Transformer

TRANSFORMER, an apparatus for changing electrical energy from a given pressure into a higher or lower pressure. It is stationary, with no moving or rotating parts, and is operative only with alternating currents. It plays such an important part in the transmission and distribution of electricity that the present extensive electrical systems would have been impossible without it. Incidentally, since transformers are operative only with alternating currents, all extensive electrical systems have had to adopt the alternating current system so as to use transformers.

History and Place in Industry.

Very early in the art it was realized by electrical engineers that, while the generation and utilization of electrical energy are safer and more economical at lower pressures and larger currents, its transmission and distribu tion are more economical at higher pressure and smaller currents. Therefore, in order that a central power house might economically serve even a small territory, it was necessary to have apparatus capable of "stepping-up" the voltage at the point of generation and "stepping-it-down" at or near the points of utilization.

Before such an apparatus was invented, physical laboratories used induction coils, similar to automobile spark-coils, for step ping-up battery voltages to high values for experimental purposes, but these were too inefficient for power applications. These coils used an open magnetic circuit and required an interrupter, a "make-and-break" attachment, functioning similarly to the dis tributor in automobile ignition. The necessity for this attachment arose from the fact that currents and voltages could be induced only by fluctuations in flux, and a fluctuating flux could be pro duced only by a fluctuating current. Therefore, since a battery tended to give a steady uniform current, an interrupter was neces sary to produce abrupt changes in current.

It was early realized that if alternating currents are utilized, no interrupter is necessary; and, if the magnetic circuit is made completely closed, the performance characteristics of such a coil are remarkably improved.

The first successful transformer was demonstrated by William Stanley in the United States. It was put in service in Great Bar rington, Mass., in the spring of 1886. Besides for transmission and distribution, transformers are used in a very great variety of services for converting alternating current energy from the pressure at which it is available to the pressure most suitable for the object in view: ringing door-bells, requiring very low safe voltages; welding ship plates, requiring very large currents; oper ating X-ray tubes; or producing "lightning" bolts requiring enor mous voltages. Their use in radio for coupling as well as for fila ment lighting and other power supply is well-known.

General Principles of Operation.--Voltage

Transformation. Fig. z is a simplified diagram of a transformer, showing a closed magnetic circuit M, a lower volt age winding L, and a higher voltage winding H. If an alter nating voltage is applied to the terminals of one of the windings, say L, leaving the terminals of the other winding, H, open, a small current flows into the ex cited winding L sufficient to pro duce a counter voltage equal to the impressed voltage. The ap paratus in always so designed that the counter voltage is al most entirely one of self-induction, the voltage consumed in the resistance of the conductor usually being less than one-tenth of 1% of this self-inductive drop. The voltage of self-induction is produced by an alternating magnetic flux in the core, which in turn is produced by the alternating current flowing in L. The relation ship between the total or maximum flux and the induced voltage, EL is EL = 4.44 4) where is the effective (root-mean-square) voltage across L produced by self-induction, f is the frequency of the impressed voltage (periods or cycles per second), is the number of turns in series in winding L, and 4) is the peak value of the alternating flux q5.