2.8 Teleprotection for earth fault overcurrent protection (optional)
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7SA522 Manual
C53000-G1176-C155-3
Activation and
Deactivation
The comparison function can be switched on and off by means of the parameter
)&77HOHS(), via the system interface (if available) and via binary input (if allo-
cated). The switched state is saved internally (refer to Figure 2-74) and secured
against loss of auxiliary supply. It is only possible to switch on from the source where
previously it had been switched off from. To be active, it is necessary that the function
is not switched off from one of the three switching sources.
Figure 2-74 Activation and deactivation of the signal transmission logic
2.8.2 Directional Comparison Pickup
The following procedure is suited for both conventional and digital transmission media.
Principle The directional comparison scheme is a permissive (release scheme). The scheme
functionality is shown in Figure 2-75.
When the earth fault protection recognizes a fault in the forward direction, it initially
sends a permissive signal to the opposite line end. If a permissive signal is also re-
ceived from the opposite end, a trip signal is routed to the trip logic. Accordingly it is a
prerequisite for fast tripping that the fault is recognized in the forward direction at both
line ends.
The send signal can be prolonged by T
S
(settable). The prolongation of the send signal
only comes into effect if the protection has already issued a trip command. This
ensures that the permissive signal releases the opposite line end even if the earth fault
is very rapidly cleared by a different independent protection.
Figure 2-75 Operation scheme of the directional comparison pickup
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