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The available knowledge of state-of-the-art of SF6 alternative gases in switching applications was collected and evaluated in an initiative of the Current Zero Club [1] together with CIGRE. The present contribution summarizes the main results of this activity and will also include the latest trends. The main properties and switching performance of new gases are compared to SF6. The most promising new gases are at the moment perfluoroketones and perfluoronitriles. Due to the high boiling point of these gases, in HV applications mixtures with CO2 are used. For MV insulation perfluoroketones are mixed with air, but also other combinations might be possible. The dielectric and switching performance of the mixtures, with mixing ratios that allow sufficiently low operating temperatures, is reported to be only slightly below SF6. Minor design changes or de-rating of switchgear are therefore necessary. Differences between the gas mixtures are mainly in the boiling point and the GWP, Plasma Physics and Technology Journal, 4 (1), ISSN:2336-2634

Further considerations are given to the use of an electromagnetic flux concentrator for arc plasma control in a rotary arc current interrupter. Such flux concentrators have been previously proposed for plasma fusion and other plasma applications. The possible extension of the proposed method for enhancing the interruption of direct currents with a rotary arc interrupter is discussed with the aid of theoretical modeling of the concentrator geometry and with its possible enhancement of ablation from the arc containing cylinders.

This contribution investigates the use of a novel approach based upon optical fluorescence for monitoring the condition of transformer oils. It describes the use of Chromatic Processing for quantifying complex fluorescence spectra of degraded oil samples and the use of chromatic diagrams in a user-friendly form to provide an indication of the oil condition. Furthermore, it is shown how the approach can be deployed to give a preliminary indication of oil condition using a basic electronic camera instead of a spectrometer based system so providing a convenient and robust approach for onsite monitoring. Comparison of the results with assessments made with conventional methods such as Dissolved Gases, Colour Index etc. are presented to show the potential of the approach.

This contribution presents the rationale, basis, and potential for continuous and event-driven online chromatic acoustic monitoring of transformers and their tap changers. Illustrations are given from a feasibility project for monitoring transformers at several substation sites in the Manchester and Stoke regions of the U.K. Examples of monitoring outputs are presented in a top-down order of information compression, representing an approach that is tailorable to substation operators' information requirements for tracking and tracing overall and individual tap change quality. It is concluded that the approach is feasible for trend sampling and continuous monitoring regimes. Ongoing work includes the evaluation of overall transformer acoustic behavior patterns and individual internal tap-change elements. The monitoring is being rolled out to 50 transformers.

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.

An approach is described for monitoring and characterizing the operating condition of high voltage circuit breakers. The approach employs optical fiber acoustic sensors to detect vibro-acoustic signals from the circuit breaker. The optical outputs are converted into electronic signals via a remote acoustic monitoring unit (AMU). The signals are then processed using a chromatic analysis technique to characterize the complex operation of the circuit breaker using only three parameters. The preliminary results obtained indicate that it is possible to distinguish changes in hydraulic pressure of the circuit breaker operating mechanism during final contact separation post-arc window for switching various levels of fault currents. This provides a means to monitor non-intrusively on line with good high voltage insulation capability and immunity to radio frequency interference.

This study considers the feasibility of monitoring forces acting on a cutting machine tool using chromatically addressed optical fibre based photoelastic sensors. The approach offers a cost–effective and versatile method for avoiding susceptibility to electromagnetic interference, with potential for providing sufficient frequency response for high-speed machining and for accommodating noisy, wide band optical wavelength signals. Measurements of the static and dynamic characteristics of such systems are presented along with results for interrupted turning in a real robust machining environment.

Objective A chromatic method is described for providing a preliminary indication of unacceptable bilirubin levels in a newly born baby in order to avoid the development of serious mental deficiencies. The aim was to investigate the reliability of a new chromatic approach using a novel template unit for a preliminary, non-invasive monitoring of the skin tissue of newly born babies with jaundice and its capability for use with different mobile phone cameras. Approach A description of the monitoring system is given along with an explanation of the monitoring technique used. Preliminary tests have been performed on 48 different neonates each being addressed by one of six different mobile phone cameras, which were randomly available to the operating clinicians. Main results The test results have a correlation (R 2) of 0.81, a sensitivity (Sn) of 0.97, a specificity (Sp) of 0.82, a positive predictive value (PPV) of 0.95 and a negative predictive value (NPV) of 0.9. Significance The significance of the results obtained is that they show the approach to have a high level of fail-safe reliability in indicating the bilirubin levels when compared with blood test results. The results also show that the approach can be used with a few different mobile phone cameras and that because of its non-invasive nature and its cost effectiveness, has the potential for remote use from a medical hospital to provide an immediate preliminary diagnosis.

