BS/EN 62621-2016 pdf download.Railway applications Fixed installations Electric traction Specific requirements for composite insulators used for overhead contact line systems.
4.1 General
Composite materials and polymers permit the manufacture of insulators for use on outdoor overhead contact line systems. The insulators consist of an insulating core which bears the mechanical load, a polymeric housing which protects the core, and end fittings by which the load is transmitted to the core. These materials allow special applications in overhead contact line systems (including in-running section insulation and flexible supports) and are also used for their advantages of lightness, resistance to vandalism and pollution performance. Despite many common features of design, the materials used and the construction details employed by different manufacturers may be quite different and may lead to different performance parameters.
Electric traction overhead contact line systems applied for railways have several characteristics not associated with power lines. They are of low height and run through urban areas, making them targets for vandalism. They are incorporated in bridges and tunnels, built for rolling stock only, and fit into small spaces. They suffer close proximity to railway generated pollution and, in tunnels and bridges are not washed by natural rainfall. They suffer movement and snatch loads due to normal pantograph contact with the wires. When used as in-running insulators, they suffer mechanical forces and abrasion by the pantograph passing at high speed where the polymeric housing may suffer deformation, tearing and parting from the core (see 4.10).
Some tests have been grouped together In this standard as “design tests”, to be performed only once on insulators which satisfy the same design conditions. As far as practical, the influence of time, circumstance and climate on electrical and mechanical properties of the components (core material, housing, interfaces etc.) and of the complete composite insulators has been considered in specifying the design tests so that a satisfactory life-time may be expected under normally known stress conditions of overhead contact line systems.
The high number of insulators installed in a restricted environment of an operational railway with limited access for maintenance or installed in harsh environmental conditions, requires a high level of reliability at the appropriate electrical insulation level for the system voltage, Including temporary and transient overvoltages. and a high level of mechanical integrity. In this case, a reasonable safety factor for mechanical and electrical properties of the insulators shall be agreed between the manufacturer and customer.
4.2 Environmental conditions
Environmental conditions such as temperature, humidity, vibration, solar radiation, pollution. etc., can have serious effects on the electrical and mechanical properties of insulators. The aging of housing material and interfaces, exposure of the core to environment and the corrosion of end fittings shall be given special consideration. When used for lower temperature. the behaviour or brittle property of the housing material and interfaces shall be considered.
NOTE When temperature falls below the crystallisation or glass transition temperature of the housing, its elasticity becomes lost This change Is reversible If a temperature rncrease takes place.
4.3 System voltages and frequencies
System voltages and frequencies specified by IEC 60850:2007 are generally applied for this standard. Values of standard system voltages (phase to ground) and the correlation between nominal voltages of the railway power distribution system and the required insulation voltages for circuits of equipment which are intended to be connected to these systems are shown in Table 1 of IEC 60850:2007.
The purchaser shall provide information on the railway electrification system and operating requirements which may affect the design of insulators.
NOTE Purchaser requirements are given in Annex A.
The dry lightning impulse withstand voltage shall be at least equal to the rated impulse voltage defined in IEC 62497-1:2010. The wet power frequency withstand voltage shall be at least equal to the short duration power frequency test level defined in IEC 62497-1:2010.
The rated impulse voltage for circuits powered by electric traction contact lines are shown in Table A.2 of IEC 62497-1:2010. Overhead lines are considered a case of inherent control. The rated insulation level is based on statistical and risk considerations. Therefore the rated impulse voltage is chosen among the preferred values given in Table A.2 of IEC 62497-1:2010, but irrespective of the correspondence with the insulation voltages and of the overvoltage levels stated in said table.
Table A.2 of IEC 62497-1:2010 is based on the worst dielectric conditions of electrodes. In overhead lines, different conditions are present and by consequence different clearances given in established standards or regulations such as IEC 60913 are allowed.
4.4 Creepage distance
The dry arcing distance, creepage distance and geometrical shed profile electrically define an insulator. Creepage distances shall be dimensioned according to the highest permanent voltage of the system. Consideration shall also be given to the insulation material and its behaviour in polluted conditions. The manufacturer may recommend greater than the minimum creepage distance to give adequate life for that material.
The overall shape and size of the insulator is defined by the customer’s spatial requirements. the mechanical and electrical performance requirements and its compatibility with existing equipment. The manufacturer can decide on shed profile.
Additional railway environmental pollution may be generated by traction braking systems, diesel and steam trains which run under electrified lines. The exhaust from steam trains is very hot (> 200 C) and should not be allowed to play on insulators. BS/EN 62621-2016 pdf download.