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DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING BSc Electronic and Electrical Engineering FINAL PROJECT PROJECT TITLE: SIMULATION OF SYSTEMATIC NOISE POLLUTION REDUCTION IN A STEP-DOWN TRANSFORMER NAMEREG NO MARCH 2019DECLARATIONThis project proposal is my original work, except where due acknowledgement is made in the text, and to the best of my knowledge has not been previously submitted to Jomo Kenyatta University of Agriculture and Technology or any other institution for the Award of a degree or diploma. SIGNATURES………………………………………… DATE ……………………………… NAME REG No.TIMOTHY NGUTHO KARANJA EN271-2581/2013TITLE OF PROJECT: SIMULATION OF SYSTEMATIC NOISE POLLUTION REDUCTION IN A STEP-DOWN TRANSFORMERSIGNATURE: ……………………………………………. DATE: ……………………………………….. NAME: JKUAT CONTENTS 1.) Table of Contents 2.) Nomenclature 3.) List of Figures 4.) List of Tables 5.) Abstract Contents TOC \o "1-3" \h \z \u DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING PAGEREF _Toc7710543 \h 1BSc Electronic and Electrical Engineering PAGEREF _Toc7710544 \h 1LIST OF FIGURES PAGEREF _Toc7710545 \h 7ABSTRACT PAGEREF _Toc7710546 \h 9CHAPTER ONE: INTRODUCTION PAGEREF _Toc7710547 \h 10Background Information PAGEREF _Toc7710548 \h 10Problem Statement PAGEREF _Toc7710549 \h 13Project Justification PAGEREF _Toc7710550 \h 15OBJECTIVE PAGEREF _Toc7710551 \h 16MAIN OBJECTIVE PAGEREF _Toc7710552 \h 16SPECIFIC OBJECTIVES PAGEREF _Toc7710553 \h 16CHAPTERTWO: LITERATURE REVIEW PAGEREF _Toc7710554 \h 17TYPES OF TRANSFORMERS PAGEREF _Toc7710555 \h 17HISTORY OF TRANSFORMERS PAGEREF _Toc7710556 \h 23Causes of transformer noise PAGEREF _Toc7710557 \h 26NOISE OF POWER TRANSFORMERS PAGEREF _Toc7710558 \h 27DESIGN AND MODELLING PAGEREF _Toc7710559 \h 29Design of Transformers PAGEREF _Toc7710560 \h 32Design of Core PAGEREF _Toc7710561 \h 34Design of Windings—Main Dimensions of Frame PAGEREF _Toc7710562 \h 36Design of Windings PAGEREF _Toc7710563 \h 37CHAPTER THREE: PAGEREF _Toc7710564 \h 39METHODOLOGY PAGEREF _Toc7710565 \h 39Figure 1.15 Transformer Design Optimization Process Flow Chart Using Iterative Method in MATLAB PAGEREF _Toc7710566 \h 41Table 1.16 List of Variables for Transformer design optimization program PAGEREF _Toc7710567 \h 41Table 1.17 List of design constraints for Transformer design optimization program PAGEREF _Toc7710568 \h 41REFERENCES PAGEREF _Toc7710569 \h 42NOMENCLATUREhP = Hysteresis loss in the Iron Coreh ??= Density of the Materiale P = Eddy current loss in the Coree ??= Density of the Materialf = Power System FrequencyT = Time period of one cycleIs = Supply CurrentI1 = Fundamental component of CurrentIrms = Rms value of the Supply CurrentB(t) = Magnetic flux DensityH(t) = Magnetic Field Intensity1 ??= Magnetic Flux in Primary Winding2 ??= Magnetic Flux density in Secondary WindingSatm ??= Mutual Saturated flux linking the Corer1 = Primary Winding Resistancer2 = Secondary Winding Resistancexl1 = Primary Winding Reactancexl2 = Secondary Winding Reactancexm = Mutual ReactanceLIST OF FIGURES 1.1 Step-up transformer1.2 Step-down transformer1.3 Air-core transformer1.4 Iron core transformer1.5 Auto transformer1.6 Power transformer1.7 Distribution transformer1.8 Current transformerLIST OF TABLESTable no Name of the table 1.14 Core type1.15 Window space factor1.16 List of variables for Transformer design optimization program 1.17 List of design constraints for Transformer design optimization program ABSTRACTThe project will focus on a sample step-down Transformer rated (23MVA, 66/11KV) noise levels and how to reduce the humming noise by 5-15dB. The main cause of transformer noise is the Magnetostriction Effect. This is where the dimensions of ferromagnetic materials change upon contact with a magnetic field. The alternation current that flows through an?electrical transformer’s coils has a magnetic effect on its iron core. It causes the core to expand and contract, resulting in a humming sound.The step-down transformer being sampled is located at Kimathi Power Substation. The substation has four engineers and four security officers working in day and night shifts. The team is subjected to noise levels of around 78dB within the facility. The transformer parameters will be simulated using Solid works to predict scope of noise levels in the substation. The Acoustics Module is an add-on to the?COMSOL Multiphysics software?that provides tools for modeling acoustics and vibrations for applications such as speakers, mobile devices, microphones, mufflers, sensors, sonar, and flow meters. By using the specialized features it will allow visualization of acoustic fields and building of virtual prototypes of devices or components.The difference between the simulated and the?measured?sound levels will be around 3-5dB.The results will be used to show whether the sound level depends on several parameters such as winding displacement, capacity, mass of the core and windings, space between laminations. These parameters will be modified to reduce levels on noise. CHAPTER ONE: INTRODUCTION Background Information Kenya Power generates power which is distributed to other power stations and substations via transmission cables. A supply line can either be an overhead line or an underground feeder, depending on the location of the substation, with underground cable lines mostly in urban areas and overhead lines in rural areas and suburbs. Distribution substation is connected to a sub-transmission system via at least one supply line which is often called a primary feeder. However, it is typical for a distribution substation to be supplied by one or more supply lines to increase reliability of the power supply in case one supply line is disconnected. Supply lines are connected to the substation via high voltage disconnecting switches in order to isolate