The use of arc-suppression coils in power systems with open-delta regulators

Arc-suppression coil systems are able to improve high voltage system reliability and safety. If these systems are used in high voltage power distribution networks which incorporate open-delta regulators, dangerous over-voltages can occur. Because the open-delta regulators increase the line to earth voltage in two phases only, out of balance line to earth capacitance currents flow through the arc-suppression coil. It is shown that under certain conditions the resultant system voltages can reach dangerous levels. It is recommended that a detailed analysis be carried out before arc-suppression coils and open-delta regulators are installed in the same power system

Magnetic flux density distribution in axial flux machine cores

[Abstract]: A three-dimensional analytical model is presented to evaluate the magnetic flux density distribution in the core of an axial flux machine. The model predicts significantly higher flux density near the outer radius of the core than that at the inner radius. This has been confirmed by experimental test results. The model also predicts the presence of a curvature-related radial component in the magnetic flux density distribution. It is argued that if it can be established that eddy currents, induced by the tendency for the flux to flow radially, have sufficient shielding effect, then radial flux can be ignored and two-dimensional modelling can be use

Feasibility Analysis of Implementing Hybrid Powered Electric Vehicle Charging Stations in Sarawak

— The transportation sector in Sarawak completely depends on fossil fuel which produces a high quantity of greenhouse gases. A suitable design of charging stations for electric vehicles (EVs) equipped with grid-integrated renewable energy resources (RERs) can help in addressing this issue. This paper proposes to enhance the execution requirements of the hybridpowered electric vehicle charging stations (EVCSs) in Sarawak. A generalized approach for modelling a renewable energy-based hybrid microgrid equipped with EVCS is presented in detail. Four types of microgrid configurations with biomass and solar photovoltaic (PV) systems have been studied to find the optimal size of each component feasible for EVCS. Each design of the hybridpowered EVCS has been analyzed in terms of economic and environmental viability using the climate data with associated monetary data. The analysis shows that the cost of lowering emission to zero is directly proportional to the total net present cost (RM 259,088) when using PV microgrid-powered EVCS. The outcome of this paper provides insight for policymakers on the technical and financial benefits of EVCS deployment. It also promotes the industry of Plug-in Electric Vehicles (PEVs) in Malaysia

A new sensorless commutation technique for brushless DC motors

In brushless DC (BLDC) drives commutation is performed by power electronic devices forming part of an inverter bridge. Switching of the power electronic devices has to be synchronised with rotor position. Determination of position, with or without sensors is an essential requirement. The most common sensorless method is based on detection of the zero crossings of back EMF signals. This technique works only above a certain speed. BLDC systems which rely solely on back EMF signals for commutation suffer from relatively poor starting performance characterised by back rotation of up to one hundred and eighty electrical degrees and fluctuations in electromagnetic torque. The aim of this project has been to investigate the possibility of a sensorless technique which is cost effective but with a performance at start-up comparable with that obtained when Hall sensors are used. Initial investigations led to a saliency based method. Theoretical analysis is presented which shows that the method is insensitive to variations in operational parameters such as load current and speed or circuit parameters such as power device voltage drops and winding resistances. Also a starting strategy, relying on saliency related measurements, is proposed which offers starting performance as good as Hall sensor based techniques

Designing printed circuit stators for brushless permanent magnet motors

Progress in a number of areas of technology has made printed circuit motors a serious contender for many applications. Modern cost effective neodymium magnets have allowed compact motor designs. Multi-layer circuit board production techniques have made the production of printed circuit coils cheaper and easier. However, in spite of the growing importance of printed circuit brushless motors, there is a lack of analytical tools to assist with their design. This paper uses geometrical analysis to allow the plotting of printed circuit tracks to be carried out more systematically. The track plotting procedures have been linked with the finite element method to predict rotational EMF waveforms. Six prototype motors were built and they were used to experimentally validate the method of predicting EMF waveforms. A general design algorithm is presented based on the suggested track plotting procedure and the EMF prediction technique

Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters

Limitation of direct current (DC) injection into the alternating current (AC) network is an important operational requirement for grid-connected photovoltaic (PV) systems. One way to ensure that this requirement is met is to use a power transformer as interface to the AC network. But this adds costs, mass, volume and power losses. In a transformerless system, the inverter forming part of the PV system has to be operated so that the DC content in its output current is below the specified limits. Ideally, there should be no DC at the output of the inverter, but in practice, in the absence of special measures, a small amount of DC current is present. A technique for elimination of the DC-offset is proposed. It is based on the sensing of the DC-offset voltage at the output of the inverter. A sensor output is used to drive a feedback system designed to control the operation of the inverter so that the DC-offset is forced to stay within the acceptable limits. A mathematical model for the DC-offset controller is derived. A design procedure, based on the model, is proposed for the controller. The results of tests performed on a system of 1 kW nominal rating provide validation for the mathematical model

DC magnetisation of transformers

A high enough DC component in the current on the secondary side of a transformer causes distortion of the primary side current. Prediction of such distortion relies on the availability of magnetization curves that extend deep enough into saturation. A simple test, carried out at rated voltage, is proposed which allows the magnetization curve to be deduced from measured data. In addition, a systematic procedure has been developed to evaluate the primary current distortion in both single and three phase transformers. Comparison between theoretical predictions and practical measurements are made with reasonable agreement between the two

Remote access laboratories in Australia and Europe

Remote access laboratories (RALs) were first developed in 1994 in Australia. The main purposes of developing them are to enable students to do their experiments at their own pace, time and locations, and to enable students and teaching staff to get access to facilities beyond their institutions. Currently, most of the experiments carried out through RALs are heavily biased to electrical, electronic and computer engineering disciplines. RALs in different Australian and European universities were mentioned and their pros and cons were also discussed. It can be argued that RALs will develop further and faster in the future with improving Internet technology; the rising costs of real experimental equipment will also speed up their development because by making the equipment remote accessible, the cost can be shared by more universities or institutions and this will improve their cost-effectiveness. Their development would be particularly rapid in large counties with small population like Australia, Canada and Russia

Evaluation of neutral voltages in arc suppression coil systems

Although arc suppression coil systems are able to detected high impedance ground faults by monitoring the neutral voltage, there are other system abnormalities which can also cause a change in the neutral voltage. The causes of abnormal neutral voltages in arc suppression coil systems are analysed and criteria are developed to differentiate between them based on the phase angle and magnitude of the neutral voltage. Using the criteria developed in this paper, modern computerised protection systems will be able to automatically take appropriate action based on the type of system abnormality, immediately, when a system abnormality occurs

Sizing nickel iron batteries for RAPS systems

Nickel-iron batteries have long life expectancy and are tolerant of abuse or poor charge regimes. However their larger internal impedance often results in premature voltage cut-out with remote area power supplies (RAPS) inverters. A new method for sizing nickel iron batteries is proposed, which incorporates a technique that helps address this problem at the design stage. An economic analysis is presented which reveals that nickel-iron batteries can represent a cost effective solution in some RAPS applications