Conventional Overhead Research Articles

Opportunities for High-Voltage AC Superconducting Cables as Part of New Long-Distance Transmission Lines

The purpose of this study is to compare possible superconducting 380-kV cables with existing overhead lines and underground cables. The study compares the required corridors and energy losses of different versions of a 1.7-km transmission system with a power of 6.6 GVA. Comparison covers the following setups: 4 × 380 kV high-voltage overhead lines, 8 × 380 kV conventional cables, 2 × 380 kV and 4 × 380kV superconducting cables with warm and cold dielectrics. The paper will present the description of the different setups as well as the calculation of energy losses. The required widths of the underground cable corridors are also considered in this study. Finally, the temperature profile and pressure drop of the superconducting cables are investigated. The main results can be summarized as follows. 1) For the assumed voltage level and power, overhead lines require a corridor width of 70 m, whereas a corridor of less than 7.7 m in width is necessary for superconducting 380 kV cables. 2) The 380-kV superconducting cable reduces the energy loss by approximately 8100 MWh per year in comparison to the conventional overhead lines. This yields a feasible energy loss reduction of up to 75%.

Techno Economic Analysis of the Use of High Temperature Low Sag (HTLS) Conductors in the Sri Lanka’s Transmission System

High Temperature Low Sag (HTLS) conductors are introduced with the intention of mitigating some of the disadvantages of the conventional overhead conductors. When compared to conventional conductors, HTLS conductors have better electrical and mechanical characteristics and by using these conductors in overhead transmission lines, some of the complex issues related to power transmissions could be resolved. However, most of the utilities are still in a quandary about using these conductors in place of conventional overhead conductors which have provided a commendable service to them over a period of a century or so. It is because of their lack of experience in using them in the field as well as because of the novel appearance of the conductors. Almost the entire transmission system in Sri Lanka comprises of overhead lines constructed using conventional conductors, especially ACSR conductors. Utility engineers therefore do not have much knowledge on HTLS conductors and also have very little experience in using them. This paper discusses the possibility of adopting the HTLS conductor technology in the Sri Lanka’s transmission system. The properties, behavior and special characteristics as well as the technoeconomic feasibility of using HTLS conductors instead of the conventional conductors are discussed in depth. Lastly, the issues and challenges related to the application of HTLS conductors are discussed. The results of this research will provide valuable information on the possibility of using HTLS conductors in the Sri Lanka’s transmission system.

Simulated and measured performance of displacement ventilation systems in large rooms

Displacement ventilation (DV) systems were initially developed as an efficient buoyant pollutant removal strategy for Scandinavian industrial halls in the 1970´s. In the following decades these systems started to be used in mechanical cooling of office buildings and auditoriums. Designing displacement ventilation systems is more challenging than conventional overhead mixing systems. Most DV system designs require simplified modeling tools. Existing simplified models of DV were validated using air temperature measurements performed in test cells that cannot reproduce the conditions that exist in large rooms with thermally active boundary conditions. There is a lack of measurements that investigate the performance of DV systems in occupied large rooms. With the goal of reducing this knowledge gap, this paper presents a set of detailed temperature and CO2 measurements in two occupied large rooms with recently designed DV systems. The measurements were performed in two recently refurbished rooms located in Lisbon: a large Concert hall and an adjacent Orchestra rehearsal room. The measurements and subsequent analysis were used to assess the actual performance of large room, state of the art, DV systems. In addition, these measurements were used to determine the modeling error of the three-node DV model implemented in EnergyPlus when simulating large rooms. Comparison between simulations and measurements revealed a good agreement: the average simulation error obtained by averaging the error of all measurements in all temperature nodes is 5.9%, with the largest deviation occurring in the floor level node (7.1% ≈ 0.4 °C) average simulation error of 5.9% (the average of error of all measurements in all nodes).

