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Minimizing the Effects of Harmonicsin

Maritime Defence Vessels

Gary Michael Gilbert, CD, mc, BEng

A thesis submittedto the Depamnent of Electrical and Computer Engineering

Royal MiIitary College of CanadaKingston, Ontario

in partial hifiIlment of the requirements forthe degree

Master of EngineeringMay 1999

O Copyright by G.M. Gilbert, 1999

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National LibraryI*l f Canada Bibliothque nationaledu CanadaAcquisitions and Acquisitions etBibliographie Services seivkes bibliographiques395WellingtonStreet 395, nieWellingtonOttawaON K1A O N 4 OttawaON KIA O N 4Canada Canada Your h b VotremHru?ce

Our llk Notre relrence

The author has granted a non- L'auteur a accord une licence nonexclusive licence allowing the exclusive permettant laNational Library of Canada to Bibliothque nationale du Canada dereproduce, loan, distribute or sel1 reproduire, prter, distribuer oucopies of this thesis in microforni, vendre des copies de cette thse souspaper or electronic fomats. la forme de microfiche/film, dereproduction s u .papier ou sur formatlectronique.The author retains ownership of the L'auteur conserve la proprite ducopyight in this thesis. Neither the droit d'auteur qui protge cette thse.thesis nor substantial extracts fiom it Ni la thse ni des extraits substantielsmay be printed or otherwise de celle-ci ne doivent tre imprimsreproduced without the author's ou autrement reproduits sans sonpermission. autorisation.

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Dedication

To my lovely wife Catherine, who has supported my scholustic endemors forseveral years, and my two children: Gary and Siobhan.

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AbstractHarmonics are generated by many different sources (m otors, transformers,

h a c e s , power converters, etc). Harmonics can cause major problems in the powerquality of distribution systems (i.e., distortion of voltage and cu re n t waveforms), and agreat deal of research has been directed at their elirnination and/or reduction. This thesisdevelops simulation models of Maritime Defence Vessels using EDSA. EDSA is a verypowerful electrical engineering software package that simplifies the simulation ofcomplex electrical distribution systems. Harmonic distortions are eliminated &orreduced using passive filters. A new technique is presented for the placement andoptimization of the filter. Dynamic load models are used to obtain redistic results. Themethod presented ensures that a power system has clean, reliable power that is unaffectedby the type of load, whether the load is linear or non-linear.

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AcknowledgmentsThis research was suggested by Dr A.Y. Chikhani and Dr. D. Bouchard. 1am

greatly indebted to Dr Chikhani for his guidance, advice, and extreme patiencethroughout both my masters and my under graduate studies. 1am also greatly indebted toDr Bouchard for his coddence in my abilities throughout my studies and his dedicationin helping me resolve important issues surrounding the development of this work.

1 would also like to express my thanks to Lt E.H. eOlivera and LCdr Hudson fortheir technical support concerning the work they had completed in harmonic studies.

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Table of Contents

.......ntroduction ..... ......................................... 1............................................... 1 General I1.2 Background .................................................................2.1 The Canadian Patrol Frigate 4.................2.2 The Maritime Coastal Defence Vessel 4........................................3 Thesis Objective 5....................................4 Thesis Organization - 6..............................................................hapter 2 7

....................armonic Theory. Analysis and Reduction Techniques 7...........................................1 Introduction 7............................2 Harmonic Analysis Techniques 7...................2.1 Time Domain Analysis Techniques 8..............2.2 Frequency Domain Analysis Techniques 10..........2.3 Summary of the Harmonic Andysis Methods 12...................3 Basic Definitions of Harmonic Quantities 13.........................3.1 Total Harmonic Distortion 13...........................3.2 Distortion Power Factor 14..........................4 Common Sources of Harmonics IS................................4.1 Power Convertors 16...................4.2 Static VAR Compensators(SVC) 17...................................4.3 Transformers 18...........................4.4 Synchronous Machines 18......................4.5 Resonance Due o Harmonics 19............................5 Harmonic Reduction Schemes 22..................................5.1 LoadModels 22.......................5.2 Harmonic Limit Compliance 24.............................5.3 AC Line Reactance - 2 6.............................5.4 Multi-Pulse Methods 27..................................5.5 Phase Shifting 28...............5.6 Active Filtering Within the Equipment 29.........................5.7 System Filtering Methods 30...........................5.7.1 Passive Filtering 30...........................5.7.2 Active Filtering 31..................5.7.3 Phase Staggering Methods -322.6 SummaryofChapter2 ................................. 3

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Mode1 Development for F ilter Placement and Optimization ............... 3 4..............................................1 Generai 343.2 System Mode1 ...................................... 3 63.3 Filter Location Algorithm .............................. 1

......................4 Passive Filter Optirnization Synthesis 45..................................5 SummaryofChapter3 57.............................................................hapter 4 58

..........................................vaiuation and Validation 584.1 HarmonicAnalysis and Mode1 Validation .................. 8

4.1.1 CPF Validation ................................. 8...............................1.2 MCDV Validation 644.1.3 Assessrnent of Models ........................... 74.2 Variable verses Static Load Models ...................... 7......................2.1 Assessrnent of Load Models - 7 1