lines from substation to perform maintenance or repair work.TransformersTransformers step down supply line voltage to distribution level voltage. Distribution substation usually employs three-phase transformers. However, banks of a single-phase can also be used. For reliability and maintenance purposes two transformers are typically employed at the substation, but can vary depending on the importance of the consumers fed from the substation.BusbarsBusbars/buses can be found throughout the entire power system, from generation to industrial plants to electrical distribution boards. Busbars are used to carry large current and to distribute current to multiple circuits within the switchgear or equipment.SwitchgearIt is a term covering primary switching and interrupting devices together with its control and regulating equipment. Power switchgear includes breakers, disconnect switches, main bus conductors, interconnecting wiring, and support structures with insulating.Other parts of the station;Outcoming feedersSwitching apparatus such as switches, fuses, circuit breakers.Surge Voltage protectionGroundingThere are several transformer types used in the electrical power system for different purposes, like in power generation, distribution and transmission and utilization of electrical power. The transformers are classified based on voltage levels, Core medium used, winding arrangements, use and installation place, etc. Different types of transformers are the step up and step down Transformer, Distribution Transformer, Potential Transformer, Power Transformer, 1-? and 3-? transformer, Auto transformer, etc.Survey and analysis of the current electrical PowerStation’s and Substations show that engineers are subjected to various noise pollution from electrical equipment’s such as alarms from control and relay panel, fire detection and alarm system, humming of the transformer and switching components.Substation acoustic field sampled (Kimathi Power Substation) has four engineers and four security officers’ working day and night shifts. They are subjected to around 300dB of noise each day. The engineers and security officers on site were not allocated with noise cancellation headphones to help them in their acoustic field environment. This lead to less concentration, fear of electrical equipment’s, and ear trauma. The case study or sample used is Kimathi Power Substation which has a variety of stepdown transformers such as 23Mva, 66/11Kv, 45Mva, 66/11Kv, and 33Mva, 66/11Kv stepdown transformers.These transformers produce a humming sound which can be heard by the residents who have settled close to the substation.The substation is located close to the residential area so as to increase proximity for distribution of power.The main cause of transformer noise is the Magnetostriction Effect. This is where the dimensions of ferromagnetic materials change upon contact with a magnetic field. The alternation current that flows through an?electrical transformer’s coils has a magnetic effect on its iron core. It causes the core to expand and contract, resulting in a humming sound.Also Electrical magnetostriction meansAs AC current flows through the core of the transformer, Hysteresis effect takes place and hence there is continuous magnetization and demagnetization of the core which leads to continuous alteration in the physical dimensions of the core. This alteration to core or Magnetostriction gives rise to the Humming sound of a Transformer. The transformer core dimensions change by 1Armstrong 10-8cm.How to measure the humming sound produced by the transformerThe noise or humming sound produced by a transformer is measured by placing a microphone at a certain distance close to it. This distance to Sound Pressure relation from microphone to noisy transformer is known as "far field" condition, where a doubling of the distance -r- will cause a 6 dB drop in the Sound Pressure Level. For practical reasons the noise is measured at a standard distance of 0.5 m. Taking an assumption example that at a certain frequency a Sound Pressure Level of 32 dB at 1 meter distance, under the "far field" condition, the noise level will be 6 dB lower at 32- 6 = 26 dB. In fact, at any reasonable distance -r- in the "far field", the noise level can be measured and converted to a level at 1 meter by means of the formula.Example 1: SPL at 1 m =SPL at r m +20 log r Example 2: SNR = 10 * log10 (var (source)/ var (noise)) in decibelsIn simulation the noise is measured by using the Acoustic model application in solid works to check on vibrations and acoustic noise produced.International noise level conditions which is 64dB for urban areas but in European countries it’s stricter at around 48dB. Problem Statement It is necessary to reduce noise levels in step-down transformer due to zero tolerance of engineers and residents to noise pollution. Noise leads to less concentration and disrupts normal functioning of personnel due to stressful working conditions. The transformer produces around 78 decibels of noise on a daily basis.There are several ways to curb noise emission in a transformer like proper transformer design, assembly and installation may help to control it to mask the noise.Precautions should be taken during installation and mounting, to minimize audible humming:Selecting a Low-Traffic Installation SiteIf the transformer is located in an area with a lot of traffic, people will find the noise irritating, especially if ambient noise is lower than the unit’s sound level. Making sure there’s at least one low-traffic space between the transformer and high-traffic areas in offices, residential buildings, etc. is vital.Avoiding Corners, Stairwells and CorridorsMounting a transformer in a corner of a room or close to the ceiling, since these locations amplify the noise. Do not install it in a narrow