (Blocking) system is desired, the system type setting "Syst
Type", is set to "Blocking". Refer to Section 2.5.1 for other recommended settings for Blocking
systems. Basic operating concepts of a Blocking system are:
1) Pilot distance measurement units PLTP and PLTG ("Pilot Ø" and "Pilot G") are set to
overreach the and the zone-3 distance measurement units Z3P/Z3G ("Zone-3 Ø"/"Zone-3
G") must be set in the reverse direction to detect reverse external faults for carrier start and
Reverse Block Logic (TBM).
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 a disturbance is detected (∆V, ∆I) which
will cause a SEND output for a minimum of 65 milliseconds via AND 50. Continued sending
will occur as the result of any reverse logic operating via OR 41 and continuation for 50 mil-
liseconds after the reverse logic resets.
3) Pilot tripping is performed when pilot distance measurement units operate and a carrier
blocking signal is not received.
The Blocking system, as shown in Figure 2-24, includes the following logic:
a. Tripping Logic (Figure 2-24)
1) For a forward internal fault, the local pilot distance measurement units PLTP or PLTG de-
tect the fault and which causes an output from OR 40 stopping the channel send circuit (∆I,
∆V starts the carrier before the distance measurement units operate), via OR 16, SQ timer
(0/150 ms) and AND 50. (The receiver receives the signal from both local and remote trans-
mitters.) At the same time, output of OR 40 will satisfy one input of AND 48 and also starts
the Channel Coordination Timer (BLKT). (See Section 3.2.7e 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, and if the local transient block is not
set (0/50 timer input to AND 51). If PILOT ENABLE (Figure 2-21) and AND 48 are satisfied,
AND 52 will produce pilot trip. Pilot trip target would be recorded the same as for POTT.
2) For a forward external fault, the local pilot distance measurement units PLTP or PLTG de-
tects the fault and operates in the same manner as for a forward internal faults. However,
at the remote terminal, the carriers units ∆I/∆V/ Reverse Z3P/Z3G/RDOG also detect this
external fault and operates the SEND relay, which keys the carrier transmitter, sending the
blocking signal to the remote terminal(s) via OR 41, AND 51, OR 18, and AND 35. The local
receiver receives the blocking signal, disables the output of AND 47; and prevents pilot trip-
ping.
b. Carrier Keying Logic
1) Reverse fault keying (Figure 2-24)
2) For a reverse fault, the ∆I and ∆V will operate and begin transmitting the blocking signal
and if local reverse "looking" measurements units, Reverse Z3P/Z3G or RDOG detects the
fault, operation of the Send relay, continues sending the blocking signal to the remote ter-
minal(s).
NOTE: The use of DI and DV for carrier start provides more security to the blocking
3) This SEND circuit includes logic AND 173, OR 41, AND 51, AND 50, OR 18 and AND 35.
The logic of OR 222A and the 32/0 ms timer circuit is to stop the internal fault SEND on a
weakfeed terminal condition.
2-18
scheme by starting carrier in approximately 4-6 milliseconds.