P. McGlone

The influence of magnetite nano particles on the behaviour of insulating oils for pulse power applications

The effects of the addition of magnetite nanoparticles on the breakdown strength of three insulating liquids have been examined. The liquids considered are: a mineral transformer oil; a synthetic ester liquid, Midel 7131, and a specialist high permittivity liquid for pulse power applications THESO. The expected increases in breakdown strength were observed in the mineral oil and synthetic ester liquids. However in the case of the high permittivity liquid no significant changes in the breakdown strength were observed. Possible explanations for the differences in the observed behavior for the THESO insulating liquid are discussed.

Uncorrelated multisymbol signals for MIMO system identification

This paper presents a new approach to the system identification of a two-input two-output multivariable system. In a similar manner to that used for the single-input/single-output system, the multi-input multi-output (MIMO) system response may be obtained directly from measured input output frequency responses. An investigation of compact multifrequency data measurement signals, which have been extensively cataloged by the authors, has provided compact multifrequency ternary and quaternary input signals that have uncorrelated spectra. They are powerful multisymbol, multilevel computer generated measurement signals whose signal power is concentrated in either two or three dominant harmonics. As the signals, which are given in this paper, have six, seven, or eight symbols in their measurement codes, both the computation time for the frequency estimates and the experimental time are minimized. Two multifrequency quaternary signals with uncorrelated spectra are used to identify a simulated distillation column. It is shown that the cross coupling terms between the measurement channels may be removed by these digital measurement signals with the same number of symbols but different measurement codes.

Performance evaluation of a differential pressure cell model

This paper describes the development of a mathematical model of a differential pressure cell and its application in MATLAB. The model is also examined in SIMULINK, for the purposes of comparison of the model with the real world. Furthermore, we also describe the application of a system identification method using a multifrequency binary test signal, for comparison with the mathematical model. The method is applied to a pneumatic differential pressure cell. The exploration of the mathematical model shows that while the majority of the subsystems are nonlinear, they can adequately be approximated by Taylor polynomials. This facilitates the modeling of the subsystem elements as linear agents. The identification results show that the cell, composed of three main components-the diaphragm, pilot relay flapper/nozzle, and the feedback bellows-has an overall first-order linear response.

Modelling and identification of differential pressure cells

This paper describes the development of a mathematical model of a differential pressure cell, and its application in MATLAB. The model is also examined in SIMULINK, for the purposes of comparison of the model with the real world. Furthermore we also describe the application of a system identification method, using a multifrequency binary test signal, for comparison with the mathematical model. The method is applied to a pneumatic differential pressure cell. The exploration of the mathematical model shows that whilst the majority of the subsystems are nonlinear, they can adequately be approximated by Taylor polynomials. This facilitates the modelling of the subsystem elements as linear agents. The identification results show that the cell, composed of three main components, the diaphragm, pilot relay flapper/nozzle and the feedback bellows, has an overall first order linear response.

Comparison between RF and electrical signals from the partial discharge activity of twisted pair cables at reduced pressures

A pressure-controlled test facility has been set up that allows the PD behaviour of polymer insulated twisted pair samples exposed to 50 Hz AC voltages in the range of 0 to 10 kV to be characterised. Resulting PD activity is quantified using the methods defined in IEC standard 60270 and by using a simple monopole antenna to detect the RF signals excited inside the pressure vessel by the discharges. This paper gives the results of preliminary tests performed on samples of wire insulated with Ethylenetetraflourethylene, Silicon Rubber and Polyvinylchloride in the pressure range between 103 and 105 Pa in atmospheric air. The dependence of PD inception voltage on the environmental pressure is reported. Changes in the behaviour of the PD activity; the correlations between the RF and electrical measurements and the frequency components of the RF signals as the applied voltage and pressure are varied are characterised and discussed.

System identification using identification patterns

In this paper, system identification techniques using identification patterns are developed for use in on-line, in-situ monitoring of sensors and systems. The dynamic properties of sensors play an essential role in the performance of measurement and control systems. Both the single-frequency identification pattern (SIP) of the squarewave and the compact multifrequency identification pattern (MIP) for other test signals are examined at the output of a system. The dynamic behaviour can then be monitored using identification patterns, where the identification pattern area, as a simple time domain aid, is examined at the output in terms of system parameters.

Investigating the self-heating test for a temperature sensor using a ternary identification pattern

The dynamic properties of temperature sensors play an essential role in the performance of measurement and control systems. Identification patterns may be used in the on-line, in-situ monitoring of temperature sensors. In this paper the self-heating test for a temperature sensor using a ternary multifrequency identification pattern (MIP) is investigated. The dynamic behaviour can be monitored using the MIP, where the ternary signal MIP area, as a simple time domain aid, is examined at the output in terms of the dominant sensor time constant.

The influence of noise in on-line frequency response estimation using a multifrequency ternary periodic signal

This paper investigates the affect of input and output noise in an on-line multifrequency measurement of a linear system. A multifrequency periodic ternary signal and a recursive algorithm, which have been introduced by the authors, are used. The results show that measurement can still be achieved in the presence of noise contamination, in either, or both of the input and output channels. The quality of measurement is extremely gratifying and only begins to suffer when the higher frequency harmonics on the output channel are subjected to vigorous noise. This reaction can be accounted for by signal-to-noise ratio criticality.

New multisymbol multifrequency signals for identification of a linear system with non-linear distortion

Many physical systems exhibit non-linear behaviour. This paper presents the use of new compact multifrequency data measurement signals to identify a linear system with a non-linear distortion at its output. The signals belong to the group of signals exhibiting antisymmetric, or half-period symmetric, properties. A theoretical framework is presented for a non-linear model when using antisymmetric test signals for frequency domain identification. It is shown that the effect of nonlinear distortion is reduced to about 50% by antisymmetric signals. This novel variety of compact multifrequency signals is used in a simulated test of a linear system with non-linear output distortion. A comparison between the new signal and a PRBS signal is reported.