Research Of Some Key Techniques For Resonance Ground Systems

Resonance grounding system is an important ground style of medium voltage network. It has many advantages, such as improving the quality and reliability of power supply, restricting the ferroresonance, avoiding restrike of the arc etc. Although resonance grouding has been widely used in modern power supply network, there are still some difficulties to be solved, including tracking and measuring of capacitive current and selection of the fault line when signal-phase-earth fault happens.There are two reasons that why it is difficult to track and measure the capacitive current. One is that the normally used formulas for calculating capacitive current have been simplified and so that the error is inherence, at the same time these formulas are hard to be applicated in both tracking and advanced style resonance devices. The other is there are errors in current transform especially when the current is small. This paper puts forward a new method called"three current dots imitating"to calculate capacitive current. It makes a good result using the Matlab validation. The paper has also analyzed the influence on the high-voltage side of transformer fault and asymmetrical fluctuation of load to the judgment of capacitive current variation, and gotten a method, which judges to capacitive current change accurately.When the single-phase-earth fault happens, the characteristics of the zero sequence currents of the fault line and non-fault lines are different, but the difference becomes smaller when the earthing resistance increases, so it is difficult to select the fault line. This paper puts forward two methods of fault line selection. One method is based on the unbalance of active power, and the other on the wavelet analysis. The validity and efficiency of the two methods are proved by digital simulation using Matlab.