corridor, hall or stairway, either. As with room corners, these areas will cause the sound to build up and be reflected back louder.Mounting the Unit on a Solid SurfaceThin curtain walls or plywood surfaces will amplify transformer noise, so units should be mounted on dense, heavy surfaces such as reinforced concrete walls or floors. For the best results, mounting surfaces should weigh 10 times as much as the unit itself.Tightening the Bolts on EnclosuresThe bolts and screws on the transformer’s cover and top should be properly tightened. Loose parts will vibrate when the transformer is running and add to the existing sound. Lifting eyebolts can also increase the noise, so make sure to remove any that were used during installation.Using Acoustical Dampening MaterialSome of the noise generated by an electrical transformer can be reduced by using materials that prevent the sound from spreading. Covering the walls of the transformer room with absorbent materials such as kimsul, acoustical tile or fiberglass may help keep the noise contained.Using Oil Barriers or Cushion PaddingLike sound dampening materials, oil barriers and cushion padding may also help insulate transformer noise and prevent it from spreading. They don’t actually cut down the sound or vibration itself, but help cut down the irritation it causes among people in nearby areas.Trying Flexible Mounting TechniquesWhile installing electrical transformers on structural walls, columns, ceilings or frames, use of external vibration dampeners along with flexible connections and mounting methods. This will prevent metal contact between the mounting surface and the unit, to reduce noise transmission.Following the Manufacturer’s GuidelinesAs with other?electrical materials, following the instructions and guidelines provided by the manufacturer. For instance, if the design includes vibration dampeners between the case and core and coil assembly mounting, the mounting bolts for these need to be removed after installation.Transformer noise has two main sources which are winding vibrations and core vibrations. The most effective way to reduce windings noise is by having a good quality controlled winding process when assembling them. This project will focus on the cores of normally silent transformers, which make noise under adverse mains conditions.This project will focus on mitigating humming noise from a transformer as it has deterrent effects on quality of working conditions and concentration. Project Justification The proposal will enable engineers and workers to work comfortably within shifts. Sound tends to travel faster at night so transformer humming noise is louder in the night than during the day time. By reducing the humming noise produced by the transformers, the work stability and quality of life will be improved not only to engineers and staff workers but to the surrounding area since the Power Substation is located in a suburb /residential area.This will help engineers and security officers work safely under international noise level conditions which is 64dB for urban areas but in European countries it’s stricter at around 48dB. OBJECTIVEMAIN OBJECTIVE To design and simulate the step-down transformer (23Mva, 66/11Kv) circuit and its parameters such as winding factors, mass of core, magnetization resistance and inductance, power and frequency etc. SPECIFIC OBJECTIVES To design mass of core and winding factors of the step-down transformer.To calculate amount of noise produced by a normal working transformer.To compare international standards of noise pollution and safety regulations and how they co-relate to the current transformer noise problem.To reduce noise levels produced by a working transformerCHAPTERTWO: LITERATURE REVIEW TYPES OF TRANSFORMERSThere are several transformer types used in the electrical power system for different purposes, like in power generation, distribution and transmission and utilization of electrical power. The transformers are classified based on voltage levels, Core medium used, winding arrangements, use and installation place, etc. Different types of transformers are the step up and step down Transformer, Distribution Transformer, Potential Transformer, Power Transformer, 1-? and 3-? transformer, Auto transformer, etc.Transformers Based on Voltage LevelsThese are the most commonly used transformer types for all the applications. Depends upon the voltage ratios from primary to secondary windings, the transformers are classified as step-up and step-down transformers.Step-Up TransformerThe secondary voltage is stepped up with a ratio compared to primary voltage. This can be achieved by increasing the number of windings in the secondary than the primary windings. In a power plant, this transformer is used as connecting transformer of the generator to the grid.Step-up Transformer fig 1Step-Down TransformerIt used to step down the voltage level from lower to higher level at secondary side as shown below so that it is called as a?step-down transformer. The winding turns more on the primary side than the secondary side.Step-Down Transformer fig 2In distribution networks, the step-down transformer is commonly used to convert the high grid voltage to low voltage that can be used for home appliances.Transformer Based on the Core Medium UsedBased on the medium placed between the primary and secondary winding the transformers are classified as Air core and Iron coreAir Core TransformerBoth the primary and secondary windings are wound on a non-magnetic strip where the flux linkage between primary and secondary windings is through the pared to iron core the mutual inductance is less in air core, i.e. the reluctance offered to the generated flux is high in the air medium. But the hysteresis and eddy current losses are completely eliminated in air-core type transformer.Air Core Transformer