Robert Blue

Infrared detection of transformer insulation degradation due to accelerated thermal aging

Regular monitoring of the paper insulation of electrical windings is necessary to ensure safe and reliable operation of oil-paper insulated electrical transformers. The degradation of the paper insulation due to thermal aging yields furanic derivatives which are specific to the paper and cannot be produced by general oxidation of the oil. The concentration of such furan compounds in the oil gives an accurate indication of the condition of the paper insulation. Normally, off-line methods such as HPLC (high performance liquid chromatography) are applied to periodically assess the furan concentration within oil samples which have been extracted from the transformer. We report experimental findings on the production of the furan compound FFA (furfuraldehyde) in an oil-paper system subject to accelerated thermal aging. Our approach is based on IR spectroscopy. This technique could lay the basis for the construction of direct online monitoring equipment suitable for monitoring of transformer winding insulation.

A novel optical sensor for the measurement of furfuraldehyde in transformer oil

Measuring the concentration of furfuraldehyde (FFA) within oil samples taken periodically from power transformers is usually carried out as a means of condition monitoring. Normally, laboratory-based techniques such as high performance liquid chromatography are applied for this measurement. We report the construction of a novel optoelectronic sensor for the determination of FFA in transformer oils to concentrations as low as 0.1 ppm. The sensor will form the basis of a compact and portable instrument that can be used by a nonspecialist operator to determine, on-site, the concentration of FFA in oil extracted from the transformer.

Comparative Study of Microfiber and Side-Polished Optical Fiber Sensors for Refractometry in Microfluidics

A simple theoretical analysis is undertaken to compare the change of guided mode index of microfiber and side-polished single mode fiber sensors to the refractive index of surrounding fluids. This is followed by an experimental investigation using a broadband Mach-Zehnder interferometer to compare the sensitivity of the two types of sensing fibers by measuring the interferometer response to fluid refractive indices ranging from 1.330 to 1.451. The experiments show that a microfiber sensor of diameter close to 5 μm and an average length of around 500 μm generates a response similar to that generated from a side-polished fiber sensor of length 7 mm. A compact microfluidic cell is fabricated to enable a microfiber based refractive index sensor to be used in a microfluidics environment. Experimental refractometric results obtained using this arrangement are reported.

A novel solid-state material for furfuraldehyde detection

The thermal degradation of solid insulation within a power transformer results in the production of FFA (2-furfuraldehyde) within the transformer oil. Measuring the concentration of FFA gives a reliable indication as to the condition of the solid insulation. This measurement has routinely been performed by using techniques such as high-performance liquid chromatrography. We report a new solid state material which has been specifically designed for FFA detection. The material can be optically interrogated to detect small concentrations (<1 ppm) of FFA within transformer oil.

Modeling and Characterization of an Electrowetting-Based Single-Mode Fiber Variable Optical Attenuator

We report an optofluidics-based variable optical attenuator (VOA) employing a tapered side-polished single-mode optical fiber attached to an electrowetting-on-dielectric (EWOD) platform. The side polishing of the fiber cladding gives access to the evanescent field of the guided mode, while the EWOD platform electrically controls the stepwise translation of a liquid droplet along the variable thickness polished cladding of the fiber. The penetration of the evanescent field into the droplet leads to tunneling of optical power from the fiber core to the droplet, from where it is radiatively lost. As a result of the variable cladding thickness, the position of the droplet along the length of the polished fiber determines the degree of penetration of the evanescent field into the droplet. The droplet position can be electrically changed; thus, controlling the optical power loss from the fiber. This approach has been used to demonstrate an optofluidic continuous-fiber VOA typically providing up to 26 dB of broadband attenuation in the 1550-nm transmission window, with a wavelength dependent loss less than 1.1 dB. In this paper, we present the theoretical modeling and experimental characterization of the system, discussing the influence of the design parameters on the performance of this VOA.

Single-mode fiber variable optical attenuator based on a ferrofluid shutter.

We report on the fabrication and characterization of a single-mode fiber variable optical attenuator (VOA) based on a ferrofluid shutter actuated by a magnetic field created by a low voltage electromagnet. We compare the performance of a VOA using oil-based ferrofluid, with one VOA using water-based 12 ferrofluid, and demonstrate broadband optical attenuation of up to 28 dB with polarization dependent 13 loss of 0.85 dB. Our optofluidic VOA has advantages over MEMS-based VOAs such as simple construction and the absence of mechanical moving parts.

Modeling and Characterization of a Vernier Latching MEMS Variable Optical Attenuator

We report on the modeling and testing of a Vernier latched MEMS variable optical attenuator (VOA) which uses chevron electrothermal microactuators to control fiber-to-fiber optical power coupling. The use of microlatches has the advantage of holding the mechanical position of the fiber, and therefore the level of attenuation, with no electrical energy supplied except only to change the attenuation. Results of analytical electro-thermo-mechanical models of the device are obtained and compared with experimental test results, showing a good agreement. A step resolution of 0.5 μm for this multi-state latched device is achieved using a Vernier latch approach. This incremental step size is smaller than previously reported latched microactuators. The VOA demonstrated an attenuation range of over 47 dB and an insertion loss of 1 dB. The wavelength dependent loss across the optical communications C-band is 1.4 dB at 40 dB attenuation and the 10-90% transition time of the unlatched VOA is measured to be 1.7 ms.

The determination of FFA concentration in transformer oil by fluorescence measurements

Condition monitoring of the paper winding of power transformers involves the measurement of the concentration of 2-furaldehyde, also called furfuraldehyde (FFA) in the transformer oil. Measuring the concentration of FFA in the oil gives a reliable indication of the condition of the paper insulation. This measurement has routinely been performed by using techniques such as high performance liquid chromatography. We report for the first time the use of fluorescence-based methods for the assessment of FFA in transformer oil.

A Review of Single-Mode Fiber Optofluidics

We review the field we describe as “single-mode fiber optofluidics” which combines the technologies of microfluidics with single-mode fiber optics for delivering new implementations of well-known single-mode optical fiber devices. The ability of a fluid to be easily shaped to different geometries plus the ability to have its optical properties easily changed via concentration changes or an applied electrical or magnetic field offers potential benefits such as no mechanical moving parts, miniaturization, increased sensitivity, and lower costs. However, device fabrication and operation can be more complex than in established single-mode fiber optic devices.

Novel disposable biochip platform employing supercritical angle fluorescence for enhanced fluorescence collection

This paper presents an overview of development of a novel disposable plastic biochip for multiplexed clinical diagnostic applications. The disposable biochip is manufactured using a low-cost, rapid turn- around injection moulding process and consists of nine parabolic elements on a planar substrate. The optical elements are based on supercritical angle fluorescence (SAF) which provides substantial enhancement of the fluorescence collection efficiency but also confines the fluorescence detection volume strictly to the immediate proximity of the biochip surface, thereby having the potential to discriminate against background fluorescence from the analyte solution. An optical reader is also described that enables interrogation and fluorescence collection from the nine optical elements on the chip. The sensitivity of the system was determined with a biotin-avidin assay while its clinical utility was demonstrated in an assay for C-reactive protein (CRP), an inflammation marker.