Notes on Electric Traction.

Progress, Volume VII, Issue 2, 1 December 1911, Page 898

Notes on Electric Traction.

BY W. M. NELSON.

The history of electric traction, though interesting and instructive to the student of engineering, scarcely falls within the scope of these notes. It may not be out of place, however, to briefly sketch a rough outline by way of introduction. The use of history is to give mental perspective, and a knowledge of industrial history should find a place in the mental equipment of every engineer. The discovery of electromagnetic induction in 1831 by the immortal Faraday opened up a vast field for invention and industrial development. It established a connection between mechanical power (i.e., force multiplied by velocity) and electrical power (electro-motive force multiplied by current) and- the most farreaching result was the invention of the dynamo, a machine for converting mechanical power into electrical power. Owing chiefly to constructional difficulties and the inferior materials available at that time, the development of the dynamo was comparatively slow, and it was not till 1850 that the reversibility of its action was realised and the electric motor, of the type in general use to-day, came into being. One of its first applications was the propulsion of a small boat on the Thames, followed by numerous attempts to propel road vehicles by electric power. The early electric motor was, however, a very primitive contrivance, and the path of the pioneer traction engineer of that day was thorny indeed. Not only were the motors in the highest degree unreliable and unmanageable, but as the only source of power available was the primary battery, this was another source of trouble, which alone was sufficient to preclude success. It is not surprising, therefore, that half a century elapsed after Faraday’s discovery of the fundamental principle before electric traction began to emerge from the purely experimental stage. In 1881 the first commercial electric tramway was opened to the public at Lichterfield, in Germany, followed in 1883 by a similar enterprise at Portrush, in Ireland, in which, by the way, the third rail method of distribution was used for the first time. American inventors then took up the problem with characteristic energy and recklessness. The primary battery having been finally abandoned as a source of power, various methods of distribution and collection were tried and discarded in turn ; and the overhead trolley, now in general use, made its first public appearance in Toronto in 1885.

■ The next stage in the history of electric traction was the development of a satisfactory traction motor, method of drive and method of control. The power required to accelerate a light car even up to . a very moderate speed is very much greater than one is led to estimate from

the fact that two horses only were used for horse car service. This is partly explained by the fact that the momentary overload capacity of the horse is enormous, and it is not to be wondered at that the traction engineers of that time seriously under-rated the amount of power required. Indeed, it took them some time to recognise this as one of the causes of repeated motor failures, and then the greatest difficulty was experienced in designing motors of sufficient power of suitable dimensions for the space available, and hardy enough to withstand the severe working conditions to which traction motors are subjected, even when carefully handled. Innumerable constructional, defects had to be eliminated by a tedious trial and error process before the traction motor could make any pretence at reliability. The necessity for a flexible drive, protection from dust and moisture without impeding ventilation, and commutator troubles due principally to the use of copper brushes, may be mentioned as examples of the numerous difficulties which beset the pioneers. ' The trials and tribulations experienced by the promoters of early commercial traction schemes and the subterfuges to which they had to resort in order to maintain the confidence of the public who controlled the purse strings make humorous reading. In America they found a virgin field for their enterprise almost entirely unhampered by the vested interests, legislative restrictions and old-world prejudices which stayed the tide of progress in Great Britain for many years. The trolley wire was particularly objected to on the score of unsightliness and danger to the publicboth very much exaggerated. Even so late as 1898 the fair city of Edinburgh, recognising the need for transport facilities, but anxious to preserve her good looks, tabooed the trolley and lavished money on cable tramways, afterwards converted at further expense to the electric conduit system. The city of Glasgow, on the other hand, making no pretence at beauty, adopted the overhead trolley/ in 1900 without hesitation and immediately made a splendid commercial success of her tramway system. At the present time the overhead trolley system is in use in 95 per cent, of the tramway systems in Great Britain, the underground electric conduit system being employed in two- cases and the surface contact system also in two cases. In America the trolley is practically universal, though the conduit system has been used in one or two exceptional cases. On the continent of Europe the overhead system is in general use, but the trolley is in many instances replaced by the Siemen’s sliding bow.

To he continued.