fig 1.3Iron Core TransformerBoth the primary and secondary windings are wound on multiple iron plate bunch which provide a perfect linkage path to the generated flux. It offers less reluctance to the linkage flux due to the conductive and magnetic property of the iron. These are widely used transformers in which the efficiency is high compared to the air core type transformer.Iron Core Transformer fig 1.4Transformers Based on Winding ArrangementAutotransformerStandard transformers have primary and secondary windings placed in two different directions, but in?autotransformer windings, the primary and the secondary windings are connected to each other in series both physically and magnetically as shown in the figure below.Auto Transformer fig 1.5On a single common coil which forms both primary and secondary winding in which voltage is varied according to the position of secondary tapping on the body of the coil windings.Transformers Based on UsageAccording to the necessity, these are classified as the power transformer, distribution transformer measuring transformer, and protection transformer.Power TransformerThe?power transformers?are big in size. They are suitable for high voltage (greater than 33KV) power transfer applications. It used in power generation stations and Transmission substation. It has high insulation level.Power Transformer fig 1.6Distribution TransformerIn order to distribute the power generated from the power generation plant to remote locations, these transformers are used. Basically, it is used for the distribution of electrical energy at low voltage is less than 33KV in industrial purpose and 440v-220v in domestic purpose.It works at low efficiency at 50-70%Small sizeEasy installationLow magnetic lossesIt is not always fully loadedDistribution Transformer fig 1.7Measurement TransformerUsed to measure the electrical quantity like voltage, current, power, etc. These are classified as potential transformers, current transformers etc.Current Transformer fig 1.8Protection TransformersThis type of transformers is used in component protection purpose. The major difference between measuring transformers and protection transformers is the accuracy that means that the protection transformers should be accurate as compared to measuring transformers.Transformers Based on the Place of UseThese are classified as indoor and outdoor transformers. Indoor transformers are covered with a proper roof like as in the process industry. The outdoor transformers are nothing but distribution type transformers. The difference between two types of results is less than 3dB.HISTORY OF TRANSFORMERSOttó Bláthy,?Miksa Déri, Károly Zipernowsky of the Austro-Hungarian Empire who?first designed and used the transformer in both experimental, and commercial systems. Later on?Lucien Gaulard,?Sebstian Ferranti, and?William Stanley?perfected the design.The property of induction was discovered in the 1830's but it wasn't until 1886 that?William Stanley, working for?Westinghouse?built the first reliable commercial transformer. His work was built upon some rudimentary designs by the Ganz Company in Hungary (ZBD Transformer 1878), and Lucien Gaulard and John Dixon Gibbs in England. Nikola Tesla did not invent the transformer as some dubious sources have claimed. The Europeans mentioned above did the first work in the field. George Westinghouse, Albert Schmid, Oliver Shallenberger and Stanley made the transformer cheap to produce, and easy to adjust for final use.The first AC power system that used the?modern?transformer was in Great Barrington, Massachusetts in 1886. Earlier forms of the transformer were used in?Austro-Hungary?1878-1880s and 1882 onward in England. Lucien Gaulard (Frenchman) used his AC system for the revolutionary?Lanzo to Turin?electrical exposition in 1884 (Northern Italy). In 1891 mastermind Mikhail Dobrovsky designed and demonstrated his 3 phase transformers in the?Electro-Technical Exposition?at Frankfurt, Germany.?There are many types of transformers with different designs used for all kinds of applications from radio to microelectronics.1830s?- Joseph Henry and Michael Faraday work with electromagnets and discover the property of induction independently on separate continents.1836?- Rev. Nicholas Callan of Maynooth College, Ireland invents the induction coil1876?- Pavel Yablochkov uses induction coils in his lighting system1878 -1883?- The?Ganz Company?(Budapest, Hungary) uses induction coils in their lighting systems with AC incandescent systems. This is the first appearance and use of the toroidal shaped transformer.1881?-?Charles F. Brush?of the?Brush Electric Company in Cleveland, Ohio develops his own design of transformer.1880-1882?-?Sebastian Ziani de Ferranti?-designs one of the earliest AC power systems with William Thomson (Lord Kelvin). He creates an early transformer. Gaulard and Gibbs later design a similar transformer and loose the patent suit in English court to Ferranti.1882?-?Lucien Gaulard and John Dixon Gibbs?first built a "secondary generator" or in today's terminology a step down transformer?which they designed with open iron core, the invention was not very efficient to produce. It had a linear shape which did not work efficiently. It was first used in a public exhibition in HYPERLINK "" ?Italy in 1884?where the transformer brought down high voltage for use to light incandescent and arc lights. Later they designed a step up transformer. Gaulard (French) was the engineer and Gibbs (English) was the businessman behind the initiative. They sold the patents to Westinghouse. Later they lost rights to the patent when Ferranti (also from England) took them to court.1884?