Functions
2.9 Teleprotection for Earth Fault Protection (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
261
2.9.7
Setting Notes
General
The teleprotection supplement for earth fault protection is only operational if it was set to one of the available
modes during the configuration of the device (address
132
). Depending on this configuration, only those pa-
rameters which are applicable to the selected mode appear here. If the teleprotection supplement is not re-
quired the address
132
is set to
Teleprot. E/F
= .
The following modes are possible with conventional transmission links (as described in Section 2.9):
Dir.Comp.Pickup
Directional comparison pickup,
UNBLOCKING
Directional unblocking scheme,
BLOCKING
Directional blocking scheme.
At address
3201
FCT Telep. E/F
the use of a teleprotection scheme can be switched
ON
or
OFF
.
If the teleprotection has to be applied to a three terminal line, the setting in address
3202
must be
Line
Config.
=
Three terminals
, if not, the setting remains
Two Terminals
.
The following mode is possible with digital transmission using the protection data interface:
Dir.Comp.Pickup
= Directional comparison pickup,
In this case, send and receive signals must be linked to the remote commands via CFC.
Earth Fault Protection Prerequisites
In the application of the comparison schemes, absolute care must be taken that both line ends recognize an
external earth fault (earth fault through-current) in order to avoid a faulty echo signal in the case of the permis-
sive schemes, or in order to ensure the blocking signal in the case of the blocking scheme. If, during an earth
fault according to Figure 2-128, the protection at B does not recognize the fault, this would be interpreted as a
fault with single-sided infeed from A (echo from B or no blocking signal from B), which would lead to unwanted
tripping by the protection at A. Therefore, the earth fault protection features an earth fault stage
3IoMin
Teleprot
(address
3105
). This stage must be set more sensitive than the earth current stage used for the
teleprotection. The larger the capacitive earth current (
I
EC
in Figure 2-128) is, the smaller this stage must be
set. On overhead lines a setting equal to 70 % to 80 % of the earth current stage is usually adequate. On cables
or very long lines where the capacitive currents in the event of an earth fault are of the same order of magnitude
as the earth fault currents, the echo function should not be used or restricted to the case where the circuit
breaker is open; the blocking scheme should not be used under these conditions at all.
Figure 2-128
Possible current distribution during external earth fault
On three terminal lines (teed feeders) it should further be noted that the earth fault current is not equally dis-
tributed on the line ends during an external fault. The most unfavourable case is shown in Figure 2-129. In this
case, the earth current flowing in from A is distributed equally on the line ends B and C. The setting value
3IoMin Teleprot
(address
3105
), 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 2-129 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
EB
or
I
EC
must then be larger than in the situation described previously.