Nurses' experiences using conventional overhead phototherapy versus fibreoptic blankets for the treatment of neonatal hyperbilirubinemia

BackgroundIn some neonatal intensive care units (NICUs), conventional overhead phototherapy is the only phototherapy available, whereas others use fibreoptic blankets only. Several NICUs use both treatments interchangeably. AimTo explore how nurses experience the use of conventional versus fibreoptic phototherapy. MethodSix qualitative in-depth interviews involving nurses at three different NICUs with experience in both treatments were conducted. ResultsFollowing experiences were revealed: i) Infants displayed discomfort while under phototherapy, whereas blanket use promoted infant satisfaction. ii) Blankets increased parents' satisfaction by facilitating bonding, breastfeeding and kangaroo care. iii) The nurses disagreed as to whether fibreoptic blankets and conventional treatment have similar effects. iv) Nurses were concerned about the possible harm and discomfort to the eyes and skin of infants caused by phototherapy. ConclusionWhen the efficacy was considered sufficient, nurses preferred blankets compared with conventional overhead, because of ability to facilitate infant comfort and parent–child interaction.

Analysis of Water Treeing Resistance Performance Characteristics of Nano Filled XLPE Cable Insulating Material

In recent times, high voltage secondary distribution network in urban areas is widely supported by XLPE cables because of its advantages over conventional overhead lines. Major problem faced in the usage of underground cables is the failure of insulation due to water treeing phenomena. It occurs mainly due to water diffusion in the base XLPE polymeric material leading to the breakdown of cable insulation over a period of time. As a result of water treeing, dielectric strength of the material reduces significantly. Recent advancements in nanotechnology shows that addition of nanofillers in the base polymeric material will enhance the thermal and electrical insulation characteristics of the material. However, very few reports are only available in the literature regarding the water treeing resistance characteristics of nano-modified XLPE material. Hence it is necessary to perform a variety of tests on nano-modified XLPE material in order to collect a large volume of data useful for electrical utilities. Considering these aspects, in this paper, important dielectric performance characteristics of nano SiO2 filled XLPE material such as dielectric constant, tan delta, volume resistivity and capacitance are studied at different %wt concentration of nano-filler. In addition, laboratory experiments were also carried out in order to understand the water treeing resistance characteristics of nano filled XLPE material under virgin and aged conditions.

Office Occupants’ Mood and Preference of Task Ambient Lighting in the Tropics

Office lighting is vital for energy savings and occupant’s visual comfort being. Energy efficient lighting has been studied extensively in the aspect of daylighting harvesting and task ambient lighting, predominantly in Temperate developed countries. However, the lack of evident on the effectiveness of low ambient task lighting in the Tropics has prompted this paper to investigate the practicality of such lighting design for the Tropics. This paper explores into the office occupant’s mood and preferences of low ambient daylight and usage of task light for the office in the Tropics. It also discusses the recorded work plane illumination level upon the usage of such lighting system. It studies the impact of such lighting design on people’s preference, work plane illumination for three office spaces with the different luminous environment. In regards to the source of ambient lighting, two offices harvest daylight, and another uses the conventional overhead lights in accordance with MS1525 recommendations. Three of the offices have 15 samples respectively and the workspace horizontal illuminance level is measured across a month. The results of before and after the provision of task light reveal that the acceptance for low ambient task lighting system and it is widely preferred. However, the task light is not necessary utilized as some people are adapted to do computer work under low ambient lighting (~50-150lux). It shows that people’s preference for work plane illuminance varies greatly. Many agree that they are in control with their personal lighting environment when an appropriate glare-free task light is being used. The paper recommends that office luminous measurement shall take other lighting parameters such as the vertical illuminance and luminance ratio into consideration for future research.

