Contaminated partial arc resistance test for sir materials used for outdoor insulators
There are several test methods used to evaluate the property of the resistance to arc for insulating materials. However, most of them are designed for the use of insulating materials indoors or in the cabinet. The necessity of the new test method for the materials used outdoors, which would allow examination of the materials under the discharge that occurred in the contaminated condition, had been discussed in the related research committee in JIEE. The contaminated partial discharge repetitively gives minor damage onto the insulator surface that will result in visible erosion and cutting of the sheds of HV insulators after a long time. In the test, the discharge with a similar nature to that on the contaminated insulator should be used.
In this paper, the test method named surface arc between the electrolyte test (SABET) is introduced in which the SiR test specimen will be exposed to the intermittent contami-nated arc. The test specimen consists of two cups touching each other across a wall. The bottoms of the cups were filled with contaminating liquid of NaCl solution. The contaminated partial arc that has the same nature as that of an outdoor insulator was generated along the wall surface. Under the discharge current of 30 mA, various combinations of the arc duration and the interval had been tried in the experiment to find the severity order of stress intensity. The results, evaluated by the number of exposures to the intermittent arcs before a breakdown to make a hole on the wall due to the accumulation of damage by the intermittent arcs, showed that a longer duration and a shorter interval gives stronger stress in general. However, the number of exposures to the arcs before breakdown was distributed over a wide range under a certain stress condition.
Next, the process to the breakdown has been studied in detail, which can be categorized in three regions. The first region: faults occurred up to 200 times exposure to the arcs showed the rapid growth of track. The second region: faults occurred from more than 200 times to 1500 times exposure to the arcs, where the generation of the carbon grains and evaporation of them almost balanced. The wide variation of the result was explained by a microscopic local non-uniform mixture of the additives such as silica filler and ATH grains among SiR that would make weak points in the material. The last region: the nature of the by-product seems to be changed slightly, where much slower progress of the damage resulted in the number of exposures to the arcs before a breakdown to became as much as several thousands.
Finally, it has been discussed to use the proposed test method: SABET as the evaluation of resistance of intermittent contaminated arcs for the materials covering outdoor insulators, considering the requirements for the insulator test.
File Size: 662,1 KB
Pages NB: 6