NOVEMBER 1, 1889.]

Germany. The venerable, but progressive city, Frankfort, wishes to introduce the electric light. After prolonged studies and a thorough inspection and testing of the central stations in operation in various capitals, and after consulting specialists of all shades of opinion, the Municipal Commission, and its technical organs decided unanimously for the alternating current system. The opinion was handed in to the town council, which required certain tests to be executed to throw a light on certain technical details. The pause before the decision is now being filled up by the rival system with an interlude which, if not harmonious, is at least very penetrating. There now appears on the Continent a clever inventor. On his triumphant passage through Germany he is button-holed at the Frankfort railway station. Why just at Frankfort ? Because the agent there of an influential continuous-current firm, which is competing for the lighting of Frankfort, wants an "authentic" opinion for effective distribution, and has for this purpose come, accompanied by a reporter. The inventor of continuous-current distribution is cunningly asked: 'Are you in favour of the continuous current? Yes or no?' 'Yes.' 'Do you wish that Frankfort should commit the error of being lighted with an alternating current?' 'Oh, no.' So cunning a manoeuvre may amuse the able mayor and town council of Frankfort, but not influence them."

A SYNTHETIC STUDY OF DYNAMO MACHINES.

(Continued from page 383.)

VII.-PARASITIC CURRENTS.

HITHERTO we have considered the E.M.F. induced in coiled conductors by their motion in various magnetic fields having given to the coils the particular shapes necessary, that the E.M.F. induced in the different parts of them, or in the several coils which form the armature, may be added together in the manner desired. But whether metal is drawn into wire and wound into coils, or used in another form, E.M.Fs. are necessarily induced in it when it is moved in a magnetic field, the difference between the two cases being that in the former the E.M.F. which is to be usefully employed has been directed as required, while in the latter currents are generated which select a direction for themselves, depending on the shape and size of the conducting substance. In the several descriptions of armature containing an iron core, it will have been noticed that this core has been invariably described as being built up of thin discs or washers separated from each other by paper or other insulating material, or of ribbon with the adjacent convolutions separated in a similar fashion, or of wire covered with an insulating varnish or a single covering of cotton. If instead of being divided in this way the iron core were solid, the E.M.Fs. induced in it would, by reason of the extremely low resistance of a large mass of solid metal, cause enormous currents to flow. The work done in producing these currents would be entirely wasted, and owing to the heat generated, the temperature of the machine would soon be raised to a destructive point. They are currents which could not be utilised, which are source of loss, and for the elimination of which every possible precaution must be taken therefore in the construction of machines. By suitably dividing the iron core as above indicated, these so-called parasitic currents may be rendered almost negligible.

The parts of the conductors which contribute to the E.M.F. of the machine are those parts only which cut the lines of force, the induction being at right angles to the direction of the motion. The induction tending to produce parasitic currents is obviously in the same direction, and to prevent the formation of the latter, the iron core upon which the conductors are wound must have planes of division perpendicular to the

497

Fig. 129 shows the lamination of the armature in a Gramme ring as usually constructed. The core is built up of soft iron washers, clamped together, and separated from each other by varnished paper, the conductors being wound over the exterior, and through the interior of the ring. N and s are the magnets, the lines of force entering and leaving the ring by its external cylindrical surface. The direction of induction in the conductors is at right angles to the direction of the motion, that is from a to b, or b to a, according to the direction of rotation, while the planes of lamination, as shown at A, are parallel to the direction of motion, and perpendicular to the direction of induction. The Siemens armature is laminated in the same manner, the core, in this instance, being built up of thin discs of soft iron, with a hole left in their centre sufficiently large to admit of attachment for driving. The iron sheet from which these washers or discs are cut vary in thickness from No. 16 to No. 22 B.W.G., or from 065 inch to 028 inch. The former is seldom employed, the general opinion being that the thickness is too great, while the latter is not infrequently used through a medium size of No. 20, or 035 inch is the size most commonly adopted. The insulating material consists generally of thin tough paper, varnished or unvarnished, of thin asbestos paper, or of Willesden paper; in some cases oxide paint alone is used, though this practice cannot be recommended. When No. 20 sheet is used, the number of washers or discs is about 25 to the inch, allowing for a good tough paper between each plate.

