13 Jun DESIGN A 23MVA 66/11KV TRANSFORMER USING SOLIDWORKS

OMO KENYATTA UNIVERSITY OF AGRICULTURE AND TECHNOLOGY

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

NAME REG NO

TIMOTHY NGUTHO KARANJA EN271-2581/2013

MARCH 2019

DECLARATION

This 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. Comment by Mercy: our Comment by Mercy: our

SIGNATURES………………………………………… DATE ………………………………

NAME REG No.

TIMOTHY NGUTHO KARANJA EN271-2581/2013

TITLE OF PROJECT: SIMULATION OF SYSTEMATIC NOISE POLLUTION REDUCTION IN A STEP-DOWN TRANSFORMER

SIGNATURE: ……………………………………………. DATE: ………………………………………..

NAME:

JKUAT

CONTENTS

1.) Table of Contents

2.) Nomenclature

3.) List of Figures

4.) List of Tables

5.) Abstract

Contents DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING 1 BSc Electronic and Electrical Engineering 1 LIST OF FIGURES 8 ABSTRACT 9 CHAPTER ONE: INTRODUCTION 10 Background Information 10 Problem Statement 13 Project Justification 15 OBJECTIVE 16 MAIN OBJECTIVE 16 SPECIFIC OBJECTIVES 16 CHAPTERTWO: LITERATURE REVIEW 17 TYPES OF TRANSFORMERS 17 HISTORY OF TRANSFORMERS 23 Causes of transformer noise 26 NOISE OF POWER TRANSFORMERS 27 DESIGN AND MODELLING 29 Design of Transformers 32 Design of Core 34 Design of Windings—Main Dimensions of Frame 36 Design of Windings 37 CHAPTER THREE: 39 METHODOLOGY 39 Figure 1.15 Transformer Design Optimization Process Flow Chart Using Iterative Method in MATLAB 41 Table 1.16 List of Variables for Transformer design optimization program 41 Table 1.17 List of design constraints for Transformer design optimization program 41 CHAPTER FOUR 42 EXPECTED RESULTS 42 CHAPTER FIVE 43 TIME-PLAN 43 CHAPTER SIX 44 BUDGET FOR THE PROJECT 44 REFERENCES 45

NOMENCLATURE

hP = Hysteresis loss in the Iron Core

h = Density of the Material

e P = Eddy current loss in the Core

e = Density of the Material

f = Power System Frequency

T = Time period of one cycle

Is = Supply Current

I1 = Fundamental component of Current

Irms = Rms value of the Supply Current

B(t) = Magnetic flux Density

H(t) = Magnetic Field Intensity

1 = Magnetic Flux in Primary Winding

2 = Magnetic Flux density in Secondary Winding

Sat

m = Mutual Saturated flux linking the Core

r1 = Primary Winding Resistance

r2 = Secondary Winding Resistance

xl1 = Primary Winding Reactance

xl2 = Secondary Winding Reactance

xm = Mutual Reactance

LIST OF FIGURES

1.1 Step-up transformer

1.2 Step-down transformer

1.3 Air-core transformer

1.4 Iron core transformer

1.5 Auto transformer

1.6 Power transformer

1.7 Distribution transformer

1.8 Current transformer

LIST OF TABLES

Table no Name of the table

1.14 Core type

1.15 Window space factor

1.16 List of variables for Transformer design optimization program

1.17 List of design constraints for Transformer design optimization program

ABSTRACT

The 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.

· Transformers

Transformers 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.

· Busbars

Busbars/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.

· Switchgear

It 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 feeders

· Switching apparatus such as switches, fuses, circuit breakers.

· Surge Voltage protection

· Grounding

There 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-ϕ and 3-ϕ 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 transformer

The 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 decibels

In 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 Site

If 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 Corridors

Mounting 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 Surface

Thin 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 Enclosures

The 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 Material

Some 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 Padding

Like 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 Techniques

While 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 Guidelines

As 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.

OBJECTIVE

MAIN 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 transformer

2

16

CHAPTERTWO: LITERATURE REVIEW

TYPES OF TRANSFORMERS

There 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-ϕ and 3-ϕ transformer, Auto transformer, etc.

Transformers Based on Voltage Levels

These 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 Transformer

The 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 1

Step-Down Transformer

It 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 2

In 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 Used

Based on the medium placed between the primary and secondary winding the transformers are classified as Air core and Iron core

Air Core Transformer

Both the primary and secondary windings are wound on a non-magnetic strip where the flux linkage between primary and secondary windings is through the air.

