Leon R. Ludwig

A New Method for Initiating the Cathode Of An Arc

AFTER presenting various theories of the cathode of an electric arc and describing numerous methods for initiating an arc cathode, a new method of starting the arc cathode is described. It is of the separating contact type, but to a considerable degree is free from the inertia difficulty of ordinary separating contacts. One form of this starter consists of a small section pointed tungsten rod placed in a mercury arc tube so that it dipped slightly to a depth of about one mm below the mercury surface. On sending sufficient current through the rod, the cathode of an arc was promptly started at the rod and mercury junction, and this starting could be regularly repeated 60 times per sec.

A Multiorifice Interrupter for High-Voltage Oil Circuit Breakers

High-voltage oil circuit breakers for high-speed operation generally use some form of multibreak contact arrangement. These breakers perform satisfactorily but lack the simplicity of the conventional slower-speed two-break construction. The development of an unusually effective multi-orifice oil-flow interrupting unit now makes it possible to reduce the required number of breaks to the point where even three-cycle 230-kv breakers appear practical with only two interrupting units per pole. High-power laboratory tests on low magnetizing and charging currents, as well as. short-circuit currents corresponding to interrupting ratings of 2,500,000 kva and above, have demonstrated the exceptional arc-extinguishing effectiveness and low arc-energy dissipation of this multiorifice interrupter for high-speed oil circuit breakers.

A New 15-Kv Pneumatic Circuit Interrupter

The demand for oilless circuit breakers of large interrupting capacity to meet the requirements of American practice directs attention toward an improved compressed-air circuit breaker which materially extends the present limitations as exemplified by continental designs.

A New High-Capacity Air Breaker

Air circuit breakers for lower voltages of simple design are being replaced by improved types, which incorporate specially designed circuit-interrupting devices for the purpose of improving the interrupting efficiency and minimizing the formation of arc flame and gases. A new form of deionizing arc interrupter is described which is equally effective for both d-c and a-c circuits. A new air circuit breaker has been designed to utilize this interrupter in which carbon arcing contacts are replaced by refractory metal, and laminated-brush-type main contacts are replaced by silver-faced solid copper. These improvements have led to greatly increased current-carrying capacity in breakers of a given size and also large increases in interrupting capacity with a minimum of noise and flame, which permits the breakers to be readily mounted in enclosures and cubicles of small physical size.

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.

Magnetic "De-ion" Air Breaker for 2,500-5,000 Volts

The theory of quenching an arc by deionizing the normally conducting arc stream, utilizing a gas blast produced by means of an intense transverse magnetic field, is elaborated. Application of design principles dictated by this theory has made it possible to develop a new form of air circuit breaker for 2,500-5,000-volt service. These breakers are completely described, the theory of the De-ion interrupters is discussed, and test results are submitted. The problem of adequately enclosing the breakers is considered and it is shown that excellent interruption can be obtained in an enclosure of small over-all dimensions.

A Vertical-Flow Outdoor Compressed-Air Breaker

The elimination of oil in indoor circuit breakers, particularly for powerhouse use, has been insistently demanded to reduce fire hazard. In an effort to meet these requirements, various types of breakers not containing oil have been built and studied. Self-contained breakers of the “De-ion” type1 have been available for several years, and the potentialities of water breakers2 have been carefully investigated. Compressed-air breakers3 for this service have been successfully developed, particularly to meet high kilovolt-ampere interrupting requirements, and the circuit-rupturing ability of these devices has been so amazingly efficient that experimental breakers using this principle have now been built and tested for high-voltage outdoor application.

A 2,500,000-Kva Compressed-Air Powerhouse Breaker

THE use of compressed-air breakers for indoor service has become established by several field installations since the presentation of papers1,2 describing these devices two years ago. At that time complete tests had been made justifying ratings to 1,500,000 kva. Since then, powerhouse requirements have demanded the development of similar breakers for 2,500,000 kva. During the same interval new laboratory facilities have been provided3 which are capable of completely testing these large breakers. This paper describes the theory and construction of this new breaker and for the first time presents test results of full 2,500,000 kva under three-phase fault conditions, together with a study of associated voltage recovery rates.

Influence on Commutation of Brush Contact Drop

IN DESIGNING electrical commutating machinery, an attempt is made usually to produce during commutation a linear change of current with time. This, however, is rarely achieved, and the current density therefore usually is not constant across the brush surface, nor is the contact drop constant. The contact drop also will change with time in any small area on the brush surface, and therefore the static curve between voltage and current measured at the brush contact cannot be used.

Effect of Transient Conditions On Application of D-C. Compound Motors

When a d-c. compound motor is started, the rise of current in the series field induces a voltage in the shunt field counter to that applied, and the shunt field current may reach several times normal value in a negative direction. This current reversal gives, in effect, a differentially compounded motor during the starting period and causes the starting torque to be materially reduced. In many applications of compound motors, therefore, predetermined performance is not obtained. In particular cases where the motor is continually started and stopped, the effect may be so serious as to dictate the choice of another type of motor, or one of a special design to minimize the undesirable action. In case the compound motor is disconnected from the line while running, and reconnected with no external resistance, the delay in establishing a flux due to the damping action of the shunt field may permit excessive currents to flow. In other d-c. motors, currents induced in the solid iron portions of the frame and poles exert a damping effect similar to that of the shunt field in the compound motor, which may at times be undesirable. A study of such transients leads to means by which they may be miinimized and provides calculation methods for predetermining motor behavior.