Switchpoint and Track Heating Trackside Control Cubicles

The Advantages of GrayBar Self-regulating Switchpoint Heating

Many Constant Wattage Systems can involve modifications to the Permanent Way, extensive track possession times, can effect the integrity of signalling systems during installation and maintenance and are frequently prone to element failure.

GrayBar Self-Regulating Strip Heating Systems suffer none of these problems and provide the following advantages;

  • Low power usage with the ability to respond directly to changes in ambient conditions and precipitation.
  • Optimum power consumption (typically 30% saving).
  • Focuses the heat onto the critical areas of the point between the ‘Heel’ and ‘Toe’ where and when it is needed.
  • High long- term vibrations and impact resistance.
  • Non-Filament Element giving long life (40+ years) with a 10 year service guarantee.
  • Element cannot overheat or burn out.
  • Flexibility of product; Easily conforms to rail profile and other Permanent Way obstructions.
  • ‘Insulated ‘ product design giving additional immunity and compatibility with signalling systems and a strong safety case for mandatory use on 3rd and 4th DC Railway Networks.
  • Long circuit lengths are possible for High Speed Turnouts.
  • Supplied as a customised kit of parts.
  • No unreliable Temperature Probes are required on track.
  • A simplified and reliable Control System can be installed.
  • Easily transportable to Site.
  • Installation is fast and straightforward minimising Track Possession Times.

 

Cross Section through Self-regulating Heater Strip

Self-regulating Heater Operating Characteristics

The semi-conducting core polymer has a positive temperature coefficient (PTC) characteristic, which provides a variable resistance to current flow, directly dependant on temperature. Therefore at low temperatures the electrical resistance of the heater core is low, allowing higher current flow and higher heat output. Core temperature is a function of ambient temperature and wind speed.

As conditions become more severe, with decreasing ambient temperature or increasing wind speed, the heater increases output to maintain the rail above freezing point. This effect occurs independently at every microscopic length of element along the same heater strip. Therefore exposed sections of rail will receive more heat than those in sheltered areas, between platforms for example.

The self-regulating heater cannot overheat and therefore, unlike constant wattage heaters, suffer burnouts where it is not in contact with the rail. For example, to bypass stretcher bars or rail chairs and other obstructions.

Where the heater is cold, the core contracts microscopically, creating many electrical paths through the conductive carbon. The flow of electricity through the core generates heat.

In warmer sections, the core expands microscopically, erupting many electrical paths. The increased electrical resistance causes the heater to reduce its power output.

In hot sections, the microscopic core expansion disrupts almost all the electrical paths. With this high resistance to electrical flow, power output is virtually zero.

 

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