4.3 Filter Location ....................................... 71..............................3.1 CPF Filter Location 724.3.2 MCDV Filter Location ........................... 74.3.3 Assesment of Filter Locations .................... 14.4 Filter Optimization .................................... 14.4.1 CPF Filter OptirnizationResults ................... 824.4.2 MCDV FilterOptimization Results ................. 44.4.3 Assessrnent of Optimization ......................854.5 Sumrnary of Chapter4 .................................86

............................................................hapter 5 - 8 7..................................onclusions and Recommendations 87

5.1 SummaryofWork .................................... 75.1 Recommendations of FumeWork ....................... 88

References ............................................................ 89

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List of FiguresH am on ic d y s i s echniques ........................................8Industrial load ...................................................1Slot harmonies in a synchronous machine .............................. 19Parallel resonance ................................................21Series resonance ..................................................22Selection of the point of common coupling (PCC) ...................... 6................se of multi-pluse convertors to cancel certain hannonics - 2 7Possible electronic phase sh ift to reduce 5 harmonic ..................... 28PWM input convertor controlling harmonic currents ..................... 9Use of passive filters to reduce specific h o n i c s .......................31

3.1 MCDV 600V power generation & distribution system ....................373.2 Topology for the distribution system of the MCDV ...................... 40.......................................3 Filter placement methodology - 4 4........................................4 Standard RLC passive filters - 4 73.5 Passive filter synthesis ............................................. 83.6 Mode1 used in determination of transfer b c t i o n ........................ 493.7 Passive harmonic filter ............................................. 50......................................PF adder distribution system 59Reduced distribution system for the MCDV ............................ 64Variable load profile in emergency conditions ..........................68Variable load profile in normal sailing conditions ........................68Variable load profile at anchor ...................................... 6 9Numbered topology diagram for the CPF .............................. 72Filter location results for the CPF (THDJ .............................. 5Filter location r e d t s for the CPF (THD, ............................. 6Filter location results for the MCDV(THD3 ............................ 79Filter location results for the MCDV (THD, ) ........................... 0

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List ofTablesThe relationship between THDIand pf,, ............................... 5Hannonic current distortion limits .................................... 5Symbols for the MCDV distribution system ............................ 8Range of component values for the passive filter ....................... 5 5Load profiles used to validate previous work .......................... 60Static frequency current injection .................................... 1Load profiles for 440V power panels ................................. 6 2Cornparison between Cymharmo and EDSA harmonic distortions ..........-63Loading profile for distributionsystem for the MCDV .................... 5MCDV 600V bus harmonic content: Micro Tran vs EDSA ................66Variable load verses static load profile for the CPF ......................70Variable load profile verses static load profile for the MCDV ..............70Filter placement summary for the CPF ................................4Filter placement summary for the MCDV .............................7 8Filter optimization results for the CPF ................................ 82Filter component values before and after optimization for the CPF ..........83Filter optimization results for the MCDV .............................. 84Filter component values before and afler optimization for the MCDV ........85

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List ofAbbreviationsAC Altemathg currentCPF Canadian Patrol FrigateDIA Diesel altematorDC Direct curentHz HertzkV KilovoltkA KiloampereM/C Motor altematorMCDV Maritime Coastal Defence Vesse!PDP Power distribution panelSVC Static var compensatorSwbd SwitchboardTCR Thyristor controlled rectifierTHD Total harmonic distortionTIF Telephone interference factor

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Chapter 1Introduction1.1 General

With ever increasing demands on power systems, there is a need to supply clean,reliable power to the consumer. In an ideal power system, energy is supplied at a singleand constant fiequency, and at a specified voltage level of constant magnitude. Theseconditions are rarely fulfilled in practice due to the introduction of nonlinear loads thataffect the power quality [Il. Every power system with nonlinear Ioads has the potentialof producing hannonics. Harmonies, in an electrical power system, are currents andvoltages with fiequencies that are integer multiples of the fundamentai power fiequency.Thus, in a power system with a fundamental fiequency of 60Hz, the second harmonic is120 Hz, the third harmonic is 180 Hz, and this repeats for al1 integer multiples of thefundamental, fiom 2 to infinity. These harmonics can cause distortions in the powersupply, and subsequently produce harmfid results for the power producer and consumeraiike [I l .

There has been significant research in the reduction and elimination o f theharmonies produced by nonlinear type loads [l-51. The resuitsof this research are thatseveral difTerent types of harmonic elimination methods are now vailable. In this work,the problem o f harmonics on Canadian Navy ships is examined. Due to the physicalnature of the naval vessels, the size and location of the hamionic elimination schemebecornes a critical factor. This thesis wiU look at two of the Canadian Navy's vessels: theCanadian Patrol Frigate (CPF) nd the Maritime Coastal Defence Vessels (MCDV).

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These two maritime vessels have dflerent problerns associated with harmonic distortion.The harrnonic distortion in the CPF powet system cause problems with the fluorescentlighting. These problems account for a dramatic reduction in the life of the fluorescentlights, and subsequentiy create an increased operational cost for lighting on the CPF. In apaper written by Dwyer et al [l], the authors connmi these problems with hamionics andfluorescent lighting.

