P Wang

Site Assessment of Multiple-Sensor Approaches for Buried Utility Detection

The successful operation of buried infrastructure within urban environments is fundamental to the conservation of modern living standards. Open-cut methods are predominantly used, in preference to trenchless technology, to effect a repair, replace or install a new section of the network. This is, in part, due to the inability to determine the position of all utilities below the carriageway, making open-cut methods desirable in terms of dealing with uncertainty since the buried infrastructure is progressively exposed during excavation. However, open-cut methods damage the carriageway and disrupt societys functions. This paper describes the progress of a research project that aims to develop a multi-sensor geophysical platform that can improve the probability of complete detection of the infrastructure buried beneath the carriageway. The multi-sensor platform is being developed in conjunction with a knowledge-based system that aims to provide information on how the properties of the ground might affect the sensing technologies being deployed. The fusion of data sources (sensor data and utilities record data) is also being researched to maximize the probability of location. This paper describes the outcome of the initial phase of testing along with the development of the knowledge-based system and the fusing of data to produce utility maps.

Application of wavelet-based de-noising to online measurement of partial discharges

For online detection of partial discharge (PD) activity within power cables and cable accessories, one of the non-conventional PD detection techniques, VHF capacitive coupling has been proved to be suitable. However, the existence of excessive interference can significantly influence the measurement sensitivity and reliability. This paper investigates the application of wavelet transforms for de-noising signals obtained using capacitive couplers. The experimental work has been carried out on a 132 kV cable loop with a known defect within the cable joint. Obtained results indicate that the wavelet analysis technique can effectively discriminate internal PD pulses among corona discharges and pulse-like interference. Further, removal of interference has been achieved by applying level dependent threshold values.

Thermal bubble motion in liquid nitrogen under nonuniform electric fields

This paper describes an experimental study into the influence of a non-uniform electric field on bubble motion and behavior in liquid nitrogen. The electric field effect on bubble motion as it rises due to buoyancy within applied dc electric fields is quantitatively investigated using a rod-plane gap. Thermal bubble motion and bubble collision with the plane electrode processes were observed in these experiments. The experimental results show that dc non-uniform electric fields have an obvious effect on bubble behavior; bubbles move closer to the plane electrode away from a higher field region to a lower one, irrespective of electric field direction. A model based on analysis of the forces acting on the bubble has been developed. This set of differential equations describes the motion of a spherical bubble in the rod-plane gap with voltage and can be solved numerically to determine bubble trajectory. Compared to experimental data, the theoretical prediction is in very good agreement.

Design and testing of an induction coil for measuring the magnetic fields of underground power cables

This paper presents the design and experimental testing of an induction coil as a magnetic field sensor with other measurement devices. The results show that the induction coil functioned as expected, giving a high sensitivity to magnetic fields at 50 Hz. Such fields emitted from power cables can be detected not only in a laboratory environment but also on a pavement.

Detection and location of underground cables using magnetic field measurements

This paper describes an experimental study into the detection and location of underground cables using magnetic field measurements. The basic theory behind the technique is discussed. A method of locating and classifying buried cables using measurements of their magnetic field is then introduced and explained. Experimental results are presented, which show that this system can give useful results in uncluttered locations. Some options for extending the system so that it can be used in cluttered locations, and for integrating the system into multi-sensor device, are discussed briefly.

The effect of an electric field on behaviour of thermally induced bubble in liquid nitrogen

The effect of a dc uniform electric field on the behaviour of bubbles in liquid nitrogen such as their growth, deformation and departure frequency has been experimentally investigated. The experiment was performed using a stainless steel mesh-plate electrode. The experimental results show that (1) prolate spherical bubbles are formed in the direction of electric field and bubble deformation increases with increasing applied voltage, (2) the bubble departure frequency decreases and the departure volume increases with increasing electric field strength, (3) any effect of the electric field polarity is not obvious. For clarifying these phenomena, the electric field distribution around a bubble has been simulated using the finite element analysis (FEA) method and the electric force acting on bubble calculated numerically. In addition, the effect of changes to thermal bubble behaviour on boiling heat transfer is also discussed. Obtained results may lay a foundation for exploring the mechanism of electrohydrodynamic (EHD) enhancement of boiling heat transfer of liquid nitrogen.

Thermal bubble dynamics in cryogenic liquids under non-uniform electric fields on superconducting power apparatus

Thermal bubbles in the liquid coolant of superconducting and cryogenic apparatus are considered to be one of the factors that reduce the electrical breakdown voltage of the apparatus. This paper describes an experimental study of the influence of a non-uniform electric field on bubble behaviour and motion in liquid nitrogen. The electric field effect is quantitatively investigated by performing experiments at various electric stresses using a rod-to-plane gap. Thermal bubble motion and bubble deformation processes were observed in these experiments. The experimental result shows bubbles move closer to the plane electrode from a higher field region to a lower one, irrespective of electric field direction in the presence of non-uniform electric fields. Furthermore, the bubble dynamic mechanism has been analysed and explained by considering the electric field distribution and the electric field force. Results show that the gradient force greatly affects the bubble dynamics.

Magnetic Field Measurement to Detect and Locate Underground Power Cable

Accurate location of buried cables is crucial for future application of trenchless technologies in urban areas. This paper describes an experimental study on detection and location of underground power cables using magnetic field measurement. To do this, a measurement system is designed to be able to measure the magnetic field of an underground power cable at a number of points above ground. It was constructed using battery powered data acquisition modules connected to a coil array, and controlled by a laptop. The experimental investigation has been carried out in a university car park, where the universitys utility map shows an isolated power cable. The results shows that the measurement system and cable location method predict a reasonable position of target cable.

A model for bubble motion in non-uniform electric fields

Electrohydrodynamic effects on bubble motion in dielectric fluids has found positive application for enhanced boiling heat transfer, for example in refrigerators. However the motion of bubbles in columns of dielectric fluid is also of interest where the presence of bubbles may adversely affect the breakdown performance of the liquid dielectric when employed as an electrical insulation. This is the case for superconducting power apparatus designs where liquid nitrogen is used as both coolant and electrical insulation. A model is presented for the bubble motion in a dielectric fluid under the influence of dielectrophoretic force. A model has been developed by analysis of the forces acting upon a bubble within a non-uniform electric field with rod-plane electrode geometry. This set of differential equations can be solved numerically to determine the bubble trajectory for a specified applied voltage. Model results are compared to experimental data for a range of voltages obtained in a column of liquid nitrogen.

Mapping the Underworld: A Step-Change in the Approach to Utility Location and Designation

Trenchless technologies (TT), unlike open cut trenching, offer the potential to install, maintain and refurbish buried utilities without the need to close long stretches of carriageway. Recent studies indicate that carbon emissions associated with trenchless installations are far smaller, and trenchless installations are more sustainable, than trenching. Yet utility companies, and their contractors, routinely shun trenchless technologies due to the perceived risk of damaging previously undetected third party assets. Mapping the Underworld (MTU) seeks to create a multi-sensor tool, and a new philosophical approach to underground mapping, to mitigate such risks and facilitate the routine adoption of TT. The novel approach is now being developed through the proof of concept stage towards field trials and the results of these proving trials form the basis of this paper. Moreover such street works, like all construction, repair, renewal and maintenance projects, must be reviewed in terms of a sustainability assessment framework to explore their real costs and benefits to the society on behalf of which, as ultimate ‘users’ of the facilities, the works are being carried out. This paper seeks to integrate the findings of a highly multi-disciplinary technology-based project with a wider research programme on the context of effective and efficient working in the streets. The lessons drawn from this programme of research extend to all aspects of pipeline engineering.