Metadyne
It is also similar to an amplidyne except that the latter has a compensating winding which fully counteracts the effect of the flux produced by the load current.
[2] Rosenberg later became the chief electrical engineer for Metropolitan-Vickers, and his machine produced a cross field by applying a short-circuit to an additional set of brushes.
The main one was the use of the constant-current output for the control of traction motors on electric vehicles and the operation of cranes, areas in which he had some practical experience, following trials in conjunction with the Alsthom Company in France.
[4] Unlike Rosenberg's solution, Pestarini, who later became a Professor at the Istituto elettrotecnico nazionale Galileo Ferraris in Turin, connected the additional brushes to an external supply to produce a transformer metadyne.
[4] Development work at Metropolitan-Vickers in the 1930s was led by Arnold Tustin, and the company held the British patents for the Metadyne.
The General Electric engineers, led by Ernst Alexanderson, were interested, but modified the design by the addition of a compensating winding, which counteracted the effect of the flux produced by the load current.
[4] During the same period, the Macfarlane Engineering Company, who were based in Glasgow, developed a variant of the cross field machine quite independently, which they named the Magnicon.
Any further increase would eliminate the flux which sustains its operation, and the current is maintained irrespective of the resistance of the load or the back emf produced by it.
Although the system is prone to the currents in the two halves of the load becoming unbalanced, this can be corrected by the provision of extra series windings, which act like an additional circuit resistance.
Parts of the magnetic circuit are normally not laminated, which creates delays between excitations and fluxes, but the machines are used in applications where a quick response is not essential.
The magnetomotive force (MMF) of this current acts on the non-excited poles, creating a working flux (Φ) and the output voltage.
As with a full-pitch Metadyne, the armature reaction of the output current is 90 degrees out of phase, and therefore opposes the original excitation.
In the early 1930s, the London Underground were aware of the development of the metadyne equipment taking place at Metropolitan-Vickers, and the potential for regenerative braking which it provided.
When the decision was taken to proceed with the new system on the O and P stock, the test train was dismantled, and the equipment was fitted to three battery locomotives[20] built by the Gloucester Railway Carriage and Wagon Company, which were part of a batch of nine vehicles supplied between 1936 and 1938.
However, the complexity of the equipment, and the difficulty of maintaining the metadyne machine, resulted in the locomotives not being used sufficiently, and they were withdrawn for scrapping in 1977.
A decision was taken to remove the equipment and replace it with a Pneumatic Cam Motor (PCM) system, using spare controllers from the 1938 tube stock.
[22] Despite the shortcomings which led to its demise, the metadyne system as introduced in 1936 on the O Stock trains was the first in the world to provide regenerative braking on an electric multiple unit.
However, conditions were not always ideal, and the substations were not really designed to cope with regeneration, which meant that often the train switched to rheostatic braking, where the power was dissipated in a resistance bank.
[1] In the period immediately before the Second World War, there was increasing interest in power-operated gun controls, although military authorities were nervous of introducing a complex system which would have to be maintained in the field.
The original design used a single Metadyne to supply a constant current to the armatures of motors mounted on several guns.
Tustin, who did most of the design work, found that the system had a large time constant, due to the inductance of the field windings.