- In Hungary?Ottó Bláthy?had suggested the use of closed-cores,?Károly Zipernowsky?the use of shunt connections, and?Miksa Déri?had performed the experiments. They found the major flaw of the Gaulard-Gibbs system were successful in making a high voltage circuit work using transformers in parallel. Their design was a?toroidal shape which made it expensive to make. Wires could not be easily wrapped around it by machine during the manufacturing process.1884?- Use of Lucien Gaulard's transformer system (a series system) in the first large exposition of AC power in Turin, Italy. This event caught the eye of William Stanley, working for Westinghouse. Westinghouse bought rights to the Gaulard and Gibbs Transformer design. The 25 mile long transmission line illuminated arc lights, incandescent lights, and powered a railway. Gaulard won an award from the Italian government of 10,000 francs.1885?-?George Westinghouse?orders a Siemens alternator (AC generator) and a Gaulard and Gibbs transformer. Stanley begin experimenting with this system.?1885?-?William Stanley?makes the transformer more practical due to some design changes: "Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the EMF present in the secondary winding. This design was first used commercially in the USA in 1886".?William Stanley explains to?Franklin L. Pope (advisor to Westinghouse and patent lawyer)?that is design was salable and a great improvement. George Westinghouse?and William Stanley create a transformer that is practical to produce (easy to machine and wind in a square shape, making a core of E shaped plates) and comes in both step up and step down variations. George Westinghouse understood that to make AC power systems successful the Gaulard design had to be changed. The toroidal transformer used by the Ganz Company in Hungary and Gibbs in England were very expensive to produce (there was no easy way to wind wire around an iron ring without hand labor).1886?- William Stanley uses his transformers in the electrification of downtown?Great Barrington, MA. This was the?first demonstration of a full AC power distribution system using step and step down transformers.Later?1880s?-?Later on?Albert Schmid?improved Stanley's design, extending the E shaped plates to meet a central projection.1889?- Russian-born engineer?Mikhail Dolivo-Dobrovolsky?developed the first?three-phase?transformer in Germany at AEG. He had developed the first three phase generator one year before. Dobrovolsky used his transformer in the first powerful complete AC system (Alternator + Transformer + Transmission + Transformer + Electric Motors and Lamps) in 1891.1880s?- Today?- Transformers are improved by increasing efficiency, reducing size, and increasing capacity. NB: 1895-Air cooled transformers built by William Stanley for a three phase AC power station. Large Westinghouse transformers from 1917 are located at the?Hydropower plant at Folsom, California.Causes of transformer noiseTransformer noise has two sources which are winding vibrations and core vibrations. The most effective way to reduce windings noise is by having a good quality controlled winding process when assembling them. The transformer cores can become noisy as well under specific secondary load conditions which can be translated (transformed) into the adverse mains conditions at the primary as discussed in this project.There are three physical phenomena that produce noise in the magnetic core:1. The movement of the 90-degree Bloch walls inside the magnetic domains, frequently called Magnetoacoustic Emission (MAE)2. The rotation of the magnetic domains, that is responsible for the bulk magnetostriction.3. The Lorentz Force Acoustic Signal (LFAS) causing mechanical forces between laminations of the core.MAE occurs in the steep section of the hysteresis loop. As not much sound is emitted and the bulk magnetostriction is small. The rotation of the magnetic domains is dominant near saturation in the hysteresis loop.The magnetostriction becomes "large" and the core laminations move considerably, thus generating acoustic noise. The rattling of laminations of the core (LFAS) depends largely on the construction of the core. The EI-type cores are more prone to make noise due to their many separated pieces of lamination which mostly are only sturdy clamped at the four corners. In toroidal cores the long role of core band is sturdy clamped everywhere due to the mechanical rolling tension and the pressure caused by the winding tension.In general: magnetostriction, occurring near saturation of the core, is the main cause of the acoustical transformer noise, while LFAS largely depends on the construction of the core. Due to magnetostriction the core vibrates at the fundamental mains frequency and its harmonics and at core resonance frequencies. In this regard it is important to notice that a noisy transformer means that a) That the transformer is badly constructed -or- b) That the transformer is forced to operate in a magnetic region close to or at core saturation.The main reason why the transformer is noisy may be a combination of the given causes. The device has become noisy and the amount of acoustical noise produced should be measured to determine whether or not the produced noise level is acceptable.NOISE OF POWER TRANSFORMERS The noise that power transformers produce is defined by IEC 60076-10 (2001) standard and is determined by three basic parameters: Sound pressure level method (Lp), Sound power level method (LW) Sound intensity method (LI). Sound pressure level is calculated according to: Lp = 10 lg (pPo)2 = 20 lg (pPo) [dB], (1) where: p – is the sound pressure [Pa] And p0 – is reference sound pressure p0 = 20 ? 