102,557 research outputs found
Public procurement: International cases and commentary
No full textIn many countries and sectors, public procurement is developing from a functional orientation to an effective socio-economic policy lever. There is a great interest among managers and academics to learn from other countriesâ and other sectorsâ change initiatives and how they dealt with the challenges they encountered. This text provides such learning opportunities, presenting case studies of public procurement, covering diverse nations, sectors and issues.The cases are combined with editorial commentary and contextualizing chapters to assist the student reader in understanding this complex topic. The text combines descriptions of cases of public procurement with cross case analysis to draw out the key dimensions to enable further examination of the central themes. Each case study concludes with three questions to aid its use as a teaching and training text.Edited by a team of internationally recognised experts in the field this innovative text illustrates the strategies and innovations within public procurement on a global scale and highlights common problems that all countries encounter. Public Procurement is vital reading for anyone with an interest in this topical area
Methods for wavelet-based autonomous discrimination of multiple partial discharge sources
No full textRecent years have seen increased interest in the application of on-line condition monitoring of medium voltage networks as the need to maintain and operate ageing cable networks increases. Detection and analysis of partial discharge (PD) activity is generally used as an indicator of pre-breakdown processes that may be indicative of insulation degradation over time. A significant challenge for on-line monitoring is discrimination between multiple partial discharge sources that will often naturally exist in the data. To discriminate between PD sources each PD signal is represented as a feature vector and a clustering algorithm is used to identify clusters in the resulting feature vector space, often after dimensional reduction. Each cluster identified in the data corresponds to a distinct PD source. In this work a comparison of clustering algorithms and dimensional reduction techniques is performed to identify clusters for a variety of PD data sets, in all cases the feature vector is created using wavelet decomposition energies. The three clustering algorithms used were Density Based Spatial Clustering of Applications with Noise (DBSCAN), Ordering Points to Identify Clustering Structure (OPTICS) and Simple Statistics-based Near Neighbour clustering technique (SSNN). The two dimensional reduction techniques considered were Principal Component Analysis (PCA) and t Distributed Stochastic Neighbour Embedding (t SNE). At present the most commonly used combination of dimensional reduction technique and clustering algorithm for PD data are PCA and DBSCAN respectively. From the comparison performed in this work it was found that t SNE combined with OPTICS or SSNN were the most successful at clustering PD data. For use in practical situations SSNN is preferred over OPTICS as it requires only a single input parameter, which generally be hardcoded, leading to a completely autonomous technique. It is therefore suggested that a combination of t SNE and SSNN is particularly appropriate for discriminating PD sources
Data driven transformer thermal model for condition monitoring
No full textCondition monitoring of power transformers, which are key components of electrical power systems, is essential to identify incipient faults and avoid catastrophic failures. In this paper machine learning algorithms, i.e. nonlinear autoregressive neural networks and support vector machines, are proposed to model the transformer thermal behavior for the purpose of monitoring. The thermal models are developed based on the historical measurements from nine transformers comprised of two 180-MVA units, four 240-MVA units and three 1000-MVA units. The data consist of load profile, tap position, winding indicator temperature (WTI) measurement, ambient temperature, wind speed and solar radiation. The results are validated against field measurements, and it is clearly demonstrated that the alternative algorithms surpass the IEEE Annex G thermal model. An incipient thermal fault identification algorithm is then proposed and successfully used to identify an issue using measurements taken in the field. This algorithm could be used to alert the operator and plan intervention accordingly
Investigation of void erosion on partial discharge activity using simulation
No full textModels of partial discharge (PD) activity have been widely used to investigate PD activity in cylindrical and spherical voids within insulation material. PD activity is known to alter void geometry due to the erosion of insulation material from the deployed charge. In this work, a PD model is produced to investigate the impact of void erosion on PD activity. The model is validated by reproducing measured phase resolved PD (PRPD) patterns for a spherical void in a homogeneous dielectric material. The impact of void erosion is then investigated by running the model with different void geometries. The results from the model show that the PRPD patterns depend heavily on the level of erosion due to the impact of the erosion on the electric field at the void surface
Measuring and simulating partial discharge activity in a spherical cavity during electrical ageing processes
