Automatic restart
Automatic reclosing (AWE) or short interruption (KU) is a term from electrical power engineering . It is usually used on electrical overhead lines operated with high voltage , since in this case the cause of the fault, such as a branch falling onto the overhead line, lightning strike or the like, often disappears by itself or is eliminated by the arc fault .
procedure
If a short circuit occurs on an overhead line , an arc fault often occurs that does not go out by itself. Since the cause of the fault is often eliminated by the arc (e.g. a branch that has fallen on the line burns), an automatic restart is carried out. The responsible circuit breaker trips when the line protection is activated, but switches on again automatically after a short period of time ("pause time"): with single-pole errors after about 0.5 to 3 seconds (sometimes variable), with three-pole errors after 0.2 up to 0.5 seconds.
If the error no longer exists after switching on again, one speaks of a successful AWE (AWE with success: AWE m. E.). If the error still persists, it is referred to as an unsuccessful AWE (AWE unsuccessful: AWE o. E.). In this case the circuit breaker trips again and remains switched off.
The times mentioned here are only rough guide values and depend on the voltage level and the network conditions as well as other factors. Several AWE cycles in succession are also possible if the protective devices and circuit breakers are designed for this.
requirements
In order for a circuit breaker to be able to perform an AWE, in addition to the necessary short-circuit power, it must be specially designed for multiple, comparatively short consecutive switching cycles: the drive , mostly spring-loaded storage drive , nowadays less often compressed air and the like. a, has the necessary energy for at least three switching operations (. For - A - From ) have available in a short time from memory. If the circuit breaker also can switch on a faulty line is the energy of four switching actions necessary ( A - For - A - Off ).
The control signals for the EVU come from a device from the network protection area . The device that detects the fault, for example a distance protection relay , gives the trip command for the circuit breaker and, after a set time ("pause time"), the on command. If this relay still detects an error after switching on, a final trip command can be issued or the cycle can start over.
Limits
As a rule, no AWE is carried out for underground cables . Faults in cable networks result in the destruction of the insulation, and often also as a cause, e.g. B. by construction work. The damaged cable section must therefore first be localized by means of cable fault location and then replaced.
In the event of a fault, no AWE is carried out for other parts of the system, such as power transformers and chokes for reactive power control. These parts of the system are often permanently damaged by errors; the cause of the error and the consequences must first be clarified.
See also
literature
- Adolf J. Schwab: electrical energy systems. Generation, transport, transmission and distribution of electrical energy . Springer, 2009, ISBN 978-3-540-92226-1 .