The MCDV hasexperienced destruction of the Silicon Controlled Rectifier (SCR)cabinet control cards, which c m also be s h o w to be a result of harmonic distortion.When the control card fails, the MCDV is left without any propulsion system and must betowed into the nearest port. This results in very expensive repairs and most irnportantlythis problem causes loss in combat effectiveness. The problems associated with thedestruction o f electronic devices, such as controller cards, are discussed in the IEEEStandard 519-1992 [2]. It is in the interest of the Canadian Navy to understand how thisharmonic distortion can cause h d l esuits and how to effectively eliminate thepro blem.

1.2 BackgroundHarmonic studies play an important role in the analysis of power distribution

systems. These harmonic studies de tem ine how the harmonics are created and how toreduce or possibly eliminate their presence within the power signal. Two of the mostcommon methods used in the study of harmonics use tirnedomain and fiequency dom ainanalysis. in the tirne-domain, Fourier analysis allows a wavefonn to be solved for its

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hd am en tal frequency and its harmonic components. However, in the frequencydomain, the use of fiequency scans can de tem ine the harmonic components of thedistorted waveform. Once the harmonic components are determined, it is necessary todetermine whether these harmonie components are at an acceptable level in accordancewith the IEEE tandard. The CanadianNavy imposes the IEEE tandard for hamionicsduring the design of the ir vessels.

If it is determined that harmonic levels need to be reduced, an effective harmonicreduction scheme must be used. These reduction schemes include various filteringmethods that include active or passive filtering [2]. The focus of this work is the use of apassive filter to reduce the hannon ic content to an acceptable level. The variousharmonic filtering devices, as well as the passive filter, will be discussed later within thiswork. However, with any filtering device, the filter needs to be connected to thedistribution system. Within the IEEE Standard 519-1992, the traditional method used todecide the placement of the passive filter is the point of cornrnon coupling (PCC).ThePCC s an arbitrary placement o f filtering devices based on the actuai sourceof thehannonic distortions. In the naval vessels, the PCC ould be the main switchboard, aflerswitchboard, forward switchboard, or any of the power panels within the distributionsystem itself

The selection of the PCC an be viewed in a paper written by Halpin et al [5] . Inthis thesis, a novel method for filter placement is developed that determines the filterplacement based on the physical limitations of the vessel itself, and not the possible PCClocations within the vessel. On a ship, it may be physically impossible to connect a filte r

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at the PCC. The filter placement method detemiines the possible physical locations forconnecting a filter.

1.2.1 The Canadian Patrol Frigate (CPF)TheCPF s responsible for a multitude of tasks, including fishery patrols,

diplomacy, and warfare. The CPF s equipped with many different devices that allow thevessel to carry out these tasks, ranging fiom sophisticated weapon systems to propulsionsystems. In order to supply to power to al1 of the loads, the CPF s equipped with fourdiesel genera toa connected to two 440 V ac switchboards. There are redundancieswithin the distribution system so that when parts of the vessel are damaged or destroyed,combat effectiveness can still be maintained.

In a previous study [3], Hudson investigated the effects of harmonics, the sourcesof hamionics, the frequencies of harmonics, and various techniques to reduce theharmonics. The results of this work established that potential problems can be created byresonant conditions within the distribution system that increased the harmonic currents byasmuch as 25% at some locations. This thesis will expand on the mode1 used inHudson's studies, and implement the proposed filter placement and optimizationtechniques to reduce the harmonic distortion within the vessel.

133 The Maritime Coastal Defence Vesse1(MCDV)The MCDV s designed to patrol the coastlines of Canada against potential threats

to the country. Unique design methods were used in the MCDV, n that the MCDV uses

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a direct cunent (dc) propulsion system that is operated by a sophisticated electncdrivesystem. The electnc drive system has power supplied by a converterwith two SCRcabinets that provide the dc power required. The conversionfrom altemating current (ac)to dc generates high harmonic cunents. These hamonic cunents are injected into thedistribution system, subsequently creatingharmfl results. Control cardswithin the SCRcabinets are affected by the harmonic currents, resulting in failure.

The power distribution system is supplied by four diesel generaton,whichproduce 600V ac, 3 phase, 60Hz to meet the needs of propulsion and auxiliaiies. Thisredundancy in power suppliesis typical of a modem day warship, and allows the vessel tosustain battle damage and still maintain battle effectiveness. Previously, the effects,sources, fiequencies,and transient effects of harmonics, and various techniques to reducethe harmonics, were investigated by DeOlivera [4]. The results of that work establishedthe harmonic problems that exist within theMCDV, nd identified harrnonic reductionschemes that could be carried out to reduce the harmonic Ieveis. This thesis uses thesystem developed in [4], and implements the proposed filter placementand optimizationto reduce the harmonic contentwithin the vessel.

13 Thesis ObjectiveThe objectiveof this thesis is to investigate the electrical power qudity of the CPF

and theMCDV y using cornputer simulations,and to validate previous work completedon the vessels. In order to completethis objective, the following goals were specified:

1. to developa load mode1 to reproduce thehamionic distortionsproduced

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by the CPF and the MCDV;2. to implement a variable load model instead of the static load model;3. to develop a method for spec ieing the placement of passive filters to

reduce harmonics; and,4. to optimize the passive filter size after its location has been determined.

