Faulty Feeder Detection Principle For Single-phase Earthed Fault In Non-effectively Grounded System Based On Zero Modal Transient Energy

In China,non-effectively earthed neutral is widely used in medium voltage distribution networks.When single-phase to earth fault occurs in a non-solidly earthed network,the three phase line to line voltages are symmetric.So tripping commands do not need to be performed immediately.It improves the power supply reliability.But the non-faulted phase voltage would increase to(?)times of original voltage.The insulation would be damaged in long time running,therefore the system result in more serio.us phase-to-phase voltage.If it wants to make to ensure safe and reliable operation,it must request promptly and accurately select fault line.However,because of the small ground current,it is difficult to detect the fault signal.Although now it has developed a variety of selection principle for single-phase grounding fault in non-solidly grounded networks.But each method has different degree of defects.The practical result is bad.So it needs further research.This paper introduces domestic and foreign existing method and points out their limitations.As a result of selection method based on the steady state characteristics is not applicable in Peterson coil grounded system.So,it analyses the transient fault characteristics and shows that the transient fault characteristics in the two kinds of grounding method are obvious.This paper proposed zero modal transient energy based principle for single-phase earthed fault detection.The zero modal transient energy function is defined as the integral of the derivative of transient zero modal voltage multiplying the mean of transient zero modal current.The magnitude of the zero modal transient energy in faulty feeder is much larger than that of healthy feeder.It is less than zero in faulty feeder and greater than zero in healthy feeder.The simulation model is established for Electromagnetic Transient Program ATP.The zero modal transient energy can be calculated by designing Matlab program and verified accuracy of the algorithm.It made a lot of simulation to study whether the change of different factors have influence on line selection.It made a further validation using the measured wave record data.This paper gets the following conclusion:this method is not affected by neutral point grounding way and if a fault occurs in different locations or fault initial angle have change,also can do the correct line selection.And this method has high sensitivity.