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Both functions are used for lines with weak infeed terminals.
The echo function allows fast tripping of the terminal on which the DEFF has operated when
applied to a line with an open terminal or a weak infeed earth fault current terminal. The scheme
logic is shown in Figure 2.4.1.4.
With the POP, when a trip permission signal is received (R1-CR-DEF = 1, R2-CR-DEF = 1) if
neither the forward looking DEFF nor the reverse looking DEFR operates, 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-DEF = 0, R2-CR-DEF = 0), if the DEFF and DEFR do not operate, the
echo function stops transmission of the blocking signal likewise. When the circuit breaker is open,
the echo function also sends back the trip permission signal or stops transmission of the blocking
signal.
Once the DEFF or the DEFR operates, transmission of the echo signal is inhibited for 250 ms by
delayed drop-off timer T1 even after they are reset.
In order to prevent any spurious echo signal from looping round between terminals in a healthy
state, the echo signal is restricted to last 200 ms by delayed pick-up timer T2.
The echo function can be disabled by the scheme switch [ECHO].
When a signaling channel is shared by the distance protection and DEF protection, it is necessary
to unite the scheme logic of both echo functions so that the echo function may not be picked up in
the event of an external fault. The echo function at this time is blocked by Z2 (or Z3) and Z4
indicated by a dotted line in Figure 2.4.1.4.
R1-CR-DEF
R2-CR-DEF
DEFFCR
T1
DEFRY
0
t
≥ 1
Z4
250ms
Z2
"Z2"
[ZONESEL]
Z3
"Z3"
CB-OR
1
0.00 - 200.00s
Figure 2.4.1.4 Echo Function in DEF Scheme Logic
Figure 2.4.1.5 shows the scheme logic of the weak infeed trip function. Weak infeed tripping is
executed on condition that a trip permission signal has been received (ECHO1_DEF-1=1 or
ECHO1_DEF-2=1), the undervoltage element UVL (UVLS or UVLG) operates.
The undervoltage element responds to three phase-to-phase voltages and three phase-to-ground
voltages. The undervoltage element prevents false weak infeed tripping due to spurious operation
of the channel.
Single-phase tripping or three-phase tripping is also applicable to weak infeed tripping according
to the reclosing mode of the autoreclose function.
&
≥ 1
&
&
≥ 1
&
&
[ECHO]
(+)
"ON"
TECCB
t
0
CS (Carrier send) signal
Signal No. Signal name
886:
CAR-S for Distance and DEF command protection (CH1)
887:
DECAR－S for DEF command protection (CH2)
R1-CR-DEF: Trip permission signal from the remote terminal 1 in 3 terminal application,
or Trip permission signal from remote terminal in 2 terminal application.
Signal No. Signal name
1856:
1857:
R2-CR-DEF: Trip permission signal from the remote terminal 2 in 3 terminal application.
Signal No. Signal name
1864:
1865:
79
0
t
&
T2
&
50ms
t
0
ECHO1_DEF-1
200ms
0
t
&
T2
&
50ms
t
0
ECHO1_DEF-2
200ms
Description
CAR.R1-1
Trip carrier signal from remote terminal 1 (CH1)
CAR.R1-2
Trip carrier signal from remote terminal 1 (CH2)
Description
CAR.R2-1
Trip carrier signal from remote terminal 2 (CH1)
CAR.R2-2
Trip carrier signal from remote terminal 2 (CH2)
6 F 2 S 0 8 5 0
CS
≥ 1
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