Research Papers - Department of Electrical and Electronic Engineering
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Publication Open Access Condition monitoring in New Zealand power transformers(nternational Conference on Condition Monitoring and Diagnosis (CMD2010), 2010) Hettiwatte, S. N; Fonseka, H. A— Transpower owns and operates New Zealand’s high voltage electricity grid which includes approximately 725 in service power transformers [1]. Presently, condition monitoring of these units is routinely carried out by oil testing (moisture, acidity and dielectric breakdown) and using dissolved gas analysis (DGA), (every year), and winding resistance, insulation resistance, and bushing power factor tests (every four years). However, since the average age of a power transformer in New Zealand is nearly 40 years [1], it is considered that online condition monitoring of important transformers or transformers that have known issues is carried out to identify any incipient faults. The online condition monitoring in existing power transformers is hoped to minimize the risk of sudden failures and thereby prolong the in service life. It is equally important to decide on what to monitor in a power transformer and how to monitor, and these are also governed by the budgetary constraints. Transpower is in the process of acquiring online condition monitoring units for some of the new large power transformers it plans to purchase and will also retrofit such units to some old transformers as required. This paper presents the condition monitoring techniques currently used by Transpower on power transformers, and the online condition monitoring techniques for new and existing power transformers.Publication Open Access A novel visualisation technique for dissolved gas analysis datasets–A case study(Australasian Universities Power Engineering Conference, 2013) Fonseka, H. A; Hettiwatte, S. N; Lee, GDissolved gas analysis is the most widely used diagnostic test in power transformers. There are established methods used in industry for interpreting DGA results. Among these are the IEEE Key Gas Method, Rogers’ Ratios and the Duval Triangle. However, collectively these methods can lead to conflicting results or unclassifiable measurements. This paper presents a visualization technique for interpreting DGA results to mitigate these effects, based on Kernel Principal Component Analysis. DGA measurements from more than 200 power transformers are used to validate the approach.Publication Embargo Switched intelligent grid networking systems(IEEE, 2014-05) Thorogood, A; Hettiwatte, S. NSwitched Intelligent Grid Networking Systems (SIGNS) is the result of research, analysis and development of an alternative process for controlling end-user electrical power quality, as well as transients on the incoming electricity supply grid. In the past power quality issues associated with the grid network were usually generated by the connected loads. This has changed in today's grid system with embedded intermittent renewable energy being included on the energy profile. The research demonstrated that it is possible to control end-user electrical power quality through the addition of battery storage at the user end of the grid and a switching device, forming an intelligent buffer between the electrical grid supply and the load. The function of the device is to select the most appropriate energy source to effectively absorb a proportion of any surges and transients, whilst offering a path for augmented alternative energy .Publication Embargo Missing measurement estimation of power transformers using a GRNN(IEEE, 2017-11-19) Islam, M. D. M; Hettiwatte, S. N; Lee, GMany industrial devices are monitored by measuring several attributes at a time. For electrical power transformers their condition can be monitored by measuring electrical characteristics such as frequency response and dissolved gas concentrations in insulating oil. These vectors can be processed to indicate the health of a transformer and predict its probability of failure. One weakness of this approach is that missing measurements render the vector incomplete and unusable. A solution is to estimate missing measurements using a General Regression Neural Network on the assumption that they are correlated with other measurements. If these missing values are completed, the entire vector of measurements can be used as an input to a pattern classifier. To test this approach, known values were deliberately omitted allowing an estimate to be compared with actual values. Tests show the method is able to accurately estimate missing values based on a finite set of complete observations.Publication Open Access CityTour Bus Locator and Bus Booking Mobile Application(NSBM, Colombo, 2018-08-25) Chandrasiri, S; Pitipana, H; Hettiwatte, S. NThe public bus transportation system has the direct impact on economic development of the country. Scheduling, tracking and monitoring of the public bus transportation is one of the major issues for any public transportation sector. Currently, there are many vehicles tracking systems available using Global Positioning Systems (GPS) technology. At present, bus passengers are unable to gather enough information which would lead up to a stress-free bus ride. Under current conditions a passenger has to wait in the bus stand without having any prior idea about the buses. ‘CityTour’ application assists passengers and the conductor to use bus service in more stress-free, well-organized and a suggestive manner. “CityTour”, is the cross-platform application implemented with the sole purpose of addressing these problems a passenger has. The application will predict the next Bus’s arrival time, seat reservation and a rating which will give an indication regarding