Dalila Mat Said

Analysis of distribution transformer losses and life expectancy using measured harmonic data

Three-phase distribution transformer in electrical power systems are usually designed for utilizing at the rated frequency and linear load. A different performance compared with that of the designed transformer occur when non-linear loads introduce harmonics to the supply. With the increasing use of nonlinear load the harmonic ay overheat the transformer leading to a poor power quality. The increased losses in the transformer due to the harmonic distortion can cause unnecessary winding loss and typical temperature rise. This paper presents the analysis and evaluation of distribution transformer losses under non-linear load by using real data. In this study, losses caused by harmonic and life of the distribution transformer were determined. Results show that an increase in the current harmonic distortion will increased in the current harmonic distortion will increase the transformer losses and hence decreased its life expectancy.

Improving the MW-Mile Method Using the Power Factor-Based Approach for Pricing the Transmission Services

The MW-Mile method is an embedded cost pricing method, which is widely used to determine transmission pricing. The method is formulated based on the distance and active power flow in each line of the transmission network. This method may be considered as the first pricing strategy proposed for recovering the fixed transmission cost, based on the actual use of the transmission network. However, this method suffers from the provision of unfair charges to the users, since it ignores the quality of the load in allocating the transmission cost. This paper proposes an improved MW-Mile method by considering not only the changes in MW flows but also the quality of the load, i.e., the power factor. In this study, the IEEE 14-bus system was used to illustrate the contribution of the proposed method in allocating transmission cost to the user in a fair manner.

A comprehensive overview of different protection schemes in micro-grids

Abstract In recent years, there has been an increasing interest in applying micro-grid systems not only to improve reliability but also to enhance power quality. One of the major challenges associated with the implementation of micro-grids is to design an appropriate protection scheme which has the ability to protect micro-grids in both grid-connected and islanded mode. In order to overcome this challenge, different approaches have recently appeared in the literatures. This paper aims to provide an introspective review of the available protection schemes used for addressing micro-grid protection issues in both grid-connected and islanded mode. In addition to description of existing protection schemes to date and categorizing them into specific clusters, a comparative analysis is done in which the merits and demerits of each methodology are evaluated.

Power supply quality improvement: harmonic measurement and simulation

This paper presents the harmonic measurement and simulation in a power distribution network and then gives suggestion of filter installation to improve harmonic distortion. The specific case study has been conducted at Faculty of Electrical Engineering, UTM building where nonlinear loads such as computers and fluorescent lamps which produce the harmonics are connected. Measurements are conducted at each subswitch board (SSB), main-switch board (MSB) and substation of the faculty. The selected networks are modelled and simulated using SKM-Power Tools for Windows software. The results from the measurement are compared with the simulation result, and it is found that there are quite close to each other. Based on the simulation, harmonic distortion improved after filter installation.

Harmonic power flow in Nigerian Power system with PV site

The penetration of distributed generation (DG) scheme in modern power system is progressively increasing because of the call for environmental friendly energy resources. Photovoltaic (PV) has been identified as one of such energy resources which can provide reliable and efficient power supply when integrated with distribution network. The installation of a single site PV module is modelled in a bus bar of the 31-bus 330kV network of Power Holding Company of Nigeria (PHCN) to characterize and predict harmonic pattern therein and also to assess bus voltage disturbance in the network due to increase in harmonic emission level. The simulation results obtained using PCFLO version 6 programme platform indicates that the system voltage variation is dependent on harmonic emission level. In a bus bar the highest and constant non-sinusoidal current Total Harmonic Distortion (THD) of 29% flows in the neutral of the apparatus in the candidate bus where the non-linear load is installed irrespective of harmonic current source magnitude.

Impact study of practical harmonic data using time series simulation

With the increasing proliferation of non-linear loads, more harmonics are expected to be injected into the distribution system. This paper presents time series simulations of harmonic analysis in the distribution system. Modeling and analysis approach is used to perform the time series of harmonic analysis. OpenDSS, an open-source distribution system simulator is utilized in order to perform the studies needed. This paper also includes several case studies based on IEEE test feeder and are analysed by utilizing the harmonic power flow analysis. The time-series simulation is performed by using the practical harmonic data obtained from the industries.

A Protection Strategy for Micro-Grids Based on Positive-Sequence Impedance

ABSTRACTIn recent years, the concept of micro-grid has appeared as an appropriate way for the integration of Distributed Energy Resources (DERs) in the distribution networks. However, micro-grids have encountered a number of challenges from control and protection aspects. One of the main issues relevant to the protection of micro-grids is to develop a suitable protection technique which is effective in both grid-connected and stand-alone operation modes. This article presents a new micro-grid protection strategy based on positive-sequence impedance using Pha-sor Measurement Units (PMUs) and a designed Microprocessor-Based Relay (MBR) along with a narrowband communication system (only to exchange digital information, not electrical power). The main attribution of the proposed scheme is that it has the ability to protect micro-grids containing either radial or looped feeders; additionally, the capabilities of automatic updating of pick-up threshold value and single-phase tripping have been considered in the...

Harmonic measurements and analyses in distribution infrastructure feeding selected institutions in Malaysia and Nigeria

Potential of harmonic generations by research institutes and universities have not been exhaustively investigated in some developing Countries. This paper therefore presents measurements and analyses of harmonic distortions in distribution infrastructure feeding selected institutions in Malaysia and Nigeria. Harmonic data were collected over extended periods using a power quality analyzer (Fluke 435) for selected time intervals in two different universities, one each from Southern Malaysia and Northern Nigeria. The acquired data were preprocessed using inbuilt Discrete Fourier Transform (DFT) and further statistically analyzed in Excel and MATLAB environments. The main results respectively, revealed a maximum total harmonic distortion in voltage and current of 1.62% and 17.14% in a Malaysian university as against 1.3% and 14% in Nigerian university. Statistical analyses based on time stamped THDV and THDI have clearly demonstrated the extent of harmonic generations in the two institutions which even though are within recommended IEEE standard, exhibited distinctive diurnal variation patterns.

Monte Carlo simulation of a microgrid harmonic power flow

Abstract With the transformation of power utility companies from vertical structure to full deregulated entities, the need for the integration of distributed generation (DG) resource in the form of Microgrid (MG) system would soon become indispensable in most deregulated power systems. This is due to renewability of such generation systems. The power quality performance in terms of intermittent energy of these DG systems supply is the major limitation to their full integration as the sole generation entities that can propel rapid decentralization of electric power systems operation. Nonetheless, the acceptable standard is to operate them in an islanding mode or as a MG optimally dispatch among generation mix. This paper developed a total harmonic distortion models for a Microgrid bus in a Nigerian grid system and applied Monte Carlo technique to reliably predict the level of harmonic power flow in the system. The result shows that the distortion increases as the demand factor of the station decreases.

Experience in online power quality monitoring through VPN

The concern towards power quality has increased rapidly due to the amount of losses it created. Throughout the world, many researchers have proposed a study on various aspects of power quality, which may be used to overcome or reduce the effects. In this paper, a project initiated by the Energy Commission of Malaysia has been carried out to find the level of power quality in Malaysia as well as to estimate the cost associated with power quality. The Malaysian data on power quality will be recorded and collected online by using the standards compliance equipments, Fluke 1750. The advanced in the communication network has made this project successful as a large amount of data can be downloaded online. The analysis of the recorded data can be made systematically as much software is available in the market which helps the consultant to develop a more user friendly database. The findings from this project will be used to determine the best possible solution for the national interest.