Qingquan Li

Space charge characteristics of multiple reigniting secondary arc in atmospheric air

In order to investigate the electrical characteristics and the morphologic development of secondary arc in atmospheric air, a simulative experimental platform of secondary arc for UHV transmission lines was built and the corresponding experimental procedure was introduced in this paper. The discharge waveforms were categorized into three stages: the short-circuit arc period, the transition period of short-circuit arc and the secondary arc, as well as the secondary arc period. And the electrical characteristics of each stage were analyzed, involved with discharge power and discharge energy. By observing the arc discharge images, the forming process and the multiple reignition phenomenon of secondary arc were displayed and analyzed in associated with the corresponding discharge waveforms. A short-cutting event of the plasma column may happen when suddenly a new, shorter current path forms and the former arc path gradually disappears because of larger arc resistance. It was also found that the arc length and the arc diameter in the experiment were consistent to the computational values. The research results present analytical basis and theoretical reference for explanation and suppression of secondary arc on UHV transmission lines.

Influence of ambient humidity on UV imaging detection of polluted plate model discharge

Ultraviolet (UV) imaging technology is now widely used in the corona discharge detection of high voltage power transmission and transformation equipment as it is much more convenient and easier to be used than other detection methods nowadays. Insulators are broadly used in todays power transmission lines. This paper mainly studies the influence ambient humidity exerts on the UV imaging detection of polluted plate model discharge. Plate model is used to simulate a RTV-coated insulator surface. The RTV-coated plate model surface is artificially polluted and set in an artificial fog chamber. The gain of the ultraviolet imager, and the distance between the ultraviolet imager and the plate model are also taken into consideration. The photon number of discharge was measured by an ultraviolet imager and the leakage current at the corresponding discharge intensity was recorded. The curves of applied voltage, ambient humidity, leakage current and photon numbers of the ultraviolet imager were drawn respectively. The data and curves were analyzed and conclusions could be drawn: The effect of ambient humidity on the discharge of contaminated RTV-coated plate model is not static, it will change from weakened to enhanced; a relatively high ambient humidity would increase the discharge and reduce the ultraviolet signal caught by UV imager.

The characteristics of secondary arc current in UHV transmission line with hybrid reactive power compensation

The hybrid reactive power compensation (HRPC) for UHV transmission lines is expected to be applied, and its mutual influence with power grid is urgent to be studied. In this paper, the characteristics of secondary arc current before and after the installation of HRPC are compared and analyzed in this model. And the characteristics of secondary arc with different neural reactors, compensation degrees and fault location are also analyzed. From the research in this paper, it can be get that the installation of HRPC has significant effect on the extinction of secondary arc, and the arcing time and secondary arc current decrease by the compensation degree of series compensation but have little connection with the shunt controlled reactor. The relation between fault position and secondary arc as well as the optimal value of neural reactor are obtained. The bypass of capacitor bank before extinction may lead to the rise of LF component frequency and it also accelerate the extinction. When it comes to the compensation degree, the bigger shunt compensation degree is, the lower frequency of LF component is, and the attenuation speed gets faster. Nevertheless, the compensation degree of series compensation acts the opposite way compared with the compensation degree of shunt controlled reactor.

Study on the influence of core material on the performance of nanosecond pulse power supply

Saturable transformer and magnetic switch are the core components to realize the function of all-solid-state nanosecond pulse power supply. In order to further explore the effect of core materials on the performance of power supply and improve the compactness of power supply by optimizing the size of magnetic components, this paper analyzes the working state of the magnetic elements at each stage of generating the power pulse. The magnetic components are optimized by using some correlation formulas. The two-stage magnetic compression circuit is simulated by OrCAD Capture CIS software, and the simulation models of Mn-Zn ferrite cores with different size and material properties are edited for each magnetic component. The output results are compared with the corresponding literatures. The results show that it is feasible to optimize the magnetic elements on the volume, and the supply can provide the final high voltage pulses with amplitude of 40 kV, repetition frequency of 5 kHz, and pulse width of about 27 ns.

The application of transient earth voltage in the partial discharge of power transformers

Partial discharge characteristics are extracted to analyze the potential shortcomings of transformers. And in order to better study the partial discharge characteristics of transformers, the detection performance of the two methods has been compared and analyzed. Using the method of transient earth voltage and pulse current to cooperate is very helpful to improve the accuracy of pattern recognition. In this paper, the method of transient earth voltage to detect the partial discharge of transformers is proposed. Then the parameters measured by this method are extracted and briefly analyzed. Four artificial partial discharge models of transformers have been set up, including needle-plate defect in oil, air gap defect in oil, surface defect in oil and sphere-plate defect in oil. The experiment uses the constant-voltage testing method to extract the characteristic parameters from phase spectrogram of maximum discharge capacity and discharge frequency by the method of transient earth voltage and pulse current based on phase analyze. Partial discharge characteristic parameters have been extracted by the method of phase-resolved partial discharge. The differences between each type of discharge characteristics and the relationship between the two methods are comparatively analyzed. And the method of pattern recognition has been used which based on support vector machines. The data have been analyzed for recognition which are obtained by the method of transient earth voltage, pulse current and the combination. According to the analysis of the two groups of data comprehensively, the accuracy of pattern recognition has been greatly improved.

An advanced partial discharge recognition strategy of power cable

Detection and localization of partial discharge are very important in condition monitoring of power cables, so it is necessary to build an accurate recognizer to recognize the discharge types. In this paper, firstly, a power cable model based on FDTD simulation is built to get the typical discharge signals as training samples. Secondly, because the extraction of discharge signal features is crucial, fractal characteristics of the training samples are extracted and inputted into the recognizer. To make the results more accurate, multi-SVM recognizer made up of six Support Vector Machines (SVM) is proposed in this paper. The result of the multi-SVM recognizer is determined by the vote of the six SVM. Finally, the BP neural networks and ELM are compared with multi-SVM. The accuracy comparison shows that the multi-SVM recognizer has the best accuracy and stability, and it can recognize the discharge type efficiently.

The Research of CDEGS in Defect Diagnosis for Grounding Grid

The paper briefly introduces the function and characteristics of the ground simulation software CDEGS, and computes the grounding grid model by using the MALZ module. The grounding grid GPR (Ground Potential Rise) and the percentage of reference power bus GPR are analyzed after the exciting current source injected into the grounding grid, and compared and analyzed with CDEGS softwares simulation calculation results, it is easy to diagnose defect and locate defect position in the grounding grid.

Close-Operation Overvoltage of No-Load Transmission Line with Fault Current Limiter

The comprehensive impacts of series resonance type fault current limiter (FCL) on power system need further investigation and verification. With regard to switching on 500kV EHV no-load transmission line, the instantaneous peak value, the free component oscillation frequency, the fundamental component amplitude and free component amplitude of terminal overvoltage waveform are simulated with and without installation of FCL considering different switching times. The relationship curves of free component oscillation period, the fundamental component amplitude and free component amplitude are gotten respectively by simulation results. The law of the influence of different fault current limiting reactance on terminal voltage of switching on no-load line is also summarized. The analysis results show that the installation of FCL is benefit for switching on no-load line.