R. E. Hellmund

Flashing of Railway Motors Caused by Brush jumping

Theories and concepts developed in connection with circuit rupturing by switches and circuit breakers are used to analyze the factors involved in the flashing of railway motors. The investigation is limited to cases where flashing is caused by brush jumping, which occurs principally with railway motors. Voltage conditions as applying at the commutator circumference and as affecting the sustenance of an arc are studied for varying designs of main poles with different ratios of armature ampere turns to field ampere turns. The effect of load current and speed is subsequently taken into account. Actual test results are compared with the theories outlined. Finally, the modifying effect of certain secondary phenomena is discussed.

Sparking Under Brushes of Commutator Machines

Sparking under the brushes of commutating machinery has been investigated in considerable detail, for the purpose of studying and analyzing the various factors which cause sparking. Among the conclusions reached are that in a detailed consideration of sparking phenomena both current density and rate of change of current density must be taken into account.

Irregular Windings in Wound Rotor Induction Motors

The importance of using regular windings in polyphase wound rotor induction motors is stressed in this paper. Harmful effects upon the efficiency, power factor, breakdown torque, and noise of the motor may result with an irregular winding, due to differential leakage. The Goerges diagram of tooth fluxes is presented for studying this phenomenon. Means of avoiding trouble of this sort also are pointed out. It is further observed that 3-phase motors having a number of poles which is a multiple of 6 are most likely to be troublesome.

The Rating of Electrical Machinery and Apparatus

THIS PAPER outlines briefly some of the technical, economic, and psychological aspects of the methods of rating electrical machinery and apparatus. Some proposed modifications of existing standards also are discussed, with the idea of bringing the standards into better agreement with present-day conditions, knowledge, and practices.

Arc Characteristics Applying to Flashing on Commutators

This paper gives the results of experimental investigations relating to arc characteristics as they apply in commutator flashing. A knowledge of these characteristics is necessary for the application of the theory outlined in a previous paper1 on flashing of commutators by the same author, as well as for the investigation of flashing due to other causes.

Application of Apparatus and Conductors Under Various Ambient-Temperature Conditions

Discussion and authors closure of paper 42–93 by R. E. Hellmund and P. H. McAuley, presented at the AIEE summer convention, Chicago, Ill., June 22–26, 1942, and published in AIEE TRANSACTIONS, 1942, August section, pages 553–8.

Analysis of Rating Methods for Intermittent Loads

The economics of rating structures for electrical equipment from the view-points of manufacturing and application are considered. Methods for dealing with periodic load applications are reviewed. The present methods have certain limitations for some practical applications. An improved method for applying motors to load cycles where the motor stops and ventilation changes in the no-load part of the cycle is developed. This method is based on certain motor-loss ratios, that is, the relation between the losses dissipated with standard temperature rise running and at standstill and the losses at the nominal or short-time rating. It permits the application of service-factor or short-time ratings to periodic loads with more exactness. Attention is called to the wide variations in permissible rms current on periodic loads for different loss ratios and changes in ventilation on a motor.

Current Ratings of Electronic Devices for Intermittent Service

Electronic devices are used extensively for switching, relaying, welding, and similar service resulting in intermittent loads. In the paper methods for assigning standard ratings suitable for such intermittent loads are investigated, both for singleanode tubes and tube circuit combinations. Vapor-filled tubes with oxide-coated filaments are treated somewhat in detail in order to develop the basic considerations. Other types of tubes, such as the pool-type and cold-cathode, are only briefly discussed. A method of rating which seems generally applicable is proposed, with the suggestion that its suitability for the great variety of conditions encountered be further investigated.

Classification and Co-ordination of Short-Time and Intermittent Ratings and Applications

Discussion and authors closure of paper 41–13 by R. E. Hellmund, presented at the AIEE winter convention, Philadelphia, Pa., January 27–31, 1941, and published in AIEE TRANSACTIONS, 1941 (July section), pages 792–8.

The Young Engineer Under Changing Conditions

The situation in which the young engineer may expect to find himself under currently changing conditions in industry is discussed in this paper. Also, the education of engineers, undergraduate and postgraduate, is reviewed from a practical point of view in the light of circumstances likely to be involved in their early activities in industry. Suggestions are given concerning undergraduate curricula, and concerning educational activities that could be carried on to advantage by the young engineer after entering industry. The necessity for a proper balance in various activities and in personal characteristics is emphasized.