Test and investigations on extra high-tension insulators: From a purchasing engineer's point of view, with special reference to methods of test for acceptance, tests for porosity and deterioration

Owing to repeated failures (the number of which increased as time went on) of 66,000-volt transmission line insulators (pin type) of the first Hydroelectric undertaking, carried out by the New Zealand Government, in 1914, and having in mind that Hydroelectrical Power was to be developed to the utmost of the Dominion's power resources — of which there are many — the investigations contained herein were commenced at the suggestion of Mr. E. Parry, B. Sc. M. I. E. E. late Chief Electrical Engineer to New Zealand Government, and has been continued for the past five years with the sanction and support of Mr. L. Birks, B. Sc. M. I. E. E. Chief Electrical Engineer to New Zealand Government, with a view to ascertaining the cause of such failures. It is the purpose of the paper to show 1. To what extent deterioration has set in on the 66,000-volt line referred to. 2. That the cause is due to the fact that the insulators were initially porous. 3. That tests at present in vogue with regard to ascertaining the porosity of insulator porcelain are totally inadequate, as the authors consider, immersion of the complete unbroken insulator under a pressure ranging from 1500 to 2000 lb. and the total amounting to 250,000 to 300,000 lb-hours the least that will give reliable results. 4. That non-porous insulators can be made that will remain good in service for an indefinite period and withstand perfectly the tests for porosity as recommended. 5. That individual testing with high frequency seems to be the only reliable method for testing for dielectric strength. 6. That a percentage test of each batch of insulators by the maker is unsatisfactory, because unless each shell of each insulator, in the case of pin insulators, and each disk in the case of suspension insulators, is definitely flashed over before being put to service, then breakdown trouble seems bound to ensue. 7. There is room for more cooperation between the insulator manufacturer and the purchasing engineer in regard to acceptance tests and the handling and maintaining of the insulator in service. If manufacturers will not agree to the tests as recommended by the authors, being made in the factory, then in countries such as this (New Zealand) which is situated so many thousands of miles from the point of manufacture, a public testing bureau should be established where undertakings could be arranged for, such tests to be made as described herein, when the cost of replacing the failures should be borne by the manufacturers. 8. That it has been found in New Zealand we have the necessary materials from which insulators can be and are being made, that will withstand the tests described equal to the imported wares.