Detection Of Ferroresonance In Neutral Non-Grounding System Based On Decomposition Characteristic Of Wavelet Packet

Operation experiences indicate that over voltage for ferroresonance may occur in multi-voltage grade network. Excessive accidents brought by ferroresonance, especially in the power network below 35 kV , have been a concerned problem. In non-grounding system ferroresonance caused by voltage transformer saturation and single-phase grounding fault are easily confused, so it is difficult to resole all the while.According to the feature of zero-sequence voltage for ferroresonance which is excited by single-phase transient grounding fault in non-grounding system, zero-sequence voltage is divided into two groups according to period of time. The two-group voltages are decomposed by wavelet package separately, and the characteristic band is chosen based on the principle of maximum energy. The difference of two-group voltages'characteristic bands is used to detect the ferroresonance, also an assistant criterion of comparing amplitude value is adopted. A lot of simulation results show that this method can distinguish among ferroresonance, single-phase transient grounding fault and single-phase permanent grounding fault correctly.In accordance with the requisition of wavelet algorithm, a hardware platform for ferroresonance detection and grounding line detection of distribution network is constructed. The project makes use of ascendant digital signal processing function and high operation speed of DSP, and on this platform ferroresonance detection and faulty line detection methods are actualized well. Experiment results show that the platform has following advantages, such as high calculation speed, high anti-interference ability, stable operation, high performance cost ratio and broad future in the application field.