184 / 2018-08-28 10:36:38

Study on the Discharge Characteristic and Detection Method on the faulty of Distribution Insulators

distribution network,insulator,binding wire,discharge characteristic,detection method

A key technology to improve the reliability of distribution network is to efficiently detect and monitor the conditions of power equipment on-line. A good on-line detection can prevent equipment from failures, and reduce the time of blackout and repair. Now, the common methods of on-line monitoring are ultrasonic based discharge detection method, infrared thermal imaging method, ultraviolet imaging discharge detection method, and UHF based discharge detection method. However, according to the feedback of on-site operation and maintenance engineers, there are still lots of limitations (e.g. whether conditions, experiences of engineer, fault degree, etc.) in these methods and the detection efficiency is very low. An outstanding characteristic of distribution network is that it has complex and long-distance network with huge quantity of equipment. Hence, with the increasing scale of distribution network, the efficiency and accuracy of on-line detection is very important, especially when the crew size of professional operation and maintenance engineer is limited. However, currently, all of four methods above cannot satisfy the high requirements of distribution network operation and maintenance.
For example, in ultrasonic based discharge detection method, only dB value is used to roughly determine the discharge capacity while other waveform features are ignored. As the ultrasonic waveform features are affected by equipment type, defection location, discharge type, source distance, environment humidity and temperature, dB value is clearly not enough to support the discharge capacity evaluation. On the other hand, UHF based discharge detection method is now often used inside substations. However, the environment of distribution network is different than the environment of substations. Therefore, theoretically, it can be used in distribution network after adaption as the environment of distribution network is simpler. In fact, none of above problems is solved due to the research on the mechanism of equipment defects and the detection technology is not enough. Take ultrasonic method for example. In order to analysis the waveform features, it is important to understand how defection type and equipment type affects the discharge. Without related theory, it is impossible to obtain a solid waveform analysis conclusion. In UHF detection, it is also necessary to analysis the electromagnetic waveform of discharge in distribution equipment. As the electromagnetic wave can be reflected by the metal surfaces surrounded or altered by ambient noise, received signals will be complex. Thus, it is important to understand how the surroundings and noises in distribution network environment affect the waveform. With the help of related theory, we can restore the original discharge wave and finally provide a reasonable evaluation result.
This paper firstly focuses on the faults of insulator as its quantity is the most in distribution network and its faulty proportion is significant as well. According to the feedback from the distribution network on-site maintenance, the insulating layer of overhead conductor is often ablated by flashover arcs which are usually generated under the binding wire on the insulators. Therefore, the simulations and experimental study to explain the mechanism of these insulator discharges are performed. This research is based on artificial pollution tests, and the discharges in different conditions/environments (i.e. pollution level, moist, damage and scratch) are reproduced. With ultrasonic, UHF and partial discharge measurement, the relationship between discharge radiation (i.e. ultrasonic and UHF) and partial discharge level in different environment is obtained. According to the relationship, a method of monitoring equipment ageing is discussed at last.