The present contribution describes a chromatic processing approach for quantifying the two dimensional, polychromatic interference patterns produced by a strained photo-elastic element and recorded with a CCD camera. The outputs from the three R, G, B channels of the camera covering a selected area of the interference pattern are processed to yield three chromatic parameters which are H (dominant signal wavelength), L (nominal signal strength), S (effective wavelength spread of signal). It is shown that the value of each of the three parameters varies with strain in a quasi cyclical manner, all being out of phase with each other. Consequently the strain measurement range and sensitivity can both be optimized by the use of the appropriate chromatic parameter within different strain ranges.

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.

Some preliminary investigations are described of speckle fields produced from light propagation in a multimode optical fibre exposed to low frequency (100 Hz) acoustic vibrations. Measurements are presented that have been made with a photodiode detector and a CCD array, the results obtained with the latter being analysed using space domain chromatic techniques. Optimum operating conditions are considered for providing good sensitivity and repeatability for detecting low frequency vibration signals (not precise parameter measurements) with an ultimate objective of monitoring fault development from the vibration of a mechanical plant.

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 a magnetic 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 a magnetic field has been investigated. It has been shown that a stable azimuthal plasma ring can be rapidly 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 reduced to zero whereby the constraining electromagnetic forces are removed and, as a consequence, the resulting plasma ring expands radially 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. The results suggest that the plasma control and propulsion is governed by a combination of effects including ablation of the material around which the plasma ring is formed and self-pressurization related to the device geometry, as well as the electromagnetic forces. Preliminary results indicate that through the use of appropriate device geometries, the arc plasma may be propelled in axially opposite directions as well as radially.

The problem of extracting quantified information from physiological and physical indicators of the fatigue level of a vehicle driver is addressed. A chromatic approach has been used for processing the physiological and physical outputs from a driver fatigue monitoring system, the physical indicator being in the form of gyroscopic signals produced by the lateral movements of a vehicle. Some preliminary results are presented which show how the chromatic signatures of the physiological and physical indicators can be used to identify fatigue thresholds and provide a more optimized estimate of tiredness.

An approach is presented for remotely monitoring person-based events at a series of locations in a domiciliary environment in order to extract information about movement between locations and to quantify the extent of any persistent events at a particular location. Each individual event is detected via a change in the optical chromaticity of a location and not the person. Movement between locations is determined using space and time-based chromaticity to analyse the dynamics of the sequence of events. An example of the deployment of the approach is presented.

Given the wide ranging concern about air pollution by particulates of sizes 2 to 10 µm, there is a need for a cost-effective, easily deployed, portable system of moderate accuracy (rather than high precision) for temporary use on sites or on board vehicles to monitor such particulate concentrations. This paper describes such a system, which is based upon a chromatic modulation technique. A brief explanation of the chromatic approach is given followed by a description of the particulate monitoring unit. The performance of this unit has been established via various calibration tests and the instrument has been deployed for real life use at a number of sites. Some preliminary results are presented from a city centre bus terminus, the depot of a major bus operator and a site close to an official monitoring station.

PurposeTo introduce chromatic methods and their application to monitoring complex systems.Design/methodology/approachComplexity is introduced and the need for holistic monitoring is suggested. The chromatic methodologies are introduced and their broad‐ranging applicability is illustrated with reference to a number of diverse applications.FindingsThe generic chromatic monitoring technology has much to offer as a way of visualising, understanding, monitoring and controlling complex processes and system behaviour.Practical implicationsThe technology is leading to new ways of characterising and evaluating aspects of system behaviour, in a holistic and non‐intrusive manner, that are difficult to measure – e.g. walking behaviour of the elderly, tiredness of drivers.Originality/valueDraws out the generic basis of the chromatic methodology and how it may be applied to a wide range of complex systems and situations to predict when and where human intervention is required.

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.

