Sim's Electrical Companion
Electric Railways
Electric railways are commonplace in the UK. There are several different systems of rail electrification:
Overhead lines
The most common system in the UK is overhead lines supplying 25kV The train connects to the system by use of a retractable Pantograph or Pan. The return path to the substation is via the running rails. This system accounts for approximately 60% of the UK rail network.
Other overhead line systems include:
120V DC Seaton Tramway, East Devon
550V DC Wirral tramway & National tramway museum
600V DC Blackpool tramway
750V DC Sheffield Super tram, Manchester Metro-link, Edinburgh Trams, Nottingham Express Transit, Croydon Tram-link & Midland Metro
1500V DC Tyne & Wear Metro at 48miles long it is the last remaining 1500V DC system in operation.
Third Rail System
The second most common system in use in the UK accounting for approximately 30% of the rail network. The most common system supplies 750V Direct Current via the third rail. The return route to the substation is through the running rail.
Other 3 Rail systems include:
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110V DC - The Volk’s railway in Brighton is the oldest, operating, narrow gauge, electric railway in the world. Built by Magnus Volk it first started operating in 1883.
250V DC Top Contact - Hythe Pier Railway - The oldest pier train still in operation since 1881.
600V DC - Glasgow Subway runs a circular 6.5 mile system since 1935.
630V DC Top contact - Isle of Wight (Island Line),
750V DC Bottom contact - London Docklands Light Railway.
Bottom contact improves the safety of track-side personnel and its stability in snowy condition
Fourth Rail Systems
London Underground uses a 630V DC 4th rail system. It is possibly going to be increased to supply the 750V DC system so more equipment can be standardised. The network covers approximately 250 miles and is the most extensive system in use in the UK aka The Tube.
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Beaulieu Motor Museum monorail uses a 4 Rail 100V system and is a great way to enjoy some of the exhibits on a clement day.
Main Features of an Electric Train
Note the illustration does not show exact locations of the installed equipment. Most is contained under the passenger accommodation.
1 AC Supply – Most commonly 25kV in the UK
2 Pantograph / Pan – Maintains connection to the supply conductors by use of a sprung mechanism or pneumatic response. The occasional interruptions in supply will be smoothed over by the use of batteries and capacitors. The Pantograph can be lowered to intentionally de-energise the medium voltage supply.
3 Circuit Breaker – Most commonly Vacuum Circuit Breakers (VCB’s) in the UK or Air Circuit Breakers in Europe. These are to prevent overloading and disconnect faults.
4 Transformer - Converts Medium Voltage Alternating Current (>1000V) to Low Voltage AC (<1000V)
5 Main Rectifier – Converts Alternating Current (AC) to Direct Current (DC). Some of the trains systems can use the DC supply and can be fed from here.
6 Inverter – Converts DC to three phase AC. It is an easier process to convert from DC compared to single phase AC hence this process. Three phase supply created would normally be line to line (U) of 400V and line to earth (Uo) 230V. 230V supply can also feed auxiliary services like Passenger socket, USB Transformers, lighting & signage etc.
7 Asynchronous motor – Runs on the three phase 400V supply – There may well be more motors than shown in the illustration.
8 Motor Blowers – Usually run on the same three phase supply as the motors. The drive motors develop a great deal of heat and the blowers are used to cool them and increase their in service lifetime. Supplied by Auxiliary inverters.
9 Auxiliary Inverter – Used to supply Battery charger rectifier, cooling fans & compressors.
10 Axle Brush – Used to direct Medium voltage to the running rail to return to the supply system transformer.
