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Journal Cover Engineer : Journal of the Institution of Engineers, Sri Lanka
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  This is an Open Access Journal Open Access journal
   ISSN (Print) 1800-1122
   Published by Sri Lanka Journals Online Homepage  [48 journals]
  • Current Transformer Performance during Transient Conditions and the
           Development of a Current Transformer Selection Criterion for Protection
           Applications

    • Abstract: One of the most crucial requirements for the correct functioning of power system protection equipment is the optimum selection of current transformers (CTs). Therefore, when selecting CTs, the protection engineer has to pay attention to steady state performance as well as transient performance of current transformers. The transient performance of current transformers varies with both system parameters and current transformer parameters. System parameters vary with the fault level and with the inductance to resistance ratio (L/R) at the fault location. In the power system of Sri Lanka, these parameters rapidly vary due to network developments. Thus, the type of the protection relay selected, the type of the protection function and the arrangement of the switchgear have a huge influence on current transformer selection. This paper discusses the development of a current transformer selection criterion for protection applications based on the transient performance of the transformers.In addition to analyzing the current transformer transient performance, PSCAD software has been used in this study to simulate current transformer performance during fault conditions with a case study done to validate the developed selection criterion. Published on 2016-07-29 00:00:00
       
  • Burnt Clay Bricks as an Alternative Filter Media for Pebble Matrix Filters
           (PMF)

    • Abstract: A novel method called PMF has proved to be suitable under tropical monsoon conditions for pre-treating high turbidity water before water is introduced to Slow Sand Filters (SSFs). The scarcity of sources of pebbles of the required quality, government regulations on pebble dredging and higher material cost were identified as key problems during the construction of the first ever full scale PMF plant in Sri Lanka at Kataragama. In order to investigate possibilities of utilizing alternative-filter media for PMF, laboratory tests were conducted using different configurations of chips and burnt clay bricks which are available readily in Sri Lanka. Two filter media configurations were tested using a laboratory scaled model at an influent turbidity of 60 NTU. The optimum configuration was selected based on the maximum turbidity removal efficiency obtained and was tested by changing influent turbidity. Broken clay bricks with sand in a 1:1 ratio are found to have greater potential as a pre-treatment media for turbidity removal. Moreover, bricks can be utilized as a feasible alternative to natural pebbles. Test results showed that in contrast to chips ,turbidity removal efficiency increased with the increment of influent turbidity when bricks were used as the filter media. Published on 2016-07-29 00:00:00
       
  • Determination of Capitalization Values for No Load Loss and Load Loss in
           Distribution Transformers

    • Abstract: A large number of distribution transformers are being currently used in the electricity distribution network in Sri Lanka. When purchasing them, it is not sufficient to evaluate only the initial price of the transformer. There are no load losses as well as load losses in the transformer during its life span, which is about 35 years. Therefore, a transformer purchaser has to evaluate the total lifetime cost of the transformer, which includes its purchase price, and the cost of losses that can occur during the life of the transformer. Traditionally, this evaluation has been done based on the Total Owning Cost (TOC). This paper discusses setting up of a methodology to calculate capitalization values for losses in distribution transformers used in Sri Lanka, using IEEE loss evaluation guide.Capitalization values for distribution transformers depend on capacity and energy costs, economic considerations and on their load profiles. In this research, capitalization values are calculated for three different load profiles of the transformers installed in rural, semi-urban and urban areas of Sri Lanka. In future, any utility can purchase distribution transformers by calculating capitalization values using the methodology presented in this study which is based on a set of economic and other parameters suitable for different applications, i.e. rural electrification, loss reduction in urban cities, augmentation of distribution transformers, etc. Published on 2016-07-29 00:00:00
       
  • Review of Roundabout Design Standards and the Development of a Roundabout
           Design Guideline for Sri Lanka