One method for the identification of incipient transformer failures due to partial discharges involves measuring the concentration of dissolved gases in the transformer oil. The number of gases monitored is often considerable (≥10), and there is a problem in tracking time varying patterns of the concentration of these gases to yield meaningful prognostic information. This contribution describes the use of chromatic processing techniques in the gas identification domain for yielding conveniently assimilable information in the form of chromatic maps for prognostic purposes. Such maps take the form of polar diagrams of various chromatic parameters such as hue (dominant species), saturation (breadth of gases per cent) and lightness (the overall concentration of gaseous species). Three categories of transformer working conditions (safe, alert and faulty) have been established based on such chromatic signatures. A simple probabilistic model, which can facilitate examination of the implication of future data gathered online, has been assembled.

To gain an increased understanding of circuit-breaker performance, and the corresponding specification and test issues, the interaction between circuit breaker and the connected network is being studied. In the course of this investigation, the modeling of high-frequency voltage transients is being addressed. The essence of the problem lies in the need to combine the electromagnetic modeling of the distributed nature of the interrupter, with the modeling of connected networks by lumped circuits and with the modeling of the electric arc plasma within the interrupter. An equivalent circuits approach is proposed for combining different levels of approximation within each modeling domain and to provide computationally economic solutions. A hierarchy of model approximations is presented and examples of their applicability are given. As a result, an insight into a number of factors (e.g., network transients, current chopping, interrupter geometry, etc.) which produce and affect high-frequency overvoltages have been produced.

The use of chromatic processing for monitoring aviation fuels under different conditions is described. The approach is based upon the use of a reflective optical fibre probe energized via two light emitting diodes. Results are presented which show how the chromatic approach can discriminate between fuels of different types and fuel contaminated with water under both quiescent and agitated conditions.

A description about the use of the chromatic methodology for monitoring an arc plasma jet utilised for heating micro particles for forming plasma sprayed coatings is given. It is shown that the behaviour of both the plasma and heated micro particles are distinguishable from their different coordinates on an H‐S polar map. Calibration with a standard ribbon lamp would appear feasible for tracking the temperature of the plasma heated micro particles.

This paper describes a method of removing noise from time series data records whilst preserving salient features of short duration, such as sharp transitions and significant peaks. A practical example is drawn from fault‐current testing of circuit breakers, for which the scheme was originally designed. It is demonstrated that the clarity of signal traces can be improved while preserving important transient features. However, the approach is generic and based upon the entropy gradient detection method used in image processing. Local entropy is used as a criterion for selecting the degree of smoothing required, so that features of interest can be preserved. Algorithm modularity allows ready adaptation for specific needs.

A chromatic detection system was designed and tested for monitoring the optical emission from a d.c. arc plasma jet with and without powder particles heated in the plasma. The chromaticity parameters measured are correlated with the arc current, gas flow rate and substrate position.

Chromatic-based algorithms are used to process data taken from a mass spectrometer sampling SF 6 gas, which has been subjected to high-current electrical discharges. The chromatic values are put on to a polar diagram representing an information plane. The technique demonstrates the benefits of this method for monitoring applications and shows clearly how the data is interpreted in the chromatic domain.

The application of the transmission-line matrix (TLM) method to the modelling of the evolving electromagnetic field within a capacitor structure is considered in this paper. The experiment of Al-Asadi et al. [Electron. Lett. 30 (4) (1994)], consisting of the capacitor connected to a source and a resistor and modelling the current following an abrupt switch-on, is reconsidered. The effect of using finer TLM meshes and extending the mesh beyond the capacitor structure is studied. The outcome of replacing the abrupt switch-on by a smooth switch-on is also examined. The method employed in Al-Asadi et al. (loc. cite) for coupling the capacitor to the network, termed the current sources method is also used in this work. The practicalities of using this method and some of its effects are examined.

An approach is described for monitoring urine samples using a portable system based on chromatic techniques and for predicting urinary tract infection (UTI) from the results. The system uses a webcam-computer combination with the screen of a computer visual display unit as a tuneable illumination source. It is shown that the system can operate in a robust manner under ambient lighting conditions and with potential for use as a point of care test in primary care. The present approach combines information on urine liquid concentration and turbidity. Its performance in an exploratory study is compared with microbiological culture of 200 urine samples, of which 79 had bacterial growth >10(5) colony forming unit/millilitre (cfu ml(-1)) indicative of UTI. It is shown that both sensitivity and negative predictive value of 0.92 could be achieved.

An autonomous sensing system is described for deployment on high voltage power lines and to provide an economical method for monitoring current on such lines. The autonomy is provided by drawing power off the line being monitored via electromagnetic induction to drive the current measuring device and for the transmission of the current data to ground level via an optic fibre link, which provides inherent electrical insulation. When the autonomy of the system is threatened, the system automatically switches to be energised from a laser source at ground control via a second optical fibre link. Test results showing the performance of the system are presented.

