The Montgomery advertiser., 1901-09-25

Fig. ez.
 ,,,say ated by air spaces a~1 the largest per- missible sizes of wire employed In con- nectlon with power transmissions the tnrnd transdormers are often adapted for a
 blowers cireuration s1, n of air from centrifugal eases niled with paraffin oil; this assists Sne insulation and conducts the heat from rs source to the walls of the box for niore e reaoy radiation; larger sizes under cover can have circulation of oil where
 py tne cooling can take place from large sns ssna.iow tanks. Sometimes the trans- larger case or tank and a forced circn. iatlon or water maintained through the intervening space. During the last few years further reduction In heating has been attained by discarding the well es- abolished types and adopting one in which the copper coils are given a larger area oI radiating surface; while the others cussessea ci.s ,a admirable e short magnetic cir inclosed as to contine their heat. The principle of the original ring type is re- sustIcated, but the actual form Is rec difference in construction between pre- vious and recept standards Is shown in figures 70 and 7l. In the core type the sheet iron strips intermesh at the corn CTS. whereby within the coils air spaces are left for assisting the circulation.
 Tn almost all cases the coarse wire is wound next to the core. The resistance Of this portion of the circuit Is usually to he made small and each turn is of shortest possible length. The practice is favored of winding each coil in two sections. so that series or multiple con- nections between them can be made and adapt the transformers for either of two voltages. Differing from the usage in case Of the induction coil. iuA which the
 lighting transformer has the fine wire connected to the supply mains and the lamps are connected to the low voltage secondary.
 tiai generator to drive an alternating cur rent through an extended circuit of the primaries Of many transformers and in them produce a secondary current of suitably low potential for lighting incan- descent lamps and of immunity from per- sonal danger was the invention of Gau- lard and sGibbs. Their system was pat ented in England in 1882 and an exhibi- tion made the next year. The transform CTS were of the induction coil type shown in figure 65. Ali the primaries were con idently unaware of the self-regulating principles Of the transformers and the claims ana specifications of the operation or the system were just the opposite to the nnaily realized facts. Instead of each customer being independent in his sec ondary supply, the turning on or off of lamps anywhere affected the potential at all the other lamps. A constant, though
 
 in the entire primary circuit-the ohmic resistance being fixed-and the generator was really able to maintain that strength when all the lamps were lighted With Few or no lamps connected the generator was powerless to drive one-tenth of that current through the circuit. The princi- pies of self.induction had been overlook ed When the secondary Is not active. no lamps lighted. the self-induotion of the primary is at It's maximum value and the resulting counter electromotive force al- though the ohmic resistance of the coil be zero. almost no current would pass through the winding The only way to reduce the load on the dynamo, yet main- tain the constant value of the primary current. would be to short circuit the secondary; not much more than normal current would flow in the secondary cir cult. for by hypothesis a constant is L., be maintained n the primary by forced regulat tion of the generator. This solu- ton of the difficulty, however, prevented the lighting of any other than the full number of lamps in each installation.
 Westinghouse secured the patent rights | for this country and organized his com pany. Attempts to make the system prac- tical and commercial resulted in dismal failure. In 1886 Stanley, who had been associated with this company, demonstra- ted that the proper arrangement for such | apparatus was not constant current through primaries in series, but was a | constant potential system with primary of each transformer independently con. nected in multiple. This correct manner had been proposed by Kennedy and oth, CTS. but had not hitherto been put to the trial. The success was instantaneous, the use free from patent monopoly. At first thought it seems little risky to connect a primary coil having only few ohms resistance to main distribution wires that may have a difference of potential of 1000 or 2.OOO volts and expect almost no cur rent to flow. yet the case. IS not unlike that of a motor running free; although the armature may have a negligible ohmic resistance. very little current suc- ceeds in flowing, for the reason that the very movement of the wires in the mag netic field results in generating a c. e. m. {. In the motor the magnetism is fixed and the wires move; in the transformer the wires are fixed and the magnetism moves. Whatever current Is drawn from the secondary flows around the iron core in the direction opposite to that in tho primary, thereby to q proportionatc amount setting up a counter magneto- motive force and reducing the self-induc- .ion. The primary cau then draw cur rent from the supply mains in measure demanded by the secondary. If the pri- mary coll can carry one ampere and has twenty times as many turns of wire az the secondary and the latter is twenty l lines the cross section of wire as the other and the supply Is at 1000 volts the | secondary can generate fifty volts and | twenty amperes. In practice such mains | would regularly be kept at 1,050 or 1, 100 | volts. producing fifty-two and one-half | or fifty-fiYe volts in the secondary. to al- l low for inevitable losses due to resistance | 1f transformer coils and house wiring. When the primaries are wound in two | sections these two would be in multiple l when connected on HOO volt mains, but | In series when adapted for a 2.200-volt | circuit. The two sections of secondary |