1.4 ThesisOrganizationThe material in this thesis is organized as follows:

a Chapter 2 provides the background on harmonic analysis techniques, harmonicsources, and various methods used to reduce harmonics;

a Chapter 3 develops the harmonic filter placement method and the optim uation ofthe filter;

a Chapter 4 presents the results obtained for the following:(a) validation of previous work(b) use of the variable load model instead of a static load(c) filter placement method(d) filter optimization

a Chapter 5 provides concluding remarks, and recommendations for fiiturework

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Chapter 2Harmonie Theory,Analysis andReduction Techniques2.1 Introduction

Harmonies are created by nonlinear loads within the power distribution system.There are many types of nonlinear loads which generate harmonies, such as motoa,transfomiers, arc h a c e s , and power converters [2]. To examine harmonic distortion, itis necessary to determine what harmonic analysis approach can be used for thedistribution system under study. The two primary approaches for harmonic studiesinclude the t h e domain and the fiequency domain. In this chapter, harmonic analysistechniques, various sources of hamonics, and possible harmonic reduction techniqueswiil be explored.

2.2 Harmonic Analysis TechniquesHannonic studies need to be carried out systematically to determine the problems

associated with a particular distribution system, and available softwareand testequipment often determines the best possible approach. There have been severaladvances in the modeling techniques that can be used for the various components within adistribution system [3-51. Figure 2.1 shows a g e n e d outline for the harmonic analysisprocedure (which is a guideline for the de termination of the harrnoaic content), and willbe explained within this chapter. Harmonic studiescan be referred to as harmonicpenetration techniques [2]. These studies are concerned with the calcuiations ofharmonic currents and voltages throughout the distribution system.

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Figure 2.1. Harmonie analysh techniquesAs cm be seen from Figure 2.1, the harmonic penetration method is broken into hvomainareas: time domain analysis and frequency domain analysis.

22.1 Time Domain Analysis TechniquesTime domain andysis represents the system mode1 using differential equations.

Solutionsare obtained by assuming initial conditions and integrating the system overtime. Once the system has reached steady state, voltage and current wavefoms areanalyzed using Fourier andysis to detemine the hamonic componentsof the wavefom.Fourier analysis is the process of decomposing distorted periodic waveforms into afundamental wave and a set of harmonies. Frequency components of the wavefom c mbe identified from the Fourier series expansion.

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The following equation shows the relationship between the fiequencyand the time

wheref(r) representsthe function in the time domainand F(w) represents the function inthe fiequency domain. To determine the specific amplitudes of the harmoniccomponents, the periodic wavefomf ( ' is represented by an infi te sumof sine andcosine functions, as follows:

1f t )= ;a , +C (ah os(hwot)+6,sin(haot) )wherea, is the average value of the function (r), a, and b, are the Fourier coefficients ofthe series, o, he fiindamental fkequency of the periodic fnction, and h the harmonicorder. TheFourier coefficients are detennined from:

L.a,, = - J f ( t ) os(hq+)dt;T

where h = 2 toWty. Fourier analysis iswell-establishedand cm be used to determineharmonic iostabilities and power system non-iinearities. However, the method is a

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computational burden and subsequently restncted to smaller distribution systems [ 6 ] .Another irnplementation of the tirne domain method is the solution obtained

through circuit analysis. Circuit analysis is used to detemin e the voltage and c m n twaveforms. Afier steady state is reached within the circuit, Fourier aaalysis can be usedto de temine the fndarnentai and subsequent harmonic components of the wavefoms.The use of circuit analysis is a computational burden; and, this technique is also restnctedto sm aller distribution systems.

23.2 FrequencyDomain AnalysisTechniquesFrequency domain analysis techniques can use either the curent injection or the

impedance-Erequency locus methods. Exam ples of applications using the fiequencymode1 can be viewed in references [7-91.The current injection method is based on theassurnption that harmonic currents are generated by nod inear loads and are independentof the voltage and cunent wavefoms [9].The nodinear load is modeled as an idealharmonic current generator. To demonsnate how the current injectionmethod can beimplemented, Figure 2.2 will be used.

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SubstationTransfomer

Figure 2.2. Indushial Lord (from [2j)

The circuit in Figure 2.2 represents a typical industrial load as a harmonic cunentsource, and is used for estimating voltage distortion, harmonie-current magnitudes andnaturai frequency. With the cunent injection method, it is necessary to calculate thevoltage at each known harmonic represented by the following equation:

v, = q r , (2-4)where 1, is the current produced by the source atNh harmonic, and 2, s the paralielcombination of the source impedance and capacitive reactance of the Khharmonic. Thecurrent injection method can solve the harmonic problems in large distribution systems.However, modeling a nonlinear device as a linear constantcurrent source can lead toinaccuracies due to the loss of information in the conversion. The constant current devicehas been shown to work quite well where the cumnt sources are known and the totalvoltage distortionis less than 10% [8].

The impedance-fiequencyloci method uses the frequency responseof a given11

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power system at the point of harmonic injection by the use of a frequency scan. Thefrequency scan will scan a range of fiequencies and obtains discrete points at eachfiequency which are normalized to the fundamental voltage or current source. The resultsfiom the fiequency scan are generally the input impedance or admittance at a particulaspoint in the distribution system, and can be displayed in the fonn of an impedancefiequency plot. The fiequency scans yield zero, negative and positive sequence results.The impedance-fiequency loci method can give the necessary inform ation required toobtain the impedance transfer function which c m be used to obtain the system transferfunction. A subsequent circuit synthesis dlo w s the fiequency dependent model of thesystem to be determined, and th is can be used in distribution systems optimizationprograrns [7]. The impedance-fiequency loci method will be used to obtain theimpedance transfer function of the system model later in this work.

