Edward Bennett

Effective resistance to alternating currents of multilayer windings

IN any multilayer winding carrying an alternating current, such as the windings illustrated in figures 1, 2, and 3, each layer of copper lies in the alternating magnetic field set up by the current in all the other layers. Eddy currents are set up in each layer in a direction to partly neutralize the magnetic intensities in the interior of the copper wire in each layer. As a result of the eddy-current losses in the copper, the effective resistance of the winding to the alternating current it carries may be many times its resistance to continuous currents.

An Oscillograph Study of Corona

A method of obtaining oscillograms of the charging current of a ten-foot (3 m.) length of wire is described. The method is to multiply this charging current — which is of the order of 0.005 amperes — by 100, by passing the current through the primary of a 1 to 100 milliampere current transformer, the secondary of which is closed through an oscillograph vibrator. The paper contains a series of oscillograms obtained by this method, showing the wave form of the charging current of wire surrounded by corona. These oscillograms were taken at air pressures from atmospheric to 0.13 cm. of mercury. They show the marked asymmetry in the current after corona forms, the relation between power loss and impressed voltage, the start of corona after switching, the marked difference in the results at high and low air pressures, etc.

Concentration of heating currents

The proximity effect, usually considered as undesirable and wasteful, may be used to concentrate heating currents in predetermined strips of conducting bodies. Both the current density and shape of the strip may be so controlled as to make this method valuable in a number of heating processes.

A Milliampere Current Transformer

(1) It is pointed out that by the use of a current transformer having a primary to secondary current ratio of the order of 1 to 100, oscillograms can be obtained of the charging current of a single high-tension insulator or of a few feet of high-tension transmission line; that is, oscillograms of currents of the order of 0.1 to 0.5 milliampere may be obtained. (2) The drawing and specification are given for a transformer for this purpose. (3) The transformer relations are discussed; the methods of determining the transformer constants are outlined, and the performance of transformers constructed in accordance with the specifications is determined. (4) A series of oscillograms is given to illustrate some of the applications of the transformer, such as to the study of corona, high-tension insulators, and leakage currents in evacuated lamps.

Control of Potential Over Insulator surfaces

To reduce radio interference caused by corona from pin insulators, adherent conducting coatings or films usually are applied to the central portions of the heads of the insulators, and metal thimbles or conducting coatings in the pin holes. By extending the coating to cover the entire head and by using a coating of the proper resistivity, the voltage at which corona occurs can be raised considerably without materially lowering the flashover voltage. This paper calls attention to the principle of controlling the potential distribution over surfaces of insulators by utilizing the resistance drop in potential resulting from the flow of charging current in high resistance films.

Control of potential insulator surfaces

To reduce radio interference caused by corona from pin insulators, adherent conducting coatings or films usually are applied to the central portions of the heads of the insulators, and metal thimbles or conducting coatings in the pin holes. By extending the coating to cover the entire head and by using a coating of the proper resistivity, the voltage at which corona occurs can be raised considerably without materially lowering the flashover voltage. This paper calls attention to the principle of controlling the potential distribution over surfaces of insulators by utilizing the resistance drop in potential resulting from the flow of charging current in high resistance films.

The proximity effect and its application to the concentration of heating currents in predetermined strips

IN ANY industrial operation such as welding, concentration of heating currents in particular parts of the metal presents obvious advantages. A method is described in this paper of concentrating these heating currents in predetermined strips of conducting plates, pipes, or other shapes. These are placed in close proximity to each other or to auxiliary conductors. They are so interconnected that heating currents concentrate largely in adjacent strips in close proximity to each other and in which the current flows in opposite directions. The shapes are connected with sources of alternating or oscillatory current of moderately high frequency. The method therefore consists in the use of an enhanced “proximity effect” to control the distribution of heating currents in bodies.

Education: Annual report of committee on education

To the Board of Directors: The continued rapid increase in scientific knowledge and in the diversity and complexity of the engineering applications and the engineering responsibilities, combine to make the four-year engineering program a less and less adequate preparation for effective engineering work.

The post college education of engineers

IN the fact-finding stage of the studied movement to “develop, broaden, and enrich engineering education” which has been sponsored by the Society for the Promotion of Engineering Education, the experiences and opinions of practising engineers have been an essential and an important contribution to the study. The study has resulted in a wealth of carefully analyzed information pertaining to the objectives of engineering education, to educational practises and results, and to the possible methods of broadening and enriching educational procedures.

Excellent seminars for practising engineers: A challenge to engineering teachers

STATED in broad and comprehensive terms, the primary responsibility of the engineering colleges is for the development of four groups of men; for engineering work namely,