Fangcheng Lu

AC Conductors' Corona-Loss Calculation and Analysis in Corona Cage

Corona loss generated from conductors is one of the important design factors of extremely high-voltage ultra-high voltage (EHV/UHV) ac transmission lines. The charge simulation method was adopted to calculate conductor corona loss in the corona cage. Every corona cage wall is equivalent to the ground plane and, therefore, the calculation model is more complicated than the power-line model above the ground surface. Two corona cages-UHV corona cage and small corona cage-were adopted in the tests. The cages are both square sections. Single conductors and bundle conductors were tested in the corona cages to verify the corona cage calculation model. And the same type of conductor was tested in the small corona cage and in the UHV corona cage to check the measuring system and the simulation program of corona loss further. Since the artificial rain rates were from 12 to 20 mm/h, corona losses were measured and calculated. The results indicate that the fundamental frequency component is the most main component of corona loss. The corona cage corona-loss calculation model is appropriate. And for single conductor LGJ-500/35 and bundle conductors, 8 LGJ-500/35, under heavy rain conditions, with the rain rate being from 12 to 20 mm/h, the roughness coefficient range is from 0.4 to 0.5 approximately.

500-kV EHV Bundle Conductors' Corona Onset Voltage Calculation and Analysis in Corona Cage at Different Altitudes

In order to research an altitudes effect on corona onset voltage of bundle conductors in a corona cage, a calculation model was established, and corresponding test proceeded. The charge simulation method was adopted to calculate space electric-ήeld strength. According to self-sustained discharge criterion in a severe nonuniform electric ήeld, and variation of altitude, the corona onset voltage calculation model of bundle conductors in a corona cage was established. The corona onset voltages of bundle conductors, which were used in the 500-kV extremely high voltage transmission line, were tested at different altitude locations, as Wuhan 19 m, Xining 2261 m, Golmud 2829 m, and Nachitai 3800 m. Corona onset voltages of 4 × LGJ - 0400/5 and 4 × LGJ - 300/25 were obtained. The corona onset voltage curves at different altitude, bundle spacing, and bundle numbers were obtained. The analysis shows that the model can be used to provide accurate values of corona onset voltage for bundled stranded conductors in the corona cage at various altitudes. With bundle spacing from 350 to 500 mm, the corona onset voltage decreases as bundle spacing increases, and the onset voltage increases as the bundle number increases. As altitude increases every 1000 m, the corona onset voltage of bundle conductors decreases by about 8.5%.

Insulator Pollution Grade Evaluation Based on Ultraviolet Imaging and Fuzzy Logic Inference

Ultraviolet (UV) imaging is an effective visual discharge detection method. In this paper, the ceramic insulator pollution discharge character was researched with the UV imager in the artificial climate chamber. According to the discharge UV image, the discharge type is divided into two typical forms, one is corona discharge, and another is the partial arc discharge. Using digital image processing algorithm, the discharge UV image region was segmented from the background image, the partial arc discharge number in certain time was counted, and the correlation of these parameters with the humidity were researched. Fuzzy logic inference was applied to realize the pollution grade evaluation. Application showed that fuzzy logic inference method can effectively to assess the pollution grade. Keywords-ceramic insulator; discharge; ultraviolet(UV) imaging; fuzzy logic inferenc

Simulation of PD location in power transformer based on Root Multiple Signal Classification method

Due to the heavy calculation and low estimation precision with little signal-to-noise (SNR) of MUSIC (Multiple Signal Classification) algorithm in partial discharge location used ultrasonic phased array, in this paper, a new location method is proposed based on Root-Multiple Signal Classification(Root-MUSIC). Firstly, Root-MUSIC algorithm is used for direction of arrival estimating of PD source. Secondly, space location of PD source is realized by crossover location principle. Finally, the result of simulation based on 7×7 plane phased array model vertifies the correctness of the new method.

Use of ultrasonic array method for positioning multiple partial discharge sources in transformer oil

Fast and accurate positioning of partial discharge (PD) sources in transformer oil is very important for the safe, stable operation of power systems because it allows timely elimination of insulation faults. There is usually more than one PD source once an insulation fault occurs in the transformer oil. This study, which has both theoretical and practical significance, proposes a method of identifying multiple PD sources in the transformer oil. The method combines the two-sided correlation transformation algorithm in the broadband signal focusing and the modified Gerschgorin disk estimator. The method of classification of multiple signals is used to determine the directions of arrival of signals from multiple PD sources. The ultrasonic array positioning method is based on the multi-platform direction finding and the global optimization searching. Both the 4 × 4 square planar ultrasonic sensor array and the ultrasonic array detection platform are built to test the method of identifying and positioning multiple PD sources. The obtained results verify the validity and the engineering practicability of this method.

