Fang Chunhua

Research on the Silicone Rubber Sheds Performance of Composite Insulator

Ten 220 kV/66 kV composite insulators were selected to study the performance of silicone rubber sheds, which were utilized different time in the northeast of China, the hydrophobicity, loss-recovery-transference of hydrophobicity, the shore hardness, the tensile, tearing, volume resistivity and dielectric strength of silicone rubber were determined. The test results indicated that there is no obvious aging apparent of hydrophobicity characteristic of silicone rubber, hydrophobicity of composite insulators with natural contamination is better; the loss-recovery-transfer of hydrophobic descend to some extent with the increasing of operation time, and the mechanical property of the sheds material with long operation time descend evidently, the Shore hardness of material meets to the criterion demand, which has no relation with operation time, the material volume resistivity present to high performance, but material dielectric strength is lower, which has no relation with operation time.

Causes, Forms and Remedies of Substation Grounding Grid Corrosion

The information in this paper includes the basic corrosion theory and forms of substation grounding grid corrosion. In order to investigate the corrosion in substation grounding grid and acquire corrosion data to give a guide for steel grounding grids design, 21 grounding grids of substations distributed in different areas of Foshan were excavated to test corrosion rates of grounding conductors. Corrosion data show that corrosion in grounding down leads and grounding conductors in cable trenches are more serious than in the main grounding grid. Corrosive factors in the substation soil samples were measured on the spots and in the lab, and the data were analyzed using the principal component analysis method for statistics. The result demonstrated that soil resistivity, pH value, water content and soluble salts content were the key factors in substation grounding grid corrosion. Different methods available for the protection of steel grounding grids are discussed in this paper. Allowance for corrosion should be provided for both uniform and pitting corrosion while selecting the area of the grounding conductors based upon the soil corrosion data.

Composite Insulators Leakage Current Measurement System Based on LabView

Leakage current(LC) is an important parameter of composite insulators in the aging process. Inspecting the change and development of LC during artificial accelerated aging tests of composite insulators can help us to analyze the mechanism of insulators aging. In this paper, a composite insulators leakage current monitoring and analyzing system based on LabView and data acquisition card is designed. The system is capable of real-time monitoring amplitude of LC, cumulative charge, the amount of pulse and displaying LC waveforms. In order to analyze the effects for the insulators aging brought by the power frequency current and pulse current separately, the system separates them from LC. The whole current waveform during specified time can be stored through the timing storage function. The system provides a powerful tool for researching the composite insulators performances. Compared with traditional data acquisition, this system has characters of low cost, high sampling precision, convenient, flexible in use and has friendly human machine interface. The long running experience in artificial accelerated aging tests indicates that the acquisition and analyzing of composite insulators LC are high precise, stable and reliable. The system makes the measurement work of the aging test fulfilled automatically which can reduce the workload and save manpower.

Development of Coupling and Decoupling Network for Surge Immunity Test

In order to simulate the effects of lightning and switching transients on power lines, coupling and decoupling network (CDN) is necessary for performing surge tests on electrical and electronic equipment. This paper presents a particular analysis of the circuit of CDN and design details according to the requirement of the standard IEC 61000-4-5. The CDN circuits are simulated by electromagnetic transients program (EMTP) to judge the suitability of the selected component values and performance of the designed CDN. Simulation results also show that increasing of decoupling capacitance or inductance can reduce the residual surge voltage on the power line inputs of the CDN. Based on the voltage drop control and residual surge voltage limiting, smaller decoupling inductance and relatively larger decoupling capacitance should be chosen if EUT has a higher rated current. The CDN developed according to the simulation results satisfy the design specifications well.

Observation of Lightning Current and Ground Potential Rise in Artificially Trigged Lightning Experiment

Lightning current and ground potential rise (GPR) results of artificially trigged lightning experiment in Binzhou of Shandong Province during the summer of 2006 are described in this paper. The variation of grounding resistance of grounding electrode is analyzed according to the data of experiment. From the waveform of lightning current, it can be found that the process of lightning flash has two return-strokes. The amplitude of the first return-stroke is 41.59 kA with 6.02/20.24 mus waveform, and that of the second return-stroke is 29.59 kA with 4.8/11 mus waveform. The previous study done by other authors on impulse ground resistance is always limited in the laboratory, which can provide the standard impulse current instead of the factual circumstance. Transient grounding resistance (TGR) including two small return-strokes response is obtained. ATP Simulation is used to calculate the impulse grounding resistance which compares to the factual circumstance. There is time difference between peak current and peak voltage, but the simulation can not tell the difference, which means their front time Tf and time to half value Tt are identical. That is because the simulation model did not take the spark discharge and its electrical parameter change into consideration. The results can help study the process of artificially trigged lightning, meanwhile it proposes the necessity to consider grounding electrodes impulse characteristics under lightning current.