Toughened glass insulators are made from glass materials, which can be divided into tongue and clevis disc insulators, spool insulators, long rod insulators which shall be required by inspecifications.
The glass used for insulators shall be heat strengthened soda lime glass and shall be smooth and free from defects and blemishes which might adversely affect the life of the insulator. The glass shall be completely non-porous and its impact strength shall be at least 35 Nm. The co-efficient of thermal expansion of the glass shall be between 8 and 9 x 10-6 mm / oC.
The impact strength and the co-efficient of thermal expansion of the glass, is to be stated in Attachment 1.
The insulators offered for transmission type disc insulators and the fog insulators (Items 20 to 23) shall be of high reliability class with a guaranteed service failure rate of less than 2 per 10,000 units per year. The tender documentation shall include documented service history from users as evidence of performance claimed.
The grade of malleable cast iron shall be either AS 1832/JMW400-5 or AS 1832/JMB350-10.
The grade of malleable cast iron is to be stated in Attachment 1.
Fittings which are forged or otherwise worked to the final shape shall be normalised after all forging operations.
Tongue and clevis disc insulators shall comply with designation U70C as defined in AS 60305 and be supplied complete with a coupling pin type 16C and one (1) off stainless steel humpback split pin in accordance with Figures 3.1 and 3.2 of AS 2947.3. Ferrous metal fittings shall be hot dip galvanised to AS 4680. The thickness of the zinc coating shall comply with the acceptance criteria set out in clause 26 of AS 2947.1. Preference will be given to the insulators that exceed these criteria. Further all insulators shall be supplied with zinc sleeves.
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