Research On Distinct Features Of Ferroresonance And Single-phase Ground Fault By PRONY Algorithms

Ferroresonance and single-phase fault are two of the common internal over-voltage faults. They will both cause insulation breakdown and eventually developed into accidents. The external performances after they occur are very similar, but how to deal with the two faults are not the same. So, able to distinguish the two faults and take appropriate measures to reduce the potential losses are necessary.When the nonlinear inductance subject to certain disturbances, coil saturation will decreases the inductance value. If it matches the capacitance value in the system and the resonance frequency is exactly equal to the power frequency of the system, ferroresonance happens. It will cause a significant increase in current and voltage, and repeat produce high expansion current in the coil. This kind of resonance will bring damage to electrical equipments, affect the safe operation of the power system. Single-phase fault is a kind of asymmetrical short-circuit fault. When it happens, it will cause the voltage to rise more than15%of the rated voltage, and make the insulation monitoring devices to issue a ground signal like ferroresonance fault. For the low voltage distribution network, the single-phase ground fault can short-term running for some time, yet ferroresonance fault must be immediately eliminated. According to the situation,this paper mainly do the following aspects of the work:1. Study the mechanism of ferroresonance and single-phase ground fault, and the characteristics of waveform. For ferroresonance is excited, the high-frequency component of the zero-sequence voltage or current is increased exponentially, and it is stable. While for single-phase fault, it’s a result of mutation due to the fault point voltage. It will decay with time passes by, so it is not stable.2. Use the software ATP to model and simulation, reproduce the conditions and reasons which cause the faults, and make a simple comparison of the simulated waveform we get.3. Analysis the principle of the Prony algorithm, then use the MATLAB software to programming the Prony algorithm. Use this program we can calculate amplitude, frequency, phase angle and the attenuation factor of the fault voltage and current signal. Choose the exponential function to fit the laws of the various parameters’change over time. Extract the high frequency component in the zero-sequence voltage and current characteristics 4. Use the program to call the simulation data, study attenuation of the parameters of the zero sequence component in each kind of fault conditions over time, mainly to compare the changes of the attenuation factor. By comparation it shows that, the attenuation factor of ferroresonance is positive, stabilized near a value and the absolute value is small; While the attenuation factor of single-phase ground is negative, gradually decay, and the absolute value is larger.5. Select a typical distribution network model, let ferroresonance fault and single-phase ground fault occurs successively. Use the criterion to distinguish the over-voltage type of the system, verify the correctness of the criterion.