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Partial discharge along the surface seriously damages the oil-paper insulation performance and ultimately leads to insulation failure, which greatly reduces the safety and reliability of the converter transformer operation. It is important to understand the failure process of oil-paper insulation under partial discharge along the surface to avoid fault occurrence. In this paper, the failure process of oil-paper insulation under partial discharge of pulsating DC and AC voltage is studied. A partial discharge test platform for oil-paper insulation under pulsating DC voltage was built. The partial discharge test of oil-paper insulation along the extremely uneven electric field was simulated by using the needle plate and column plate discharge model. The oilpaper insulation under two kinds of voltages under the extremely uneven electric field was analyzed in depth. The similarities and differences of the failure process and their causes, the insulation design and operation and maintenance recommendations for preventing flashover under the extremely uneven electric field are proposed.

Compared with traditional Z-source and quasi-Z-source inverter, tapped-inductor quasi-Z-source inverter (TL-qZSI) has higher booster multiple, lower capacitance stress and higher conversion efficiency. Therefore, it is very suitable for grid-connected photovoltaic power generation system. This paper analyzes the voltage boosting theory of the TL-qZSI and applies it into grid-connected photovoltaic power generation system. For the imbalanced power grid voltage sag situation, this paper puts forward a low voltage ride-through (LVRT) control strategy. System realizes the unity power factor running and has a good LVRT ability under imbalanced power grid voltage sag. At last, the simulation and experimental results are shown to verify the correctness of the control method.

The line loss control project is important task for energy conservation and loss reduction. The loss comparison of special lines in the distribution grid is an important part of this project. In this paper, the errors in the line loss comparison work are analyzed in detail based upon the actual working experience. A new method of believable bound selection for special line loss comparison work is introduced, and the example shows the accuracy of the method.

This paper mainly focuses on the power plant subsystem of the HAVC (hybrid automatic voltage control) system in the 500 kV power grid of Northeast China, which is developed by the State Key Lab of Power Systems of Tsinghua University. The developing process and the field experiment in Suizhong power plant of Northeast China are included in this paper. The field experiment confirms that, the designed HAVC subsystem in the power plant could achieve the desired functions.