EXCITER

Elec. Engineer

DIAGRAM OF WOOD COMPOUND ALTERNATOR. (See page 558).

shown in the illustration on this page, an electric motor drives a rose bit by means of flexible shafting, which the workman passes over the surface, and by means of which the casting can be cleaned up even into its innermost recesses with ease and dispatch.

In a corner of this room, also, the insulation of the commutators of the continuous current machines is tested in a novel way. Instead of applying a direct high potential a small series-wound machine with a Siemens armature is employed, giving normally about 200 volts potential. The terminals of the machine are connected by wires with two consecutive bars of the commutator and the machine is then short-circuited at a point directly above an air blast outlet. Upon the separating of the conductors again and opening the short circuit, the air blast blows out the arc, and the high self-inductive discharge of the machine,

CLEANING A CASTING BY ELECTRIC MOTOR.

incandescent machines. For the direct current incandescent machines a flat twin wire is employed, and each layer of conductors is insulated from the next by a winding of

Irish flax thread, an eighth of an inch being left between the turns of the thread. This affords a cushion for the superimposed layer of wire, adds to the insulation and more particularly affords a means of ventilation, as the air has free play between the spacing of the flax thread. All machines of the same capacity in watts are wound

ARMATURE WINDING.

with the same size of this duplex wire and vary only in the grouping of the conductors in series or multiple, or combinations of these two. Thus, for instance the 110 volt machine is wound with four layers in multiple constituting one effective turn; the 220 volt machine in four layers constituting two effective turns; and the 500 volt machine four layers in series, constituting four turns. The armatures of the alternating machines are all wound with the same size of flat ribbon conductor inch wide by .035 inch thick. By thus keeping the sizes of wires on all the armatures uniform, much confusion and error is avoided, while on the other hand it obviates the necessity of maintaining in stock continuously a large number of various sizes of wire much of which would but very rarely be called for.

The further half of this shop is devoted exclusively to the winding of arc light armatures, a view of which is given on page 557. For the winding of these armatures Mr. Wood has devised a very ingenious system by which the winding of the coil is begun at the centre and proceeds outwardly, both ends being wound at the same time. By this means the difference of potential between consecutive turns is maintained at the lowest possible limit and is only equal to the difference of potential in one turn; this method of winding also permits of better insulation than is possible where the coil is wound continuously from one end. The iron core consists of a ring wound from No. 10 iron wire which is specially annealed in annealing furnaces. Special hard drawn brass wire is used for binding on the periphery of the armature.

One of the most fruitful sources of trouble in armatures is the breaking of the short connection leading from the armature coil to the commutator, usually forming a fragile web which is easily snapped by the lightest touch when the machine is running. In order to make these short lengths of wires as strong as possible, independently of the size of wire of which the coil is wound, the following method is employed. If the armature wire, for instance, is No. 13 wire, it is cut off a little over half an inch beyond the point where it emerges from the end of the ring under the

binding wire. A length of No. 9 copper wire, which has been previously drilled at one end for one-half inch with a No. 13 drill, is then slipped over the protruding end of the armature coil like a cap and soldered. The other end of this stout No. 9 wire is then connected to the commutator. This connection is made by means of a screw, and in order to insure a good contact the wires are first pressed against the commutator spoke by means of a screw vise, after which a screwdriver is applied to the screw. This process evidently relieves the screw and prevents the frequent stripping of the heads as the result of application of too much force in order to bring about good contact.

V.

Another flight of stairs brings us to the department devoted entirely to the manufacture of arc lamps, wattmeters, ampere meters and voltmeters, views of which are shown on page 560. In the excellence of its equipment and systematic methods here employed this department of the works has probably no superior anywhere. It goes without saying that all parts are made to gauges and jigs, thus insuring uniformity and interchangeability.

The chief characteristic of the Wood lamp is its simplicity and fewness of parts, as shown in the engraving, page 559. Its continuous operation is insured by three cut-outs, two of which are automatic, and one operated by hand when trimming the lamp. In this way all possible opening of the circuit is avoided. The lamp is regulated by series and shunt coils. The mounting of these coils, a small detail in itself, will serve to indicate the care bestowed on even the smallest part of the company's apparatus. Thus, in order to insure thorough insulation, the lamp coils are wound on brass spools made as follows: A wrought brass head is soldered to the end of a tube, the free end of which is screw-threaded to receive the threaded washer forming the other flange of the spool. Before screwing on this second flange, however, the insulating discs of press board are slipped on the spool and thus remain intact, requiring no slit to be made in them, as would otherwise be the case. The winding of the arc