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Ni Z.-R.,North China University of Water Conservancy and Electric Power | Wang Y.-A.,Jinan Power Supply Company
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2014

The synchronization of merging unit in smart substation and limitations of the method of validating whether the current at each side of differential protection is synchronous by using on-site phase and differential current check are analyzed. The design requirements of field testing instrument with merging unit delay characteristics of smart substation is proposed. The system structure and the detailed design of field testing instrument is introduced based on the design requirements. Finally, the detailed calculation and comparative analysis of tester time granularity and the time response with the merging unit is done. Analysis shows that, the tester can validate that the merging unit delay parameters are set correctly, which can prevent incorrect setting and accord with the site acceptance requirements. Source


Zuo P.,Tsinghua University | Li J.,Beijing Institute of Technology | Song X.,Jinan Power Supply Company | Yuan J.,Tsinghua University
IEEE Transactions on Plasma Science | Year: 2013

The railguns can be classified into three types by the interior surface shape of rails, which are the type of plane-rail, convex-rail, and concave-rail. In this paper, the characteristics of current distribution in rails and armature are analyzed and compared for those three types, during the rising, dropping, and the flat part of the exciting current source. This current distribution is simulated by the finite element software ANSYS. The convex-rail type gun is of the weakest opposite direction current phenomenon, and its current distribution on the rail section is the most even. The evenness of the current distribution can be adjusted by changing the height of the convex part. The current density at the corner of armature is very large in the plane-rail and the concave-rail types, which results in stress concentration and probably damage of armature or rail surfaces. © 1973-2012 IEEE. Source


Du B.X.,Tianjin University | Liu Z.X.,Tianjin University | Xiao M.,Jinan Power Supply Company
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2015

As one kind of the basic insulating materials, polyimide has been widely used in turn to turn insulation and turn to ground insulation in inverter-fed motors. However, the pulse voltage from the converter often causes overvoltage and localized high electrical field in the insulation system. During applying the pulse voltage, charges accumulate on the surface of the insulator, which could affect the dielectric property and cause the breakdown of insulation. Direct fluorination is a method to modify the surface layer of the polymers without changing the bulk properties. As a result of the fluorination, hydrogen atoms are replaced by the fluorine atoms and the component of the polymer surface is changed, which can influence the surface charge accumulation and affect the electrical properties. The experiment in this paper was focused on the effect of pulse duration and pulse number on surface charge of the polyimide films. The polyimide films with the fluorination time of 0, 15, 45 and 60 min were prepared. Surface charging was performed by corona discharging using repetitive pulse power at the temperature of 20 °C with the relative humidity of ~15%. The repetition frequency was 1 kHz and the pulse duration was 50, 110 and 210 μs, respectively. The surface charge decay was measured using a specific probe coupled with an electrostatic voltmeter. The results showed that the surface charge increases with increasing the pulse number and the duration of the microsecond pulse. © 2015 IEEE. Source


Zhou K.,University of Canterbury | Qiu Z.,Jinan Power Supply Company | Watson N.R.,University of Canterbury | Liu Y.,University of Canterbury
IET Power Electronics | Year: 2013

The mechanism of harmonic current injection from single-phase grid-connected converters is comprehensively investigated. The measurable impacts from grid voltage, converter commutation, power factor, PWM modulation and control strategy are demonstrated on the harmonic current injection. According to the mechanism, a tailor-made control solution which employs a low pass voltage-loop filter and internal model principle-based hybrid current controller, is proposed to eliminate the harmonic current injection from the single-phase grid-connected converters. Experiments are performed to verify the validity of the mechanism and the proposed control method. It not only presents an effective tailor-made solution to the elimination of harmonic current injection from grid-connected power converters, but also provides a mechanism-based benchmark tool to further develop rational grid requirements on the harmonic injection levels in the grid integration of distributed generation units. © The Institution of Engineering and Technology 2013. Source


Zhang B.-D.,Tianjin University | Li G.-F.,Jinan Power Supply Company
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2010

An accurate model of the distribution network is indispensable to calculate line loss and optimize the structure correctly for a 10 kV distribution network. Because the power flow calculation sequence of the model is huge and time-consuming for creating, all loads between breakers are simplified by a generalized node, and its interior structure is described with the help of a group of the power flow calculation subsequences. A kind of method for creating power flow calculation sequence by district is proposed. At the same time, in view of multistep loads, the heuristic rules of the branch-exchange algorithm are modified and the method of revising power flow calculation sequence is designed. These suggestions have been adopted successfully in the system of operation optimization and assistant decision of the 10 kV distribution network, which is located in Shangqiu power supply bureau, Henan Province. Source

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