Study On Application Of Multirate Filter Banks Theory To Single Phase Earthed Fault Line Detection Of Neutral Point Non-Effectively Grounded System

Neutral point grounded mode of power system is closely related to issues such as the reliability of power supply, personal and equipment security, insulation level, over-voltage and relay protection, communication disturbance, electric arc grounded and grounded device. The power distribution network in China has widely adopted neutral point un-grounded or neutral point grounding by Petersen coil which is also called neutral point non-effectively grounded system. Because the current after single-phase earthed fault is small and the feature of the fault current is so difficult to extract, fault line detection of neutral point non-effectively grounded system becomes a technical puzzle.Therefor this paper first systematic analyzes the theories and programs of various existing single-phase earthed fault line detection in the neutral point non-effectively grounded system and summarizes the problems existing in present line detection theory. Then dose an in-depth theoretical study on fault characteristics of the steady state and transient state of single-phase earthing in neutral point non-effectively grounded system. The result has proved that an obvious transient state process will appear after single-phase earthed fault, and transient fault signal quantity which contains more adequate fault features is much stronger than steady state. So using transient fault signals has higher reliability and sensitivity. But it's still a challenge to pick up the fault characteristics from transient fault signals by employing signal processing method. Multi-rate filter banks not only divide a wide-band signal x(n) into M narrow-bands signals, but also use these M narrow-bands signals to perfect reconstruct signal x(n). Apparently it's very practical and reliable to employ multi-rate filter banks to divide wide-band transient fault signals, because it doesn't lose fault messages and its parallel structure is helpful to picking up the fault characteristics parallelly. Because zero-sequence current can be gained more easily and can include a large number of fault messages after single phase earthed fault, this paper makes use of multi-rate filter banks to pick up the characteristics of zero-sequence current and raise a new methed of fault line detection, that is, to divide transient zero-sequence current messages after single phase earthed fault of non-effectively grounded system into a number of sub-band signals by using multi-rate filter banks. Then it deals with these sub-band signals, picks up the fault characteristics, analyses and compares them, decides the fault line. This paper makes use of MATLAB and PSB toolbox to build models and imitate on single-phase earthed fault of neutral point non-effectively grounded system. Emulation experiment indicates that the method proposed in this paper is feasible, it can correctly realize the fault feeder.