A new sparse design method on phased array-based acoustic emission sensor for partial discharge detection

The acoustic detecting performance of a partial discharge (PD) ultrasonic sensor array can be improved by increasing the number of array elements. However, it will increase the complexity and cost of the PD detection system. Therefore, a sparse sensor with an optimization design can be chosen to ensure good acoustic performance. In this paper, first, a quantitative method is proposed for evaluating the acoustic performance of a square PD ultrasonic array sensor. Second, a method of sparse design is presented to combine the evaluation method with the chaotic monkey algorithm. Third, an optimal sparse structure of a 3 × 3 square PD ultrasonic array sensor is deduced. It is found that, under different sparseness and sparse structure, the main beam width of the directivity function shows a small variation, while the sidelobe amplitude shows a bigger variation. For a specific sparseness, the acoustic performance under the optimal sparse structure is close to that using a full array. Finally, some simulations based on the above method show that, for certain sparseness, the sensor with the optimal sparse structure exhibits superior positioning accuracy compared to that with a stochastic one. The sensor array structure may be chosen according to the actual requirements for an actual engineering application.

Experimental verification of the sparse design of a square partial discharge acoustic emission array sensor

This study experimentally verified the sparse design of a square partial discharge (PD) acoustic emission array sensor proposed in Xie et al (2014 Meas. Sci. Technol. 25 035102). Firstly, this study developed a square PD acoustic emission array sensor and determined the material, centre frequency, thickness, radius, etc of the element of this array sensor through analysis and comparison with others. Moreover, in combination with a sound-absorbing backing and a matching layer, a single acoustic emission array sensor element was designed, which laid the basis for the experimental verification of the ensuing sparse design. On this basis, the assembly of the square acoustic emission array sensor was designed. It realised the plug-and-play ability of the array elements and formed the basis for the experimental study of the following sparse design. Subsequently, this study established and introduced an experimental system and methods for PD positioning. Finally, it experimentally investigated the sparse design of a square PD acoustic emission array sensor. The 9-element square PD acoustic emission array sensor was used as an example to study the positioning effects on PD using the acoustic emission array sensor in optimum and random sparse structures respectively. The results suggested that: (1) the PD acoustic emission array sensor and corresponding experimental system were effective in detecting and positioning the PD; (2) the square PD acoustic emission array sensor proposed in Xie et al (2014 Meas. Sci. Technol. 25 035102) was feasible. Using this array sensor, it was possible to optimise the sparse distribution structure of this acoustic emission array sensor.

The Partial Discharge Locating Experimental Study in Transformer Based on Ultrasonic Phased Array

Partial discharge locating detection is a key project in transformer insulation mechanism research and quality control. And it is an important foundation in transformers condition maintenance. The theory of partial discharge location based on ultrasonic array is an effective improvement of partial discharge locating. But in experimental studies, the problem of sensor array element coupling performance is inconsistent, the results of many cross-point locations are also different, and the success rate and the locating accuracy in double-platform locating are not better than imagined. Based on these problems, three practical methods and techniques are presented in this paper. Firstly the pencil test method is used to test the coupling performance of the elements of the array sensor to improve the success rate of localization; secondly, taking repeated measurements at the same place and the weighted average method to improve the accuracy of measuring; thirdly the multi-platform and global search method are used to improve the positioning accuracy of PD source locating. Finally, the locating experimental system is established based on the ultrasonic phased array in oil. The Experimental results show that the locating errors is less than 10cm, verifies the three methods can effectively improve the partial discharge array ultrasound locating success rate and locating accuracy.

Urban medium voltage distribution network planning based on ASAGA and TSP path optimization method

Urban medium voltage distribution network planning is a large-scale combinatorial optimization issue. This paper analyses the cable single-ring network mode which is commonly used in current urban medium voltage distribution network, and proposes a new method of planning. Adopt adaptive simulated annealing genetic algorithm combined with path optimization method of travelling salesman problem to plan open-loop network. The coding strategy is optimized and the efficiency of evolution is improved. In order to obtain a closed-loop network, the minimum weight complete matching algorithm combined with the shortest path method is used to achieve tie-lines optimization, and it ensures that the planning result is of global optimum. Practical example proves that the proposed method can effectively solve the issue of urban medium voltage distribution network planning, and it is more instructive to actual urban medium voltage distribution network planning.

Harmonic wave analysis of conductor corona current based on wide frequency band measurement

Corona current is one of important corona characteristic research contents. In order to analyze conductor corona current harmonic wave characteristic, a corona current measurement system is developed. The synchronous collect of the voltage and current signal is realized by the GPS technology. The corona current signal is transmitted to the lower computer through the wireless network. And the current signal collected in this way is safe and reliable. The measurement system can be used to measure the wide frequency band corona current. Advanced Hanning windowed interpolation FFT algorithm was adopted, and conductor corona current harmonic wave was analyzed. Corona current harmonic characteristics before and after corona onset were compared. Research results show that, after corona onset, corona current odd harmonic increases in evidence, and even-order harmonic increase less relatively. Triple-frequency harmonics and quintuple harmonics increase obviously very much, and conductor corona current harmonic analysis can be used to research conductor corona characteristic.