Compared 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 1.3

Iron Core Transformer

Both 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 1.4

Transformers Based on Winding Arrangement

Autotransformer

Standard 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 1.5

On 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 Usage

According to the necessity, these are classified as the power transformer, distribution transformer measuring transformer, and protection transformer.

Power Transformer

The 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 1.6

Distribution Transformer

In 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 size

· Easy installation

· Low magnetic losses

· It is not always fully loaded

Distribution Transformer fig 1.7

Measurement Transformer

Used to measure the electrical quantity like voltage, current, power, etc. These are classified as potential transformers, current transformers etc.

Current Transformer fig 1.8

Protection Transformers

This 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 Use

These 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 TRANSFORMERS

Ottó 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 coil

1876 – Pavel Yablochkov uses induction coils in his lighting system

1878 -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 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.

1.

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 noise

Transformer 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 ( = 20 lg () [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 ( [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 ( ) [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

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 MODELLING

Descriptive Models

A 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 Models

An 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 Models

A 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 Models

Both 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; and

· System 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 Models

System 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 Model

The 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 include

· stochastic or deterministic;

· steady-state or dynamic;

· continuous or discrete; and

· Local 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).

Visualization

Computer 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 Transformers

Design 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.

A simple two-winding transformer construction will consist of each winding being wound on a separate soft iron limb or core which will provide the necessary magnetic circuit.

This magnetic circuit which will be known more commonly as transformer core will be designed to provide a path for the magnetic field to flow around, which will be necessary for induction of the voltage between the two windings.

However, this type of transformer construction where the two windings will be wound on separate limbs will not be very efficient since the primary and secondary windings will be well separated from each other. This will result in a low magnetic coupling between the two windings as well as large amounts of magnetic flux leakage from the transformer itself. But as well as this O shapes construction, there will be different types of transformer construction and designs which will be available and to be used to overcome these inefficiencies thus producing a smaller more compact transformer.

The efficiency of a simple transformer construction will be improved by bringing the two windings within close contact with each other hence improving the magnetic coupling. Increasing and concentrating the magnetic circuit around the coils will improve the magnetic coupling between the two windings, but it will also increase the magnetic losses of the transformer core.

It will provide a low reluctance path for the magnetic field, and the core will be designed to prevent circulating electric currents within the iron core itself. Circulating currents / eddy currents cause heating and energy losses within the core decreasing the transformers efficiency.

These losses will be because of voltages induced in the iron circuit, which will constantly be subjected to the alternating magnetic fields setup by the external sinusoidal supply voltage. One way of reducing these unwanted power losses will be to construct the transformer core from thin steel laminations.

In all types of transformer construction, the central iron core will be constructed from a highly permeable material made from thin silicon steel laminations. These thin laminations will be assembled together to provide the required magnetic path with the minimum of magnetic losses. The resistivity of the steel sheet itself will be high, thus reducing eddy current loss by making the laminations very thin.

These steel transformer laminations will vary in thickness’s from between 0.25mm to 0.5mm and as steel will be a conductor, the laminations and any fixing studs, rivets or bolts are electrically insulated from each other by a very thin coating of insulating varnish or by using an oxide layer on the surface.

Transformer Construction of the Core

The construction of a transformer will be dependent upon how the primary and secondary windings will be wound around the central laminated steel core. The two most common basic designs of transformer construction will be the Closed-core Transformer and the Shell-core Transformer.

In the closed-core type (core form) transformer, the primary and secondary windings will be wound outside and surround the core ring. In the shell type or (shell form) transformer, the primary and secondary windings will pass inside the steel magnetic circuit (core) which will form a shell around the windings.

Transformer Core Construction

 

In these both types of transformer core design, the magnetic flux linking the primary and secondary windings will travel entirely within the core with no loss of magnetic flux through air. In the core type transformer construction, one half of each winding will be wrapped around each leg (or limb) of the transformers magnetic circuit.

The coils will not be arranged with the primary winding on one leg and the secondary on the other but will instead be half of the primary winding and half of the secondary winding being placed one over the other concentrically on each leg so as to increase magnetic coupling thus allowing practically all of the magnetic lines of force go through both the primary and secondary windings at the same time. However, in this type of transformer construction, a small percentage of the magnetic lines of force will flow outside of the core “leakage flux”.

