Lijun Jin

Discrimination of insulator contamination grades using information fusion of multi-light images

Flashover occurs more easily on contaminated insulators, which causes great economic losses and has bad effects on power system stability. A new method is introduced to discriminate the contamination grades of high voltage insulators, using information fusion of visible images and infrared images of the insulators. Firstly, three heating models of running insulators-No Dry Band, Dry Band and Dry Band Arc are established and solved by numerical analysis method to find out the differences in temperature rise under different running states. Secondly, we smear 10kV insulators in different contamination grades. Then we take their visible images by camera and infrared images by infrared thermal imager after applying the rated AC voltage for hours in artificial fog chamber in different relative humidity. After image processing, we extract 36 disk color features from the visible images and 7 disk temperature features from the infrared images, and screen out the best features using Fisher discrimination. Then, two BP (Back Propagation) neural networks are trained, one of which takes the selected visible image features as the inputs while another uses the selected infrared image features and relative humidity. Furthermore, we fuse the information of visible images and infrared images on feature level, which raises the accuracy in identifying the sample images. This method may provide effective information for insulator cleaning and flashover prevention.

Assessment of Electric-Field Exposure Using Reliability Analysis

Excessive exposure to high levels of electromagnetic fields can induce adverse health effects. Numerical calculation is often used in the exposure assessments. However, in the traditional methods, the relative variables are all assumed to have fixed values without considering the effect of staff activity. To improve the deficiencies caused by this assumption, a new method for the exposure assessments based on the reliability theory was proposed in this investigation. As an example, the electric-field exposure in the booster station of a power plant with several paths was studied by the new method. The exposure reliability index and the failure probability of each path were first determined. Then, based on the determined reliability indices, the influence of the bus framework on the exposure was discussed by the sensitivity study, and a series system was set up to evaluate the electromagnetic exposure of the entire booster station. The proposed approach could be employed to assess the electric field in the substations by taking into account the staff activity, in order to improve the management of the occupational exposure in the power transmission and distribution projects.

Layout optimization of framework in substation in view of electromagnetic environment

Layout of the metal framework, which is widely placed in the power engineering, has effects on the electric field distribution. And moderate electromagnetic environment contributes to the health of staff in the high-voltage substation. Hence, in order to improve the exposure situation in the outdoor substation, the present study optimized the layout of the framework by using a probabilistic method. The exposure failure probability of each working path was calculated under various arrangement schemes, based on the practical environmental field and the level of field staff can bear safely. The occupational exposure situation was improved by finding out framework arrangement with the smallest failure probability, which corresponds to the safest exposure. The obtained results indicate that compact but uneven longitudinal gap between columns, the rhythmically placed beams, and medium sized root span of the column help to create optimal electric field exposure in the substation.

Discrimination of transmission line insulator contamination grades using visible light images

Flashover occurs more easily on contaminated transmission line insulators, which causes great economic losses and has bad effects on power system stability. An accurate and safe detection of insulator contamination grades is required. In this paper, a new method is proposed to discriminate insulator contamination grades using visible light images. Firstly, ZSW-10/4 insulators are smeared in different contamination grades, and their visible light images are shot under illumination ranges from 10,000lux to 100,000lux. Secondly, both software methods and hardware methods are adopted and compared to eliminate the effects of illumination. After image processing, insulator surface color features in several color spaces are calculated. Results of Fisher criterion shows that hardware methods work better in eliminating illumination effects, and mean value of V component in YUV color space is selected for discriminating contamination grades. Finally, BP (Back Propagation) neural networks are established, whose testing accuracy rates are over 90% in discriminating contamination grades. Further, a general formula between mean value of V component and ESDD (Equivalent Salt Deposit Density) is obtained.

Research on the dielectric recovery of SF 6 circuit breaker based on the flow field control

The intelligent operation of circuit breaker can choose and adjust the fit prearranging work condition of the interrupter and/or operating mechanism automatically accordance with the opening message that is sent from power system, in order to improve the SF6 dielectric recovery strength. Under the conditions of breaking, the electric field and flow field of arc chamber have been calculated. Simulation shows that it has great effect of the opening velocity and the flow field distribution on the dielectric recovery. A new scheme of controlling the flow field by using the gas flow control ring is put forward. So that the dielectric recovery strength of SF6 circuit breaker becomes the controllable parameter in intelligent operation.

Design of capacitance parameter measuring instrument based on virtual instrument

In this paper, a capacitance parameters of high-precision digital measuring instrument was designed, based on the VI (virtual instruments), using LabVIEW software platform and applying current comparison measuring principle. This system possesses current comparison based on Magnetic Potential Balance Principle, PC subject, the integrated data acquisition modules and I/0 control module. Magnetic potential balance has been achieved by controlling coil turns. With the function of PC, accurate test results have been gained. Because of using the closed-loop control and the successive approximation method to control relay, the system achieves equilibrium sharply. This system has been used to test the capacitance of capacitor, dielectric loss value and the inductance of reactor, which has advantages to more accuracy and stability, convenient operation, and adjusting quickly and a wide range of uses.