Allan Greenwood

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.

A Guide to the Application of Vacuum Circuit Breakers

The paper shows that the vacuum circuit breaker is well suited for the duties that a circuit breaker must perform. Reasonable care must be taken under certain circumstances when applying these breakers. Such applications are identified and simple corrective measures are proposed.

HYDC Vacuum Circuit Breakers

The effectiveness of the commutation principle, using vacuum interrupters as a means for interrupting high direct current at high voltage, has been demonstrated convincingly by a large number of tests. Currents in excess of 15 kA at 20 kV have been interrupted by a single device in an inductive circuit. Tests are reported in which higher current were cleared by paralleling interrupters. Interrupters have been tested in series, indicating that the principle can be extended to high voltages. A high speed mechanism is described which was designed specifically for circuit breakers of this type. The necessary technology for producing HVDC circuit breakers appears to be at hand.

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.

Identification and Evaluation of a System Condition which can Affect the Performance of Air-Magnetic Circuit Breakers

A circuit condition has been identified that can cause interruption difficulties for 15 kV air-magnetic circuit breakers. The interaction between the system and the circuit breaker has been studied by field and laboratory tests. A solution to the problem, which assures reliable performance of the equipment, has been developed and extensively tested.

An investigation of the transient behavior of an aluminum potline installation

OVER A PERIOD of several years, a number of transformers and induction regulators supplying energy to aluminum potlines and similar installations have been damaged by insulation failures; the failures were apparently due to abnormal overvoltages. The transformers used for these applications usually step down from 13.8 kv to a secondary voltage in the range 600 to 900 volts depending upon the installation. A basic impulse level of at least 40 kv is normal for the secondary winding; insulation failures occurring on these windings are an indication of the severity of the voltage transients. An excellent photograph showing typical coil damage appears in a paper by Pope, et al.1

Transient behavior of an Aluminum pot-line

OVER A PERIOD of several years a number of transformers and induction regulators supplying energy to aluminum pot-lines and similar installations have been damaged by insulation failures, apparently resulting from abnormal overvoltages. The transformers used for these applications generally step down from 13.8 kv to a secondary voltage in the range 600 to 900 volts. A basic impulse level of at least 40 kv is normal for the secondary winding. The fact that insulation failures occur on these windings is an indication of the severity of the voltage transients, and clearly shows that they are out of the range of normal switching transients. However, in many cases it is difficult to see how such voltage surges could invade the low-voltage system from the high-voltage side of the power transformers. This points to some other means of surge generation in the low-voltage circuit, and a likely cause is current suppression.

Breakdown strength of nitrogen at high temperatures

IN A-C circuit-interrupting devices, the post-arc period immediately after current zero is of paramount importance. This period is characterized by the rapid cooling and deionization of the hot gases between the contacts, which build up the dielectric strength of the gap. Simultaneously, however, the circuit transients resulting from the interruption of the current impose a rapidly increasing voltage across the contact gap. This so-called recovery voltage may break down the gap and re-establish the arc.