Generally, operating procedures associated with faults in the power system can be classified as follows:

1-Pre-fault stage :

Operations in this stage aimed to preventing of  faults and so interruptions in the power system. In this way, power system’s reliability will increase. So this operations is called reliability centered maintenance (RCM). This type of operation itself  is classified into three categories :  preventive maintenance (PM), predictive  and preventive maintenance (PPM ) and condition monitoring (CM).

2-Concurrent with fault stage:

At this stage, the fault must be detected and isolated from the power system. This operation is done automatically by the  protection system.

3- Before fault locating :

At this stage, the approximate range of  fault locations will be  determined.  This stage is called power system step restoration. In this stage, operators by re-closing of some circuit breakers in power system and monitoring that they trip again or not,  can estimate a more accurate range of fault locations.

Even in some cases, because of transient faults, the whole of system may be restorated (fault natural clearance). Sometimes auto-reclosers and sectionalizers is used to do this step automatically.

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