2.2.3 Summaryof the Hamonic AnaIysis MethodsThe different approaches for harmonic analysis begin with the classification of the

different harmonic d y s i s methods that are available. The modeling of the distributionsystem in the fiequency domain is the most extensively used approach [SI. Frequencydomain methods are very effective in the detemination of theTHD within the system,whereas tirne domain methods can become a computationai burden and rely on the initialconditions of the network. The outline of the harmonic analysis approach shows thevarious paths that can be used to determine the harmonie content for a given distributionsystem. The methods used in this thesis to determine the hannonic distortions will be in

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the fiequency domain.

2.3 Basic Definitions of Hirmonic QuantiticsMien discussing harmonies, it is necessary to understand how the different

ham onic properties are calculated. Harxnonic indices provide the necessary frameworkrequired to discuss harmonic components for a given network. An in-depth analysis o fthese harmonic indices can be viewed in [SI, nd therefore this section will briefly reviewthe prevalent h m o n i c indices.

2.3.1 Total Harmonic DistortionThe total harmonic distortion(MD)s used to determine whether or not a

distribution system is considered to have acceptable levels of harmonic distortion(acceptable levels can be found in IEEE Standard 519-1992 [2] . The total harmonicdistortion(THD)or the voltage (V) and the current (1) are calculated by the followingfonnulsle:

THD,,

where h is the harmonic component value ranghg fiom 2 to infinity. The resuits are

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usually multiplied by 100 to express the amount of distortion as a percentage.

2.3.2 Distortion Power FactorThe distortion power factor is used when determining the PCC within the

distribution system, nd is calculated with the following formula:

The relationship between the total anddistortion power factors is denved by thefollowing formulae:

where Y , is the voltage fidamental, 1, is the curent bdarnental, Y' is the root meansquaredof the resultant voltage, 1, is the root mean squared of the resultant cunent,P isthe average power contributedby the harmonics, andpA, is the totai power factor.According to [SI,only a small portionof the average power (P) is contributed byhmonics. Equation (2.10) can be expressedby the following equation:

where P, is the average power excluding harmonics. Table 2.1 shows the relationship

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between theTHD, and pf,,

Table 2.1. The Relationship between THD, nd pf,, (from [S])Table 2.1 shows how the distortion power factor decreases as the THD, increases.

The power factor relationship shown in (2.1 1) indicates that the harmonic distortion canbe reduced by the use of power factor correction. The power factor indicates the degreeof resistiveness or reactiveness of an electrical system. Power factor conection is thereduction of the lagging reactive component to bring the distribution system closer tounity. However, in the case of the distortion power factor, the use of passive or activeharmonic filters should be used to improve thedistortion power factor instead ofconventional means of power factor correction, such as the addition of a capacitor [5] .When the harmonic filters reduce the harmonic distortion, from Table 2.1, the distortionpower factor will increase and subsequently improve the power factor of the distributionsystem.

2.4 Common Sources of HarmonicsHarmonic problemswithin the distributionsystem are caused by excessive

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voltage distortion in the power supply system [2]. This distortion c m involve thecombination of excessive harmonic injections fiom various non-linear loads, and thus theisolation of individual sources of harmonic distortion can become a dificult task. Thereis a need to understand isolated sources of harmonics within a given distribution system.Once dl known sources of harmonics are detem ined, it becomes simpler to investigatepossible solutions to eliminate these harmonics fiom the distribution system. In thesystem mode1 used in this work,possible sources of harmonics include the following:

(a) power convertors;(b) static var compensatoa;(c) transfomen; and,(d) synchronous machines.

2.4.1 Power ConvertonSolid sta te power convertersareused increasingly in thyristor controlled reactive

power com pensators, motor controllers, single phase power supplies, and cornputers. Thepower converter is a major source of harmonics within the distribution system [IO, 11.The amount of harmonic current for a static power converter depends on the acwavefonns at the converter terrninals, converter configuration, type of control, ac systemimpedance and dc circuit parametea. The main source of harmonic currentsare thephase coneolled rectifier and the inverter. One ype of commonly used convertor isrefened to as theppulse convertor, where the value of the pulse number @) is the totalnumber of successive non-simultaneous commutations occun ing within th e convertor

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during each cycle when operated without phase control. The value o f p can also berepresented by the number of pulses present in the dc output voltage. Specific exarnplesand applications of various p-pulsed convertors can be viewed in reference [ 6 ] .

The currents produced by ap-pulse power converter can be represented by thefollowing equations: I, = I,/h;and,

where h represents the harmonic order andp is the number of pulses of the converter.The equation is valid if the following conditions are met:

(e) the converter input voltages are balanced;(f) unequal cornmutating reactance exists between phases; and,(g) unequally spaced firing pulses are present in the converter bridge.

therwise, the converter will produce non-characteristic harmonics which are not integermultiples of the fundamentai frequency. These harmonics are considered inter-harmoniesdue to theu non-characteristic nature [6].

