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What Is The Third Rail

what is the third rail

What is the Third Rail

The third rail, also called 3rd rail or conductor rail, is a type of contact rail. A train with electric energy as the main power runs on a railway composed of two steel rails. In order to supply power to the train, a live rail is added next to the railway, which is the third rail. The third rail is usually located between two rails or outside one of the steel rails. The collector (third rail contact shoe) of an electric train touches and slides on an electric third rail to transmit electricity to the train. The third rail on train tracks, together with other power supply components, forms the third rail system, which is responsible for supplying power to the tram track. Track power supply is a mature railway power supply method, and the third rail electrification is the main form of railway electrification, which is commonly used in mass transportation system.

Advantages of 3rd Rail Over Overhead Conductive Rail

Overhead conductor rail
The third rail

Overhead conductor rail and the 3rd rail have been used in urban subway and urban tram rail transit for many years, and the technology is becoming more and more mature. But the 3rd rail has more obvious advantages than overhead conductive rail.

  • The cost of the electric third rail is lower than that of the overhead conductive rail, and it is less affected by natural disasters.
  • The third rail is more suitable for installation in tunnels with smaller clearance than overhead conductive rails.
  • The subway third rail does not need to be erected under tension and is not prone to breakage accidents. Even in the event of a failure, the scope is smaller and the reliability is higher, thus reducing the maintenance workload.
  • The installation position of the 3rd rail is relatively low, there are no obvious tall parts, the urban landscape is good, and it is easier to take protective measures against electromagnetic pollution.

Main Structure of the Third Rail System

The main components of the electric 3rd rail system for the trolley tracks include the third rail, insulation supports, end elbows, expansion joints, protective covers, central anchors, electrical connections, ground connections, etc.

 third rail diagram

The third rail

The third rail is the main structure of the third rail power supply system. In the early days, the third rail was generally made of low-carbon steel, which had the advantages of wear resistance, low price and simple installation. But at the same time, it has some disadvantages, such as large self-weight, high resistivity, large power loss, and so on.

3rd rail

In order to reduce the resistivity, reduce the number of traction substations in the power supply system, and reduce the energy loss of the third rail during operation, the steel-aluminum composite third rail was developed. The steel-aluminum composite third rail is a contact rail formed by mechanically combining a stainless steel belt with an aluminum alloy profile. It adopts a special structure to make the stainless steel stuck on the aluminum alloy profile, so that it will not fall off. A high-conductivity aluminum profile is used as the conductive body, and stainless steel is used as

the top wear-resistant surface of the 3rd rail. AGICO RAIL has been deeply involved in the field of a steel-aluminum composite third rail for many years and can manufacture various types of steel-aluminum composite third rails.

Compared with the traditional low-carbon third rail, the steel-aluminum composite third rail has the following advantages.

  • The steel-aluminum composite 3rd rail has good electrical conductivity and large current capacity. The conductivity of aluminum alloy is 3-4 times that of low carbon steel.
  • The steel-aluminum composite 3rd rail is light in weight and easy to install. The weight of the steel aluminum composite 3rd rail is less than half of the weight of the low carbon steel 3rd rail with the same section, so it does not need lifting equipment, is easy to bend and has low installation cost.
  • The steel-aluminum composite third rail has good corrosion resistance, wear resistance and long service life. The sliding contact surface of the steel-aluminum composite third rail is mostly made of chrome stainless steel, which has good corrosion resistance and wear resistance, which can extend the life of the 3rd rail and the power receiving shoe.
  • The steel-aluminum composite 3rd rail has good economic benefits. In the case of the same transportation volume, the voltage and traction energy consumption required to adopt the steel-aluminum composite 3rd rail are proportionally reduced, and the required substations and transformers can be arranged farther and the capacity can be reduced. In addition, the steel-aluminum composite third rail is light in weight and low in installation costs.
Third rail contact shoe

Insulation supports

Insulation support is a device that supports and insulates the third rail in the third rail system. Generally, third rail insulators include insulator type and integral insulation support. According to the different materials, there are porcelain, epoxy resin, and silicone rubber materials.

End elbows

The end elbow is installed at the fracture of a section of the electric third rail and is used to guide the power receiving shoe to enter or smoothly leave a section of the subway third rail. The end elbow is generally processed and manufactured by the third rail on train tracks of the same model as the 3rd rail system.

Protective covers

The function of the protective cover is to prevent people from accidentally touching the third rail and other live equipment. It is generally made of glass fiber reinforced resin material.

Protective cover

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