10-6 [Pa]. The sound power level LW is calculated according to: LW = 10 lg (wWo) [dB], Where: W – represents the sound power [W] and W0 – is reference sound power W0 = 10-12 [W]. Sound intensity level LI is calculated according to: LI = 10 lg ( iIo) ) [dB], Where: I – is sound intensity [W/m2] and I0 – is reference value of sound intensity I0 = 10-12 [W/m2]. The sound level A (LpA, LWA, LIA) is frequency adjusted value of calculated sound level that takes into account nonlinear sensitivity of the human ear to different sound frequencies. Human ear is the most sensitive to frequencies around 1000 [Hz], and is less sensitive to lower and higher frequencies. For a particular frequency of sound level A stands: LpAf = Lpf + ΔLf , Where: Lpf - is not adjusted linear value of sound level and ΔLf – is correction to be taken on the basis of empirical values per octave. The total noise level in the case of multiple sound sources (LWA1, LWA2, LWA3 ...) can be calculated according to the following formula: LWA = 10 lg Σ 100,1LwAi For n equal noise sources of level the total noise level is LWA = LWA0 + 10 lg n . Measurements of power transformer’s noise are performed according to IEC 60076-10 (2001) standard. Measurements are performed during tests for short circuit at nominal current at a distance of 300mm, 1000mm or 2000mm from contour which is the main radiation plane of transformer’s trunk. During tests, mainly sound pressure level LpA and sound power intensity LIA are being measured. The main plane of radiation is imaginary surface that surrounds the transformer’s tank and passes through vertical projection of the line around transformer at a defined distance. For transformers with natural cooling the measurement points are at a distance of 300mm from the main plane of radiation. For dry transformers the distance should be 1000mm.DESIGN AND MODELLINGDescriptive ModelsA?descriptive model?describes logical relationships, such as the system's whole-part relationship that defines its parts tree, the interconnection between its parts, the functions?that its?components?perform, or the test cases that are used to?verify?the system?requirements. Typical descriptive models may include those that describe the functional or physical?architecture?of a system, or the three dimensional geometric representation of a system.Analytical ModelsAn?analytical model?describes mathematical relationships, such as differential equations that support quantifiable analysis about the system parameters. Analytical models can be further classified into dynamic and static models. Dynamic models describe the time-varying state of a system, whereas static models perform computations that do not represent the time-varying state of a system. A dynamic model may represent the performance of a system, such as the aircraft position, velocity, acceleration, and fuel consumption over time. A static model may represent the mass properties estimate or?reliability?prediction of a system or component.Hybrid Descriptive and Analytical ModelsA particular model may include descriptive and analytical aspects as described above, but models may favor one aspect or the other. The logical relationships of a descriptive model can also be analyzed, and inferences can be made to reason about the system. Nevertheless, logical analysis provides different insights than a quantitative analysis of system parameters.Domain-specific ModelsBoth descriptive and analytical models can be further classified according to the domain that they represent. The following classifications are partially derived from the presentation on?OWL, Ontologies and SysML Profiles: Knowledge Representation and Modeling?(Web Ontology Language (OWL) & Systems Modeling Language (SysML)) (Jenkins 2010):properties of the system, such as performance, reliability, mass properties, power, structural, or thermal models;design?and technology implementations, such as electrical, mechanical, and?software?design models;subsystems and?products, such as communications, fault management, or power distribution models; andSystem applications, such as information systems, automotive systems, aerospace systems, or medical device models.The model classification, terminology and approach is often adapted to a particular application domain. For example, when modeling?organization?or?business, the behavioral?model may be referred to as workflow or?process?model, and the performance modeling may refer to the?cost?and schedule performance associated with the organization or business process.A single model may include multiple domain categories from the above list. For example, a reliability, thermal, and/or power model may be defined for an electrical design of a communications subsystem for an aerospace system, such as an aircraft or satellite.System ModelsSystem models can be hybrid models that are both descriptive and analytical. They often span several modeling domains that must be?integrated?to ensure a consistent and?cohesive?system representation. As such, the system model must provide both general-purpose system constructs and domain-specific constructs that are shared across modeling domains. A system model may comprise multiple views to support planning, requirements, design, analysis, and?verification.Wayne Wymore is credited with one of the early efforts to formally define a system model using a mathematical framework in?A Mathematical Theory of Systems Engineering: The Elements?