Earth fault

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Earth fault is a term from electrical engineering and means that an electrical conductor has an unintended electrically conductive connection to the earth potential. This usually represents a fault. Depending on how high the conductivity of this connection is, it can also be a short circuit if the circuit is regularly earthed elsewhere .

Earth fault in power engineering

Stork's nest on a pole for medium voltage as a possible cause of an earth fault

In the field of electrical power engineering , an earth fault represents a fault with a high risk potential.

It describes a fault in which an outer conductor is in contact with earth. In a network with an earthed star point , an earth fault corresponds to an earth short circuit , which under certain circumstances can lead to the single-pole fault being switched off by a network protection device, fuse or automatic circuit breaker (depending on the voltage level).

A medium or high voltage network with an insulated or with an earth fault compensation equipped star point can be operated at a ground fault on. In these networks, there is no immediate shutdown by a network protection device. However, the system operator's staff must start troubleshooting immediately (VDE 0105). Medium-voltage networks may be operated with earth faults for up to 30 minutes to four hours - if the defect lasts for a long time, there may be thermal overloads in the area of ​​the earth fault extinguishing coil .

The following problems occur during operation in the event of an earth fault:

  1. Depending on the power of the network, high currents flow at the fault location without earth fault compensation and with an earthed star point. As a result, very high step voltages can briefly occur at the fault location .
  2. Because of the extreme heat development, arcing faults are particularly dangerous and can occur both as a short circuit between the outer conductor and as an earth fault. In order to counteract the relatively more frequent earth fault with arcing in medium or high voltage networks up to 220 kV, the current at the fault location is minimized by means of earth fault compensation, among other things, and the arc is extinguished at the fault location without interrupting operations.
  3. When the outer conductor is terminated to earth, the earth assumes the potential of the outer conductor. This also means that the voltage of the intact outer conductor to earth corresponds to the voltage of the outer conductor to the outer conductor. In three-phase networks, the voltage between the intact outer conductors and earth is increased by a factor , whereby the insulation of the equipment is more stressed. In the case of higher voltages (e.g. in 400 kV networks), earth fault compensation is not used because of this excessive voltage. In this case, the line is switched off immediately and, in the case of overhead lines, automatically switched on again after a short time, since the cause of the fault is often eliminated by the brief arc fault (e.g. a branch of a tree that touches the line burns).

literature

  • Electrical engineering expertise. 25th edition. Verlag Europa – Lehrmittel, 2006, ISBN 978-3-8085-3159-4 (Chapter 11.3).