Flicker Transfer in Radial Power Systems

Loads which exhibit continuous and rapid variations in their current can cause voltage fluctuations that are often referred to as flicker. One good example for such loads is arc furnaces which are usually fed by dedicated feeders from the high voltage busbars in transmission systems. The flicker generated from such loads will propagate to the upstream HV point of common coupling (PCC), and from there to the downstream through the transmission and sub transmission systems. This paper demonstrates how the generated flicker is propagated from the HV PCC to the downstream in radial networks exhibiting different levels of attenuation depending upon the load composition of the downstream. Theoretical investigations on flicker transfer have been carried out using simple and more advanced modelling of loads and simulations of radial transmission and sub transmission networks having different load types. The behaviour predicted by the theoretical work is supported through field measurements that have been carried out in an actual network

Investigations of a novel small animal PET scanner with depth of interaction using GATE and a newly developed data rebinning application

Current Positron Emission Tomography (PET) detectors suffer degradation in the spatial resolution at the edges of the field of view. This occurs as a result of the lack of depth of interaction (DOI) information which causes uncertainty in deducing the Lines of Response (LOR) between coincident events. The Centre for Medical Radiation Physics at the University of Wollongong has developed a novel detector module for use in small animal PET which will provide depth of interaction information while retaining the sensitivity of current scanners. This will result in superior imaging together with the ability to locate smaller lesions. This work focuses on preliminary investigations of the suitability of replacing the bulky scintillator crystals and photomultiplier tubes of traditional PET detector modules with compact LYSO scintillator crystals individually coupled to Si photodetectors. Preliminary simulations focused on optimising the detector module were per- formed using the GATE Monte Carlo package. Data from the simulations was processed using a newly developed sinogram binning application. This application is exible and able to adapt to numerous detector geometries based on user input. Depth of interaction information is automatically considered when binning the sino-gram. Comparison of data from Monte Carlo studies processed with the sinogram binning application and experiments using a microPET Small Animal PET scanner are presented to illustrate the suitability of the sinogram binning application for future Monte Carlo PET data processing. The spatial resolution results which are provided indicate this detector module is capable of providing superior performance to monolithic scintillator crystal detector modules. Furthermore, notable advances can be made towards a significant reduc-tion of the radial elongation artefact at the edges of field of view. Other parameters which are important to the process of quantifying the performance of a small ani-mal PET scanner are also presented including optimisation of energy windows, the crystal size and detector configuration

Evaluation of MegaVoltage Cone Beam CT image quality with an unmodified Elekta Precise Linac and EPID: a feasibility study

In order to increase the accuracy of patient positioning for complex radiotherapy treatments various 3D imaging techniques have been developed. MegaVoltage Cone Beam CT (MVCBCT) can utilise existing hardware to implement a 3D imaging modality to aid patient positioning. MVCBCT has been investigated using an unmodified Elekta Precise linac and 15 iView amorphous silicon electronic portal imaging device (EPID). Two methods of delivery and acquisition have been investigated for imaging an anthropomorphic head phantom and quality assurance phantom. Phantom projections were successfully acquired and CT datasets reconstructed using both acquisition methods. Bone, tissue and air were 20 clearly resolvable in both phantoms even with low dose (22 MU) scans. The feasibility of MegaVoltage Cone beam CT was investigated using a standard linac, amorphous silicon EPID and a combination of a free open source reconstruction toolkit as well as custom in-house software written in Matlab. The resultant image quality has 25 been assessed and presented. Although bone, tissue and air were resolvable 2 in all scans, artifacts are present and scan doses are increased when compared with standard portal imaging. The feasibility of MVCBCT with unmodified Elekta Precise linac and EPID has been considered as well as the identification of possible areas for future development in artifact correction techniques to 30 further improve image quality