Shell type transformer cores will overcome this leakage flux as both the primary and secondary windings will be wound on the same center leg or limb which will have twice the cross-sectional area of the two outer limbs. The advantage here will be that the magnetic flux will have two closed magnetic paths to flow around external to the coils on both left and right hand sides before returning back to the central coils.

Thus the magnetic flux circulating around the outer limbs of this type of transformer construction will be equal to Φ/2. The magnetic flux will have a closed path around the coils, this will have the advantage of decreasing core losses and increasing overall efficiency.

Transformer Laminations

The coils will be firstly wound on a former which has a cylindrical, rectangular or oval type cross section in order to suit the construction of the laminated core. In the shell and core type transformer constructions, in order to mount the coil windings, the individual laminations will be stamped or punched out from larger steel sheets and be formed into strips of thin steel resembling the letters “E”s, “L”s, “U”s and “I”s.

Transformer Core Types

 

These lamination stampings when they will be connected together will form the required core shape. An example is when two “E” stampings plus two end closing “I” stampings were to give an E-I core forming one element of a standard shell-type transformer core. These individual laminations will be tightly butted together during the transformers construction in order to reduce the reluctance of the air gap at the joints which will be producing a highly saturated magnetic flux density.

Transformer core laminations will be usually stacked alternately to each other in order to produce an overlapping joint with more lamination pairs being added to make up the correct core thickness. This alternate stacking of the laminations will also give the transformer the advantage of reduced flux leakage and iron losses. E-I core laminated transformer construction will be mostly used in isolation transformers, step-up and step-down transformers as well as the auto transformers.

Transformer Winding Arrangements

Transformer windings will form another important part of a transformer construction, because they will be the main current-carrying conductors wound around the laminated sections of the core. In a let’s say single-phase two winding transformer, two windings would be present. The one which will be connected to the voltage source and will create the magnetic flux called the primary winding, and the second winding called the secondary in which a voltage will be induced as a result of mutual induction.

If the secondary output voltage will be less than that of the primary input voltage the transformer will be known as a “Step-down Transformer”. If the secondary output voltage will be greater than the primary input voltage it will be called a “Step-up Transformer”.

Core-type Construction

The type of wire which will be used as the main current carrying conductor in a transformer winding will either be copper or aluminum. While aluminum wire while be lighter and generally less expensive than copper wire, a larger cross sectional area of conductor will be used to carry the same amount of current as with copper so it will be used mainly in larger power transformer applications.

Small kVA power and voltage transformers will be used in low voltage electrical and electronic circuits which will tend to use copper conductors as these will have a higher mechanical strength and smaller conductor size than that of equivalent aluminum types. The downside will be that when complete with their core, these transformers will be much heavier.

Transformer windings and coils will be broadly classified in to concentric coils and sandwiched coils. In core-type transformer construction, the windings will usually be arranged concentrically around the core limb with the higher voltage primary winding being wound over the lower voltage secondary winding.

Sandwiched or pancake coils will consist of flat conductors wound in a spiral form and will be so named due to the arrangement of conductors into discs. Alternate discs will be made to spiral from outside towards the center in an interleaved arrangement with individual coils which will be stacked together and separated by insulating materials such as paper of plastic sheet. Sandwich coils and windings would be more common with shell type core construction.

Helical Windings or screw windings will be another very common cylindrical coil arrangement which will be used in low voltage high current transformer applications. The windings will be made up of large cross sectional rectangular conductors wound on its side with the insulated strands wound in parallel continuously along the length of the cylinder, with suitable spacers inserted between adjacent turns or discs in order to minimize circulating currents between the parallel strands. The coil will progress outwards as a helix resembling that of a corkscrew.

Transformer Core

The insulation will be used to prevent the conductors shorting together in a transformer which would be usually a thin layer of varnish or enamel in air cooled transformers. This thin varnish or enamel paint will be painted onto the wire before it will be wound around the core.

In larger power and distribution transformers the conductors will be insulated from each other using oil impregnated paper or cloth. The whole core and windings will be immersed and sealed in a protective tank containing transformer oil. The transformer oil will act as an insulator and also as a coolant.

Transformer Dot Orientation

We will not just simply take a laminated core and wrap one of the coil configurations around it. We would but we will find that the secondary voltage and current will be out-of-phase with that of the primary voltage and current. The two coil windings will have a distinct orientation of one with respect to the other. Either coil would be wound around the core clockwise or anticlockwise in order to keep track of their relative orientations “dots” will be used to identify a given end of each winding.

