Advanced Materials Research Vols. 805-806

Abstract: This paper does aging test about zinc oxide varistor and collects the waveform data from the arrester before and after aging, then uses numerical calculation and FFT to analyze the waveform data. Through comparing the changes of characteristic parameters before and after aging such as power loss of varistor, leakage current and every harmonic current, this paper can get the relationship between varistor aging and leakage current, especially the changes of resistive fundamental and harmonic current after aging. Based on analysis and study of aging characteristic parameters of the arresters, it can provide the basis of the judgment for putting forward a new online monitoring method and contributes to the application and development of MOA monitoring technology.

Abstract: A methodology of diagnosing the winding insulation defect according to data of transient voltage and current from the impulse voltage test is put forward in this paper. Lightning impulse test for transformer is divided into half-wave and full-wave at the moment. According to the full voltage and reduced voltage at two pressure processes. The transient voltage and current from the impulse voltage test can be divided into Series of harmonics. The insulation defect is diagnosed by dividing impulse voltage and current into series of harmonic and structuring discriminant function according to the longitudinal ratio method and cross ratio method for the corresponding period of harmonic voltage and current. The methodology is also applicable to diagnose whether there are insulation damage in the windings those have passed the lightning impulse test.

Abstract: When the overhead transmission line is galloping, a variety of natural disasters occur on the role of the natural conditions, the vibration of conductor is one of the more serious harm to the power system. Over the past decade, as the construction of EHV and UHV, wire cross-section, tension, suspension height and span of overhead transmission lines are increasing, and hence the number of conductor vibration is significantly increased. Vibration in a large scale will led to frequent tripping or even broken line or tower collapses, which cause large area power failures and impact security and stability operation. Online monitoring method for overhead transmission line dancing is mostly needed to add additional equipment, however, once situated on the route environment overlying ice or high winds and other inclement weather, online monitoring is difficult to achieve. This paper presents a method, which is made correlation analysis based on the voltage and current acquired from both ends of the transmission lines, online monitoring of line galloping can be achieved.

Abstract: In recent years,transmission lines icing leads to failure and accidents,such as large area ice flashover, fittings damaged, line dancing, pole (tower) failure, lines breakage even large-scale power outage, causing serious threat to grid. Nowadays, icing monitoring system mainly relies on detecting the meteorological parameters and the changes of dynamic characteristics for early warning, but the methodologies need additional equipment for data collection. In order to ensure the security and reliability of the grid, a safe, effective and economical methodology of monitoring transmission lines icing has great significance. The project proposed a Transmission Line Icing monitoring principle and algorithm, the method based only on the voltage and current from both ends of transmission lines can be generated dynamically monitoring criterion line icing. According to the criterion maximum, line icing center area, extent and severity can be recognized. The criterion of the method is used as a mathematical scanner, swept from one end of the line to the other end, comprehensive judgments are made on the basis of comprehensive criteria for integrated maximum value, thus the method has a high diagnostic accuracy and reliability. The methodology proposed in this paper is different from the current monitoring methodology; additional hardware devices are not required, and the methodology is simple and practical, has strong operability and enormous economic benefits, adapting to the requirements of the development of the smart grid.

Abstract: A novel method for detecting turn-to-turn short circuit is proposed in this paper. This detection makes the transient voltage and current applied in the transformer port as the information source. The transformer model is structured according to its low-frequency characteristics. By comparison the extreme value of the criterion function proposed in this paper, the transformer turn-to-turn short circuit fault can be detected. Based on good results in the simulation, the methodology is proved effective and practical.

Abstract: Water tree, electrical tree and electrochemical tree formed by premature defects of the cable can induce fault. The failure rate of the cable connecter which is higher than cable itself can emerge water tree, electrical tree and electrochemical tree. Meanwhile, the flashover, partial discharge and overheated of the cable joint are also the important reasons for fault. The oscillatory wave of detecting the power cable insulation defects based on is put forward in this paper in terms of the problems existed in the cable detection technology. With the application of oscillatory wave and signal source on the spot, this method dynamically generates reference database of detecting the cable insulation defects, to discriminate the fault patterns correspond to the maximum of function and detect the type, location and severity of cable insulation's defects. Water tree fault of premature cable itself and cable joint can also be detected in this method.

Abstract: Metal oxide surge arresters (MOA) is a power system overvoltage protection device, and the online monitoring of the MOA is an important means to ensure the safe operation of the power system. This paper presents a new MOA insulation defects monitoring method. This method is based on the relative change in capacitance to MOA insulation defects as characteristic parameter, the aging classified as a kind of local defects, the system disturbance contains higher harmonic of transient voltage and current as the signal source, dynamically generated MOA partial insulation discriminant function of the defects in the diagnosis. The maximum value of the discriminant function corresponds to the local insulation defects. The proposed method contributes to the MOA monitoring methods and the development of technology.

Abstract: GIS is currently widely used in the power system and is the Developing Trends of Electrical appliances manufacturing. At present, a lot of research on GIS PD, but the study of the recognition of the PD severity is less. By analyzing a large number of partial discharge sample data, a new GIS PD severity diagnostic method is proposed in this paper. Partial discharge is divided into three stages (initial stage, development stage and dangerous stage) in the method according to the severity of the partial discharge. These three stages are fitted with non-linear mapping and get the fitting parameters. GIS partial discharge fault reference database can be dynamically generated with these fitting parameters. The similarity between the detected data and the reference data is discriminated with the least square method and Supplier division method, and then the GIS PD severity can be diagnosed. A large number of simulation results initially confirmed the effectiveness and feasibility of the proposed method.

Abstract: Power transformer is the key equipment in power system. In view of the issues of the current bushing monitoring method, a new detection method of bushing insulation defects is proposed in this paper. According to the internal structure of bushing, the internal insulation defects are divided into three categories, including partial moisture, pollution, local insulation defects, the outer insulation of the bushing is equivalent to a resistance chain model. The entire bushing insulation is considered as a parallel between inner insulation and external insulation (inner Insulation is the main). This detection makes uses of the transient voltage measured from the transformer bushing and the transient current measured from the end shield down-lead as the signal source. The reference data dynamically generated is used to diagnosis and distinguish Insulation defects of Transformer bushing, according to the monitoring data of the bushing and the maximum of the reference data, the type of the bushing insulation defect and the severity can be sentenced. A large number of simulation results initially confirmed the effectiveness and feasibility of the proposed method.

Abstract: The development direction of transformer monitoring and diagnosis is remote and intelligent. But the existing systems have the following problems: lack of diagnostic knowledge and methods, poor flexibility etc. To solve these problems, the architecture of a remote monitoring and diagnostic system for transformers based on multi-agent techniques is presented. On the basis of ultra high frequency (UHF) partial discharge (PD), core earth current and dissolved gas analysis (DGA), the hierarchical decomposition model is established. The tasks, functions and structure involved in the collaboration agents are defined. Then, the fusion strategy from multi-experts conclusions is proposed based on diagnostic confidence and weights. In final, the system implementation is described. Some functions of the system have been put into service and worked well.