Anthony David Stokes

Vibration monitoring by using a dynamic proximity sensor with interferometric encoding

An optical sensor for the dynamic measurement of proximity is presented. The sensor combines an extrinsic geometric transducer with interferometric encoding for high vibration sensitivity. Static calibration showed a unique variation in interference contrast over at least 60 fringes, leading to a measurement range of 20 mum and a resolution of at least 0.033mum. Dynamic excitation by using low-amplitude vibrations at 3.6 kHz showed a similar contrast variation, verifying fringe discrimination up to the sixth order. With verification of dynamic performance over all 60 fringes, the sensor should offer a low-cost approach to vibration monitoring in electrical switchgear.

Energy transfers within arcing faults in electrical equipment

An arcing fault often develops from an insulation failure within electrical equipment. Arcing faults are substantially unconstrained free-burning arcs within electrical equipment. In order to assess the hazards of arcing faults to personnel in the immediate vicinity of the fault it is necessary to understand their nature and be able to quantify the hazards. This involves an understanding of the energy dissipation and the energy transfers in the near vicinity of these uncontrolled arcs. This paper sets out to describe the physics of arcing faults and uses this to describe the energy transfers within an arcing fault. This is the basis for describing the potential energy transfers to personnel in the vicinity of an arcing fault.

TIME RESOLVED SPECTRUM OF THE FUSE ARC PLASMA

This paper presents the radiation spectrum of the arc plasma in a simple experimental model of a high voltage, high breaking capacity (HBC) fuse. A crowbar circuit is applied to force the arcing current to zero. A 62.5 μm diameter multi-mode silica fibre is used as a light-pipe to carry the plasma radiation from within the arc space of the experimental fuse to the spectrograph. Temporal resolution is obtained by a specially designed opto-electronic circuit that moves the fibre along the entrance slit to the spectrograph. Si II, Si III, Ag I and O II lines have been detected in the plasma. It has been observed that only Si II lines last for the whole time for which the arc was scanned. The disappearance of the O II and Si III lines suggest that the plasma temperature drops significantly towards the later stages of arcing.

Closure to discussions of "Electric arcing burn hazards"

For original article and discussions see ibid., vol.42, no.1, p.134-45, Jan./Feb. 2006. The authors respond to discussion comments by C.M. Wellman (p.142), P.S. Hamer (p.143-4) and T.E. Neal (p.145).

Estimating Arc Temperature in a Model High Breaking Capacity Fuse

Summary We present estimates of the temperature at different times during the arcing period of an experimental model of a sand-filled, high-voltage, high breaking capacity fuse. The model fuse does not interrupt current automatically but the technique described here could well be used in actual current-limiting high-voltage fuses to measure the time-resolved arc temperature. The test fuse is energized using a synthetic test circuit which supplies the fuse a prospective current of.5 kA at 6 kV, 50 Hz. An optical fibre is used to carry light from the fuse’ arc to a spectrograph which is used to isolate spectral lines of interest. The spectrum is recorded by an intensified photodiode array. By gating the image intensifier in front of the diode array a complete spectrum is recorded in several microseconds. By varying the timing of the gate pulse the arc spectrum can be obtained at any desired time during the arcing period. The arc temperature is determined from the relative intensities of Si II spectral lines. The arc temperature is found to vary between 7,000 and 27,000 K at different instants during the arcing period.

Application of ray tracing to the design of a monolithic nonplanar ring laser

This paper presents some simple and useful-ray tracing techniques for the design of a monolithic nonplanar solid-state ring laser. With appropriate constraints the approach gives a complete cavity stability map and the angular and dimensional tolerances required for fabrication.

Noise analysis on a correlation OTDR

The signal to noise ratio (SNR) of a correlation optical time domain reflectometer (OTDR) is deduced. The comparison between a correlation OTDR and a conventional OTDR is made. Our work reveals that a correlation technique can improve the SNR in the application with moderate resolution and fibre length.

Experience with using Cyrogenic Techniques for Recycling Arced SF6 Gas for use in Switchgear

Abtract SF6 gas is an essential component of modern switchgear due to its unique insulating and arc-quenching properties. Unfortunately, it is also an expensive gas and a potent greenhouse agent. Australian utilities have encountered two distinct problems with the management of SF6. Firstly, utilities accumulate partly filled bottles of gas from new installations and also as a result of maintenance activities. Secondly, utilities capture the SF6 when it is removed from switchgear, but this gas may be heavily contaminated. The utilities cannot reuse gas of uncertain quality in switchgear, but disposal is both difficult and expensive. This paper describes the initial experiences of using a new system based on cryogenic techniques for consolidating both small quantities of gas and also removing contamination, including air, from used gas. The recycled gas is suitable for reuse in switchgear.

Electron Temperature and Arc Diameter in a Sand-Filled HBC Fuse

The electron temperature as a function of time in a model high-breaking-capacity fuse has been determined from measurement of the relative intensity of the Si II spectral lines at 505, 597, and 636 nm. The fuses used in this paper consisted of a 0.55-mm-diameter Ag wire fusible element surrounded by silica (SiO2) sand. The spectra were resolved with a grating spectrometer and recorded by a gated image intensifier coupled to a linear photodiode array for prospective currents of 1.25- and 4.5-kA amplitudes and for arc lengths of 112 and 240 mm. The electron temperatures varied during the life of the arc from no significant change (for 1.25-kA peak prospective current through the long fuse) to ~50% decrease (for 4.5-kA peak prospective current through the short fuse). Average temperatures, excluding data points at the early and late times during the arc discharge when the most extreme temperatures were measured, were as follows: 1.8 × 104 K and 1.1 × 104 K at 1.25- and 4.5-kA peak prospective currents, respectively, for the 112-mm fuse and 1.4 × 104 K and 1.5 × 104 K at 1.25- and 4.5-kA peak prospective currents, respectively, for the 240-mm fuse. The individual data points, however, exhibited a wide scatter about the line of best fit. Detailed analysis of the data indicates that it is essential to include the intensity of all of the doublets previously listed when measuring the plasma electron temperature and that self-absorption at 636 nm is, at least for the present experiment, not a source of error. The measured electron temperatures were used to calculate the Spitzer conductivity of the plasma which, together with the measured electrical characteristics of the arc, enabled the variation of the diameter of the arc over time to be estimated.

Estimation of the plasma’s particle densities during the arcing period of a high-voltage fuse

We report in this paper the results of the estimated number densities for the plasma species during the arcing period in a model sand-filled high-voltage fuse. The model fuse was energized at 6 kV, using synthetic test circuit, and a prospective current of 1.25 kA, 50 Hz, was passed through it. The arcing period has been investigated using spectroscopic means. The fuse arc is supposed to be composed of O I, O II, Si I, Si II and Si III particles. Using the estimated values of electron density and temperature, and assuming the plasma to be in Local Thermodynamic Equilibrium (LTE), Sahas and Brunner equations are applied to determine the particle densities of ionized and neutral particles in the plasma. The model high-breaking capacity high-voltage fuse, under the given testing conditions, shows that its arc remains highly ionised throughout the arcing period.