There are many causes of power failures in an electricity network. Examples of these causes include faults at power stations, damage to electric transmission lines, substations or other parts of the distribution system, a short circuit, or the overloading of electricity mains.

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Hello dear

Power system failure cause by itself. If you think about a whole system there must be some validation as well as limitations. In case of power system, in generator section over load, under load, mechanical unstability, prime mover failure, open circuits short circuit, insulation failure, some times overheat, reverse current power flow so many causes can be vital issue for failure incident. In some practical field, I have expericed rapid blckout of one portion of power system hamper all power system parameter in exiting healthy side, including frequency, voltage, current fluctuation.

Thank you 

yes i agree with sir. abnormal conditions(deviation in voltage,frequency,current) leads to failure of power vsystem in long tenure due to cascading effect. 

 I think your desired question is to find a methodology to predict failure of a power by system by using probabilistic method of equipment failure rate under reliability evaluation. If what I say is true,  I think this is a good point to discuss about even the philosophy of reliability evaluation cannot be served such purposes.

violations of reliability indices are indications of probable failure of power system. uncertainty in measurement as well as prediction may cause to rise confidence interval.

The transmission & distribution line parameters causes power system failure if cross their permissible limits. Such as voltage magnitudes, load angle, series impedance etc.