    • Abstract: In Sri Lanka, the geometry of roundabouts has a considerable influence on their operation. The increase in road traffic and the large number of long vehicles that ply on the roads have contributed to the malfunctioning of some of these roundabouts. The objectives of this study were to review the roundabout design guidelines, identify issues in the existing roundabouts and prepare a roundabout design guideline appropriate for Sri Lanka. Twenty four roundabouts located in some of the major cities were selected for the study. The design parameters of the geometries of the selected roundabouts were compared with those recommended in five major design guidelines. Data on the main geometric parameters of each roundabout were collected through field measurements and calibrated satellite images. The dimensions and the design parameters of these roundabouts were compared with those stated in a few international roundabout guidelines. A swept path analysis was carried out on selected roundabout layouts for single unit trucks to determine the adequacy of their entry widths, circulation widths, exit widths and operational speeds. The entry radiiwere higher than those recommended in the international standards. The design parameters of the existing roundabouts that required improvements were identified and suitable values for the selected design parameters have been proposed. Most of the roundabouts meet the minimum requirements specified in the international guidelines for the centre island diameter (100%), circulation width (92%), and exit radius (92%). Published on 2016-11-22 00:00:00
       
  • From the Editor Vol.49 (4)

    • Abstract: No abstract available Published on 2016-11-22 00:00:00
       
  • A Comparison of Methods of Estimating Missing Daily Rainfall Data

    • Abstract: The availability of a long and complete rainfall record is very important for carrying out a hydrological study successfully. However in general, the data series in these records may contain gaps for various reasons. The objective of this study is to analyse the different methods available for filling gaps in rainfall data records and propose a method suitable for a river basin situated in a mountainous area in Sri Lanka. Towards this end, daily rainfall data from ten gauging stations in the upper catchment area of BaduluOya were collected. Seven different techniques were studied to ascertain their suitability. The methods studied were the Arithmetic Mean method, Normal Ratio method, Inverse Distance Weighting method, Linear Regression method, Weighted Linear Regression method, Multiple Linear Regression method and the Probabilistic method. The data generated for the target stations were compared with actual observations made, based on error statistics, Error Standard Deviation (STD),Root Mean Square Error (RMSE) and Correlation Coefficient (CC). The results of the study showed that for target stations that have only one neighbouring station with a high correlation coefficient, the Probabilistic method and the Linear Regression method give good predictions. For stations that have relatively low correlation coefficients with the neighbouring stations, the Inverse Distance Squared method and the Normal Ratio method outperformed the others. To obtain accurate results from the Multiple Linear Regression method and the Weighted Linear Regression method, it is necessary to have a set of neighbouring stations that have fairly high correlation coefficients with the target station. Published on 2016-11-22 00:00:00
       
  • Identification of the Polyethylene Grade Most Suitable for Natural
           Rubber-Polyethylene Blends used for Roofing Applications

    • Abstract: In Sri Lanka, roofing materials are manufactured with clay, metal, plastic, wood and asbestos, and each of these has its own inherent drawbacks. Asbestos due to the economic advantages it offers, is now the most widely used roofing material in the country. However, it has scientifically proven health risks. The Government of Sri Lanka has initiated action to ban the use of asbestos as a roofing material. The focus of this study is on the development of a roofing material formed of rubberthermoplastic blends containing Natural Rubber (NR) and Polyethylene (PE). Polyethylene is being currently used as a roofing material, but since it is lightweight it needs to be anchored tightly to the roof structure. Rubber being an energy absorbing material, can be incorporated into thermoplastics to make the latter more tough. Polymer blending is a current trend which is being used to develop technically advanced new materials from commonly available polymers. Polymer blends has an excellent combination of physicochemical properties of each of their parent materials. Sri Lanka exports natural rubber and thus there is a good opportunity to make value-additions to raw rubber exports. Similarly, the development of a new material will address the current problems associated with the use of asbestos as a roofing material. This study shows the most suitable grade of PE from among its most common grades such as High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE) and Linear Low Density Polyethylene (LLDPE), for blending with natural rubber The best blended composition that will have standard properties of a roofing material such as tensile strength, tear strength, hardness, water absorption level, thermal conductivity etc., is then identified. Published on 2016-11-22 00:00:00
       