CENTRE OF SHAFT

FIG. 130.

In fig. 130 is shown the direction of lamination in a disc armature, the core of which is constructed by winding on a central ring a ribbon of soft iron, along with a ribbon of asbestos paper, the core, A, when

finished, forming a laminated structure with the planes of lamination perpendicular to the direction of induction, and parallel to the direction of motion. N and N are the magnet poles by which the lines of force enter the ring, and it will be noticed that here, as in the Gramme and Siemens armatures, as must in fact be the case in all armatures, the lamination is such that the lines enter and leave by the edge of the iron, or parallel to the planes of division. In the earlier days the necessity for observing this was not recognised, and in disc armatures flat washers were employed instead of ribbon for constructing the armature core. The lamination was thus parallel to the direction of the induction, with the result that a large amount of work was wasted in the generation of parasitic currents.

[NOVEMBER 1, 1889.

which leads to farther trouble in the truing up. The use of wire instead of plates seems, on the whole, doubtful economy, and having found a decided saving in the use of plates, we are of opinion that wire should be employed only when it cannot be done without.

In alternating current machines the same rules are followed for the lamination of the armature cores. The alternators with their coils wound as in the Gramme machine have their armature cores, whether stationary or rotating, made of soft iron washers, while disc alternators with poles on each side of the armature, as in fig. 130, have their cores made of ribbon, with insulating material between the adjacent convolutions. The alternators in which the armature coils are laid on

If the magnet pole embraces the circumference as well as the sides of the disc, fig. 131, the lines of force enter the core by three sides, and the conductors become inductively active on the top as well as on the sides. In this case the core should be made of rectangular iron wire covered with a single layer of cotton to prevent adjacent wires from being in contact. Wire is specified because it is only by its use that lamination at right angles to the direction of the induction on all three sides of the core can be properly secured. In some cases a few radial slots have been

FIG. 132.

turned out of the core as shown in fig. 132, with a view to the prevention of parasitic currents on the circumferential part of the armature, but the device has not proved very successful, as the degree of lamination thus obtained is insufficient. A mechanical objection to the wire core for this type of armature arises from the fact that there cannot be secured with it quite the same rigidity as when ribbon is employed. To the use of wire in Gramme or Siemens armatures there arises no objection from this point of view, as it can be wound on a gunmetal body between end flanges, as shown in fig. 133, but there comes with its use the constructional objection that it cannot be wound on truly, and that in consequence the armature requires to be put into the lathe several times during the operation of winding for the purpose of truing it up. There is no advantage in employing wire for the cores as depicted in fig. 129, save on the score of economy, for the parasitic currents are eliminated in these by lamination in one direction only. All wire cores possess the disadvantage of having the magnetic continuity broken, as the lines of force entering the armature have to pass through several thicknesses of insulating material before getting to the bottom layers of wire. This means that greater magnetising force must be employed. It is certain that in wire cores the lamination cannot be so perfect as in sheet ones, until the wire gets very small in section,

CENTRE OF SHAFT FIG. 133.

the surface of an iron core have the latter, whether fixed or moving, built up of washers, separated from each other by an insulating substance. Alternators in which the iron cores of the field magnets are subjected to inductive action, due to a magnetic flux varying in intensity and distribution, require to have the magnet cores also laminated, in order that there may be generated in them no parasitic currents. But the rule for the lamination of the magnet cores is the same as for the armature, namely, that the planes of division shall be perpendicular to the direction of the induced E.M.F., and parallel to the direction of the motion. (To be continued.)

THE KENSINGTON AND KNIGHTSBRIDGE

CENTRAL STATION.

AMONG the central stations worked by accumulators in London, one of the earliest is that of the Kensington Court Electric Light Company, situated in High Street, and established by Messrs. Crompton & Co. This is moreover, the first station to make use of underground canalisation in naked copper. The distribution is effected by feeders under the mean potential of 100 volts. The feeders, as shown in the accompanying figure, reproduced from L'Electricien, are insulated and placed in trenches of brick under the pavement: at the point where they join the distributing system is

fixed a wire returning to the works and enabling the difference of potential between these points to be measured and kept constant. The system of distribution consists of a thick band of naked copper, suspended to the middle of a wide trench. For this purpose, at certain intervals across the trench, are placed beams of wood fixed in the sides and supporting, by means of irons, two insulators of varnished glass; these are connected with other insulators fixed upon the band of copper by a cord which serves at the same time to stretch the conductors.