2.4.2 StaticVAR Compensaton (SVC)The static var compensator with thyristor controlled shunt reactor (TCR) s an

effective and reliable means of power system voltage regulation. Static varcompensators, with thyristor controlled shunt reactors, are used in high power voltageregulation systems. The TCR will generate both harmonic and inter-harrnonic currents[6]. In a baianced, three-phase operation, the TCR will produce odd orders of harmoniccurrents,and, in a balanced three phase delta configuration system fomng a six-pulse

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TCR, nly hm on ics of order 6n t l will ex ist The harmonic content will be reduced asthe puise order is increased [SI. The SVC ymm etry of control pulses provides a balancewithin the system; otherwise, the system is unbaianced and the amount of harmoniccurrent increases. However, the balance of the SVC canbe altered by the followingproblems: fuing pulse imbalauce, fundamental supply voltage imbalances, equipmentasymmeies, and transformer saturation. These problems have been investigated byseveral authors, for example [10,111.

2.43 TransfomersThe harmonic distortion caused by tr an sfom en is primarily due to the inrush of

magnetizing current when the transformer is in the transient stage fiom unloaded to partlyor fully loaded conditions. It is at this stage that the transformer cm generate excessivelyhigh harmonic currents. An inde pt h analysis of the harmonic generation fiomtnuisformen was carried out by Arrillaga et al 1121, and it is shown how the powerquality is afFected by transformers.

2.4.4 SynchronousMachinesThe synchronous machine can produce harmonics due to armature slots which are

comm on in these types of devices. Figure 2.3 illustrates how the high frequency spaceharmonics produced by the slots inherent in the synhronous machine distort thefndamental wavefom . It is important to note that each of the harmonic components isformed due to the physical do ts of the generator.

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Figure 23. Slot Harmonics in a Synchronous Machine (from [Z])The order of the do t hannonics is d e h e d by the following formula and has been

derived in references [3] and [12]Harmonie-Order = 2m 1 (2.13)

where m is the number of dot s in the synchronous machine. According to [5], theharmonics associated with slot harmonics are generally small; however, the synchronousmachine contributes to the overall THD of the distribution network and must beconsidered.

2.4.5 Resonance Due to HarmonicsHarmonic filters are designed to block the flow of harrnonics f h m their normal

path. Without harmonic filters, the distribution system would be primarily inductive innature, even at harmonic frequencies. When harmonic filters are part of a distributionsystem, the system may resonate at the resulting natural frequency. These naturalfrequencies cm be troublesome if they are near the harmonic fiequency, in particular theodd harmonics [Il]. Two of the most common problems that can arise from theintroduction of the harmonic filter are parallel and series resonance.

Parallel resonance occurs when the parallel inductive and capacitive reactance of19

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the system are equal at a resonant fiequency. The paraliel combination of the capacitorand the source impedance of the equivalent circuit that is created at theGequency isvery large in value to the harmonic source. The resonant fkquency of the parallelcombination is calculated with the foilowing formula [SI:

where A N A , is the short-circuitMVA at the point where the filter is introduced in the

distribution system, and W A R s the rating of the harmonic filter. If compensatingharmonic current is injected at this point, significant voltage and current distortions willresult due to the large impedance that is produced at the resonant fkquency. The effect ofthe parallel resonance is the magnification of the harmonic currents injected by a non-linear load. The size of the load is the major factor in the attenuating harmonic distortioncaused by this resonant condition. As the load increases, the magnification of theharmonic currents at resonance decreases due to the lower impedance path that is createdby the changing load. Therefore, the system is more susceptible to harmonic distortiondue to paralle1 resonance when the system is lightly loaded or m d y motors.

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Figure 2.4 shows the circuit that illustrates parailel resonance.

Figure 2.4. ParaHel Resonance (from 151)

In Figure 2.4, X, represents the compensating device andX, represents the lineimpedance. At resonance, these quantities are equal in value.

Series resonance occurswhen the senes inductive and capacitive reactance of thesystem are equal at a resonant frequency and the series irnpedance is very low in valuecompared to the hannonic source. The resonant frequency of the senes combination iscalcuiated with the following formula [SI:

In series resonance, there is no magnification of the compensating harmonic cunent;however, there are two primary results: interference in communication lines and voltagedistortion. The main problems that are caused with series resonance are capacitor andfuse failures, due to overload conditions.

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Figure 2.5 shows the circuit that illustrates series resonance.

Figure 2.5. Series Resonance (from [5])

In Figure 2.5, X, represents the compensating device andX, epresents the lineimpedance. At resoaance, these quantities are equal in value. It should be noted that inthe case of a filter,X, will be the filter impedance.

2.5 Hannonic Reduction SchemesThere are severai methods for addressing the problems of harmonics within a

distribution system, and the best solution for a given systemwill depend on that particularsystem. Fundamentally, harmonics are similar in nature; however, the size of the systemin question will determine which method should be used to investigate the harmoniccontent and subsequent reduction schemes. For the purposes of this work, only passivefiltering methods are investigated (due to cost restrictions and the physical restrictionsofthe systern models).

