Siemens siprotec 7SA6 User Manual page 314

Functions
Time Settings
Transient Blocking
6-132
from A is distributed equally on the line ends B and C. The setting value ,R0LQ
7HOHSURW (address ), which is decisive for the echo or the blocking signal, must
therefore be set smaller than one half of the setting value for the earth current stage
used for teleprotection. In addition, the above comments regarding the capacitive
earth current which is left out in Figure 6-80 apply. If the earth current distribution is
different from the distribution assumed here, the conditions are more favourable as
one of the two earth currents I
described previously.
A
I = I
EA
Figure 6-80 Possible unfavourable current distribution on a three terminal line during an
external earth fault.
The send signal prolongation 6HQG 3URORQJ (address ) must ensure that the
transmitted signal reliably reaches the opposite line end, even if tripping is very fast at
the sending line end and/or the signal transmission time (channel delay) is relatively
long. In the case of the permissive schemes 'LU&RPS3LFNXS and 81%/2&.,1*
this signal prolongation only comes into effect if the device has already issued a trip
command. This ensures the release of the other line end even if the fault is cleared
very rapidly by a different protection function or other stage. In the case of the blocking
scheme %/2&.,1* the transmit signal is always prolonged by this time. In this case it
corresponds to a transient blocking following a reverse fault. This setting can only be
®
changed with DIGSI 4 under "Additional Settings".
The release of the directional tripping can be delayed by means of the permissive
signal delay 5HOHDVH 'HOD\ (address ). This is only required for the blocking
scheme %/2&.,1* to allow sufficient transmission time for the blocking signal during
external faults. This delay only has an effect on the receive circuit of the teleprotection;
conversely tripping by the comparison protection is not delayed by the set time delay
of the directional stage.
The setting parameters 7U%ON :DLW 7LPH and 7U%ON %ORFN7LPH are for the
transient blocking with the comparison protection. This setting can only be changed
®
with DIGSI 4 under "Additional Settings".
The time 7U%ON :DLW 7LPH (address  ) is a waiting time prior to transient
blocking. In the case of the permissive schemes, only once the directional stage of the
earth fault protection has recognized a fault in the reverse direction, within this period
of time after fault detection, will the transient blocking be activated. In the case of the
blocking scheme, the waiting time prevents transient blocking in the event that the
blocking signal reception from the opposite line end is very fast. With the setting ∞
there is no transient blocking.
or I must then be larger than in the situation
EB EC
+ I
EB EC
I
EC
B
I
EB
7SA6 Manual
C53000-G1176-C133-1