What is the difference between 3rd rail and 4th rail?
In 3rd rail systems, the current returns to the supply though the ordinary running rail(s). In a 4th rail system, a second insulated rail is provided, and current return is via a second set of pickup shoes through to the second insulated rail.
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More than 30% of the UK rail network currently uses a third rail to power the train, commonly in the southeast and in dense urban areas around the country. One of the significant advantages of third rail electrification is its cost-effectiveness.
Train campaign. The third rail is probably one of the most difficult dangers to see. It looks just like an ordinary rail, but it carries 750 volts – easily enough to kill you.
Ghost trains – also known as parliamentary trains – date back to the 1960s and are services that run over a line – or stop at a station – so infrequently that they often go unnoticed.
The four rail system was first used in the early twentieth century. The isolated traction current return allowed a train's position to be detected using DC track circuits, and reduced any earth leakage currents that could affect service pipes, telephone cables, or cast iron tunnel liners.
When Britain enjoys a summer heatwave, rails in direct sunshine can be as much as 20°C hotter than air temperature. Because rails are made from steel, they expand as they get hotter, and can start to curve this is known as 'buckling'.
The maximum speed currently possible in the UK is 186mph, achieved by Eurostar trains on the HS1 line between London and the Channel Tunnel. The HS1 line is used by Eurostar services and Javelin commuter services from Kent, although the latter have a max speed of 140mph.
Modern trains can travel seamlessly from conventional track to high-speed track. They simply travel slower while on conventional track. Passenger service on the conventional freight lines that criss-cross the United States today is limited to 90 mph at best.
This is why birds do not die from landing on power lines, and subway rats do not get electrocuted even if they run across the third rail; they are not bridging the energized wire or rail to a grounded part of the structure.
TIL Rats and birds don't get electrocuted by the third rail because they don't form a grounding connection. This is not some property inherent to rats and birds. This is because when they touch the third rail, they aren't touching anything else.
As wireless technologies advanced in the 1960s, freight railroads began adding extra locomotives to the rear of trains to give them enough power to climb steep hills. This is how distributed power was born.
Third-rail supply is employed only by urban rapid-transit railroads operating on low-voltage direct current. … transmute the overhead wire or third-rail current to a supply of variable voltage and frequency suitable for feeding to three-phase alternating-current motors.