Chromatic systems were originally developed for monitoring the optical emissions of plasma. This contribution describes how the technology has been utilised on low- and high-pressure plasma systems. The speed of operation of chromatic systems has allowed their use in the monitoring of fast changing plasma, such as arcs and laser plumes. The chromatic methodology has now been extended from the optical domain and is used for more general signal processing. This more general application of the chromatic method is outlined and is related to the plasma processing industry.

A system is described that uses a low‐cost off the shelf camera and computing components, along with software developed at the Centre for Intelligent Monitoring Systems (CIMS), to provide an economical solution to colour matching problems. It is aimed primarily at applications in which small differences between the colours of objects need to be identified. In a prototype system, tests have so far yielded favourable results in comparison with existing quality assurance, which relies on the judgement of a human expert. Colour differences between samples at the limit of human perception are repeatably detected.

An optical-fibre probe is described for monitoring the production and build-up of particulate material in high-voltage SF6 circuit breakers, using the wavelength-dependent scattering of polychromatic light in conjunction with a chromatic modulation technique. It has been shown that the probe can be installed and routinely operated in a reliable manner within the tank of a 145 kV/40 kA circuit breaker during live arcing tests. Experimental results show that the severity and duration of arcing as well as the transient evolution of particle production and settling can be determined with the probe. As such, the results provide a means for tracking particulate conditions in a high-voltage circuit breaker with minimal intrusion into the circuit-breaker volume. It is concluded that the particulate mass per unit volume, formed by a single half cycle of arcing at the rated fault current, is only 0.1% of the total mass of SF6 within the circuit breaker. The particulate material may remain in suspension within the circuit-breaker tank for approximately 30 minutes after the arcing event. The formation of a film of particles on the probe following settling may provide a means for determining the fault-current arcing history of an interrupter.

Optical polarization processes in a parallel-sided glass element used in a Faraday rotation current sensor have been considered. In such sensors the path length necessary to produce sufficient rotation of the plane of polarization is produced by a multiplicity of reflections within the glass element. It is shown that such reflections induce ellipticity of polarization and that this affects the current-sensing performance of the sensor. Two reflection cases, corresponding to total internal reflections at a glass-air interface and reflections by aluminium-coated surfaces, are considered. The latter are shown to produce higher optical attenuation but a lower degree of elliptical polarization. The implications of the induced elliptical polarization in relation to chromatically modulated polychromatic light are considered. It is shown that the resolution of the Faraday sensing is improved by minimizing the ellipticity of the polarization with the aluminium-coated reflections. However a greater dynamic range and signal strength may be achievable with the total internal reflection element.

A technique is proposed for determining the location of an arc-discharge filament in a circuit breaker or a plasma torch utilizing only three photo-detectors, with the same spectral sensitivity, to observe the optical radiation emitted from the arc. The three detectors are placed at different azimuthal positions perpendicular to the central axis of the arc filament and are arranged symmetrically with respect to the central axis of the arc chamber and with their angular responses non-orthogonal. Outputs from the photo-detectors are analytically processed to yield two chromatic parameters, (the nominal radial mode) and (the dominant azimuthal mode), which define the arc location in the laboratory frame (, ). and are defined by algorithms used in chromatic processing. As an illustration, the technique has been applied to interpret some experimental results for determining the location of an arc filament lying within the nozzle of a gas-blast circuit breaker.

A technique for interpreting acoustic signals is presented based upon the use of Gabor type devices. This interpretation technique processes the information acquired from vibration sensors and presents the information as three time-varying parameters which represent the dominant signal frequency, the nominal breadth of the frequency content of the signal and its effective energy content. The technique is an extension of the chromatic analysis used successfully in the optical domain. The information produced by this analysis proves to be more convenient for defining a signal than that yielded by the conventional Fourier transform approach. By way of an example, the Gabor transform based technique is applied to the monitoring of acoustic signals generated by a high-voltage circuit breaker (as used on power transmission networks). Results are presented which indicate that the technique is capable of quantifying trends in complicated time-varying acoustical signals.