2.5.1 Load ModelsIn any reduction scheme, the load mode1 used for of the distribution system is very

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important [2 ] .Research in ha m on ic studies has shown the importance of using anaccurate system model when studying a specific distribution system [3,4,12- 151. Withinthis research it was established that the variable load model should be used whensufic ien t data is available. The ability to produce an accunite system model for hamioniccalculations, whether they arein the fiequency domain or the t h e domain, is difficult.The load models that are used in the hannonic studies are static or variable in nature-Static load models are represented as a constant impedance, constant cunent, constantMVA or a combination of the three. The static Ioad model s a e r s fiom the Iack ofsensitivity towards voltage and fiequency changes which constitute one of the majordrawbacks of the model. The variable load model can be broken into two types [15] and[16]:

(a) component-based approach; and,(kt) measurement-based approach.The component-based approach builds the load model fiom information on the

dynamic behavioa o f individual components and load components for a particular bus.For larger distribution systems, the s w e y s of load components are very dificu lt tasks.The rneasurement-based approach involves placing senson at various load buses todetermine model structures and model parameten. h i s approach has the advantage ofdirect measurements of actual load behaviors and can yield load models directly in theform needed for existing computerprogram input. The variable load model used in thiswork and described in Chapter 4 uses the measurement-based approach as detailed in[131-

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2.5.2 Harmonic LimitCornpliancen i e placement of the harmonic reduction filter is typically limited to thePCC nd

is outlined in [2]. There are two standards for the placement of harmonic reductionschemes and the groups who produce these standards are the following: InternationalElectrotechnical Commission(IEC), nd the E E E [ 5 ] . According to the IEC, l1 parts ofa distribution system must comply with the accepted harmonic limit, whereas the IEEErequires the point of common coupling (PCC)o comply with the harmonic limit. ThePCC s a place in the distribution system where one or more nonlinear loads arecomected to a common node.

The placement of the PCC s empirically determined by calcdation of the shortcircuit capability of the distribution system. Distribution systems cm have higher levelsof harmonic cunents without higher levels of voltage distortion. The IEEE ecommendsthemaximum Total Demand Distortion for different voltage levels, as Table 2.2 outiinesfor odd harmonic components. The short circuit anaiysis provides the value that is usedto determine the bounds of the allowable current distortion at the PCC. From Table 2.2,1 is the short circuit current and 1 is the maximum demand load current at thefundamental fiequency at the PCC. The calcdation of the Total Demand Distortion issimilar to the calculation for the THD shown in Equations 2.5 and 2.6, except loadcurrent is used instead of the fiindamental current.

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1 1 s h c 1 7 s h < 2 3 s h < 3 5 s h TDD17 23 352.0 1.5 0.6 0.3 5.03.5 2.5 1.O 0.5 8.04.5 4.0 1.5 0.7 12.05.5 5.0 2.0 1 O 15.07.0 6.0 2.5 1.4 20.0

Table 23. Harmoaic CurrentDistortion Limits (from [2])

The PCC an be located on either the primary or secondary side of a transformerdepending on where other utility customers are located. For example, in Figure 2.6, theother utility customersarewt fed by the secondary sideof the transformer, and thereforethe PCC s located on the prirnary side of the transformer. The placement of the PCCwould be on the secondary side of the t d o r m e r if the secondary side of the transformer

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fed other utility costumen.

PCC

-elecon of the PCC where other Customers can be suppliedFigure 2.6. Selection of the Point of CommonCoupling (from 121)In a paper written by Thiem et al [lq, the method for finding the PCC within a

distribution system is presented. The authors describe a procedure for selecting the PCCbased on the sources of the harmonic distortions. However, the method does not considerthe physical location of the PCC, nd therefore it could not be used in smaller distributionsystems, such as those found in naval vessels.

2.5.3 AC Line ReactanceAC Iine reactance can be added to a distribution system by theuse of an inductor-

input filter which wouid improve the performance of three-phase 6-pulse converters. Theinductance slows the transition of the cu re nt transfer that existswhen commutation

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2.5.5 Phase ShiftingThe use of phase-shifting transformers to reduce the harmonic content is

accomplished by the addition of the output of more than one converter. One converterc o d d have thyristors (SCRs) gated to operate with a 15 degree lag and the other convertergated to operate with gate-turn-off thyristors(GTOs) perathg with a 15degree lead,producing a phase shiR of 30 degrees, and would eliminate most of the harmonic.Thismethod c m only reduce one harmonic at a time; therefore it could be effective ifthere is one dominant harmonic that needs to be eliminated. Figure 2.8 illustnttes how aphase shift c m be obtained electronically by using two converten. Thismethod is similarto the multi-pulse method with the addition of the phase-shifting transformers, and thecost would not make this harmonic reduction scheme very practical.

GTOsgated at + f 5"

Figure 2.8. PossibleElectronic Phase Shift to Reduce Sth Harmonic (from [6])

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2.5.6 ActiveFilteringWithin the EquipmentThe developrnent of variable-fiequency drives (VFD) has led to the creation of

sophisticated microprocessors that have Uicreased the capabilities of the VFD itself. TheVFD c m be used to control the amount of power being supplied to the dc load. Thismethod is demonstrated in a paper written by Simonetti et al [18]. In this paper, theauthors have shown the effectiveness of the VFD o reduce the harmonic content withinthe system. Figure 2.9 illustrates the Pulse Width Modulation (PWM) input convertercontrolling hannon ic currents. This method is restncted to small power levels, and couldnot be implemented with the naval vessels under study.

High-frequencyGTO converter

Figure 2.9. PWM Input Converter Contro llhg Harmonie Currents (from [ 6 ] )

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25.7 System FilteringMethodsSystem filte a (passive, active or phase staggering) have been in use for several

years. System filtering methods offer a quick solution to the harmonic problems within agiven distribution system. With the developments in the system filtering methodprovided by this thesis, the system filter, specifically the passive filter, becomes a viableoption.