(Wymore 1967). Wymore established a rigorous mathematical framework for designing systems in a model-based context. A summary of his work can be found in?A Survey of Model-Based Systems Engineering (MBSE) Methodologies.Simulation versus ModelThe term?simulation, or more specifically?computer simulation, refers to a method for implementing a model over time (DoD 1998). The computer simulation includes the analytical model which is represented in executable code, the?input?conditions and other input data, and the computing infrastructure. The computing infrastructure includes the computational engine needed to execute the model, as well as input and?output?devices. The great variety of approaches to computer simulation is apparent from the choices that the designer of computer simulation must make, which includestochastic or deterministic;steady-state or dynamic;continuous or discrete; andLocal or distributed.Other classifications of a simulation may depend on the type of model that is being simulated. One example is an agent-based simulation that simulates the interaction among autonomous agents to predict?complex?emergent?behavior (Barry 2009). They are many other types of models that could be used to further classify simulations. In general, simulations provide a means for analyzing complex dynamic behavior of systems, software, hardware, people, and physical phenomena.Simulations are often integrated with the actual hardware, software, and operators of the system to evaluate how actual components and users of the system perform in a simulated?environment. Within the United States defense community, it is common to refer to simulations as live, virtual, or constructive, where live simulation refers to live operators operating real systems, virtual simulation refers to live operators operating simulated systems, and constructive simulations refers to simulated operators operating with simulated systems. The virtual and constructive simulations may also include actual system hardware and software in the loop as well as stimulus from a real systems environment.In addition to representing the system and its environment, the simulation must provide efficient computational methods for solving the equations. Simulations may be required to operate in real time, particularly if there is an operator in the loop. Other simulations may be required to operate much faster than real time and perform thousands of simulation runs to provide statistically valid simulation results. Several computational and other simulation methods are described in?Simulation Modeling and Analysis?(Law 2007).VisualizationComputer simulation results and other analytical results often need to be processed so they can be presented to the users in a meaningful way. Visualization techniques and tools are used to display the results in various visual forms, such as a simple plot of the state of the system versus time to display a parametric relationship. Another example of this occurs when the input and output values from several simulation executions are displayed on a response surface showing the sensitivity of the output to the input. Additional statistical analysis of the results may be performed to provide probability distributions for selected parameter values. Animation is often used to provide a virtual representation of the system and its dynamic behavior. For example, animation can display an aircraft’s three-dimensional position and orientation as a function of time, as well as project the aircraft’s path on the surface of the Earth as represented by detailed terrain maps.Design of TransformersDesign of transformers will consist in designing the:Cross section of the core, Fixing up the frame size of the transformer core, Design of windings, and Design of tank. This criterion can be one of the following:(a) Design the transformers for maximum efficiency or minimum total losses. The efficiency of transformer is maximum when iron loss or rather constant loss will be equal to I2R loss. If the transformer is to work on full load for most of the time, and the efficiency is to be maximum at this load, copper loss on full load will be made equal to iron loss.This equation will give the ratio of weights of active materials for the criterion of maximum efficiency at the mean working load.(b) Another criterion for which the transformer can be designed is the minimum first cost of the transformer, i. e., makes the cheapest transformer. It involves finding the ratio of weight of iron to weight of copper for this condition.(c) The third criterion for the design of transformer is on the basis of minimum annual cost, i. e., capital charge on cost of transformer + depreciation + cost of energy losses = minimum,This criterion will need a lot of information regarding the load curve of the system where the transformer is used, cost of energy at different load factors, load factor of the system, etc., in addition to the normal cost of transformer materials, etc. This will be a complicated problem and can be solved only with the help of computer software.Design of CoreVoltage per turn Et = K√S volts, K depends on the material and labour costs, etc., and on the type of transformer such as shell or core type and single phase or three-phase.Where S=kVA output of transformer and K is constant. The approximate mean values for criterion of load for maximum efficiency will be given in Table belowTable 1.4TypeSingle phase 3 Phase power 3 Phase distributionCore type0.77 to 0.850.60 t0 0.900.45 to 0.75Shell type 1.00 to 1.201.00 to 1.500.80 to 1.25Net cross sectional area of the core will be found out by choosing K and then Et and the flux density Bm. By choosing Bm and δ, AiAw will be found from relation in case of the 3 phase and in case of single phase.The core design will be design to conform to a standard frame. The Figure 1.) will show a frame giving the main dimensions of a three phase core type transformer d will be the diameter of the core, D will be the distance between the centres of the limbs. W will be the width of the core frame. L will be the length of the window. Aw will be the area of each window.The core will be built of 0.35 mm thin strips arranged in a number of steps so as to obtain nearly round cross sectional area so that a better space factor for accommodating iron in the most useful way will be achieved.The number of steps usually chosen is 3, 4, 5, 6, 7 or 9. For a larger size transformer, more steps will be used if this is found feasible. The area of the iron section in the steps in terms of