Application of deficit irrigation to container-grown hardy ornamental nursery stock via overhead irrigation, compared to drip irrigation

Growth control of container-grown hardy nursery stock generally requires substantial labour investment. Therefore the possibility of alternative growth control using deficit irrigation is appealing. Increasing water costs and limited availability of abstraction licences have added further incentives for nursery stock producers to use deficit irrigation. There are still, however, concerns that inherent non-uniformity of water uptake under commonly used overhead irrigation, and differing irrigation requirements of diverse crops and substrates, may limit the commercial relevance of a protocol developed for single crops growing in 100% peat and irrigated with a high precision drip system. The aim of this research was to determine whether growth control of hardy nursery stock is possible using deficit irrigation applied with conventional overhead irrigation. Over two years, crop growth under an overhead irrigation system was compared under full irrigation and two severities of deficit irrigation. Initially, two crops of contrasting canopy structure i.e. Cornus alba and Lonicera periclymenum were grown. In a subsequent experiment one crop (Forsythia×intermedia) was grown in two substrates with contrasting quantities of peat (60 and 100%). Deficit irrigation was found to be highly effective in controlling vegetative growth when applied using overhead irrigation—with similar results as when drip irrigation was used. This comparable response suggests that deficit irrigation can be applied without precision drip irrigation. Scheduling two very different crops with respect to their water use and uptake potential, however, highlighted challenges with respect to application of appropriate deficits for very different crops under one system; responses to deficit irrigation will be more consistent where nursery management allows for scheduling of crops with very different architecture and water use under different regimes. The effectiveness of deficit irrigation in controlling the growth of Forsythia was similar when a reduced peat based substrate was compared with pure peat; additionally, flowering was enhanced.

Simplified modeling of displacement ventilation systems with chilled ceilings

Displacement ventilation (DV) flows are more complex than conventional overhead mixing systems since the stratified room environment cannot be modeled using the traditional fully mixed room air approach. A successful DV designer must be able to control the vertical room temperature profile and manage the position of the lower boundary of the upper air layer that contains heat and pollutants. The inclusion of a chilled ceiling (CC) in the DV system increases the complexity by adding the need to manage the CC cooling power so that it does not disrupt the DV stratification. This paper presents the extension of an existing DV nodal model so that the effects of the CC in room airflow and air temperatures can be predicted. The model uses three air nodes and focuses on the thermal plumes as the drivers of the airflow and room air heat exchange. The proposed model is validated using twelve different test chamber configurations from three independent experimental studies. When compared with existing models the proposed model achieves improved precision and model flexibility while using less air nodes. The last section of the paper presents a set of CC/DV design charts that can assist system designers in early design phases.

Direct current lightning tests on Optical Ground Wires

In the last 19 years, the Mexican Federal Electricity Commission (CFE), proprietary of the transmission lines in all the country, has proceeded to replace its conventional overhead earth wires by Optical Ground Wires (OPGW) which is expected to lead to a better incentive. Indeed, those wires include in addition to the traditional protection aspect against atmospheric discharges, the ability to remotely control and operate the grid as well as passing telecommunications. The OPGW's are designed based on the electrical and mechanical specifications required by the end user to fit a given application. Nevertheless, the position of the wire at the top of the transmission towers is to protect the power phases below against lightnings. Therefore, the designer should guaranty its physical integrity as well as its additional functionalities under any atmospheric conditions which can be realized through direct current lightning tests as defined by the national specification given in CFE E000-21-2011 and the international standard IEC 60794-1-2. In addition, it is necessary to define the polarity applied during the tests in order to obtain a representative level of damages found in the field. Implementations of the this specification and the international standard has been carried out and various tests have been conducted on OPGW's for the Mexican utility grid. The results have been compared to actual damages found in the field.

