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Materials of the composite long rod insulator

 The requirement about the materials of composite long rod insulators in some tender.

1. Core of the composite long rod insulator
It shall be a glass-fiber reinforced (FRP rod) epoxy resin rod of high strength. The rod shall be resistant to hydrolysis. Glass fibers and resin shall be optimized. The rod of the composite long rod insulator shall be electrical grade corrosion resistant (ECR), boron free glass and shall exhibit both high electrical integrity and high resistance to acid corrosion.
2. Housing & Weathersheds of the composite long rod insulator
The FRP of the composite long rod insulator rod shall be covered by a seamless sheath of a silicone rubber compound of a thickness of minimum 3mm. The housing & weathersheds of the composite long rod insulator should have silicon content of minimum 30% by weight. It should protect the FRP rod against environmental influences, external pollution and humidity.  It shall be extruded or directly molded on the core. The interface between the housing and the core must be uniform and without voids. The strength of the bond shall be greater than the tearing strength of the polymer. The manufacturer shall follow non-destructive technique (N.D.T.) to check the quality of jointing of the housing interface with the core. The technique to be followed with detailed procedure and sampling shall be furnished by the Supplier and finalized during finalization of MQP.
The weathersheds of the composite long rod insulator shall be of alternate shed profile. The weathersheds shall be vulcanized to the sheath (extrusion process) or molded as part of the sheath (injection moulding process) and free from imperfections.  The vulcanization for extrusion process shall be at high temperature and for injection moulding shall be at high temperature & high pressure. Any seams / burrs protruding axially along the composite long rod insulator, resulting from the injection moulding process shall be removed completely without causing any damage to the housing.  The track resistance of housing and shed material shall be class 1A4.5 according to IEC60587. The strength of the weathershed interface shall be greater than the tearing strength of the polymer. The composite long rod insulator shall be capable of high pressure washing.
3. End Fittings of the composite long rod insulator
End fittings of composite long rod insulator transmit the mechanical load to the core.  They shall be made of malleable cast iron spheroidal graphite or forged steel.  They shall be connected to 
the rod by means of a controlled compression technique.  The manufacturer shall have in-process Acoustic emission arrangement or some other arrangement to ensure that there is no damage to the core during crimping. This verification shall be in-process and done on each insulator. The system of attachment of end fitting to the rod shall provide superior sealing performance between housing and metal connection. The gap between fitting and sheath shall be sealed by a flexible silicone rubber compound. The sealing shall stick to both housing and metal end fitting. The sealing must be humidity proof and durable with time.
End fittings shall have suitable provisions for fixing grading rings at the correct position as per design requirements.
4. Grading Rings of the composite long rod insulator
Grading rings shall be used at both ends of each composite insulator unit for reducing the voltage gradient on and within the insulator and to reduce radio and TV noise to acceptable levels. The size and placement of the metallic grading rings shall be designed to eliminate dry band arcing/corona cutting/ exceeding of permissible electrical stress of material. The insulator supplier shall furnish design calculations using appropriate electric field software showing electric field at surface of housing, inside housing & core and at the interface of housing and metal fittings with the proposed placement and design of corona ring. Grading rings shall be capable of installation and removal with hot line tools without disassembling any other part of the insulator assembly.
The design & supply of grading rings shall be in the scope of the composite insulator supplier.
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