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These motors have been largely applied to the propulsion of electric launches and electric tramcars.

The armature core of the Victoria Dynamo, a longitudinal section of which is shown in Fig. 109, consists of a wrought-iron ring upon which is coiled a spiral of No. 30 B. W. G. charcoal iron tape, the convolutions being insulated from each other by a tape of equal width of insulating paper coiled together with the iron tape. About one-seventh of the gross area of the core is occupied by this insulation. Although the iron tape is excessively thin, there is still a tendency to heat, which can only be explained by the circumstance, that on the outer periphery, where the lines of force are at right angles to the axis, they pierce the tape on its broad surface, and thus

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GÜLCHER DYNAMO.

277

cause it to become hot. To mitigate the evil radial grooves are turned into the core from the outside, thus subdividing the wide tape into a number of narrow strips. The core is supported by five gun-metal arms, each arm consisting of two halves, which are clamped together by screw-bolts, and to make the fastening more secure, slots are cut out of the wrought-iron ring and part of the core into which the extremities of the arms enter. In the dynamo here illustrated the core contains 7.8 square inches of iron in cross-section, and it is wound with 60 coils of 165 mils wire, each coil consisting of 6 turns. Total number of turns 360. The machine gives a current of 150 amperes at 75 volts pressure when running at 800 revolutions a minute.

The Gülcher Dynamo is very similar to the Victoria in general arrangement, but differs from it in the way the core of the armature is constructed. In the " In the "Gülcher," which is the earlier machine of the two, the core consists of a malleable iron ring of H-section, provided with external Pacinotti projections, which, for purposes of ventilation, are perforated. Flat iron washers are laid on either side of the central web, between the top and bottom flange of the H-shaped ring, which are kept a small distance apart by insulating pieces, and are also perforated to admit air to the interior of the core. In this arrangement those lines of force which enter the core in a direction more or less parallel to the spindle, pierce the iron washers on the broad surface and cause them to heat. To remedy this evil, the original design has been altered by employing a ring of T-section, the head of the T being directed towards the centre, and iron tape being coiled on either side of the middle web. When the winding of the

tape is completed, the outer periphery of the core is turned in a lathe to a semicircular section. In this manner only the edges of the iron tape, but not its broad surface, are presented to the lines of force, and thus heating is avoided.

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