Effects of Fertilization on Media Chemistry and Quercus rubra Seedling Development under Subirrigation

Excessive fertilization may induce physiological drought and/or ion toxicity, which can reduce growth or cause mortality in cultured plants. Although nursery subirrigation produces stock of forest trees of equal or better quality to conventional overhead irrigation, detailed analyses of fertilization responses specific to these systems are lacking. We evaluated the effects of fertility applied as a 15N–9P–12K controlled-release fertilizer at rates equivalent to 0, 1.2, 1.8, 2.4, 3.0, or 3.6 g nitrogen (N) per plant on media properties and northern red oak (Quercus rubra L.) seedling development grown with subirrigation. Aboveground plant growth and nutrient content of seedlings increased up to 1.8 g N/plant but declined at higher rates and total mortality occurred for treatments of 2.4 to 3.6 g N/plant by the end of cultivation. Root biomass generally declined with increasing fertilization. Media electrical conductivity (EC) increased with increasing fertility, particularly in the upper media layers, where values exceeded 3.0 dS·m−1 at the highest rates. Fertilization had little effect on media pH. Predawn leaf water potential and osmotic potential (ψS) were reduced at high nutrient applications. Thus, increasing fertility beyond ≈1.8 g N/plant in this subirrigation system apparently resulted in accumulation of excessive fertilizer salts in media and/or ion toxicity, which caused plant mortality. Because subirrigation systems are prone to persistence of residual fertilizer salts in the medium and holding tanks, fertilization prescriptions must be carefully tailored to species and cultural systems to prevent potential for plant damage associated with overfertilization.

Electric arc power collection system for electric traction vehicles

One of many problems in electric traction vehicles is supplying the necessary power to the vehicle. The main difficulty with a conventional overhead system is the maintenance of good contact between the sliding pantograph and the catenary system. As an alternative to the pantograph–catenary system for power collection by contact, there are some methods of power transfer to a moving vehicle without contact: capacitive coupling, electromagnetic-wave transmission, inductive coupling and through an arc plasma. This paper proposes an electric arc power collection system to be used at electric traction vehicles such as tramways and trains. Starting from Nottingham’s equation on the approximation of volt-ampere characteristic of the direct current electric arc, a mathematical model which includes the variation of the electric arc length, depending on the moving electrode rotations speed, is being proposed. Next, the test bench, especially designed for the analysis of power transfer through the electric arc, between a fix and a moving electrode, is presented. Practically, a simulation of an electric traction system running was developed, in which the main dc motor is supplied from a source of continuous variable voltage from a dc generator by means of the electric arc developing between a copper disc and the graphite skate contact, the key element of a tramway pantograph built at a scale of 1:4. A longitudinal argon blow-out has been used to sustain the electric arc. The electric arc characteristics at various arc column lengths, various moving electrode rotations and various argon blowing speeds along the arc column, have been analyzed. Also, from experimental tests, the variation of the rotation velocity of the moving electrode against length of the arc column, has been obtained for different blowing speed of the argon gas. There is a good correlation between experimental data and computing results of electric arc characteristics for different rotation velocity of the moving electrode and different length of the arc column, in stationary conditions.

An Insight on Right of Way and its Cost for Power Transmission Cable and Conventional Overhead Transmission Lines

This paper provides the complete information related to Right of Way (RoW) for the construction of new power transmission line (TL) in terms of present cost for overhead transmission line and underground XLPE transmission cable. The former part of the paper describes the general procedure and rules for acquisition of land for RoW by transmission asset owner (TAO) while in the later part the cost associated to acquire RoW and its impact on the cost of adjacent land have been detailed. It also discusses the actual dismantling cost including the cost of waste metal what TAO get after completion of lifecycle of TL due to increase in metal prices. In this paper cost of RoW after completion of lifecycle of TL is also highlighted. This paper compares the cost of RoW for overhead transmission line and underground XLPE transmission cable for construction of new TL. Also for old transmission infrastructure cost of RoW for change from overhead transmission line to underground XLPE transmission cable is detailed by application of replacement model.

