Siemens siprotec 7SA6 User Manual page 315

Echo Function
7SA6 Manual
C53000-G1176-C133-1
The transient blocking time 7U%ON %ORFN7LPH (address ) must definitely be set
longer than the duration of severe transients resulting from the inception or clearance
of external faults. The transmit signal is delayed by this time in the case of the
permissive protection schemes 'LU&RPS3LFNXS and 81%/2&.,1* if the
protection had initially detected a reverse fault. In the case of the blocking scheme
%/2&.,1* the received (blocking) signal is prolonged by this time.
The preset value should be sufficient in most cases.
In the case of line ends with weak infeed, or not sufficient earth fault current, the echo
function is sensible for the permissive scheme so that the infeeding line end can be
released. The echo function may be activated under address  )&7 :HDN
,QIHHG ((&+2 RQO\) or deactivated (2))). With this "switch" it is also possible to
activate the weak infeed tripping ((&+2 DQG 75,3, refer also to Section 6.7).
The comments above regarding the setting of the current stage ,R0LQ 7HOHSURW
(address ) must be noted as well as the margin heading "Earth Fault Protection
Prerequisites".
The echo delay time 7ULS(FKR '(/$< (address ) must be set long enough to
ensure that no unwanted echo signals are generated due to differences in the pick-up
times of the earth fault protection fault detection at the two line ends during external
faults (through-fault current). Typical setting is approx. 40 ms (presetting). This setting
can only be changed with DIGSI
The echo impulse duration 7ULS (;7(16,21 (address ) may be matched to the
configuration data of the signal transmission equipment. It must be set long enough to
ensure that the received signal is reliably detected taking into consideration possible
differences in the operating times of the protection and transmission equipment at the
two line ends. In most cases approx. 50 ms (presetting) is sufficient. This setting can
only be changed with DIGSI
The echo function settings are common to all weak infeed measures and summarized
in tabular form in Section 6.7.
®
4 under "Additional Settings".
®
4 under "Additional Settings".
Functions
6-133