Joseph Slepian

Extinction of an A-C. Arc

The transition from high conductivity to high resistivity which an a-c. arc undergoes on extinction is studied. Theory and approximate calculations are given for the rate of recovery of dielectric strength of the arc space for short arcs, and results are given of experiments on short arcs, and arcs in holes and slots in insulating material and insulating plates. The influence of chemical activity in arc gases is discussed. Factors contributing to the success of the a-c. oil circuit breaker are suggested.

Theory of the Deion Circuit-Breaker

Three major features incorporated in the Deion circuit-breaker are discussed. They are: deionization at solid surfaces, the function of the static balancer, and cold electrode arcs.

Energy and Energy Flow in the Electromagnetic Field

A new method for deriving the usual Poynting vector is given. This method also yields other equally valid energy flow vectors with the same or other equally valid postulated electromagnetic energy densities. Examples of such alternative Poynting vectors with their associated energy densities are given. A definition is given which distinguishes between the conduction and displacement currents in matter. It is shown that by addition of a term, the postulated energy flow widely used by electrical power engineers and based on wattmeter readings becomes a valid alternative Poynting vector.

Extinction of a Long A-C. Arc

The extinction of an a-c. arc is analyzed as depending on two factors, the rate of recovery of dielectric strength of the arc space after current zero, and the rate at which voltage tending to reignite the arc is applied by the external circuit. In the short arc, most of the recovered dielectric strength resides in a deionized layer next to the cathode but in the long arc the rest of the arc space contributes largely to the dielectric strength. The breakdown gradient of the still ionized arc space is defined, and using a thermal ionization theory, a formula for growth of breakdown gradient is derived. The extinction of long a-c. arcs in the open is greatly influenced by the sectional area which the arc stream has at current zero. By confining arcs to slots and holes, the rate of deionization at current zero is greatly increased, and so large voltages per cm. of arc can be interrupted. A gas blast passing turbulently through an arc stream greatly accelerates deionization at current zero and so is effective in increasing the capacity of the a-c. arc to interrupt high-voltage circuits. The expulsion fuse is an example of a gas blast circuit interrupter, the gas blast resulting from the decomposition of the fiber fuse case. The oil circuit breaker is also a gas blast circuit interrupter, the blast arising from the gases produced by the decomposition of the oil.

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.

The electric arc in circuit interrupters

Abstract It is pointed out that the arc performs useful and necessary functions in circuit interruption and that if the arc is eliminated, other devices which are more expensive and less reliable must be used to carry out these functions. The synchronized interruption of the circuit which the arc effects is considered for the ideal reactive circuit and for the oscillatory circuit. The part which the natural period of the circuit plays in circuit interruption is discussed in some detail. The resistance breaker is discussed. Arc characteristics for various conditions are discussed. The theory of the high vacuum switch is given. The great effect turbulence has upon the interrupting capacity of arcs is discussed and to this effect is attributed the efficacy of expulsion fuses, oil circuit breakers, the compressed air switch and the expansion breaker. Other proposed theories of the oil circuit breaker, compressed air switch and the expansion breaker are examined. The use of lightning arresters in circuit interruption is discussed.

Voltages Induced by Arcing Grounds

THE subject of arcing grounds in transmission systems is one of the greatest interest to operators of power systems of any extent. The almost universal grounding of the neutral in this country is done primarily to alleviate the destructive effects produced by arcing grounds. However, in spite of its great importance, a clear understanding of what happens in an arcing ground in not general. There is no agreement as to the magnitudes of voltages and surges produced, and the various theories proposed call for different properties of the arc. The authors therefore considered it well worth while to attempt in the laboratory to duplicate the conditions of an arcing ground on a transmission system and by spark gap determinations of voltages and by oscillograms to determine the maximum voltages developed and to discriminate between the various theories proposed.

Arcs in Low-Voltage A-C. Networks

The extinction of a-c. arcs at current zero is reviewed, and arc reignition characteristic and circuit reignition characteristic are defined. From a study of arc reignition characteristics of short arcs remote from insulation it is concluded that such arcs are incapable of interrupting practical low-voltage a-c. network circuits. The extinction of arcs in practical network cables is then ascribed to the deionizing action of gas blasts coming from decomposing adjacent insulation. Experiments with arcs in cables, and arcs between parallel plates remote from insulation, and closely bounded by insulation, confirm this view. Inorganic insulating materials may also assist in arc extinction by generating gas blasts by their decomposition. Of the various inorganic materials tried, boric acid was the most effective. Charring of organic insulation may be expected to cause it to lose its arc extinction aiding characteristic.

Energy Flow in Electric Systems- the Vi Energy-Flow Postulate

The conditions which a valid postulated electric-energy flow must satisfy are given and are stated to be insufficient for its unique determination. The commonly used Vi energy-flow postulate is shown by examples to be not generally valid, but by adding a simple term it can be made equally valid with other valid energy-flow postulates. Various examples are given of the application of this corrected energy-flow postulate. On power systems the engineer commonly limits his use of the uncorrected Vi postulate to applications where the correcting term should have a negligible net effect. Various examples of such use are discussed.

The Expulsion Fuse

The general theory of extinction of a-c. arcs is reviewed. The expulsion fuse is stated to depend upon the gas blast produced by rapid decomposition of fuse tube material under the heat of the arc. Comparison of interrupting capacities of a soapstone fuse tube and a fiber fuse tube supports this view. The effectiveness of the gas blast is stated to be due to the high degree of turbulence it introduces into the confined arc space. The theory of the action of such turbulence is discussed. Data are given as to the composition and volume of gas ejected from a fiber fuse tube. The voltage interrupting capacity vs. ampere characteristics as obtained experimentally, are given for a fiber tube, and a boric acid lined tube. The curves for boric acid lie much higher than for fiber. The characteristics were found to depen dvery materially on the number of half cycles of arcing. Reasons are given for the shape of the characteristics, and their dependence on length of arcing time. Data are given showing the effect of variation in size and shape of the tube section. The design problem is discussed of obtaining sufficiently large voltage interrupting capacity at smaller currents without the development of excessive pressures or unmanageably large volumes of flame at large currents. The use of flame suppressors for deionizing the issuing flame is mentioned.