AC EMU Group

FAQ

What is an AC EMU?

Alternating Current describes the type of electricity the train uses. If you plot a graph of current or voltage against time, AC (generally) follows a sine wave, like "~", as opposed to DC (Direct Current) which plots a steady line "-". Although over a given period of time AC appears to cancel itself out, it still produces power in its negative phase - the current simply flows in the opposite direction. The control circuits in the train take care of the change in direction so that the motors don't turn one way then the other.

For most trains, the AC is rectified (thus becoming DC) before being fed to the motors, although some newer trains use AC throughout their systems. The advantage of using an AC power supply is that it allows a higher amount of power to be supplied, and the loss of power in the supply cables is less.

An AC supplied AC traction motored train actually rectifies DC then rectifies AC at the required frequency. The input frequency is 50 Hz whereas the frequency to the motors is variable. This is why they seem to sing to you as they accelerate, increasing the frequency and acoustic note.

Multiple Unit describes a type of train which is (generally) made up of two or more coaches permanently coupled together which can be run as a train on its own (i.e. not requiring a separate locomotive), but which can also be coupled to another such set of coaches to make a longer train all under the control of one driver. Formations of 2, 3 and 4 carriages per unit are the common, although there are others.

Why Save One?

Cynically one may ask the question, "Why save anything once you have finished with it?" However there are often very good reasons for keeping examples of "things". The rapid progress in technology often means that devices become obsolete within a very short period of time. The railways, over a period of 175 years, has a rich history of technological advancement, from the very first horse drawn wagons to the latest high-speed, tilting trains of today.

Specifically regarding AC EMU's, there is a history to follow going back at least 100 years. Changes in aesthetic design are the most obvious, but behind the scenes the electronics nowadays bear very little or no resemblance to the originals. For example until relatively recently, all AC EMU's required the use of a rectifier to convert the AC supply to DC for the motors. Rectifier technology advanced from the point of requiring relatively large oil cooled devices with hundreds of diodes constructed from a substance called "germanium" to lightweight air cooled devices using a relatively small number of silicon diodes; and now of course, to the point where rectifiers are no longer needed at all.
Likewise, power control circuits have evolved from using a "tap changer" where different voltages were fed into the rectifier from a number of voltage connections on the transformer, to "thyristor" control circuits which provide infinitely adjustable power.

Why are you saving other items?

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There is more to the history and development of AC EMU's than just the vehicles themselves. Also, if the Group was to be looking after any vehicles, having the Manuals, Diagrams and Pictures would be a great help.

Where Would One Go if Saved?

There are a number of possible locations, which would depend on the type of vehicle saved and the uses planned for it at that location. The Group's Class 308 vehicle is currently located at The Pumphouse Museum, Walthamstow.

Why Become a Member?

Preserving obsolete trains is a very expensive business. Without pooling the resources of several dozen or even hundred people it is impossible. For example one of the major costs associated with preserving EMU's is the fact that many were built using asbestos. By law the asbestos has to be removed before the train can be sold, and it can cost several thousand pounds as it is a highly specialised, dangerous procedure to carry out. Furthermore, there are (potentially) running costs, storage costs, renovation and restoration costs... the list could be endless.

Additionally, there is the physical care and attention in terms of man hours. Many of the likely candidates for preservation will have been unused for months or even years, and will require maintenance and cleaning on an ongoing basis.

Do you offer Child Membership?

Yes, we offer Junior Membership for anyone under 16 years old at the time of joining.

How much is it?

Membership rates for One Year are - £12 Adult - £8 Junior

Can I Join Online?

Yes, see this page.

What Do I get?

As a Member of the Group you will get the following

A Bi-Monthly Newsletter

A number of members' discounts

The chance to volunteer in the running of the group

Restoring vehicles that the Group may be owner or custodian of

Access to the 'Members Only' Yahoo Group

Where can I see AC EMU's in action?

Currently, AC EMU's are in service in the following areas:
London:
Liverpool Street routes to Southend, Braintree, Colchester, Clacton/Walton, Harwich/Ipswich, and Chingford, Enfield, Hertford, Bishops Stortford and Stansted.
Fenchurch Street to Southend.
Kings Cross/Moorgate to Hertford/Stevenage, Peterborough, Cambridge and Kings Lynn.
St Pancras/Moorgate to Bedford.
Euston to Birmingham, Crewe, Liverpool and Manchester.
Paddington to Heathrow.

Leeds:
Routes from Leeds to Ilkely, Skipton and Bradford and Doncaster

Plus areas around Edinburgh and Glasgow.

In addition to the operating services, there is a Preserved AC EMU at Summerlee Museum