J. E. Humphries

Diagnostic measurements on rotary arcs in hollow polymeric cylinders

Rotary arcs in hollow polymeric cylinders have been monitored using electrical and optical techniques. The arcs burning within hollow cylinders were driven by electromagnetic forces. The arc voltage, current, dielectric strength below the arc gap, the optical emissions from the chamber were measured along with high-speed photography. The diameters of the hollow cylinders and magnitude of the applied magnetic field were varied. The arc voltage, especially the extinction peak prior to current zero, increased for larger bore cylinders and higher magnetic fields. By comparing the arc voltage waveforms and arc photographs, this was shown to be because the arcs were elongated. Luminosity was detected even after current zero, when polytetrafluoroethylene was in the arc chamber. The extensive experimental results obtained have enabled empirical mathematical expressions to be derived which yield approximate indications of current interruption capabilities under different operating conditions.

Current Interruption Using Electromagnetically Convolved Electric Arcs in Gases

Measurements were described as current, voltage, and local dielectric strength for a current interrupter which utilized a novel form of electromagnetically convolved electric arc in air. Experiments have been performed with various interrupter structures and operational conditions. Precurrent zero-voltage extinction peaks and post-arc local breakdown voltages have been measured and are compared with values for nonconvoluted arcs in nitrogen and SF6. An empirical relationship between the extinction peak voltage and various design and operational parameters is presented. Signatures for the various interrupter structures under different operational conditions have been obtained by using a chromatic methodology and embodying the extinction peak and a local breakdown voltage.

RLC-Induced Current Oscillations in Convoluted Arcs With Independently Activated Magnetic Fields

Experimental results on atmospheric-pressure arc plasma convolutes in air around a polytetrafluoroethylene cylindrical shroud containing a magnetic field ( B-field) producing coil are presented. In this paper, the B-field coil is energized by a current separate from that flowing through the arc, and a separate RLC circuit was connected across the arc gap. Thus the magnitude and time duration of the B-field are independent of the arc current and the high-frequency current oscillations produced by the parallel RLC circuit. Experimental results for the time variation of the current through and voltage across the arc plasma for these different conditions are presented, along with high-speed photographs of the oscillating current arc. The effects of varying the B-field upon plasma pulsations formed by the independent B-field and RLC current oscillations are discussed.

Electromagnetically convoluted arcs for the interruption of quasi direct current

This paper describes a novel technique for interrupting direct currents (D.C.) with an electromagnetically convoluted arc in air at atmospheric pressure. Investigations are reported on the effects of using a separate current for producing the arc convolving electromagnetic field (B-field) to that being interrupted and using a separate R, L, C circuit in parallel with the arc contacts. Experimental results are presented for the time variation of currents flowing through the arc gap, the B-field coil and the parallel R, L, C circuit, along with the voltage across the arc gap.

A Novel Approach to Power Circuit Breaker Design for Replacement of SF6

This contribution explores the role of PTFE ablation in enhancing current interruption for various background gases in high voltage circuit breakers. An assessment of the current interruption capability has been made in terms of the arcing duration and the contact gap length at which critical arc extinction is achieved. These observations are supported by measurements of the magnitude of extinction and re-ignition voltage peaks. Most previous and other current experimental work on gas filled circuit breaker design follows conventional wisdom in investigating arcing behaviours at elevated gas pressures (usually up to 6 bar). But in this work we concentrate on the effects of using low gas pressures (less than 1 bar) in the presence of a close-fitting shield of ablatant polymer material (PTFE) that surrounds the electrode assembly of an experimental high power circuit breaker. We demonstrate that for several different gases, arc extinction capability compares well under these conditions with SF6, suggesting that SF6 could be replaced entirely in this novel system by more environmentally friendly gases. Moreover, the critical contact gap lengths at extinction are only slightly greater than when using SF6 at 6 bar. Weight loss measurements from the ablatant shield suggest that a chemical puffer action is the most likely mechanism for achieving the observed arc extinctions in this system.