Siemens siprotec 7SA6, Manual

Page: 307 / 876

Functions
6-117
7SA6 Manual
C53000-G1176-C156-2
under address
2501 FCT Weak Infeed
(
ECHO only
) or disabled (
OFF
). With this
“switch” the weak infeed tripping function can also be activated (
ECHO and TRIP
,
refer also to Section 6.9).
The notes regarding the setting of the distance stages above, and the margin head-
ings “Distance Protection Prerequisites” must in any event be noted.
The echo delay time
Trip/Echo DELAY
(address
2502A
) must be set long enough
to avoid incorrect echo signals resulting from the difference in fault detection pick-up
time of the distance protection functions at the two line ends during external faults
(through-fault current). A typical setting is approximately 40 ms (presetting). This set-
ting can only be modified with DIGSI
®
4 under “Additional Settings”.
The echo impulse duration
Trip EXTENSION
(address
2503A
) can be set to adapt
to the circumstances of the signal transmission equipment. It must be long enough to
ensure that the receive signal is recognized even with different pick-up times by the
protection devices at the line ends and different response times of the transmission
equipment. Generally a setting of approximately 50 ms (presetting) is sufficient. This
setting can only be modified with DIGSI
®
4 under “Additional Settings”.
The setting for the echo function is the same for all measures taken against weak in-
feed and summarised in tabular form in Section 6.9.
Note:
The “
Echo–Signal
“ (FNo
4246
) must be allocated separately to the output relays
for the activating the transmitter, as it is not contained in the transmit signals of the
transmission functions. On the digital protection data interface with permissive over-
reach transfer trip mode, the echo is transmitted as a separate signal without taking
any special measures (Figure 6-55).