  • Effect of Fine Percentage on the Properties of Sub-base Material

    • Abstract: Finding sub-base material as per required specifications is a major issue in many parts of Sri Lanka. Therefore, in some cases, crushed stone is used as an alternative to sub-base material. Since good quality material is scarce, it is worthwhile to study the use of marginal materials to ensure sustainable development of the highway sector. The specification used in Sri Lanka for road constructions is the Standard Specification for Construction and Maintenance of Roads and Bridges (SCA/5) (SSCM) (ICTAD, 2009). Sub-base material is classified as lower sub-base material and upper sub-base material according to their Liquid Limit (LL), Plastic Limit (PL), Maximum Dry Density (MDD), California Bearing Ratio (CBR), and Sieve Analysis. A questionnaire survey was conducted among those engaged in the construction industry, to collect information on sub-base construction and on issues connected with the current specification relating to the passing percentage of the fine fraction. As a result, an experimental study was conducted by altering the fine fraction of soil from 0% to 40%. It was also verified whether the grading band of No.200 sieve passing can be relaxed up to a certain percentage if the soil sample satisfies the specified CBR, Plasticity Index (PI) value and swell percentage requirement. It was found that the proposed changes have been adopted in AASHTO and Road Note 31 specifications. Furthermore, linear regression models were fitted to assess the CBR of material in relation to fine fractions (percentage passing of 425 μm, 300 μm, 75 μm sieves). These passing percentages were identified as the most important percentages in predicting the CBR of the soil tested. Published on 2016-11-22 00:00:00
       
  • Assessment of the Impacts of Electricity Subsidies in Sri Lanka

    • Abstract: The government of Sri Lanka has been providing over decades, subsidies on electricity to uplift the living conditions of Sri Lankans. This research project scrutinizes whether the objectives of providing electricity subsidies have been fulfilled. Furthermore, both positive and negative impacts of the electricity subsidy are descriptively discussed. Appropriate remedial actions are proposed to lessen the effects of indirect negative impacts that are identified. Through the analysis, it was found that some of the primary objectives of the electricity subsidy have not been achieved. One of the most subtle negative impacts of the electricity subsidy is the encouragement it provides to subsidized consumers to use energy inefficient equipment. A case study was conducted in Ratnapura district to investigate the energy inefficient equipment usage and to quantify the resulting electricity wastage. The findings of the study were used to estimate the amount of electricity wasted in the entire country through the use of inefficient equipment. Furthermore, it was found that the existing tariff structure encourages energy inefficient equipment usage and that it therefore acts in contradiction to the fundamentals. The replacement of incandescent lamps by energy efficient equipment is analyzed as a means of saving electricity and meeting the demand during peak times in the night, and resulting savings estimated. Moreover, the investment on replacing incandescent lamps by energy efficient equipment is estimated and its financial returns evaluated. It is also revealed that there are many loopholes in the criteria used for selecting consumers for receiving the subsidy. The major shortcoming is that it allows unwanted people to enjoy the subsidy. It is seen that modifications are needed for the electricity subsidy eligibility criteria to ensure that only needy people receive the subsidy. Published on 2016-11-22 00:00:00
       
  • Path Ahead for Public Sector Engineers

    • Abstract: Sri Lanka is blessed with high calibre, technically competent engineers. However, the lack of proper administrative and regulatory systems in the country is cited as the main reason for the lacklustre performance of its public sector engineers. Engineers have to think differently, act more proactively and try out new processes and procedures to ensure that the organisations where they work are service centric and socially responsive. Public sector engineers have to be aware of their own limitations and should seek external guidance whenever necessary. Local engineers can make use of international concepts, methodologies, guidelines, codes of practice and tools towards this end. Strategic planning processes in the public sector organisations need radical changes. Engineers should apply the "systems view concept‟ holistically to assess the effectiveness of the management structure of their organisations. The organisational culture needs to be enriched with consultative decision making processes and teamwork. The Institution of Engineers, Sri Lanka (IESL) has to act as a facilitator in this process. The ultimate aim should be to embrace business excellence elements to be an integral part of each organisation concerned. Published on 2016-11-22 00:00:00
       
 
 
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