The Ontario Prehospital Advanced Life Support Study represents the largest prehospital study yet conducted, worldwide. This study will involve more than 25,000 cardiac arrest, trauma, and critically ill patients over an 8-year period. The study will evaluate the incremental benefit of rapid defibrillation and prehospital Advanced Cardiac Life Support measures for cardiac arrest survival and the benefit of Advanced Life Support for patients with traumatic injuries and other critically ill prehospital patients. This article describes the OPALS study with regard to the rationale and methodology for cardiac arrest patients.

A brief description is given of chromatic optical fibre sensing with particular reference to the monitoring of semiconductor plasma processing. Via this particular example it is shown how such chromatic sensing forms a convenient basis for interconnecting the sensing function of fibre based devices with modern signal processing methodologies enabling intelligent monitoring systems to be assembled. The generic nature of chromatic sensing is illustrated by reference to a number of sensors for addressing different measureands and the route for extending the methodology for the intelligent monitoring of high voltage circuit breakers is indicated as an example of the wider application of the approach.

A novel approach for asymmetrical fault type classification on a parallel transmission line is described in this paper. The method is based on applying chromatic monitoring methodology on the negative and zero sequence components of the three phase currents of either sender or receiver end of a transmission line. Different asymmetrical Faults scenarios at different locations, with various fault resistance are simulated using MATLAB software and its associated Simulink and Simpowersystem toolboxes. The simulated outputs are transformed chromatically into effective magnitude and dominant phase shift parameters. In this paper a new concept of fault classification for asymmetrical faults is presented based upon chromatic maps of dominant phase shift and relative magnitude parameters.

A PC-based neural-network processing system is described for the interpretation of chromatic sensor information monitored remotely using a CCD camera. Chromaticity based monitoring provides a means of simple data pre-processing to reduce system noise due to total intensity variation. However, sensing elements using chromaticity usually show complex variations in chromaticity with measurand changes. This contribution shows how these complex variations may be processed to yield high resolution values of a measurand. The paper presents a novel application of neural networks for monitoring temperatures using thermochromic materials and to perform 2-D pressure analysis using photoelastic materials. The inherent complex mapping and generalisation abilities of multi-layered perceptrons (MLP) make them ideal for processing the detected signals. Results are presented showing that the neural network can provide levels of resolution and performance for remotely addressing chromatic transducers, which are acceptable for detailed metrological applications.

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 are 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.

An experimental study has been undertaken into the effects of changes in the spectral content of broadband light used for addressing a photoelastic strain sensor upon the calibration curve of such a transducer. A simple analysis is presented to show how compensation could be provided for random system drifts which produce such spectral variations. This has led to the design of a prototype photoelastic strain sensor with inbuilt compensation means. Some initial results are presented to demonstrate the performance of the transducer.

There have been sporadic reports over many years of parasitic arcing occurring on PTFE nozzles in high voltage circuit breakers. Recent experimental work has established guidelines for operating conditions likely to enhance such arcing. This contribution provides additional evidence for the role played by the unique properties of PTFE in inducing such parasitic arcing. Electrostatic field calculations are presented which show that field enhancement consistent with the unique dielectric behaviour of PTFE can explain many of the experimentally measured trends. The relevance of the unique behaviour of PTFE to the operation of and conditions which prevail in high voltage interrupters during reactive load duties are also considered.

A rotary arc interrupter is described in which the magnetic field is generated by a current other than the fault current flowing through the coil. This is shown to have advantages not only at low currents, less than 500 A, but at higher currents up to a few thousand amperes, resulting in a significant increase in arc rotation speed. Information on the arc shape and speed is obtained from optical fibres viewing close to the arc.

The expansion of an arc of helical form is governed by both electromagnetic and aerodynamic forces, themselves functions of the arc current and electric field strength through complex interactions. In attempting to describe the arc's expansion the product of these two quantities, the power input, can be usefully exploited. As the arc's helical length increases, the arc voltage builds up until it opposes the driving voltage, leading to current limitation and interruption. Experimental results showing the evolution of electric field strength with current arc also presented.

An optical sensor multiplexing system is described which uses code division multiplexing (CDM). A novel CDM code has been developed for use with spatial light modulators (SLMs) which has advantages compared with conventional CDM codes. Conventional codes introduce significant crosstalk levels in the demultiplexed signals which can be reduced by using long pseudo random bit sequences (PRBSs). The new code, however, ideally introduces no crosstalk which allows much shorter PRBSs to be used with the additional benefit of a reduced duty cycle time. In a test system with twelve sensors the measured signal-to-noise ratios (SNRs) were in the range 68+or-2 dB and the crosstalk levels were less than -70 dB.