This method of identifying the orientation or direction of a transformers windings will be called the dot convention. Then a transformers winding will be wound so that the correct phase relations will exist between the winding voltages with the transformers polarity being defined as the relative polarity of the secondary voltage with respect to the primary voltage.

Transformer Construction (Dot Orientation)

 

The first transformer will be shown by its two dots side by side on the two windings. The current which will be leaving the secondary dot will be in-phase with the current entering the primary side dot. Thus the polarities of the voltages at the dotted ends will also be in-phase so when the voltage will be positive at the dotted end of the primary coil, the voltage across the secondary coil will also be positive at the dotted end.

The second transformer will show that the two dots at opposite ends of the windings which will mean that the transformers at primary and secondary coil windings will be wound in opposite directions. The result of this will be that the current leaving the secondary dot will be 180o out-of-phase with the current entering the primary dot. So the polarities of the voltages at the dotted ends will also be out-of-phase so when the voltage will be positive at the dotted end of the primary coil, the voltage across the corresponding secondary coil will be negative.

The construction of a transformer will be such that the secondary voltage will be either in-phase or out-of-phase with respect to the primary voltage. In transformers which have a number of different secondary windings, each of which will be electrically isolated from each other and it will be important to know the dot polarity of the secondary windings so that they will be connected together in series-aiding (secondary voltage is summed) or series-opposing (the secondary voltage is the difference) configurations.

The ability to adjust the turns ratio of a transformer will often be desirable to compensate for the effects of variations in the primary supply voltage, the regulation of the transformer or varying load conditions. Voltage control of the transformer will be generally performed by changing the turns ratio and therefore its voltage ratio whereby a part of the primary winding on the high voltage side will be tapped out allowing for easy adjustment. The tapping will be preferred on the high voltage side as the volts per turn are lower than the low voltage secondary side.

Transformer Primary Tap Changes

 

The primary tap changes will be calculated for a supply voltage change of ±5%, but any value could be chosen. Some transformers will have two or more primary or two or more secondary windings for use in different applications providing different voltages from a single core.

Transformer Core Losses

The ability of iron or steel to carry magnetic flux will be much greater than it is in air, and this ability which will allow magnetic flux to flow is called permeability. Most transformer cores will be constructed from low carbon steels which will have permeability’s in the order of 1500 compared with 1.0 for air.

Thus a steel laminated core will carry a magnetic flux 1500 times better than that of air. When a magnetic flux flows in a transformers steel core, two types of losses occur in the steel. One is eddy current losses and the other is hysteresis losses.

Hysteresis Losses

Transformer Hysteresis Losses will be because of the friction of the molecules against the flow of the magnetic lines of force required to magnetize the core, which will be constantly changing in value and direction first in one direction and then the other in order to influence the sinusoidal supply voltage.

This molecular friction will cause heat to be developed which will represent an energy loss to the transformer. Excessive heat loss will overtime shorten the life of the insulating materials as used in the manufacture of the windings and structures. Thus the transformer will need to be cooled.

Transformers will be designed to operate at a particular supply frequency. Lowering the frequency of the supply will result in increased hysteresis and higher temperature in the iron core. So reducing the supply frequency from 60 Hertz to 50 Hertz will raise the amount of hysteresis which will be existing, decreasing the VA capacity of the transformer.

Eddy Current Losses

Transformer Eddy Current Losses on the other hand will be caused by the flow of circulating currents induced into the steel caused by the flow of the magnetic flux around the core. These circulating currents will be generated because the magnetic flux the core will be acting like a single loop of wire. Since the iron core will be a good conductor, the eddy currents which will be induced by a solid iron core will be large.

Eddy currents will not contribute anything towards the usefulness of the transformer but oppose the flow of the induced current as they will act like a negative force generating resistive heating and power loss within the core.

Laminating the Iron Core

Eddy current losses within a transformer core can not be eliminated completely, but they can be greatly reduced and controlled by reducing the thickness of the steel core. Instead of having one big solid iron core as the magnetic core material of the transformer or coil, the magnetic path is split up into many thin pressed steel shapes called “laminations”.

The laminations used in a transformer construction are very thin strips of insulated metal joined together to produce a solid but laminated core as we saw above. These laminations are insulated from each other by a coat of varnish or paper to increase the effective resistivity of the core thereby increasing the overall resistance to limit the flow of the eddy currents.

