End fitting of railway insulator of Indian market
The end fittings of silicone composite insulator for 25KV railway overhead traction have specific requirements. The end fittings shall be made of spheroidal graphite cast iron to grade: 400/15 of IS:1865-1991 or forged steel fittings to BS-970(Part-II). Approval of the type test of the insulator implies employment of metal fittings of the particular make, whose material and design used during type test and the same shall be approved. In the event of insulator manufacturer resort to change in make, material or design of metal fitting, in house prototype tests (Mechanical tests) shall be required to be repeated. In addition to the above, RDSO may carry out the inspections of incoming metal fittings. Both the metal fittings of an insulator shall be of the same material and making process.
End fittings of insulators shall be free from cracks, seams, shrinks air holes or rough edges. The surface of metal parts shall be smooth with the projecting points or irregularities which may cause corona.
The metal fittings of insulators shall be hot-dip galvanized in accordance with specification No. ETI/OHE13(4/84)-latest, after machining. The galvanized surface shall be smooth, uniform adherent, reasonably bright continuous and free from imperfections such as flux, ash rust, stains, bulky white deposits and blisters. The mass of zinc coating on threaded portion of the hook of stay arm insulator shall not be applicable. The minimum weight of zinc coating shall be 1000g/sq meter (minimum) for all types of metal fittings and 750 g per sq meter for stay arm insulator hook.
The threads of the tapped holes in metal fittings of stay arm, operating rod and post insulator shall be cut after galvanization and protected against corrosion by application of suitable grease. The threads of hook for stay arm insulator shall be cut before galvanization. All the tapped holes shall be suitable for fixing galvanized bolts and shall conform to IS:4218 (Part I TO VI)-latest.
This is one of an Indian project for railway composite insulators, though this technical requirement of fittings is not universal for all project in India, but we can see that the requirement of insulator fittings usually conform to more than one technical standard, like BS, IS, and sometimes insulators Indian market comply with IEC standard. No matter which standard they follow, end fittings of silicon composite insulators are significant in overhead line running and shall be well inspected and tested before put into use. The testing machine produced by famous Chinese brand “Contune Intl” and its collaborating brand “Conhen” is proved to be capable for such mechanical loading test of end fittings as well as complete insulators, for tensile load test, cantilever test and other test described in different technical standard.