On the basis of compare virtue and defect for existed discriminances, this paper elicited calculational expression of the open phase terminal voltage and calculated the frequency for current and voltage of the phase that is switched off with shunt compensators, and criterions to determine temporary fault and permanent fault is proposed. A integrated criterion based on the amplitude relationship and the phase angle relationship is proposed for transmission line without shunt reactor, which can also be applied to long and heavy load transmission line by determining the range of reliability index. There is great surge show on graph of terminal voltage and current when is temporary fault while permanent fault has not for transmission line with one end or two shunt reactors. Accordingly, a voltage criterion based on this surge is proposed. Finally, the validity of criterions are validated by simulating typical transmission line.

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