Du Lin

Fault location for transmission line based on traveling waves using correlation analysis method

This paper described the principle of transmission line fault location based on traveling waves. The principle and of correlation analysis is introduced, then the method using correlation analysis in fault location is given. Transmission line model is established with EMTP-ATP. Basing on the model, some kinds of fault are simulated. The feasibility of this algorithm is proved based on simulation results. By comparing with the classical wavelet analysis, this paper gave the advantages of this algorithm in two cases: noise influence suppression and accuracy of near distance fault location.

Pattern recognition of partial discharge with fractal analysis to characteristic spectrum

While partial discharge (PD) pattern recognition is widely considered as an important method to test insulation degradation, the major problem encountered is the extraction of PD pattern features. Using the analysis of the three-dimensional statistical spectrum, this paper adopts fractal theory to extract PD pattern features. From designed model tests and fraction calculation results, it is shown that the method is effective in extracting PD pattern features which are helpful in PD pattern recognition based on three-dimensional statistical spectrs.

A practical PD online monitoring system used for transformers

In this paper, we develop a partial discharge (PD) online monitoring system with frequency band from 50 kHz to 1 megahertz used for transformers. The monitoring system mainly consists of wide-band signal detectors for multi-terminal measurements, signal pre-processing circuit, high speed A/D converter and cascaded 2nd order IIR lattice digital notch filter. The major measures to suppress narrowband interference are the signal pre-processing device and the digital notch filter. With analysis to field monitored signal from a transformer at a 220 kV substation, it is shown that the monitoring system can detect and extract the discharge pulse signal effectively. With PD pattern recognition method, the monitoring system can get more stable and reliable detection results.

A Fault Diagnosis Method for Power Transformers Based on Wavelet Neural Network and D-S Evidence Theory

Transformer faults are quite complicated phenomena and can occur due to a variety of reasons. There have been several methods for transformer fault synthetic diagnosis, but each of them has its own limitations in real fault diagnosis applications. In order to overcome those shortcomings in the existing methods, a new transformer fault diagnosis method based on a wavelet neural network optimized by adaptive genetic algorithm (AGA) and an improved D-S evidence theory fusion technique is proposed in this paper. The proposed method combines the oil chromatogram data and the off-line electrical test data of transformers to carry out fault diagnosis. Based on the fusion mechanism of D-S evidence theory, the comprehensive reliability of evidence is constructed by considering the evidence importance, the outputs of the neural network and the expert experience. The new method increases the objectivity of the basic probability assignment (BPA) and reduces the basic probability assigned for uncertain and unimportant information. The case study results of using the proposed method show that it has a good performance of fault diagnosis for transformers.

Identifying the Overvoltage in Distribution Networks Based on Support Vector Machine

The internal and external overvoltage in distribution networks are the main reasons of accidents. Based on overvoltage data in distribution network recorded by overvoltage on-line monitoring system, this paper analyzes the characteristics of zero sequence voltage waveform. The maximum amplitude and RMS value of zero sequence voltage, the minimum RMS of low frequency component of three phase voltage in stable range and other five parameters are selected as characteristic parameters to identify internal and external overvoltage. According to the operation data and record, all overvoltage data record by on-line monitoring system were labeled as internal or external overvoltage and the discrimination function is constructed by support vector machine method. The test results of field acquired overvoltage data indicate that the identification parameters and method base on the zero sequence voltage and SVM are correct and effective.

Study on Power Transformer Fuzzy Risk Assessment Based on Borda Number Theory

Transformer is the key equipment of transforming voltage and exchanging power in the power system. Its safe and reliable operation directly influences the safe level of the power system. The risk assessment of transformer is very significant to improve the reliability of the power system. A fuzzy comprehensive risk assessment model of transformer based on Borda number theory is proposed in this paper. At first, the fault types and risk factors of the transformer are analyzed. Secondly fuzzy theory is applied to quantify the risk factors. And then Borda number theory is employed to analyze influence degree and occurrence probability of transformer. At last, the assessment examples of transformer show the good reliability of this method.

Programmable voltage regulating method for high voltage DC power supply based on digital potentiometer and linear photoelectric coupling

In order to solve the disadvantages caused by mechanical slide rheostat that they were big errors and low precision, a novel voltage regulation method for high voltage DC power supply was introduced. The key of this method were digital potentiometer Maxim 5455 and linear photoelectric coupling LOC110, and application programs were compiled using Visual Basic which was graphical compiling language, furthermore the communication between exterior and computer was carried out by ICP7044D module, in consequence the output value of high voltage DC power supply could be regulated with computer. The measured results showed that this method could accurately, conveniently and rapidly regulate the output value of high voltage DC power supply.

Study of an Assessment Method for the Reliability of Tap-changers in Power Transformer Based on Fault-Tree Analysis

Based on the further analysis of typical failure modes and influences of tap-changers in power transformer, the fault-tree of tap-changers is set up by using fault-tree analysis(FTA) techniques and the assessment method for the reliability of tap-changers, combined with the index of the importance and the method of Improved Analytic Hierarchy Process(IAHP), is put forward. The assessment examples show the method can deduct the failure modes of tap-changers clearly, meanwhile, find out the weaknesses in time during the operation and get better assessment results.

Partial discharge pattern recognition using fractal dimension

This paper brings forward a modified differential box-counting (MDBC) method to evaluate the fractal dimension (FD). And on the base of the new method, this paper proposes and studies the FD and the 2nd order generalized dimension of partial discharge (PD) gray intensity image as two kinds of PD pattern features. Furthermore, high gay intensity image is constructed for extraction of FD as a new PD pattern feature. A PD image is divided into two equal parts according to power frequency phase angle and then we extract 6 fractal features for recognition to a PD image. Large quantities of PD samples are acquired by PD models test and used for testifying the proposed method. Using with fractal features and designed backpropagation neural network, we acquire satisfactory recognition results for discharge model samples.

Research on the measurement error of capacitor voltage transformer under various insulation characteristics

Capacitor voltage transformer (CVT) is one of the most important measuring and protecting devices in power system, whose measurement error is relevant with insulation characteristics of voltage divider. In daily operation, dielectric aging, moisture, dielectric breakdown etc. will exert a mixing effect on its insulation characteristics, changing voltage dividers equivalent parameters, further resulting in the measurement error. This paper proposes a more accurate model to represent CVT, which takes insulation characteristics of voltage divider into consideration. After theoretical analysis and software simulation, the relationship between measurement error and insulation characteristics is obtained. It indicates that varying of insulation characteristics in CVT will cause a reasonable measurement error.