After end fittings of HV insulators have been crimped onto the core by crimping machine, the entire electrical insulators are supposed to be able to bear certain specific mechanical load as they will be used on overhead lines to support conductors and other line fittings. Here let’s see how international standard IEC 61109 defines such test:
10.4 Assembled core load-time tests
10.4.1 Test specimens
Six insulators made on the production line shall be tested. The insulation length (metal to metal spacing) shall be not less than 800 mm. Both end fittings shall be identical in all aspects to those used on production line insulators, except that they may be modified beyond the end of the connection zone in order to avoid failure of the couplings.
The six insulators shall be examined visually and a check made that their dimensions conform with the drawing.
NOTE If the manufacturer only has facilities to produce insulators shorter than 800 mm, the design tests may be performed on insulators of those lengths he has available, but the results are only valid for up to the tested lengths.
10.4.2 Mechanical load test
This test is performed in two parts at ambient temperature.
10.4.2.1 Determination of the average failing load of the core of the assembled insulator MAV
Three of the specimens shall be subjected to a tensile load. The tensile load shall be increased rapidly but smoothly from zero to approximately 75 % of the expected mechanical failing load and shall then be gradually increased in a time between 30 s and 90 s until breakage of the core or complete pull-out occurs. The average of the three failing loads MAV shall be calculated.
10.4.2.2 Verification of the 96 h withstand load
Three specimens shall be subjected to a tensile load. The tensile load shall be increased rapidly but smoothly from zero up to 60 % of MAV, as calculated in 10.4.2.1 and then maintained at this value for 96 h without failure (breakage or complete pull-out). If for any reason the load application is interrupted, then the test shall be restarted on a new specimen.
Tensile load test shall be done with a tensile testing machine which can perform above mentioned test with specific mechanical load, time of tensile load and how such tensile strength is performed, increased and hold. This mechanial load testing machine shall be able to detect and identify the slipping out of end fitting and show this break to inspection people. After the test, this tensile testing machine shall record the process of test for inspector’s review.
The horizontal tensile testing machine produced by Contune International Coorperation is able to fullfil this test.
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