At intervals are holes, closed by an air-tight slab, through which the canalisation can be inspected. The derivations for the consumers are established all the

NOVEMBER 1, 1889.]

more easily in London, as the cellars extend underneath the footpaths; it is then sufficient to make a hole in the bottom of the trench so as to let the wire pass through, which is fixed upon the canalisation by means of little bolts.

The station contains three Willans and Robinson steam motors working directly some Crompton machines, making 350 revolutions per minute, and giving 900 ampères and 110 volts.

The accumulators of the Crompton-Howell type are always mounted in derivation upon the machine, and absorb or restore energy according to the charge of the circuit of utilisation. A commutator, made specially for this purpose, enables the number to be varied without the circuit being cut.

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diaphragm placed about one-eighth of an inch from the poles. An endless iron tape, A, passes through a small hole in the centre of the diaphragm, D, and between two jaws attached to the same, and thence over guide wheels. When an alternating current is passed through the coil it produces a vibration of the diaphragm, which, being communicated to the jaws, forces the tape outward through the diaphragm. While the tape passes over the pulley nearest the diaphragm in one direction, the pulley, B, curiously enough, revolves in a direction opposite to what it would under ordinary circumstances. This very curious phenomenon has not yet been satisfactorily explained, but is no doubt due to the results of compound vibrations in the apparatus.

Besides this there are a large number of other interesting things shown. One of these is an alternating

*Abstract from article in New York Electrical World on Paris Exhibition.

tions and fixed inside a laminated frame. The armature also consist of six similar coils attached to the outside of an iron disc core.

A little mechanical assistance has to be given to the motor to start it, but it quickly gets up to its normal speed, about 1,500, the brushes being meanwhile shifted till all sparking is avoided. Once, however, it has got into the same phase as the dynamo which is supplying it with current, the brushes are rocked backward until they touch the contacts, A, A, which immediately shortcircuits the brushes and lifts them off the commutator, thus cutting the armature completely out of circuit. The motor then continues to rotate by induction from its field. An arrangement is attached to the motor shaft to short-circuit automatically the armature when the motor is in phase. Two semi-circular segments, which will be noticed inside the commutator, fly outward by centrifugal force and abut against the commutator segments, thus short-circuiting them when the right speed is attained.

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REVIEW.

Electricity in our Homes and Workshops. By SYDNEY F. WALKER. London: Whittaker & Co., Paternoster Square; George Bell & Sons, York Street, Covent Garden.

The general contents of this book are as follows:I. Glossary of Terms; II. The Electric Circuit; III. Magnetism; IV. Galvanic Batteries; V. Electric Bells; VI. Electric Mining Signals; VII. Telephonic Apparatus. The work is eminently a practical one and it is deserving of considerable praise, the title, however, is we think distinctly misleading as the author really deals only with electric bells and telephonic apparatus, whereas one would expect that the electric light and transmission of power were to be included. It is true that a good deal which has reference to the latter subjects is considered in the first two chapters, but it leads up to nothing.

As is so often the case the author fails to understand, and consequently to make clear, the electro-mechanical units; for instance on page 17 he says, "the watt is the unit of work done and is equal to 33000 foot lbs.," but a few lines further down he says, "the watt is equal foot lbs. per minute."

to

33000 746

746

Chapters IV, V, VI and VII, which, form the bulk of the book, are eminently practical; we notice, however, that on page 80, an illustration of a trough Leclanché battery is made to do duty for a trough Daniell, which it only resembles in outward form. The statement on the same page that the Daniell is now almost obsolete for telegraph work is distinctly incorrect. With the exception of the few defects pointed out and one or two others, there is but little to find fault with, but, on the contrary, there is a good deal worthy of commendation.

NOTES.

Train Lighting by Electricity.-A system of train lighting by electricity was introduced by the Cheshire Lines Committee on Saturday last. The electricity is generated in the break van, on Radcliffe's system, a dynamo being fixed in the brake van, and driven by means of a stout leather belt, which passes through the floor and round the axle of the vehicle. It is so arranged that the dynamo always revolves in one and the same direction, no matter which way the train is travelling. For the purpose of maintaining the light during stoppages, a set of accumulators is provided, and these are automatically connected by means of a switch with the dynamo on the current generated by the latter attaining sufficient strength to overcome that of the accumulators.

