Starting, Blocking And Tripping Logic - Siemens SIPROTEC 7SD600 System Manual

Numerical line differential protection SIPROTEC 7SD600 V3.0
4.3.8

Starting, blocking and tripping logic

As soon as the fundamental component of the diffe
rential current reaches 85 % of the set value (parame
ter "10I-DIF>") and the local current threshold (para
meter "10I1>Frg")is exceeded, protection start is
recognized (indication "Dev.Sta", Fno. 501,
"DIF.GS", Fno. 3022).
In special applications, it may be desirable to slightly
delay the protection trip command. To this end, an
additional delay can be set (parameter "10T Del").
A blocking function is provided by the differential
current monitoring "Spill Current". There is a mo
nitoring threshold (parameter "10I-SpC") for the
differential current which is typically set smaller than
the rated line current. If this threshold is exceeded
for a set time (settable in the range from 5 to 60 s),
(parameter "10I-SpC"), an indication "B.DIF D" Fno.
3030 is output and the differential protection is blok
ked (starting is suppressed). The blocking is canceled
as soon as the differential current drops below this
threshold. A hysteresis of 5 percent is provided.
This monitoring detects circuit-interruptions between
the summation transformer and the main CT during
normal operation, and prevents an unwanted trip if
the test switch is accidentally opened at only one end
of the line.
Siemens AG January 1999
Method of operation
System manual Order no. E50417-G1176-C069-A1
The device is fitted with a Lockout function that can
be enabled via parameter "01 L.Out". With this func
tion, the trip command issued by one of the protec
tion functions (diff. protection, transfer trip, remote
trip), does not reset when the starting drops off or
after a delay time, but is stored permanently.
Failure of the auxiliary supply voltage also leads to a
renewal of the TRIP command. This lockout state is
signaled and can be marshalled to the LED (indication
"Lockout" Fno. 3031).
It can be reset via the "Reset LED" key or via a bi
nary input programmed to this effect >Res.LO, (Fno.
3008). Whether this function is carried out via keypad
and/or binary input can be set as a parameter
"01L.0.Fr".
The differential protection function may be switched
to the states "on", "off" or "signal only", depending
on parameters and binary inputs.
Furthermore, the actual state of the differential pro
tection is alarmed (parameter "10DIFPRO").
Figure 4.7 shows the logic diagram of the differential
protection, including the associated binary input and
output functions.
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