Circuit breakers are subject to continual wear and should therefore be monitored and maintained regularly. For instance, the arc that occurs during a switching operation (e.g., a protective shutdown) leads to material wear on the contact pieces and thus makes a considerable contribution to the wear. Contacts generally cannot be checked in a simple manner, without cost-intensive disassembly and turn-off of the power. Therefore, periodic circuit breaker maintenance is usually performed, if appropriate with maintenance brought forward if protective shutdowns with high currents have occurred. Therefore, in general the switch is maintained too often. The maintenance causes avoidable costs, and an additional risk of damage being caused during maintenance. On the other hand, in the case of excessively long maintenance intervals, there is a risk, however, of wear or contact wear not being identified at an early stage. Here there is the risk of a malfunction, but at the least a loss of performance of the switch.
Therefore, it would be desirable to determine the wear on the contact pieces more reliably. However, the wear is difficult to measure or predict since it is influenced by a multiplicity of factors. It is generally assumed that the contact wear is brought about by the cumulative energy conversion (power loss) when an arc occurs with the circuit breaker having been opened. Solely counting the number of faults that have occurred at a circuit breaker therefore cannot yield an accurate estimation with regard to the contact wear.
EP 1475813 A1 describes methods for determining contact wear in electrical switching installations for high or medium voltage, wherein a contact current that flows through the switch during a switching operation is recorded with the aid of a current converter and an evaluation is made with regard to contact wear. In order to determine a state variable characterizing the contact wear, a current measurement signal of the current converter is first measured as a function of time, the presence of a measurement error is detected upon the occurrence of deviations between the expected contact current and the current measurement signal, and, upon detection of the measurement error, at least one characteristic current value is determined from the current measurement signal and used for determining the state variable. DE 10204849 A1 also describes a method for determining contact wear.
However, the known methods for determining wear can still be improved with regard to their reliability. It is also desirable to obtain methods which, in a multiplicity of different switching situations, yield such reliable results that they are suitable for automated (e.g., remote) diagnosis and maintenance. Cost-intensive maintenance work can be reduced in this way. At the same time, reliable continuous state monitoring can be realized. It is also desirable to identify and eliminate problems and wear before they become critical.