TRANSFORMER

an appliance whereby an electric current may be utilized to produce another current differing either in voltage or in some other respect from the first. There are many types of transformer on the market, for these appliances are widely used in the transmi ion of electrical energy. As a general rule the object of the transformation is either to produce a current of lower voltage than the original | current, which is done by means of a step-down transformer, or to produce a current of higher voltage, for which a step-up transformer is required. A static transformer is employed to obtain from one alternating current another alternating current; the voltage of the latter may be varied when required, but the frequency of both is the sam me. This type of transformer usually consists of a primary and a secondary circuit, insulated from one another and wound concentrically on a closed cylindrical iron core. The core is formed of stampings varnished or covered with thin paper to insulate them from one another and thereby to prevent eddy currents. The whole is usually immersed fn a heavy insulating oil, which greatly fncreases the dielectric strength. By the pa age of an alternating current in the primary circuit, a similar current 4s induced in the secondary, the voltage of which depends upon the relative number of turns in the two coils. Thus, if the number of turns in the secondary coil be much le than the number in the primary, the voltage of the induced current will be accordingly lowered; while by suitably increasing the number of turns in the secondary coil the induced voltage may be raised to an amount limited only by the insulating power of the dielectric employed. Ifit be desired to produce a current of different phase from that pa ing through the primary, a phase transformer must be employed. This is merely an ordinary static transformer wound in a particular way so as to produce, it may be, a three-phase from a two-phase unit, a polyphase from | Machines known as rectifiers are emto loyed in cases where it is nece ary En storm an alternating current into a direct current. These consist of two cla es—viz., electrolytic rectifiers and mechanical rectifiers. One type of the former consists of two series of cells arranged in opposite senses and joined fn parallel. These cells are fitted up with carbon and aluminium electrodes 4n a solution of alum. Hach series of cells pa es a current in one direction only, and they therefore have the alternating current. The mercury vapor rectifier is another well-known type. Of the mechanical rectifiers one of the best known is the Ferranti, much used in are lighting. In this instrument an alternating-current motor is run ‘in step’ with the alternator supplying the The A TRANSFORMERS, RADIO. Tho; use of transformers of various descriptions in radio as well as all other alternating current work is extensive. All inductive tuners such as are used in prace | tically all transmitting and receiving sets, make use of transformer action. ' Loose couplers, vario couplers, oscillation transformers, etc. fall into this cla , although they are not usually so considered. These and some other transformers in use in the radio field, dispense with iron cores because of the exce ively high hysteresis lo es at high frequencies. oscillation transformer permits the transfer of energy from the closed circuit of the transmitter to the open circuit of the aerial system, and allows adjustment of the damping of the waves and their wave length. It consists of a helix of bare copper tube or wire, supported on suitable insulators, and 4 secondary Winding, on a spool or bobbin, pivoted at one end of the helix. Some oscillation transformers consist of spirals of copper strips, so mounted that their relation to each other can be varied. The use of closed and open core transformers for the production of high voltages for radio telegraphy is common. These are usually oil immersed, although the dry type with air blast cooling is also in use. In the usual transformer, the frequency of the secondary current is the same as that of the primary. The transformers used in the Joly-Arco System for producing undamped oscillations are unique in that they are designed to | double the frequency of the supply current. This is accomplished by employing a third winding on each core which carries a direct current and which fully saturates the magnetic circuit, thus resulting in a doubling of the frequency. In another system designed by Joly, the frequency may be tripled by supplying the third coil with an alternating current. Transformers are used in receiving sets when an amplification of the signals is desired. For radio freally omitted; but this is not the case with audio frequency transformers. This cla of transformers must be designed with great care, if the signals are not to be distorted. A | ELEC opeted When the distance e distribution. 1 The electrical method of power trans- | mi ion po e es several advantages over any of the other methods commonly employed. Space is economized; vibration, and heat are absent; there comparatively little lo in transmi ion; the electric motors which the power is transformed mechanical energy po e very efficiency; and the system is exceedingly adaptable and flexible, owing to facility with which motors may moved from one place to another, cording as circumstances may To transmit power by electrical the e ential factors are: (1) a station where the current is generated; (2) cables leading from the central tion to the point where the current be used; (3) motors for transforming electrical energy into mechanical For comparatively short distances the direct current or the alternating current may be used; the former has advantage of cheapne of ‘line,’ latter that of simpler machinery. long-distance transmi ion, however, alternating current is by far the economical and practically holds field. This is owing to the fact power is the product of voltage current; and, since heavy require heavy, expensive cables, arrangement that increases the and diminishes the current must for economy by allowing lighter to be used. Owing to commutating difficulties it is generally inadvisable practice to increase the voltage continuous currents much beyond volts, though on occasion pre ures high as 23,000 volts have been employed. Alternating currents, on the other may be easily obtained at 50,000 and upwards, and it is with single-phase or polyphase current at pre ures of order of magnitude that long-distance transmi ion is usually carried out. general purposes, three-phase is found to be the most suitable. electrical operations nece arily in the production and handling of high-pre ure currents are simple easily performed. At the central a number of polyp has ers may be ed to produce current at, say, volts. By means of ‘step-up’ ' formers this current is raised to the er pre ure required. At this pre ure the current is now transmitted to the distant receiving station, it is again reduced by ‘step-down’ transformers to the voltage of tion, and, if need be, is transformed the same time into continuous by rotary converters. The voltage which current is distributed according to the purpose for which to be used. For lighting, the pre ure employed is generally about 230 volts, noise, while for tramways aud other forms of is traction from 400 to 500 volts are: actual allowed. The maximum distance to by which at present electrical power can into be profitably transmitted for commercial | high purposes is in general about 100 miles, but with favorable local conditions that: the figure has been already considerably ' be exceeded.