Electric Lighting at Bradford.-The Gas and Electric Lighting Committee of the Bradford Corporation have more than exhausted the £15,000 which was granted some time ago for the purpose of establishing works for supplying the inhabitants of the town with the electric light. At a special meeting of the Town. Council on Saturday, an additional sum, amounting to £25,000, was granted in order to enable the committee to complete the works begun, and also to enable them to meet the extra and unexpected demand for the supply of the electric light.

Electric Lighting at Exeter.-The electric light is making rapid progress at Exeter, and is being adopted in most of the public buildings. The Half Moon and Clarence Hotels have recently been fitted up with the electric light, and the arrangements work satisfactorily. The hotels were illuminated for the first time on Monday evening. In each case the installation consists of 130 Edison incandescent lights of about 2,000 C.P. each, which throw a steady light on all parts of the buildings. Every light is under separate control. This public display will do much towards recommending the light to the townspeople of Exeter.

Barnsley and the Electric Light.-An installation has been completed at the foundry of Messrs. Qualter and Hall.

A Long Incandescent Circuit. In reference to the long distance circuit the New York Electrical World says: "The Heisler Company inform us that the circuit there (Ottawa) is actually 45 miles in length. They believe this, with reason, to be the longest incandescent circuit in the world, and they question whether it is approached by an arc circuit. If our readers know of anything that at all approximates to this, we shall be glad to hear from them. It is certainly a most remarkable instance of flexibility of system and of the delivery of electrical current at an extremely remote point. As we hinted in our note on the subject, arc light electricians must look to their laurels."

Proposed Electric Lighting at Eastbourne. - The lighting committee of the Eastbourne Town Council reported to the last meeting that, "At a meeting of this committee, held October 17th, a letter was read from Messrs. Langham and Sons, solicitors, on behalf of the Eastbourne Electric Lighting Company, Limited, enclosing, for submission to the Corporation, a draft of the provisional order which the company proposes to apply for to supply the electric light within the borough of Eastbourne, and stating that the directors of the company will be happy to consider any suggestion which the corporation might desire to make upon the subject." It was resolved that a special meeting of the Council should be convened to consider the advisability, or otherwise, of the corporation giving consent to such provisional order.

NOVEMBER 1, 1889.]

Electric Lighting in Brussels.-It will be remembered that the Town Council of Brussels has invited the presentation of schemes for the introduction of the electric light throughout the town. Six firms have submitted their plans, which comprise various wellknown systems, but amongst these is one which is novel. This plan, says Industries, has been prepared by M. Van Rysselberghe, the well-known inventor of the long distance telephone system. He proposes to distribute not electric current but hydraulic power, and to generate the current by means of hydraulic motors placed on the premises of the subscribers. The cost of having the current from a distance to the point of consumption, in the case of the Théâtre de la Monnaie, enormously increased the total expense of the installation. In this case the current is furnished by the gas works at Laeken, and the whole installation has cost 180,000 francs, whereas a local plant could have been put up for 20,000 francs. According to Van Rysselberghe's present project, large pumping stations would be erected outside of Brussels, and water under a pressure of 750 lbs. would be conveyed by means of various sub-centres, where small local generating plant would be established.

Edinburgh Exhibition.-Sir Thomas Clark, Chairman of the Executive, presided over a large number of guarantors on Friday last. The Chairman mentioned that the guarantee fund had reached £22,000, but it had been proposed that the fund should still be kept open, and they would soon, he thought, have £30,000. He moved in accordance with former resolutions, that it be remitted to the Executive Council to carry out the exhibition, which was unanimously adopted.

Repeal of Chilian Import Duties.-The Financial News says:-" Manufacturers will, perhaps, note that the Chilian Government has decided that after January 1st, no import duties will be charged on tools, machinery, railway plant, or materials for telegraph and telephone installations entering Chili. That should benefit this country more than any other, provided we don't let any rival cut in before us."

