| With the rapid development of society, people's dependences and requirements on power quality are also getting higher and higher. According to statistics, more than 95% of the power outages that power users suffered are caused by the distribution network fault, therefore, the online monitoring and fault identification of the distribution network is of great significance to the safe operation of the power grid and the development of the smart grid. Traditional power transformer has shown more and more inadaptability in online monitoring of distribution network voltage and current due to its size, weight, insulating cost, steady-state accuracy and transient response, and it is also difficult to be applied in distribution network fault identification. In this paper, an integrated voltage and current fault online monitoring system is proposed based on the non-contact measurement method, and on the basis of this, a method to identify faults according to the changes of voltage and current is proposed. The main work of this paper mainly embodies on the following aspects:(1) A new idea to realize voltage non-contact measurement is proposed by electric field coupling, and the basic measurement principle of electric field coupling probe is studied. By establishing the equivalent model of the sensor, the differential structure of the electric field coupling voltage sensor working on self-integration mode is determined. On the basis of this, the PCB type electric field coupling voltage sensor is made. A non-contact current measurement method by Rogowski coil is proposed, and the working principle of Rogowski coil is analyzed. The transient response of Rogowski coil is carried out through theoretical deduction and MATLAB simulation analysis. Combine with the need of power frequency measurement, a Rogowski coil with magnetic core is made, whose skeleton is silicon steel. Based on the electric coupling voltage sensor and Rogowski coil, a non-contact integrated voltage and current sensor is manufactured by combining them.(2) According to the demand of distribution network fault online monitoring, measurement hardware circuit, which is used for signal conditioning and digital acquisition of probe's output voltage and current signal, is designed and implemented. The PC software program is developed by LabVIEW, which implements the display, analysis and saving for the measurement waveform data. Bidirectional communication between hardware circuit and PC software program is implemented by using WIFI wireless network and UDP protocol.(3) A method to identify the fault by the variation of voltage and current in the process of fault is proposed, and the feasibility of this method is proved by theoretical analysis. A distribution network fault simulation model is established based on PSCAD/EMTDC, the simulation result demonstrates the correctness of the method. The sensor was installed in actual distribution network with good effects. It shows that the non-contact voltage and current integrated measurement system can play a unique role in the online monitoring and fault identification of distribution network.(4) The distribution network experimental platform is set up for testing and verification of non-contact voltage and current integration online monitoring system. The steady-state measurement performance of the voltage sensor and current sensor is verified through comparison with Tektronix high-voltage probe and SDD clamp type current transformer as standard. Besides, the sensitivity of voltage sensor and current sensor is calibrated. On the basis of this, the ratio correction factors of voltage sensor and current sensor are obtained by linear degree fitting, which can be used for the processing and correction of data and waveform through PC software. In addition, the switching operation of the voltage sensor and the current sensor is also carried out to verify their transient performance. Finally, a complete test of the system is carried out, and the results show that the system can realize the real-time online monitoring and remote data transmission of distribution network, and it can be applied in online monitoring and fault diagnosis field as a kind of non-contact intelligent system. |
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