Zang Chunyan

Using ultraviolet imaging method to detect the external insulation faults of electric device

Ultraviolet Imager is a new type instrument for electric devices fault detection, which has small volume, light weight and is convenient for carrying and recording. It can help the security inspectors to pay attention and find out some early faults of electric devices, so that can avoid heavy accidents of power grid. However, at present this kind of instrument is not widely used in the power system and its functions need to be more studied. This paper does the investigations on some common external insulation faults of electric devices, such as the breakage, zero-value and contaminated insulator or insulation pole, loose equalizer ring, stream broken of electric transmission line and so on. By the CoroCAM504 UV Imager it gains a number of UV images and related parameters such as the UV photon number and discharge site. The results of the experiments and spot detecting show that, the UV method can do valid detection on the early external insulation faults of electric devices under the certain conditions. At the same time, the paper also gives out some guidelines on how to use the UV Imager properly.

Research on Mechanism and Ultraviolet Imaging of Corona Discharge of Electric Device Faults

At present, the detection methods of electric device faults are often undertaken by infrared imaging system, ultrasonic imagining system, etc. However, these techniques have some inherited shortcomings. As to the high insulation level of an ultra high voltage system, the long distance from ground exists. Thus it needs a more effective detection technology for the safety of power system. This paper studies on the mechanism of UV light and corona discharge, recommends the maximum UV photon number as the important parameter to evaluate the serious degree of defects, extracts the UV spectrum characteristics of various typical faults of electric device, and discusses about the insufficient part of UV detection. The research results will help power system maintenance to develop on-line monitoring of power network and get an accurate defect point and type.

Influence of Characteristic Parameters on Contact Bounce in Reed Systems of Relays

The contact bounce of relays, which is the main cause of electric abrasion and material erosion, is inevitable. This paper presents an investigation of the parameters influencing the dynamics characteristics of contact bounce under different current loading. An experimental model system, which simulated the direct-driven reed systems of relays, was designed. The measurements of small bouncing displacement and dynamic contact force have been achieved separately by using a high-precision laser displacement sensor and a piezoelectric quartz sensor. Several results have been obtained: With driving force augmenting, the range of dynamic contact force variety, the maximum impact speed and over-travel of contacts increase, but the maximum bouncing displacement and time decrease, and the first coefficient of restitution tends to increase while the subsequent coefficients tend to decrease. With load current increasing, the over-travel of contacts increases, but the range of dynamic contact force variety and the maximum impact speed decrease, while the maximum bouncing displacement and time decrease at the first then increase. The coefficients of restitution have a decreasing tendency along with the current increasing. The experimental results would be helpful to the further study of the characteristic of contact bounce in DC electromagnetic relay.

Investigation on change laws of arc burning time of the arc plasma

Arc burning time is the time interval from arc burning until arc quenching, which is one of the main symbol parameters of the arc plasma characteristic. As the length of arc burning time can do great influence on the arc energy and the two-phase change process of the break arc directly, it is significant for us to do some researches on its influence factors and change laws. To take the DC break arc between the low power relay contacts for an example, the paper studied the arc burning processes of two typical arc plasma — high purity nitrogen arc and air arc. When the relay contacts break resistant or inductive loads, it gained the relationships between the arc burning time with different atmospheres and load characters, as well as the change laws of arc burning time with the change of arc current and voltage. It also gives some deep analysis and discussions on the experimental results, which combined with the physical mechanism of two-phase change process of the break arc. Finally the paper built a basic mathematics model of arc burning time on the typical arc plasma, which can be helpful for the researchers to know more information about the arc burning process.

Study on Application of Ultra-Violet Instrument in External Insulation Detection of Electric Device

At present, the application of UV detection technology in power system is concerned by more and more people. Its using guides and standards are discussed warmly. Combined with the simulation experiment, the relationships between the number of UV photons, instrument gain and photograph distance are studied. And the corresponding relationship between the number of UV photons and the parameters of corona discharge such as the quantity of partial discharge, corona current are also studied in the severe non-uniform electrical field. The results show that the gain and distance have some effects on the number of UV photons. Users need to choose proper instrument gain and focus in application. UV photon number can be taken as an important index to judge the intensity of corona discharge.

Dynamic Analysis of Contact Bounce of Aerospace Relay Based on Finite Difference Method

Abstract Contact bounce of relay, which is the main cause of electric abrasion and material erosion, is inevitable. By using the mode expansion form, the dynamic behavior of two different reed systems for aerospace relays is analyzed. The dynamic model uses Euler-Bernoulli beam theory for cantilever beam, in which the driving force (or driving moment) of the electromagnetic system is taken into account, and the contact force between moving contact and stationary contact is simulated by the Kelvin-Voigt viscoelastic contact model. Analytical results have been complemented by the finite difference calculation of the nonlinear partial differential equations of reed system. The calculation results indicate that with the driving force (or driving moment) being increased, the closing time of contact is decreased, but the maximum bouncing displacement and bouncing time tend to be decreased first and then increased, which means that there are minimum values of maximum bouncing displacement and bouncing time. The closing time of contact, the maximum bouncing displacement, and bouncing time all tend to be decreasing with the pushrod being approaching the contact. The model can be used as design tool to improve relay performance and reduce contact bounce.

Research on Arc Burning and Contact Bounce of DC Relays by High Speed Photograph Method

Arcs in DC relays have the characteristics of short burning time and little brightness. A high speed photograph experiment was designed and performed in this paper. In the experiment, the whole burning processes of arcs were captured and some parameters such as arc diameter, length and grey level were obtained from the photos by digital image processing technology. Combining with the waveforms of arc voltages and currents, the relationships of arc voltages & arc lengths, arc currents & arc diameters by fitting functions were obtained as well. On the other side, the movement speed curves of contacts and some analysis on contact bounce were discussed in the paper. The results may be referred to when manufacturers design the parameters of small power DC relay.

Some Factors That Influence Film Growth on Sealed Relay Contacts

In order to examine the surface film growth on the contacts of sealed relay, we designed a set of experiments to simulate the film growth and also did some verification. Analysis of average contact resistance values of normally closed contact and normally open contacts in certain environments was conducted for the contact samples with or without aging or burnish operations. Some discussions were made to determine the influence of these operations on film growth. Combined with checking the environments of some sealed relay samples, several conclusions were reached and also some advices for improving the production technology of sealed relay were given.

Fault model construction based on gas chromatography of insulation oil by data mining technique

By DataCruncher, the gas chromatography data of a series of transformers are collected and processed. The data are mined. The fault model of the transformers is constructed. The relationship between the contents of the dissolved key gases and other summed parameters and the occurrence of fault in transformers is formulated. It approved that by this model it can give high precision of prediction in transformer fault diagnosis. The predicted result is agreement other methods.