Electrokinetica The Electro-mechanical Museum

Air Ministry Mark II 20kVA Mobile Generating Set - Arrival

The generator comes to London

Genset radiator

Genset radiator

Lucien acquired the plant with a view to taking it out on the road to power outdoor ‘heritage’ events. It was initially parked up in Northamptonshire and at first it was hoped that a ballast tractor could be used to tow it down to the workshop in London. Whilst the trailer was generally sound, the brakes needed work and the tyres were in uncertain condition. Time did not permit remedial work being done on the spot, so it was arranged for Edward to bring it in on his low-loader. A full inspection was carried out on arrival. Due to the originality of the outfit and the nostalgic ambience inside the trailer we decided not to overhaul it completely, but to carry out specific repairs to bring it up to spec. The essential works were identified as follows:

Work begins

Alternator couplings

Alternator couplings

The first task was to locate coupling parts and other mechanical spares. Some were available as ‘new old stock’, others were located on derelict engines, a few had to be made in the workshop. A separate line of investigation was started in pursuit of original documentation. Because the set was not assembled by Lister, their documentation only covered the engine; the familiar and comprehensive plant handbook issued with most of the Dursley-built sets never existed for this model. Lister expert David Harris gave us the historical background, while radar technical man Don Adams pinned down the specifics about this model and alerted historian Bob Jenner. The original Air Ministry document ‘Air Publication 2526N’ was tracked down by Bob at RAF Neatishead in Norfolk, where director Doug Robb kindly let us scan it. Armed with this, and Don Adams’ original course notes taken down during the RAF technical briefings given to radar crews and engineers, which he helpfully sent us in electronic form, we were able to establish the whys and wherefores of the set’s complex switching system and determine what had been altered for the Mass Radiography duty.

Unravelling the modifications

A plate on the switchboard identified the ‘Isleworth Garage’ as the contractor responsible for modifications on behalf of the Ministry of Works. The non-original flywheel, which bears a later serial number than the engine, seems to have been fitted to provide a ring-gear for the starter motor. (electric start was often omitted from WD sets as there was usually a more reliable supply of manpower than of battery power!) The fuel tank had been removed from the set and fitted under the floor, making it easier to fill from outside, for which purpose a fuel lift pump had been added. All handy improvements, courtesy of Isleworth Garage and the MoW. But what had they done to the switchboard! Switches had been altered and dismantled, busbars cut and rearranged, a transformer and fuses were missing... Plenty of work would be required to restore the board to its original configuration. The likelihood remained, however, that the set saw more service with the Mass Radiography Unit than with the RAF, so it was decided that most of the modifications should be left in place, with a small amount of (reversible) reinstatement of missing parts.

Genset switchboard

Genset switchboard

Switchboard innards

Switchboard innards

Switchboard layout

Switchboard layout

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