Composite long rod insulators test procedures
Author:Summer   time:2/22/2016 9:53:29 PM  read:548times

Composite long rod insulators test procedures are referred to the test standards, the test procedures in the paper were as follows which including wetting and flashover testing.

Preparation
Before the tests, all samples were carefully cleaned so that all traces of dirt and grease were removed and dried naturally. The surfaces of the samples were coated by a very thin layer of dry kieselguhr to destroy the hydrophobicity which would be at the degree of WC4 or WC5. Because the layer of kieselguhr was very thin, the effect of the kieselguhr on non-soluble deposit density NSDD (in mg/cm2) could be neglected.

Article polluting
In 1 hour after preparation, the solid layer method was used to apply to the pollution layer on the samples where sodium chloride and kieselguhr were electric and inert materials, respectively.
The ratio of Salt Deposit Density SDD (in mg/cm2) to Non-Soluble Deposit Density NSDD was 1:6 and the values of SDD/NSDD were 0.03/0.18, 0.05/0.30, 0.08/0.48, 0.15/0.90 mg/cm2, respectively.

Arrangement
The tested insulators were equipped by two corona rings on the ends and hung up vertical in the chamber. The minimum clearances between any part of the samples and any earthed object were larger than 3.5 m, which satisfied with the requirements in.

Wetting
After 24 hours natural drying, the pollution layer on the insulators was wetted by the steam fog, the inputting intensity of fog was 0.05±0.01 kg/h•m3. The hydrophobicity would gain a certain recovery and transfer after 24 hours natural drying of the polluted samples, which would be different from the tests after only 1 hour drying. The pollution layer on the insulators could be wetted completely after 7-15 minutes time. In the whole wetting process, the temperature in the chamber was controlled lower than 35 ℃.

Flashover testing
After the pollution layer was wetted completely, dc voltage was applied to the samples. A negative polarity applied voltage generally result in lower flashover voltage than does positive polarity for suspension (cap-and-pin) type insulators, but no substantial polarity differences have been experienced with long-rod insulators in tests
Only one sample of Type A, B, C and D, 5 times polluting were carried out at one salt deposit density. For every time polluting, 5-7 times flashover tests were carried out, in which 3-4 flashover voltages, deviating from their average lower than 10%, were valid values. The flashover voltage Uf (in kV) was the average of 19 valid values at the salt deposit density and the standard error σ (in %) was calculated with the 19 valid values.
For Type E, there were 3 samples, only 3 times polluting were carried out for every sample at one salt deposit density. 4-5 times flashover tests were carried out for every time polluting, in which 3 flashover voltages, deviating from their average lower than 10%, were valid values. The flashover voltage Uf was the average of 27 valid values and the standard error σ was calculated with the 27 valid values.

Simulation of high altitude
The low air pressure was used to simulate the high altitude. The air pressure P (in kPa) is the synthetical reflection of the air temperature t (in ℃), the relative density δd of dry air and absolute humidity ha (in g/cm3) of air, thus, P can be used to character the influence of the air parameters on the discharge voltage. Shows that the relationship between the air pressure and the altitude H (in km) is as following:
In this paper, the altitudes of 232 m and 2500 m were simulated in the chamber, whose corresponding air pressures were 98.6 kPa and 74.6 kPa, respectively.
For the artificial pollution tests under the high altitude conditions, the air in the artificial climate chamber was taken out so that the air pressure were 5-7 kPa lower than calculated value corresponding the pre-concerted altitude, then the steam fog was used to wet the sample. When the sample had been wetted completely and the air pressure in the chamber had reached the calculated value, the flashover test was carried through. In the whole test process, the air pressure in the chamber should be kept invariably.


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