2.9 Teleprotection for Earth Fault Protection (optional)
247
7SD5 Manual
C53000-G1176-C169-1
Echo Function In the case of line ends with weak infeed, or not sufficient earth current, the echo func-
tion is sensible for the permissive scheme so that the infeeding line end can be re-
leased. The echo function at address 2501 FCT Weak Infeed can be activated
(ECHO only) or deactivated (OFF). By means of this „switch“ the weak infeed tripping
function can also be activated (ECHO and TRIP, refer also to Section 2.10.1).
Please do not fail to read the comments regarding the setting of the current stage
3IoMin Teleprot (address 3105) in the above margin heading „Earth Fault Pro-
tection Prerequisites“.
The echo delay time Trip/Echo DELAY (address 2502) must be set long enough to
avoid incorrect echo signals resulting from the difference in pickup time of the earth
fault protection functions at all line ends during external faults (through-fault current).
Typical setting is approx. 40 ms (presetting). This parameter can only be altered with
DIGSI
®
under Additional Settings.
The echo impulse duration Trip EXTENSION (address 2503) may be matched to the
configuration data of the signal transmission equipment. It must be long enough to
ensure that the receive signal is recognized even with different pickup times by the
protection devices at the two line ends and different response times of the transmis-
sion equipment. In most cases approx. 50 ms (presetting) is sufficient. This parameter
can only be altered with DIGSI
®
under Additional Settings.
An endless echo signal between the line ends can be avoided (e.g. interference cou-
pling in the signal path) by blocking after each output of an echo signal a new echo for
a certain time Echo BLOCK Time (address 2504). The typical setting is approx. 50
ms. After the earth fault protection signal was sent, the echo is equally blocked for the
time Echo BLOCK Time. This setting is only possible via DIGSI
®
at Additional Set-
tings.
If the distance protection and earth fault protection use a common transmission chan-
nel, spurious tripping may occur when the distance protection and the earth fault pro-
tection create an echo independently of each other. For this scenario, parameter
Echo:1channel (address 2509) must be set to YES. The default setting is NO.
Note
The „ECHO SIGNAL“ (No. 4246) must be allocated separately to the output relays for
the transmitter actuation, as it is not contained in the transmit signals of the transmis-
sion functions.
The echo function settings are common to all weak infeed measures and summarized
in tabular form in Section 2.10.1.
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