Taking the Chenjiaqiao Changshou electromagnetically coupled power loop as an example, which is the main channel for sending Sichuan power eastward, the necessity of contingency analysis of the tripping of line without fault and single line permanent ground (SLG) fault on UHV line prescribed in the Guideline on Security and Stability for Power System is analyzed.

A new scheme to distinguish permanent fault and instant one occurred on the EHV transmission line is proposed.

Single-phase adaptive auto-reclose technology possesses many advantages compared with traditional reclosing technology,as the important measure of avoiding permanent fault.

The current situation of the research on distinguishing permanent faults from instantaneous faults in transmission lines is presented.

At present, most self-adaptive auto-reclosure schemes are dependent on the voltages sampled from the transmission lines to distinguish between the instant faults and the permanent fault, therefore have some limitation in the applications.

For transmission lines with no shunt reactor,the magnitude and the angle of the recovery voltage of fault phase under permanent faults are quite different from that under transient faults.

Two methods, voltage detecting method and compensated voltage detecting method, are proposed for detecting the permanent faults and transient faults of multiple line traction network.

Finally the relay can identify that the line has transient faults or permanent faults by the value of secondary arc current.

The zero-sequence model of single phase earth fault is made on the basis of distributed parameter lines.

But when the old direct server can not recovery in time, the newdirect server will become a latent single fault spot, this will reduce the system utility.