AT THE REQUEST of infrastructure maintenance contractor GTRM, a 25 kV polymeric post insulator has been developed specifically for use in upgrading catenary for 200 and 225 km/h operation on Britain’s West Coast main line. Once the polymeric insulator has been approved by Railtrack, it will be used to replace A26 and A27 porcelain insulators.
The main advantage, compared with porcelain, is the ability of polymeric insulators to withstand mechanical shock without breaking into pieces. An overloaded porcelain insulator which breaks in two normally results in the contact wire dropping, and a passing train can become de-wired with serious consequences. Damage by vandals is likely to be less serious, and weight reduction from 33 to 16 kg makes installation easier.
The EVA housing that includes the insulator sheds is moulded on to a core of resin-bonded glass fibre, that is crimped or swaged within the metal end fittings. It is the core that provides mechanical strength, but direct moulding of the housing (which was previously shrink fitted) creates a reliable bond that prevents the ingress of moisture. A seal is also applied between the RBGF core and the end fittings.
EVA insulators have proved to be highly resistant to tracking and flashover in highly polluted situations. Experience in Japan in a tunnel exposed to diesel exhaust and a saline atmosphere from the sea nearby showed that EVA required less frequent washing and had fewer flashovers than other types of insulator in the same location.
Reader Enquiry Numbers
Tyco Electronics, Ireland 136
CAPTION: A26 porcelain insulator (left) compared to the EVA polymeric post design (right)