No full textThis paper considers partial discharge (PD) activity in an air-filled cavity under accelerated ageing condition. During ageing, PDs in the cavity bombard the inner cavity surface with charged particles leading to surface erosion and eventually complete failure. The time-evolution of phase-resolved partial discharge (PRPD) pattern demonstrates evidence of the formation of an eroded hole. Analysis of PD statistical quantities for distinct patterns is obtained in terms of apparent charge and the number of PDs per cycle. The physical parameters of the test sample such as the cavity radius, the material thickness, the applied voltage and the relative permittivity are used to implement a Finite Element Analysis (FEA) model, which is used to develop a PD model. The simulated PD behavior was analyzed in terms of PRPD patterns and statistical quantities in order to make a comparison with measurement results.</p
Investigating the dependence of partial discharge activity on applied field structure
No full textModels of partial discharge (PD) activity have been used to successfully replicate PD data from experiments under controlled conditions. These experiments have typically investigated PD activity from an artificial defect, often a gaseous void, surrounded by a homogeneous dielectric material in a parallel plate electrode arrangement where the applied electric field acts in one direction. In this work PDs from gaseous voids in elliptical applied fields, found in three-phase cable joints, are modelled. PD activity was shown to be highly dependent on void location, with PDs per cycle and apparent charge magnitudes varying significantly between void locations. It was also shown that the measured apparent charge from PD is highly dependent on the direction of the discharge and the distance of the void from the measuring electrode. The limitations of the model are discussed and the improvements that will be made in future work introduced
International research study of public procurement
No full textIn this chapter we examine the specific issue of public procurement, its importance to local, regional, national, and international economies as evidenced in a unique international comparative research study – the International Research Study of Public Procurement (IRSPP). First the public procurement literature is examined. Then the story of IRSPP is told – why and how it was formed, and the five phases of research that have been conducted to date since 2003. The phases build on prior phases as knowledge and priorities for research have unfolded. To date IRSPP has contributed to knowledge and changed public procurement practice internationally, specifically relating to understanding international differences and similarities, understanding sectoral issues, examining capacity and capability, exploring the strategic role of public procurement in supporting and delivering economic stimulus packages, and examining how governments can improve engagement of small to medium enterprises in government procurement contracts. It is concluded that it is not necessarily the case that the developed world is outperforming less developed nations; powerful lessons have been learnt from developing nations in terms of their ability to use public procurement as a lever of economic and societal reform and integrate it more fully in government policy and practice
Implementing Government Policy in Supply Chains: An International Coproduction Study of Public Procurement
No full textPublic procurement is the commercial arm of governments, contracting for goods, and services to feed public sector service provision. However, mainstream operations and supply chain management journals have published little on supply chains to governments, public procurement, and the significance of engaging small businesses in government supply chains. Policy feedback theory and thirteen coproduced international case studies of public procurement and small business agency dyadic relationships are used to explore this space. The research highlights the importance of both public procurement and small business as areas of policy and supply chain management research. Policy feedback theory is introduced as a means to understand relationships and is applied to a coproduction study to understand how supply chain management research can both explore and change policy
Physical models for field based partial discharge measurements
No full textCurrent models of partial discharge (PD) behaviour are focused on the reproduction of deterministic, experimental data. This data is traditionally taken under strictly controlled conditions and thus exhibits minimal noise. This contrasts field PD measurements which exhibit high levels of stochasticity and extreme sensitivity to on-site conditions. In this paper partial discharge measurements are simulated from three-phase cable experiments, which aim to imitate conditions found in the field. The results show good agreement between experimental and simulated data, in terms of both phase resolved plots and non-linear invariants. The numerous additions and improvements required to describe PD behaviour in field equipment are discussed, and will form the basis for future work
Modeling partial discharge in a three-phase cable joint experiment with minimal adjustable parameters
No full textA general physical model of partial discharge (PD) has been developed and used to simulate discharges within a void at the tip of a metallic spike defect within a three-phase 11 kV paper insulated lead covered (PILC) cable joint. Discharges are modeled by altering surface charge density at the void boundary using a logistic function distribution. The model was validated against experimental data, and a good agreement was observed with minimal free parameters. The model was then used to investigate the impact of single phase energization on PD activity in three-phase PILC cable joints. It was concluded that PD testing of three-phase PILC cable joints should be performed at raised temperatures with the cable fully energized as this results in a higher frequency of PD activity, and reduces the level of background PD from cable terminations. This research represents a further step towards developing PD models that can describe measurements taken from operational high voltage plant
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