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A new approach for the electromagnetic control and propulsion of a current carrying electric arc plasma ring is described. The essence of the approach is to form and manipulate the arc plasma outside rather than inside an electromagnetic field (B-field) producing coil so that pulsed plasma thrusts can be produced in a choice of different directions. The interaction of the electric arc, formed in atmospheric pressure air, with such B-field has been investigated. It has been shown that a stable azimuthal plasma ring can rapidly be produced by the simple process of separating two annular contacts. Pulsed plasma propulsion is obtained when the arc plasma, and B-field sustaining current is automatically reduced to zero, whereby the constraining electromagnetic forces are removed and, as a consequence, the resulting plasma ring radially expands outwards. Several different measurement techniques have been deployed for investigating the behavior of the plasma ring. These include electrical probing, B-field probing, and high-speed plus video photography. Experimental results are shown to be in good agreement with theoretical estimates based upon a Sedov's self-similar model. Index Terms--Ablation, arc discharges, magnetic fields, plasma arc devices, plasma control.

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. Index Terms--Ablation, arc discharge, circuit breakers, dielectric measurements, magnetic fields, optical fiber measurements.

A rotating arc circuit breaker is described which uses an auxiliary current source to generate the magnetic field for driving the arc. Test results obtained using optical fiber measurement systems have shown that there are three main arcing phases. Initially the arc rotates at an essentially constant but low velocity, subsequently its velocity oscillates between this and much higher values, and finally the arc plasma may become diffuse in nature. Test results obtained with dielectric strength probes have indicated that a unidirectional flow of arc heated gas is generated. The flow is away from the moving contact of the interrupter so promoting good dielectric strength in this critical contact region. The combination of the optical fiber and dielectric probe results indicates two possible modes of gas pumping represented, respectively, by a fan and a piston-type action of the arc. Simplified analytical models for both modes are developed with predictions obtained showing good agreement with the experimental results. Discussion of experimental results suggests that the transition from oscillatory velocity changes to diffuse arcing represents an important parameter for scaling the geometries of future interrupters and arc heaters. Index Terms - Arc discharges, circuit breakers, electromagnet coupling, helical arcs, magnetic fields effects, optical fiber measurement, [SF.sub.6].

Contact erosion is one of the most crucial factors affecting the electrical service lifetime of high-voltage circuit breakers (HVCBs). On-line monitoring the contacts’ erosion degree is increasingly in demand for the sake of condition based maintenance to guarantee the functional operation of HVCBs. A spectroscopic monitoring system has been designed based upon a commercial 245 kV/40 kA SF6 live tank circuit breaker with copper–tungsten (28 wt % and 72 wt %) arcing contacts at atmospheric SF6 pressure. Three optical-fibre based sensors are used to capture the time-resolved spectra of arcs. A novel approach using chromatic methods to process the time-resolved spectral signal has been proposed. The processed chromatic parameters have been interpreted to show that the time variation of spectral emission from the contact material and quenching gas are closely correlated to the mass loss and surface degradation of the plug arcing contact. The feasibility of applying this method to online monitoring of contact erosion is indicated. [ABSTRACT FROM AUTHOR]

Experimental results for the operation of a device which generates radially propagating pulses of plasma are reported. These are produced from a convoluted arc plasma column formed using a suitably configured magnetic field (B-field). Both quasi-steady-current and alternating-current arc plasmas in atmospheric pressure air have been studied. High-speed photographic records of the convoluted plasma column during the main arcing phase are presented along with video images of propagating plasma clouds formed when the B-field and arc current collapse. Measured time variations of current and arc voltage during the main current phase are correlated with features on the photographic records. Results are presented, showing the effect of different operating conditions upon the propagation rates of the plasma pulses. [ABSTRACT FROM AUTHOR]

Contact erosion is one of the most crucial factors affecting the electrical service lifetime of high-voltage circuit breakers (HVCBs). On-line monitoring the contacts' erosion degree is increasingly in demand for the sake of condition based maintenance to guarantee the functional operation of HVCBs. A spectroscopic monitoring system has been designed based upon a commercial 245 kV/40 kA S F 6 live tank circuit breaker with copper-tungsten (28 wt % and 72 wt %) arcing contacts at atmospheric S F 6 pressure. Three optical-fibre based sensors are used to capture the time-resolved spectra of arcs. A novel approach using chromatic methods to process the time-resolved spectral signal has been proposed. The processed chromatic parameters have been interpreted to show that the time variation of spectral emission from the contact material and quenching gas are closely correlated to the mass loss and surface degradation of the plug arcing contact. The feasibility of applying this method to online monitoring of contact erosion is indicated.

Objective: To evaluate and present 10-year outcomes of the Nova Scotia Breast Screening Program (NSBSP), a population-based screening program in the province of Nova Scotia, Canada, total population 900 000., Setting: Organized Breast Screening Program in Nova Scotia, Canada., Methods: Rates of participation, abnormal referrals, cancer detection rates, and benign:malignant (B:M) rates for core biopsy and surgical biopsy were calculated for asymptomatic women receiving a mammogram through the NSBSP 1991-2001., Results: Of 192 454 mammograms performed on 71 317 women, 33% were aged 40 to 49 years, 39% aged 50 to 59 years, 23% aged 60 to 69 years, and 5% aged 70 years and over. Cancer detection rate increased in each age group respectively: 3.7, 5.8, 9.7, and 13.5 per 1000 population on first-time screens. The positive predictive value of an abnormal screen increased with increasing age groups. Benign breast surgery decreased with increased use of needle core breast biopsy (NCBB). Open surgery decreased from 25 to 6 surgeries per 1000 screens. Of 1519 open surgical procedures (1328 women), 878 cancers were removed, with 37% 10 mm or less, and 61% 15 mm or less. In 613 women in whom the node status was assessed, 79% were negative., Conclusion: A quality screening program incorporating NCBB in the diagnostic work-up is effective in the early detection of breast cancer and results in less open surgery, particularly in younger women.