Functions
2.11 Measures for Weak and Zero Infeed
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
273
2.11
Measures for Weak and Zero Infeed
In cases where there is no or only weak infeed present at one line end, the distance protection does not pick
up there during a short-circuit on the line. On lines where there is only a single-sided infeed, a pickup by the
distance protection is only possible at the infeed end. On lines where the starpoint is only earthed behind one
line end, there is also no pickup at the line without zero sequence current. The missing pickup means that the
release signal for the remote end cannot be created. The settings and information table applies for the following
functions.
2.11.1
Echo Function
2.11.1.1 Function Description
Figure 2-140 shows the method of operation of the echo function. The echo function can be activated (
ECHO
only
) or deactivated (
OFF
) under address
2501
FCT Weak Infeed
(weak infeed FunCTion). You can also
activate the weak infeed tripping function (
ECHO and TRIP
and
Echo &Trip(I=0)
) with this „switch“. Refer
also to Section 2.11.2. This setting is common to the teleprotection functions for the distance protection and for
the earth fault protection.
If there is no fault detection or no earth current at one line end, the echo function causes the received signal to
be sent back to the other line end as an „echo“, where it is used to initiate permissive tripping.
In applications with one common transmission channel used by both the distance and the earth fault protection
spurious trippings may occur, if distance protection and earth fault protection create an echo independently
from each other. In this case parameter
Echo:1channel
has to be set to
YES
.
If the conditions for an echo signal are met by the distance protection or the earth fault protection (see also
Sections 2.7 and 2.9 under „Echo Function“), a short delay
Trip/Echo DELAY
is initially activated. This delay
is necessary to avoid transmission of the echo if the protection at the weak line end has a longer fault detection
time during reverse faults or if it picks up a little later due to unfavourable short-circuit or earth current distribu-
tion. If, however, the circuit breaker at the non-feeding line end is open, this delay of the echo signal is not re-
quired. The echo delay time may then be bypassed. The circuit breaker position is provided by the central in-
formation control functions (refer to Section 2.25.1).
The echo impulse is then transmitted (alarm output
„ECHO SIGNAL“
), the duration of which can be set with
the parameter
Trip EXTENSION
. The
„ECHO SIGNAL“
must be allocated separately to the output relay(s)
for transmission, as it is not contained in the transmit signals
„Dis.T.SEND“
, „Dis.T.SEND L*“ or
„EF Tele
SEND“
.
Note
The
„ECHO SIGNAL“
(No. 4246) must be allocated separately to the output relays for the actuation. It is not
contained in the transmit signals of the transmission functions.
After output of the echo pulse or during the send signal of the distance protection or the earth fault protection,
a new echo cannot be sent for at least 50 ms (presetting). This prevents echo repetition after the line has been
switched off.
In the case of the blocking scheme and the underreach schemes, the echo function is not required and there-
fore ineffective.