The Telephone Extension in Russia.-We hear it is proposed to organise a new telephone service between Moscow and St. Petersburg, a distance of 400 miles.

New Catalogues.-We have received from Winfields Limited, a copy of their book of patterns of electric light fittings, to which we have already alluded in a previous issue. This publication is one of the evidences that at last the Birmingham firms who have been foremost in the production of gas fittings are beginning to recognise the fact that the electric light is becoming a formidable competitor with the older illuminants. One would have expected that some of the more progressive firms, at any rate, would, ere this, have taken a more prominent position than they have done in the manufacture of metal fittings, but better late than never, and the book now referred to shows that the oldestablished house of Winfields is prepared to supply fittings for the electric light in a great variety of patterns in brass, brass and copper, and iron. Some of the wrought iron work with copper enrichments appear particularly effective, and almost equally so that in a combination of polished brass and copper. From the Electric Supply Company of Chicago we have received their list, No. 560, of electric light and power supplies. For completeness, accuracy of detail, originality of arrangement, and excellence of printing and illustrations, this is probably the most complete list of the kind ever issued. Its value is enhanced by the addition of some valuable tables and formulæ compiled by the highest electrical authorities, and now presented with such modifications as are suggested by the latest knowledge and investigation.

501

Electrical Business on the Tyne.-Electrical firms in Newcastle are having a very prosperous time, and provision is being made for a large extension of manufacturing facilities. In addition to the works being erected for Messrs. C. A. Parsons & Co., a large addition is being made to the present works of Messrs. J. H. Holmes & Co., which only a couple of years or so ago were put up on a scale which it was supposed would be sufficient for the business they could reasonably hope to secure. Messrs. Ernest Scott & Co., who have more recently entered the lists as makers of electrical machines and lamps, are making most important alterations at their works, including the construction of an erecting shop, 90 feet by 45 feet, with a 15 ton overhead traveller, and special engine for testing dynamos. to give up to 100 horse-power. There is also a new

pattern shop and drawing office, 90 feet by 30 feet, with wood-working tools of the latest designs. The brass finishing shop is also being doubled, to cope with orders for switches, lamps, and other descriptions of electrical brass work. They have in course of construction as many as 50 dynamos (varying in size from 25 to 700 lights) of the new type introduced by Mr. Mountain. They are also turning out a large number of arc lamps for both home and foreign orders. A speciality of this firm is high-class brass and gun metal castings, which are made from the smallest size up to 10 tons weight, the foundry being the largest on the Tyne. On the occasion of a recent visit to these works, we were shown a very compact combined engine and dynamo for 100 lamps for ship work, the engine speed being 350 revs. per minute. We hope to have the opportunity of illustrating this in a future number. The firm is busy also in fitting up installations in mills in the Lancashire and Yorkshire district, as well as a large mansion near Tenby, and recently completed the lighting of the River Wear Commissioners' chain testing shop at Sunderland by means of a Griffin gas engine and an 80-light dynamo. A special search head lamp attached to the men's caps, and used for examining the chain links, was designed by the manager of the department, Mr. Hartness.

American Electric Street Railways.-The New York Electrical World published in a recent issue a table of electric railways, from which it is seen that there is a total of 1,260 miles of track and 1,884 cars operating on 179 roads.

Dick, Tom and Harry.-It is well not to entrust the wiring of your home to any of the above. Quite recently the inhabitants of three consecutive houses gave orders for their respective residences to be wired during their absence from London, and were surprised, dismayed and disgusted to find on their return that the Electric Supply Company declined to turn on the current owing to defective insulation.

A New Electric Submarine Boat.-A new boat has been introduced by Lieut. Halpine, of America. It is propelled by an electric motor and storage batteries. The boat is in shape a large metallic cylinder pointed at both ends, in which the motor and battery are contained. The weight of these is so disposed that the vessel is kept at a proper depth and position in the water. The boat is kept under the control of an operator on shore or on a ship by means of special electrical mechanism on the boat, connected by single insulated wire with switching mechanism, and a portable battery at the operator's position.

A Chance for Electric Traction.-Tenders are wanted for working, under lease, of about 11 miles of tramways for the Corporation of Huddersfield. The lines are laid so as to be suitable for either animal or steam power (and, we imagine, electrical traction). The Town Clerk will supply all particulars.