2.4 Distance protection Z<
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Problem situations
Sometimes in certain type of network when fault 1 and 2 both
appear in very short distance from the incomer the short circuit
distance Z1> protection might disconnect the whole ring. Same
would happen even if the DEF –algorithm is not used since
short circuit distance protection happens to see the fault inside
the zone.
Figure 2.4.3-1 Two earth faults very close to the incomer. SC distance
protection Z1> operated
Figure 2.4.3-2 Two earth faults very close to the incomers at different ends
of ―same‖ line. Both lines will be separated from the network due the
activation of SC-distance stage.
Note! Simple over-current and earth-fault protection is preferred to have as a
back-up for “DEF algorithm”.
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