Dynamic Characteristics of a Four-Bar Linkage-Type Continuously Variable Valve Actuation Mechanism Based on ADAMS

This paper proposes a simple mechanical CVVA mechanism using a four-bar linkage, a rotating 1st cam and two oscillating 2nd cams in addition to the conventional overhead camshaft valve train system. The fundamental operating principle of the CVVA mechanism is described. A multi-body dynamic model of the CVVA mechanism of single cylinder in ADAMS is developed according to the kinematic design and topological structure of the mechanism. Valve motions and compressive loads of the mechanism are analyzed through the various lift phases and camshaft rotating speeds. The results of the dynamic simulation demonstrate that the CVVA mechanism sustains proper performance in the valve timing and event control through the whole speed range.

Supply air temperature impact in underfloor air distribution systems under Korean climatic conditions: Energy, humidity and comfort

Underfloor air distribution (UFAD) systems have received increasing attention during the past decades due to potential advantages over conventional overhead (OH) forced air systems. Among design and operating parameters, air handling unit (AHU) supply air temperature (SAT) has significant impacts on the overall UFAD performance. In this study, the detailed whole-building energy simulation program, EnergyPlus version 6.0, was used to perform the analysis on the impact of SAT on the UFAD system performance such as energy, humidity and comfort under Korean climatic condition. It turns out that raising AHU SAT causes increased HVAC energy consumption due to heating and fan energy increase despite the cooling energy reduction. The increase in the heating energy was mainly due to the increased central AHU heating coil demand increase with the higher SAT. In addition, raised SAT elevated relative humidity in the room space during the summer season due to the fact that higher SAT set-point in the central AHU was not able to sufficiently dehumidify conditioned air compared to the lower SAT. However, the increased SAT reduced the number of hours when the occupants might feel cold during the heating season in the interior zone where the heating is not provided.

Adoption of Overhead Rigid Conductor Rail System in MTR Extensions

The conventional overhead catenary system for both 1500V d.c. traction system and 25kV a.c. traction system have been used in the existing railways of Mass Transit Railway Corporation Limited (MTRCL) in Hong Kong for over 20 years. Another type of overhead line system, the overhead rigid conductor rail system has now been increasingly used in the tunnel sections of underground metro system in Europe, Mainland China and South Korea. The non-tension and low resistance characteristics of the rigid conductor rail system have advantages in enhancing and improving various aspects including energy efficiency, reliability, maintainability and availability of the overhead line system. This paper gives an outline of the overhead rigid conductor rail system and the benefits of adopting such system for the new MTR extensions including West Island Line, Kwun Tong Line Extension, South Island Line (East) and Shatin to Central Link. The result of simulation study to demonstrate the acceptable dynamic performance for the interface with the pantograph of rolling stock for line operating speed up to 130kph is included in this paper.

The iPad as an alternative to conventional technology for effective teaching

The iPad connected to a data projector in the class room can effectively replace conventional technology such as computers, overhead projectors, document cameras, and white boards. A selection of apps that can mimic the tasks of the existing technology will be demonstrated. The Keynote app can be used as the main tool for presenting the course content. The NotesPlus app can be used to replace the conventional overhead projector and the whiteboard. For those who are accustomed to the polythene rolls in the overhead projector, PaperView app will mimic the polythene roll with the ability to carry it around. A few apps to annotate .pdf files will be demonstrated. The BoardCam app will be used to mimic the document camera in teaching. The focus will be on demonstrating how the different apps are used seamlessly to present the course content to the students

Researches on Reactive Compensation for Long-Distance and Highcapacity Hybrid Submarine Cable Lines

