Electricity in Mining.

Thames Star, Volume XXIX, Issue 8604, 8 March 1897, Page 2

Electricity in Mining.

(Continued from last Monday.)

Looking at the achievement related in the last chapter from the standpoint of our " wisdom after the event," £33,500 would seem to be a large sum to pay for knowledge and practical experience; but the fact remains that if Trafalgar Colliery had not been thus driven into a corner, electrical transmission might have been thrown back many years. Necessity is the mother of invention in this case as in many others, and we must thank her and: Capt. Brain for the signal success which he achieved. Coming back to the historical thread of our story, the reader will have seen that the electrical transmission which solved the water problem first came into actual operation in the works in 1882. At a spot 180 ft from the mouth of the shaft, Capt, Brain erected a steam engine and a generating dynamo, and the wires traversed a distance of about 7000 ft before reaching to that portion of the "dipple" where the receiving dynamo and the pumping apparatus were located. The Cornish engine, driven at practically no cost by the waste colliery coal, developed the power, which was transformed and transmitted to the pumps. This is the first practical instance on record of electrical power transmission either as applied to mining, or as used in any industry on a working scale. ANTICIPATION «ND REALISATION. A ref erene to the pioneer work now under review is to be found in the lecture of 1877, wheu Capt. Is rain informed the Bristol Mining Institute that he was then designing a set of electrical apparatus for pumping the water out of the workings, at a spot situated a considerable distance from the bottom of the shaft; also that he had a small electric engine (receiving dynamo) constructed for the purpose. It was not till four years later that the task was actually accomplished, but in a paper written for the South Wales Mining Engineers in 1882, the Capt. records the full realisation of those ideas which in '77 were branded as Utopiau. These two documentary relics form the connecting links of a highly interesting bit of history, aud a quotation from the later essay will be useful from an historical point of view. In the course of his review, Capt. Brain describes briefly the circumstances aud result of the original experiment with the inclined plaue above ground, aud also devotes a few words to stating the

PREVAILING ECONOMIC CONDITIONS, explaining the peculiar position of tlie colliery with regard to its waste coal. Having prefaced his work with a reference to the high efficiency obtained by electrical transmission of power, the writer proceeds as follows :—" There are also other facilities which are equally great, if not greater, in importance thai the gudsti'on of regaining a Mgh percxitaga of ths- work exp'-niei, which, will th 1? application of electrical transmis-

sion specially adapted for mining purposes; these features are more prominent where engine coal is, comparatively speaking, of small value. When, by expending the same amount of capital for machinery instead of horses, the small coal can be substituted for corn, hay, &c, it speaks well for tho manager and the colliery where the change is made." EFFICIENCY IN TRANSMISSION. But, at the same time, Capt. Brain has not lost sight of the question of efficiency, for in another portion of his j paper he remarks :—

"The maximum value of the efficiency in the electrical transmission of power, notwithstanding the great progress the science has made, is not yet clearly defined. Professor Sylvanus Thompson states that where economy in working is required, an efficiency of over 80 per cent, can be obtained. Professors Perry and Ayrton state that they have obtained CO per cent- with, comparatively speaking, small motors, and, conditions being more favorable with large dynamo electric generators and motors, a higher result may be expected. However, it being generally admitted that 50 per cent, of the work expended on the driven generator maohine can be regained from the driving motor machine, and taking into consideration the authorities in favor of a higher percentage, we may_ safely calculate upon 50 per cent, as the minimum amount of power available with a properly arranged electrical plant adapted for the work to be done. The possibility of regaining a percentage of power as high as the the minimum named, in any position or at any point in the workings of mines, regardregardless of distance from the surface, is of itself sufficient to be worth the attention of those not only engaged in coal and iron, but in metalliferous mining also."

It will be seen by the above excerpt that Captain Brain was at this time ('B2) disposed to discount very largely the value of the efficiency, placing the maximum loss at 50 per cent. As regards the actual working results at Trafalgar, no figures were published giving the practical value of the efficiency till 1887. But before going into this branch of the subject, it will be necessary to return once more to the consideration of primary factors. As wo stated in our introductory article, the percentage of LOSS OF TRANSMITTED POWER is mathematically calculable. For instance, under average conditions, 100 natural horse power would—after transmission from the Pelton wheel to the generator—become 97J theoretic and 94 practical electric h.p.; and the practical volume of the transformed energy would be 80 percent, of 94 per cent, when reproduced in the receiving dynamo In fact, the loss from Pelton wheel to generator may be set down at 6 per cent.; from generator to receiver a further 20 per cent.; and from reeciver to objective point at about 3£, through mechanical motion. To deal in practical quantities, one hundred horse power thus becomes 94 when it leaves the generator, 75 l-sth when it arrives at the receiver, and 7256 when it reaches the objective point. This is taking the operation under ordinary average circumstances as met with in mining, and in fixing the percentages a liberal margin has been allowed so as to prevent the possibility of the loss en route being under-esti-mated. In the great majority of cases the sum total of this loss does not exceed 25 per cent.; and at the present moment there are in America many electric plants transmitting at an even higher ratio of efficiency. {To he Continued.)