Specifications

Overcurrent Protection SIPROTEC 7SJ81
5/12 SIPROTEC Compact · SIEMENS SIP 3.01 · Edition 3
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for Low-Power CT and VT Applications – Application examples
Busbar protection by overcurrent
relays with reverse interlocking
Applicable to distribution busbars
without substantial (< 0.25 x I
N
)
backfeed from the outgoing feeders.
Line feeder with load shedding
In unstable power systems (e.g. soli-
tary systems, emergency power sup-
ply in hospitals), it may be necessary
to isolate selected consumers from
the power system in order to protect
the overall system. The overcurrent-
time protection functions are effective
only in the case of a short-circuit.
Overloading of the generator can be
measured as a frequency or voltage
drop.
Fig. 5/11 Busbar protection via overcurrent relays with reverse interlocking
Fig. 5/12 Line feeder with load shedding
Busbar
Infeed
50/50N 51/51N 50/50N 51/51N 50/50N 51/51N
50/50N 51/51N
t0 = 50 ms
Reverse interlocking
I>>t0
I>>
I>t
I>>
I>>
I>tI>t
52 52 52
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Busbar
I>, I>>,
I>>> IN>>
50 50N
79M
51 51N
49 46 86
Final trip
27 81U
V<
f<
>
I2>
I>, Ip
IN>,
INTOC
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Visio-LSA4842-us.pdf
Visio-LSA2216-us.pdf