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Short-Circuit and Earth Fault Indicators

Short-circuit indicators are devices which are tripped by a magnetic field induced by the current flow in a conductor when a short-circuit occurs and indicate that the device has tripped.
Short-circuit indicators are mainly used for more efficient and quicker fault location in medium voltage distribution networks (radially fed, open-ring or closed-ring networks). They are mounted on current-carrying busbars, cables or overhead lines that are subject to monitoring. Any fault condition that exceeds pre-set trip currents of the short-circuit indicator produces a trip signal leading to a visual indication without information on the direction of the fault. This signal can also be remotely indicated.
If additional decentralized power feeders, e. g. from photovoltaics or wind parks, are connected to the existing energy distribution network. In case of a short-circuit fault, the substation transformers and decentralized feeding sources feed in parallel i. e. from two directions to the fault in the distribution system. In such cases, short-circuit/earth fault indicators with indication of fault direction are required.
Short-circuit indicators can also be used as earth fault indicators provided that a single-phase current fault of sufficiently high level occurs in the faulty line section. In cases where low current faults occur, it is recommended to use short-circuit indicators with additional summation current transformers.
The fault is located between the last tripped short-circuit indicator and the first untripped short-circuit indicator.

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