the circumscribing diameter is given by , where K=iron space factor.This will be due to there being steps instead of one solid round section of the core. Ai=stacking factor due to paper or varnish insulation between the laminations of the core. This will be taken as approximately 0.92.Fig.2 shows typical sections of 3 step and 6 step cores with the approximate widths of the lamination pieces used.Fig. 2 (a) 3 steps core section (b) 6 steps core sectDesign of Windings—Main Dimensions of FrameWhen the net area of the core have been determined, and the current density δ chosen depending on the type of cooling of the transformer, kw Aw is found out from the kVA rating from equation . Kw will be the window space factor, i. e, the ratio of the area of copper to the area of the window. For higher voltages, the window space factor will be smaller as more clearance space is required to give the necessary insulation levels. Approximate space factors for window Kw for various voltage ranges will be given in the Table below by Choosing a suitable value of Kw , the window area Aw will be determined. The height and width of the window can be adjusted to accommodate the windings in the required arrangement and to give thedesired leakage reactance.The normal ratio of height/width of window is 2 to 4.Table 1.15Window Space Factor KwkVA3kV10kV30kV100kV1000.280.200.14-8000.370.270.200.1520000.400.310.230.16100000.450.370.280.21Design of WindingsGiven that the voltage per phase on the high voltage and low voltage side of a transformer, the number of turns in the high voltage and low voltage side will be found out when the voltage per turn is chosen and where T1, T2 are turns per phase on the high voltage and low voltage side respectively and V1 , V2 are corresponding voltages per phase.Current in h. v. winding amperesCurrent in l. v. side amperesChoosing the current density δ amps/mm2 the cross sectional area of conductor for h. v. winding and for low voltage side Checking the weight of iron and copper and their rat proceeding to the detailed design of the windings.The windings of transformers will be designed to best possible performance electrical characteristics with proper mechanical strength to withstand the stresses due to short circuit and with proper ventilation keeping them within the permissible temperature rise for the windings.CHAPTER THREE: METHODOLOGYModel of a power transformer will be simulated using solid worksVarious parameters of a transformer such as voltage and current ratings (Power), winding parameters, magnetization resistance and inductance, frequency, mass of core, number of windings will be modified in the solid works.Acoustic module will be used to measure the vibrations and noise in the core and windings of the transformer.This figure shows the flow chart for design of a power transformer.READ THE INPUT DATA KVA, V1,V2, FREQUENCY)SET THE BOUND VALUES OF K-FACTOR, Bm, DELTA OF HV & LV WINDING & STIFFENERRUN THE PROGRAM WITH MAX. & MIN. VALUE OF K, Bm, DELTA OF HV & LV WINDING, No. Of STIFFENERDESIGN OF THE LAMINATION (CORE)DESIGN OF THE HV WINDINGDESIGN OF THE LV WINDINGCALCULATION OF THE PERFORMANCE PARAMETERSCOST OF THE TRANFORMER UNITGO FOR NEXT ITERATIONPRINT OUTPUT FOR ALL THE POSSIBLE DESIGN SELECT THE SUITABLE OPTIMAL DESIGN BASED ON OPTIMIZATION CRITERIA AND NOISE OUTPUT LEVELS STARTENDIS OBJECTIVE FUNCTION ACHIEVED?ARE THERESPECIFIED CONSTRAITS SATISFIED?SELECT THE SUITABLE VALUES FOR CALCULATION OF DESIGN PARMETERS FROM STANDARD TABLES ON EXCELSHEETTHE TANK DESIGNREAD THE INPUT DATA KVA, V1,V2, FREQUENCY)SET THE BOUND VALUES OF K-FACTOR, Bm, DELTA OF HV & LV WINDING & STIFFENERRUN THE PROGRAM WITH MAX. & MIN. VALUE OF K, Bm, DELTA OF HV & LV WINDING, No. Of STIFFENERDESIGN OF THE LAMINATION (CORE)DESIGN OF THE HV WINDINGDESIGN OF THE LV WINDINGCALCULATION OF THE PERFORMANCE PARAMETERSCOST OF THE TRANFORMER UNITGO FOR NEXT ITERATIONPRINT OUTPUT FOR ALL THE POSSIBLE DESIGN SELECT THE SUITABLE OPTIMAL DESIGN BASED ON OPTIMIZATION CRITERIA AND NOISE OUTPUT LEVELS STARTENDIS OBJECTIVE FUNCTION ACHIEVED?ARE THERESPECIFIED CONSTRAITS SATISFIED?SELECT THE SUITABLE VALUES FOR CALCULATION OF DESIGN PARMETERS FROM STANDARD TABLES ON EXCELSHEETTHE TANK DESIGNFigure 1.15 Transformer Design Optimization Process Flow Chart Using Iterative Method in MATLAB Table 1.16 List of Variables for Transformer design optimization program Sr. No. Variable Range 1. K-factor 0.35 to 0.55 2. Flux density (Bm) 1.45 to 1.75 Wb/ m2 3. Current Density of LV winding 1.9 to 3.5 A/mm2 4. Current Density of HV winding 1.9 to 3.5 A/mm2 5. No. of Stiffener 2 to 8 Table 1.17 List of design constraints for Transformer design optimization program Sr. No. Constraints Range 1. No Load Loss <11000 watt 2. Load Loss <70000 watt 3. Percentage impedance 7<%z<10 4. Efficiency >99% 5. Gradient of LV winding 9<GLV<23 6. Gradient of HV winding 9<GHV<23 7. Deflection 5<def<9 mm REFERENCES [1] Lj. Lukic, N. Pejcic, “A New Generation of Transformers with Wound Core Patented by ABS Minel Trafo Serbia”, Paper on call, Proc. 7th InternationalSymposium Nikola Tesla, pp. 51-56, 23. November 2011,Belgrade, 2011.[2] Lj. Luki?, M. Djapi?, “Transportation and Manipulation processes in the Overhaul of Energy Transformers”, Proc. The Seventh Triennial International Conference Heavy Machinery HM2011, A Session – Railway Engineering, Volume 7, pp. 25-32, Kraljevo – Vrnjacka Banja, June 29th - July 2nd, 2011.[3] R. ?i?kar, ?Optimization in design process of industrial tranformers” , Master Thesis, University of Zagreb, Faculty of mechanical engineering and shipbuilding Zagreb, 2011 W. M. Zawieska: A Power Transformer as a Source of Noise, International Journal of Occupational Safety and Ergonomics (JOSE), pp. 381–389, Vol 13, No 4, 2007. ................
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