| Power transformer is an important electrical equipment in power system,how to guarantee its safety and stability,it is related to the safety and stability of the whole power system.Differential protection is one of key protection of transformer because of its simple principle and reliable performance.When the transformer is in no-load or in the process of voltage recovery after external fault resection,the inrush current will be generated,which may cause differential protection wrong operation Therefore,how to identify magnetizing inrush current,prevent wrong operation of differential protection and improve the sensitivity of no-load switching at internal faults(especially inter-turn short circuit),is still an unavoidable problem in the study of transformer differential protection.This paper analyzes the characteristics of transformer inrush current and the factors that affect the peak,intermittent angle and second harmonic.It presents a new algorithm of identifying magnetizing inrush current and internal fault current based on waveform sinusoidal correlation degree,based on waveform sinusoidal correlation.Firstly,the waveform sinusoidal correlation degree is defined and its calculation method is given.Then the criterion to identify the internal faults and inrush currents are developed on this basis.MATLAB simulation results show that this method can accurately and reliably identify inrush current,and even in the case of the inter-turn short circuit of the transformer,it has a higher sensitivityIn addition,a method based on comprehensive correlation criterion is proposed to identify the inrush current.Then the criterion to distinguish the inrush currents and internal faults are developed according to the above method and two kinds of inrush current identification methods based on the waveform correlation which have different data under different working conditions,MATLAB simulation results show that this method has higher sensitivity and reliability. |
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