the quality of the service offered. Bus conductor has a say in whether a passenger gets a seat or not. ‘CityTour’ application enables the “real-time” passenger bus communication that would lead to a better collaboration and make their day-to-day work easier for both the parties.Publication Embargo Estimating transformer parameters for partial discharge location(IEEE, 2014) Hettiwatte, S. N; Wang, Z. D; Crossley, P. APartial discharge (PD) location in power transformers using electrical methods require transformer parameters to estimate the PD location. Previous research using a lumped parameter model of a transformer consisting of inductance (L), series capacitance (K) and shunt capacitance (C) has shown an algorithm for PD location. This algorithm does not require L, K and C values for the transformer in their explicit form. Rather, the products LC and LK are required. This paper presents three methods of estimating LC and LK values for a power transformer, which could then be used for PD location. The paper shows that all three methods give identical results confirming that either of these methods could be used for estimating LC and LK values. Results based on impedance measurements from two transformer windings are also presented.Publication Embargo Improvement of voltage magnitude and unbalance in LV network by implementing residential demand response(IEEE, 2017-07-16) Rahman, M. D. M; Hettiwatte, S. N; Shafiullah, G. M; Arefi, A; Pezeshki, HMaintaining voltage levels in low voltage (LV) distribution network within the standard limits is the main constraining factor in increasing network hosting ability for high penetration of rooftop photovoltaic (PV). Distribution system operator must be able to take corrective approach to avoid critical voltage unbalance and magnitude violations where rooftop PV generation is high. This study presents an effective method for voltage management in distribution networks through implementation of optimal residential demand response (DR) and transformer tap setting using a particle swarm optimization algorithm. The method is comprehensively verified on a real Australian distribution network with considerable unbalance and distributed generations. The simulation results show that PV penetration of the network can be further increased with the proposed approach.Publication Embargo Incipient fault diagnosis in power transformers by clustering and adapted KNN(IEEE, 2016-09-25) Islam, M. D. M; Lee, G; Hettiwatte, S. NDissolved Gas Analysis (DGA) is one of the proven methods for incipient fault diagnosis in power transformers. In this paper, a novel DGA method is proposed based on a clustering and cumulative voting technique to resolve the conflicts that take place in the Duval Triangles, Rogers' Ratios and IEC Ratios Method. Clustering technique groups the highly similar faults into a cluster and makes a virtual boundary between dissimilar data. The k-Nearest Neighbor (KNN) algorithm is used for indexing the three nearest neighbors from an unknown transformer data point and allows them to vote for single or multiple faults categories. The cumulative votes have been used to identify a transformer fault category. Performances of the proposed method have been compared with different established methods. The experimental classifications with both published and utility provided data show that the proposed method can significantly improve the incipient fault diagnosis accuracy in power transformers.Publication Embargo Corrosion detection in steel reinforced aluminium conductor cables(IEEE, 2014-09-28) Jaffrey, N. A; Hettiwatte, S. NAluminum Conductor Steel Reinforced (ACSR) cables, as part of transmission lines, are used in severe environments in coastal areas and industrial zones for many years. These cables are affected by galvanic corrosion in the interface between the aluminum and steel strands. This paper investigates the existing methods of corrosion detection used in ACSR cables of overhead transmission lines, and estimates the location of corrosion through simulation in a computer program. The paper also analyses two promising methods of corrosion detection, namely “electromagnetic induction” and “time domain reflectometry (TDR)”, and explains in detail their principle of operation and efficiency. The paper then thoroughly investigates the time domain reflectometry techniques by implementing it in a computer program, and the simulation results are discussed.Publication Open Access Application of Parzen Window estimation for incipient fault diagnosis in power transformers(The Institution of Engineering and Technology, 2018-12) Islam, M. D. M; Hettiwatte, S. N; Lee, GAccurate faults diagnosis in power transformers is important for utilities to schedule maintenance and minimises the operation cost. Dissolved gas analysis (DGA) is one of the proven and widely accepted tools for incipient fault diagnosis in power transformers. To improve the accuracy and solve the cases that cannot be classified using Rogers’ Ratios, IEC ratios and Duval triangles methods, a novel DGA technique based on Parzen window estimation have been presented in this study. The model uses the concentrations of five combustible hydrocarbon gases: methane, ethane, ethylene, acetylene and hydrogen to compute the probability of transformers fault categories. Performance of the proposed method has been evaluated against different conventional techniques and artificial intelligence-based approaches such as support vector machines, artificial neural networks, rough sets analysis and extreme learning machines for the same set of transformers. A comparison with other soft computing approaches shows that the proposed method is reliable and effective for incipient fault diagnosis in power transformers.