Toshiba GRL100-701B Instruction Manual page 69

The delayed pick-up timer TCHD is set as follows taking into account the transmission delay time
of the blocking signal and a safety margin of 5 ms.
TCHD setting = maximum signal transmission delay time(*) + 5ms
(*) includes delay time of binary output and binary input for the blocking signal.
2.3.2.5 Protection for Weak Infeed Terminal
The POP and UOP are provided with an echo function and weak infeed trip function. Both
functions are used for lines with weak infeed terminals.
Figure 2.3.2.5 shows the scheme logic for the echo function.
With the POP, when a trip permission signal is received (R1-CR=1, R2-CR=1) if neither forward
overreaching zone 2 or zone 3 nor reverse looking Z4 have operated, the echo function sends back
the received signal to the remote terminal. With the UOP, when reception of a blocking signal is
stopped (R1-CR=0, R2-CR=0) if neither forward overreaching zone 2 (or zone 3) nor reverse
looking Z4 have operated, the echo function stops sending the blocking signal to the remote
terminal. When the circuit breaker is open (CB-OR = 1), too, the echo function sends back the trip
permission signal or stops sending the blocking signal. Timer TECCB is used to set the time from
CB opened to the echo logic enabled.
The terminal on which the forward overreaching element has operated can be tripped at high speed
by this echoed signal.
Once the forward overreaching element or reverse looking element have operated, transmission of
the echo signal is inhibited for 250 ms by delayed drop-off timer T1 even after they have reset.
In order to prevent any spurious echo signal from looping round between the terminals in a healthy
state, the echo signal is restricted to last for 200 ms by delayed pickup timer T2.
The echo function can be disabled by the scheme switch [ECHO].
The setting element necessary for the echo function and its setting range is as follows:
Element
TECCB
ECHO
ECH
R1-CR
1
Z4
≥ 1
"Z2"
Z2
[ZONESEL]
Z3
"Z3"
CB-OR
TECCB
t
1
0.00 - 200.00s
[ECHO]
(+)
" ON "
BRR setting = 1.2 × (BFR setting at remote end)
Range Step
0.00 – 200.00 s 0.01 s
OFF/ON
T1
0 t
&
≥ 1
250ms
0
&
Figure 2.3.2.5 Echo Logic
Default
0.10 s
ON
t
200ms
0 t
&
50ms
 68 
6 F 2 S 0 8 5 0
Remarks
Echo enable timer
Echo function
T2
0
619:C/R_DISECHO
&
ECH