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3 Operation Theory
3.10 Switch Onto Fault (SOTF) Protection
3.10.1 SOTF Protection Theory
In some feeder applications, three-pole fast tripping may be required if a fault is present on the
feeder when it is energized. Such faults may be due to a fault condition not having been removed
from the feeder, or due to earthing clamps having been left on the following maintenance. In either
case, it may be desirable to clear the fault condition in an accelerated time, rather than waiting for
the time delay associated with overcurrent protection.
Switch onto fault overcurrent protection and zero sequence accelerated overcurrent protection are
equipped in this equipment. Acceleration before or after tripping can be configured by setting the
logic setting [SOTF.Opt_Mode]. Acceleration after tripping includes accelerated tripping for
manual switching-onto-fault or automatic reclosing-onto-fault. Current settings and delays of
these two accelerated tripping protections can be configured independently.
If acceleration after tripping is selected, the SOTF element is enabled for the predefined time
[SOTF.t_En] after the auto-recloser operates. And the SOTF element is enabled for the
predefined time [SOTF.t_En] fixedly after manual closing signal is issued, and the typical value is
"3s".
The logic diagram of the switch onto fault protection is shown as below.
Ia > [50PSOTF.I_SetF]
Ib > [50PSOTF.I_SetF]
Ic > [50PSOTF.I_SetF]
[50PSOTF.En]
[50PSOTF.En1]
[50PSOTF.Blk]
[79.Ready]
[SOTF.Opt_Mode]
[79.Close_3PSx] (x:1~4)
SOTF.ManClsCB
I
> [50GSOTF.3I0_Set]
01
[50GSOTF.En]
[50GSOTF.En1]
[50GSOTF.Blk]
Where:
[50PSOTF.I_Set] is the current setting of the SOTF overcurrent protection;
"t
" is the setting [50PSOTF.t_Op], the time setting of the SOTF overcurrent protection;
SOTFOC
[50PSOTF.En] is the logic setting of the SOTF overcurrent protection;
[50PSOTF.En1] is the binary signal for enabling the SOTF overcurrent protection;
[50PSOTF.Blk] is the binary signal for blocking the SOTF overcurrent protection;
3-38
&
&
0
t
&
EnSOTF
0
t
EnSOTF
&
Figure 3.10-1 Logic diagram of the SOTF protection
Date: 2014-04-08
t
0
&
SOTFOC
t
0
&
SOTFROC
PCS-9611 Feeder Relay
[50PSOTF.St]
[50PSOTF.Op]
[50GSOTF.St]
[50GSOTF.Op]
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