A steady state Model for prediction of amplitude and phase errors in measuring current transformers

Foreseen expansion and increasing complexity of power distribution networks will increase demand for accurate metering of electric energy flow. The current transformer (CT) is widely used in measurement systems and has direct effect on the overall accuracy of electric power measurement. Therefore, its design and performance are of great importance. A steady state model of a CT is proposed to relate its performance to basic magnetic properties of its core. It enables a CT amplitude and phase errors to be predicted from the magnetic permeability and power loss of its core. Therefore it can be easily implemented at the design stage of these devices. The accuracy of the model has been verified against experimental data and the predicted CT errors were found to be in a good agreement with measured values. A negligible leakage reactance design CT is considered in this work, but an additional parameter would have to be considered for gapped cores or non– uniformly distributed windings. CT errors are determined by magnetic properties of its core in a wide flux density range. Measurement of magnetic properties at very low flux densities can be extremely challenging due to low signal-to-noise ratio. An accurate, low flux density measurement system has been developed for the investigation of CTs. It features digital triggering, cycles and moving averaging techniques, innovative digital compensation, customised digital feedback algorithm and is capable of measuring magnetic properties of materials at flux densities as low as few µT. This setup can be used for testing variety of ferromagnetic materials for other low flux density applications such as magnetic shielding

Free vibrations of the column taking into account compressive and thermal load

Free vibrations of slender systems are the subject of many scientific and research works. In this work, the boundary problem of free vibrations of a compressed column, which is additionally heat loaded, is considered. The issue of heat flow in the column is solved using the Finite Element Method. Averaged distribution of material properties is obtained in individual segments of the column in subsequent heating times. The mathematical model of free vibrations takes into account the thermal expansion of the material and the effect of changing the Young's modulus resulting from the effect of heat load. The boundary problem of the free vibrations of the considered system is limited to the linear range (the linear component of natural frequency is considered). The influence of the heat source exposure time on the course of characteristic curves (on the plane: load – natural frequency) is determined. The results are presented for various column diameters

Experimental verification of 2.4 kVAr and 12 kVAr prototype variable inductors controlled by virtual air gaps with magnetic orthogonality

This paper describes experimental verification of single-phase variable inductor prototypes rated at 2.4 kVAr (75 mH, 10 A, 230 V, 24 kg) and 12 kVAr (43 mH, 30 A, 400 V, 78 kg). Results for much smaller devices rated at 1-10 Var are also shown. The variability of inductance of the main AC winding was achieved by adding a DC winding, wound through the apertures placed symmetrically in the core such that both windings were magnetically orthogonal. Local saturation caused by the magnetic field due to DC winding creates virtual air gaps. This method is capable of lowering the main inductance by over 90% if no real air gap is present, but for industrial applications the range of variability is likely to be closer to 20-30% range, depending on the size of the real air gap in the magnetic circuit. The amount of variation/control can be improved by using more than one control winding. Very good repeatability of performance was observed, with relatively small total harmonic distortion introduced due to control. The experimental findings agree with a generalised analytical model

A proposed optical-based sensor for assessment of hand movement

The purpose of this research is to evaluate two types of sensor that can be applied to monitor human finger flexion in real time. Currently, flex sensors are the most commonly used resistance sensors in glove-based systems. However, measurements show that current flex sensors have problems associated with hysteresis error, low sensitivity at small angles, and considerable time drift with large bending angles which render them unsuitable for tracking hand motion at low speed. In contrast, the developed optical sensor prototype has good repeatability, sensitivity and low temporal drift, as well as offering the capability of accurate measurements in both clockwise and anticlockwise directions. The sensor is based on the principle of crossed-polarization detection, and consists of one LED, two rotatable polarizers and one photodiode amplifier which enables the detection of changes in polarized light intensity proportional to angular rotation

Instrumentation for monitoring animal movements

Behavioural experiments often require continuous monitoring of the responses that animals make in different situations and in response to various stimuli. Formerly, recording visual observations of animals followed by the manual post hoc analysis of the data was the most commonly employed approach and has the advantage of being non-invasive. However, manual data extraction can be very time-consuming and introduces a risk of bias in identifying salient responses. Although techniques have been developed for specific applications to automate the analysis of behaviours, including some commercial solutions, many are not always adequate for the particular situation or sufficiently flexible to measure the desired movement. We have developed and implemented a relatively low cost system for video recording and reliably extracting data characterizing animal's kinetic responses. This instrumentation has been successfully utilized in our investigations of pigeon head movements by enabling us to record and compare behavioural responses to different types of stimuli

Instrumentation to investigate the magnetoreception of homing pigeons by using applied magnetic fields

The remarkable ability of diverse animals to orientate and navigate during migration and homing over long distances has fascinated scientists for years. However, how the birds sense and process the magnetic field information in their brains is not known [1]. Recent advances have brought new insights into how field direction, intensity, and polarity are neurally encoded by single cells [2]. Several bird species are believed to possess physiological mechanisms that enable them to navigate using the magnetic field. Generally, it is accepted that there are two sensory magnetoreception mechanisms: a light-dependent cytochrome-based magnetic compass and a magnetite-based map [3]. To date, reproducing experimental results has been problematic perhaps related to the difficulty in controlling magnetic field conditions [4]. We describe here a special instrumentation setup of three-dimensional Helmholtz coils, which are used to cancel out the Earth's magnetic field and then generate a field within the range of the Earth's magnetic field, controlled by a specific current source. The magnetic mapping within the volume of the constructed system is measured and compared against magnetic modeling. The visual programming language, LabVIEW (version 2012SP1) of National Instruments (NI)[5], is used to control the system to generate any specific magnetic field condition