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2.9
Backup Time Overcurrent Protection
The 7SD610 features a time overcurrent protection function which can be used as
either a back-up or an emergency overcurrent protection. All elements may be config-
ured independently of each other and combined according to the user's requirements.
2.9.1
General
Whereas the differential protection can only operate correctly if both devices receive
the protection data of the respective other device properly, the emergency overcurrent
protection requires only the local currents. As an emergency overcurrent protection it
automatically replaces the differential protection as short-circuit protection, if data
communication of the differential protection is faulty (emergency operation). The dif-
ferential protection is blocked as a result.
If the overcurrent protection is set as a back-up overcurrent protection, it will work in-
dependently of other protection and monitoring functions, i.e. also independently of
the differential protection. The backup overcurrent protection can also be used as sole
short-circuit protection if no suitable channels for the communication between the pro-
tection devices are available during the initial commissioning.
The overcurrent protection has directional and non-directional stages for the phase
currents and for the earth current; these are:
• two overcurrent stages with a definite time characteristic (O/C with DT),
• one directional overcurrent stage with a definite time characteristic (O/C with DT),
• A further overcurrent stage which has an additional enable input and can therefore
• One overcurrent stage with inverse time characteristic (ID),
• one directional overcurrent stage with a definite time characteristic (O/C with DT),
These six stages are independent of each other and are freely combinable. Blocking
from external criteria via binary inputs is possible, as well as switch-onto-fault tripping.
During the single-pole pause, all earth stages of the overcurrent protection are auto-
matically blocked.
It is also possible to release one or more of the stages in switching-onto-fault condi-
tions. If not all stages are required, each individual stage can be deactivated by setting
the pickup threshold to ∞.
2.9.2
Function Description
Measured Values
The phase currents are fed to the device via the input transformers of the measuring
input. The earth current 3·I
If I
transformer = In prot. line, see section2.1.2 of P.System Data 1), the
earth current will be directly available as measured value. It is used considering the
I4/Iph CT factor (address221).
If the ground current of own the neutral line is not connected to the fourth current input
I
the device will calculate the ground current from the phase currents. Of course, all
7SD610 Manual
C53000-G1176-C145-4
be used as an emergency stage e.g. if the remaining stages are used as backup
stages, or as a stub protection.
is connected to the starpoint of the current transformer set (address 220 I4
4
(address 220 I4 transformer cannot be parameterized to In prot. line),
4
2.9 Backup Time Overcurrent Protection
is either measured directly or calculated.
0
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