In order to balance reactive power, reduce line losses, prevent excessive power frequency and switching over-voltage and adjust and control the line voltage etc. The long-distance and high voltage transmission lines are needed reactive power compensation. High voltage overhead transmission lines and high voltage submarine cable (including mixed-submarine) transmission lines are different, for example, the capacitance in the submarine cable lines is larger than in the conventional overhead lines. Therefore, the reactive power compensation on the EHV transmission lines which contains submarine cable lines is focus on the compensation of submarine cable lines. The reactive power compensation in 500 kV AC submarine cable interconnection project for Hainan power grid and Guangdong power grid[1], which is the first 500 kV long-distance and high-capacity sea trails interconnection project in China and which is just completed soon, is researched by Electro-Magnetic Transient Program——PSCAD/EMTDC (Power System Computer Aided Design/ Electro Magnetic Transient in DC System in this paper). The simulation results verifies that the role of shunt reactor which could absorb charging power and suppress the power frequency overvoltage for the long-distance and high-capacity hybrid submarine cable lines. The conclusions can offer references to suppress power frequency overvoltage and the reactive power compensation in extra high voltage transmission lines which is the mixed mode of overhead transmission lines and submarine cables.

Thermal decay in underfloor air distribution (UFAD) systems: Fundamentals and influence on system performance

Underfloor air distribution (UFAD) is a mechanical ventilation strategy in which the conditioned air is primarily delivered to the zone from a pressurized plenum through floor mounted diffusers. Compared to conventional overhead (OH) mixing systems, UFAD has several potential advantages, such as improved thermal comfort and indoor air quality (IAQ), layout flexibility, reduced life cycle costs and improved energy efficiency in suitable climates. In ducted OH systems designers have reasonably accurate control of the diffuser supply temperature, while in UFAD this temperature is difficult to predict due to the heat gain of the conditioned air in the supply plenum. The increase in temperature between the air entering the plenum and air leaving through a diffuser is known as thermal decay. In this study, the detailed whole-building energy simulation program, EnergyPlus, was used to explain the fundamentals of thermal decay, to investigate its influence on energy consumption and to study the parameters that affect thermal decay. It turns out that the temperature rise is considerable (annual median = 3.7 K, with 50% of the values between 2.4 and 4.7 K based on annual simulations). Compared to an idealized simulated UFAD case with no thermal decay, elevated diffuser air temperatures can lead to higher supply airflow rate and increased fan and chiller energy consumption. The thermal decay in summer is higher than in winter and it also depends on the climate. The ground floor with a slab on grade has less temperature rise compared to middle and top floors. An increase of the supply air temperature causes a decrease in thermal decay. The temperature rise is not significantly affected by the perimeter zone orientation, the internal heat gain and the window-to-wall ratio.

Power system analysis of Hanlim superconducting HVDC system using real time digital simulator

Jeju island is located approximately 100km south from the mainland of Korea, and had a peak load of about 553MW in 2008. The demand increases 7.2% a year over the last 5years. Since the wind profiles of Jeju island are more favorable than mainland of Korea, many companies have shown interest in the wind power business at the Jeju island. Moreover KEPCO has a plan for renewable energy test too whose power will be delivered by HVDC system. One kilometer length of total 8km was designed as superconducting DC cable. Rest 7km will be the conventional overhead line. In this paper, the authors have developed a simulation model of the power network around 8km HVDC system using real time digital simulator (RTDS).

Water and Nutrient Uptake and Use Efficiency with Partial Saturation Ebb and Flow Watering

Subirrigation for production of potted ornamental plants reduces the waste of water and fertilizer inherent to conventional overhead watering systems used in greenhouses. Ebb and flow watering systems for flooded floors typically operate slowly so that the substrate takes up water to near effective water-holding capacity during each irrigation event. We used a system that rapidly delivered water to and removed water from the production surface to restrict the water provided to the plants. We examined several parameters that vary between this fast-cycle ebb and flow watering on a flooded floor compared with slow-cycle watering. Water and fertilizer use was reduced by 20% to 30% with fast- compared with slow-cycle watering. Biomass and stem height at bloom were also reduced by 10% to 20% under fast-cycle saturation. This watering method did not affect the rate of flower development or plant nutrient composition. Volumetric water content of the substrate was the only measure that was affected by location on the flooded floor. Despite the fast ebb and flow on pitched floors, none of the aspects of plant growth was affected by location on the floor. This method of watering shows promise as a means to produce uniform crops of container-grown plants while conserving water and fertilizer.