The result of all this insulation is that the unwanted induced eddy current power-loss in the core is greatly reduced, and it is for this reason why the magnetic iron circuit of every transformer and other electro-magnetic machines are all laminated. Using laminations in a transformer construction reduces eddy current losses.

The losses of energy, which appears as heat due both to hysteresis and to eddy currents in the magnetic path, is known commonly as “transformer core losses”. Since these losses occur in all magnetic materials as a result of alternating magnetic fields. Transformer core losses are always present in a transformer whenever the primary is energized, even if no load is connected to the secondary winding. Also these hysteresis and the eddy current losses are sometimes referred to as “transformer iron losses”, as the magnetic flux causing these losses is constant at all loads.

Copper Losses

But there is also another type of energy loss associated with transformers called “copper losses”. Transformer Copper Losses are mainly due to the electrical resistance of the primary and secondary windings. Most transformer coils are made from copper wire which has resistance in Ohms, ( Ω ). This resistance opposes the magnetising currents flowing through them.

When a load is connected to the transformers secondary winding, large electrical currents flow in both the primary and the secondary windings, electrical energy and power ( or the I2 R ) losses occur as heat. Generally copper losses vary with the load current, being almost zero at no-load, and at a maximum at full-load when current flow is at maximum.

A transformers VA rating can be increased by better design and transformer construction to reduce these core and copper losses. Transformers with high voltage and current ratings require conductors of large cross-section to help minimise their copper losses. Increasing the rate of heat dissipation (better cooling) by forced air or oil, or by improving the transformers insulation so that it will withstand higher temperatures can also increase a transformers VA rating.

Then we can define an ideal transformer as having:

No Hysteresis loops or Hysteresis losses  → 0

Infinite Resistivity of core material giving zero Eddy current losses  → 0

Zero winding resistance giving zero I2*R copper losses  → 0

CHAPTER THREE:

METHODOLOGY

· Model of a power transformer will be simulated using solid works

· Various 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

,

V

1

,

V

2

,

FREQUENCY

)

SET THE BOUND VALUES OF K

–

FACTOR

,

Bm

,

DELTA OF HV

&

LV WINDING

&

STIFFENER

RUN THE PROGRAM WITH MAX

.

&

MIN

.

VALUE OF K

,

Bm

,

DELTA

OF HV

&

LV WINDING

,

No

.

Of STIFFENER

DESIGN OF THE LAMINATION

(

CORE

)

DESIGN OF THE HV WINDING

DESIGN OF THE LV WINDING

CALCULATION OF THE PERFORMANCE PARAMETERS

COST OF THE TRANFORMER UNIT

GO FOR NEXT

ITERATION

PRINT OUTPUT FOR ALL THE POSSIBLE DESIGN

SELECT THE SUITABLE OPTIMAL DESIGN

BASED ON OPTIMIZATION CRITERIA AND NOISE OUTPUT LEVELS

START

END

IS OBJECTIVE

FUNCTION

ACHIEVED

?

ARE THERESPECIFIED

CONSTRAITS

SATISFIED

?

SELECT THE

SUITABLE VALUES

FOR CALCULATION

OF DESIGN

PARMETERS FROM

STANDARD TABLES

ON EXCELSHEET

THE TANK DESIGN

Figure 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

CHAPTER FOUR

EXPECTED RESULTS

The project will focus on reducing the humming noise by 5-15dB for optimum working conditions to be achieved.

CHAPTER FIVE

TIME-PLAN

ACTIVITIES	JAN	FEB	MAR	APR	MAY	JUN	JULY	AUG
Documentation
Proposal Writing
Literature Review
Proposal Presentation
Design and simulation
Results
Final Report writing
Final Presentation

Table 5.1

CHAPTER SIX

BUDGET FOR THE PROJECT

EQUIPMENT	QUANTITY	TOTAL
PRINTING PAPERS	500	2000
MICROPHONE	1	2000
CONSULTATION(PRIVATE SECTOR)	3	3000
TRAVELLING TO SITES	2	300
		7300

REFERENCES

1. [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. [2] Lj. Lukić, M. Djapić, “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. [3] R. Žičkar, „Optimization in design process of industrial tranformers” , Master Thesis, University of Zagreb, Faculty of mechanical engineering and shipbuilding Zagreb, 2011

4. 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.

5. EEE2508 – ELECTRICAL MACHINE DESIGN Prepared by Mr. P. M. ANANGI

Student Sign………………………………… Supervisor Sign…………………………………………….

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