Thomas H. Lee

Theory for the Cathode Mechanism in Metal Vapor Arcs

It is shown that in the cathode drop region of a metal vapor arc, there are four equations and two limiting conditions relating five dependent variables. The five dependent variables treated are temperature of the cathode spot, electric field at the cathode, total current density, current density carried by electrons, and the radius of the spot. When these equations are combined, a current level is found below which no solution exists. It is proposed that this current corresponds to the point at which a vacuum arc extinguishes in an alternating‐current circit. Experimental measurements of the current level at which this event occurs have been made, and the results are compared with the theoretical calculations.

Theory and Application of the Commutation Principle for HVDC Circuit Breakers

The commutation principle for HVDC circuit breakers is described whereby the current in the circuit is brought to zero by a bucking current from a precharged capacitor. Circuit features are described to render this procedure easier for the interrupter and typical component requirements are discussed. The functions of current interruption and energy absorption should be separated; to this end, one type of surge suppressor is described. With breakers of this type, multi-terminal HVDC systems could be operated much like comparable AC systems, with only minimal dependence on terminal controls. A tapped line is given as an example.

Development of Concact Materials for Vacuum Interrupters

Conventional contact materials cannot simultaneously meet three of the most critical functional requirements of the high capacity vacuum interrupter. This paper describes the development of a new class of vacuum interrupter contact alloys which offer exceptional properties combining high interrupting capability, high dielectric strength, and anti-welding. The mechanism by which anti-welding is achieved is described and substantiated by test results.

Transient Resistance of Conductors

Practical calculations of transient resistance effects in conductors are reported. Included are the current density distributions in cylindrical and semi-infinite solid conductors for an applied surface step electric field E, and the density in a flat wide conductor. Two analogies are used to yield useful results: thermal diffusion in a cylinder and voltage transients on a semi-infinite transmission line. Results are applied to the calculation of time constants of a transmission line and force build-up in a solenoid.

Developmenbt of Power Vacuum Interrupters

The practicality of using vacuum interrupters for switchgear applications has been demonstrated by the successful development of a number of prototype devices. Interrupting tests have been made at currents up to 43,000 amp (amperes) at 15.5 kv and recovery rates up to 6,000 volts/μsec (per microsecoind). This has been achieved by resolvinlg many difficult technical problems, so that the vacuum interrupter now closelyr approaches the functional specification of an ideal interrupting device.

Surge Suppressors for the Protection of Solid-State Devices

Semiconductor devices are sensitive to overvoltages and must be protected against such potential sources of damage. Typical devices used for this purpose are capacitors, selenium diode suppressors, and avalanche diodes. In many industrial applications, however, switching overvoltages contain so much energy that these devices are inadequate, not in terms of voltage limiting capability, but in terms of energy absorbing capability. Some high energy overvoltages are described and methods of calculating both their magnitude and energy content are presented. The difficulties of protecting semiconductor devices against these overvoltages are discussed, particularly for those cases where it is desirable to have the surge suppressor on the dc side of the installation for economic reasons or for protection against possible surges generated from the dc side. A surge suppressor developed specifically for high energy overvoltages is then described, and typical test results are presented.

Electrical Breakdown of High-Temperature Gases and Its Implications in Post-Arc Phenomena in Circuit Breakers

The breakdown strength of a hot gas and the kind of breakdown, dielectric or thermal, is believed to depend upon the electrical conductivity of the gas. Two methods have been applied to measure conductivity, one using a low-voltage probe and the other a microwave beam. The results yielded by the two methods gave better than an order of magnitude agreement. It is found that breakdown depends upon electron concentration and, more specifically, that the type of breakdown is also determined by it. These results shed light on post-arc conditions in circuit breakers.

Generalized Damping Curves and Their Use in Solving Power-Switching Transients

The equivalent circuits applicable to many power system switching conditions can frequently be reduced to one or more series or parallel RLC (resistance-inductance-capacitance) circuits. It is shown that the responses of these circuits to a variety of stimuli can be expressed on a per-unit basis, as families of dimensionless curves involving one parameter. Such curves are presented and are then used to solve representative power-switching problems.

Development of Experimental 20-kY, 36-MW Solid-State Converters for HVDC Systems

Two 20-kV, 36-MW converters, one used as a rectifier and the other as an inverter in a pump-back configuration, have been operated successfully demonstrating the feasibility of SCRs for high-voltage high-current applications. Effects of commutation transients within the converters and on other apparatus have been thoroughly explored and analyzed.

Forces and stresses in an electromagnetic field

IN MANY engineering problems, it is required to calculate the forces on dielectric and magnetic materials when they are placed in an electromagnetic field. Quite often, it is also desirable to know the force density (the distribution of the forces over the entire volume and the surface) of the material. Methods of calculating the forces and the force densities are given in many books on electromagnetic theory. The treatment of the problem generally leads the reader to believe that the solution to the problem is known and that the equations given are correct. However, if one investigates the equations given in different literatures, one finds that they differ considerably and they give completely different force densities. The author failed to find in the literature a single paper which discusses all the different methods and which points out the most important differences among the theories. The author also found that the differences among the theories are generally not well known to engineers. It is for this reason that this paper is written. Typical questions discussed are as follows: 1. How do the forces originate? 2. Where are they located? 3. Is there any shear force acting on the material? 4. After a ferromagnetic material is saturated, is there any further increase in force as a result of an increase in the field intensity?