2.5.7.1 Passive FteringThere are two primary types of passive filters: series and parailel. The series filter

is designed to have a high impedance at the tuned fiequency, which blocks the unwantedfiequency component fiom continuing to travel through the distribution system. Theparallel filter is designed to have a low impedance at the tuned frequency to trap theunwanted harmonic component. The frequency of the harmonic, and the power levelswithin the distribution system, dictate the filter size. Prelirninary research has shown thatpassive filters can effectively elirninate or reduce the desired harmonic component withinthe distributionsystem [19,20].

nie parallel passive filter is designed to reduce the impedance at the desiredfrequency to a low value to ensure the unwanted harmonic component is shunted toground. The amount of harmonic power for the specific harmonic component should beused in the design of the filter, ensuring that the filtercm handle this power level. It maybe advisable to iatroduce another passive filter to sp lit the power to ensure that each filteris not overloaded by harmonie currents fiom the distribution system. Under certain fault

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conditions, the passive filter c m introduce more problems than the harmonic value it wasdesigned to reduce. Therefore, different fault conditions must be applied during design toinvestigate possible problems, such as those discovered by Hudson [3]. These problemscouid be parallel and series resonance as described in sections 2.4 and 2.5, respectively.To reduce the Likelihood of parailel or series resonance occurring, the passive filtershould not be designed to reduce an integer multiple of the supply fiequency [2], butshould be off tuned fiom the harmonic component for which it has been designed [19].For example, if the passive filter is designed to reduce 5" harmonic effect, then the filtershould be tuned for 4.8 times the fundamental instead of five times the fbndamental.Figure 2.10 illustrates the use of passive filters to eliminate harmonies.

Frequencyselective Hamionic cunentslowimpedancepaths t-----1

0

#

Inductive sourceimpedancedefinesavailable shod-cimua curent.

Figure 2.10. Use of Passive Filters to Reduce Specific Harmonies (from 161)

2.5.72 Active FilteringActive filtering is very effective, as he active filter is designed to eliminate the

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unwanted harmonics dynamicaily. The active filter eluninates the unwanted h m o n i c sby introducing currents to cancel the unwanted hannonic via electronic circuitry based onexisting harmonic at any given moment [211. One of the main drawbacks to the activefilter is the cost; however, if cost is not a concem, the active filter c m be more effectivethan either the passive filter or the phase staggering method. There has been work in thearea of a hybrid filter which combines properties of the passive and active filter [22].More recently, Chicharo et al [23], demonstrated the use of an adaptive infnite impulseresponse line enhancer filter that tracks he fundamental fiequency of the inverter outputvoltage and harmonic line current in a power system to actively reduce the harmoniccontent by providing the filter the required harmonic signal information, thus proving tobe an effective method of harmonic reduction. The active filter can be used in amultitude of applications, including the systemmodels under study within this work;however, the primary drawback is the increased cost of the active filter due to itscomplexity.2.5.73 Phase StaggeringMethods

The phase staggeringmethod of harmonic reduction is implemented when thereare multiple loads that can be fed fiom different phase-shifting transformers. Thedistribution system hannonics are reduced by feeding the current for the equipmentthrough phase-shifbg ansformers. The harmonics fiom one transformer will be 180degrees out of phase with those other transformer, subsequently canceling the hamoniccomponent. The phase s t a gge~gnethod ismost effectivewhen each of the converters

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are equally loaded [2].2.6 Summary of Chapter 2

Chapter2 provided the background on the harmonic analysis techniques,harmonic sources, and various methods used to reduce harmonics. Each distributionsystem under study must be treated differently and thoroughly understood before theharmonics within the system can be effectively analyzed and subsequently reduced.

The next chapter will develop the passive filter placement method andoptimization. In Chapter 3, the direction o f the harmonic analysis and subsequentfiltering reduction schemes are illustrated.

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Chapter3Model Development fo r Filter Placement and Optimization3.1 General

In the previous chapter, harmonic analysis techniques and possible reductionschemes were introduced. For the purposes of this work, the use of the passive filterwasselected due its lower cost and relative size. This thesispresents a novel passive filterplacement scheme and a method to locally optirnize the filter. Filter placement is animportant issue in the reduction of hannonics because of the potential problems that c mbe created with the introductionof the filter itself, kcluding parallel or series resonance.Therefore, it is important that the filter placement be thoroughly sirnulated before acniallyphysically placing it within the distribution system. Previously, filter placement has beenrestricted to the PCC. This thesis will shifi fiom the concept of the PCC o an empiricallydetermined method that allows the harmonic filter to be placed where the physicailimitationsof the system under study allow.

For both the CPF and theMCDV, he previous work [3] and [4] respectivelydetermined the ideal placement of the PCC. In the case of the maritime coastal vessels,the ideal PCC atjust outside the SCR cabinets could not be realized due to physicallimitationsof the compartrnentswhere the cabinets are located. The passive filterrequired for the MCDV s similar in size to the SCR cabinet; therefore the filter could notbe physically placed beside it. However, there is enough physicd space for the filter to beinstalled in other locations throughout the vesse1and still reduce the effects of theharmonic distortion. In the case of the CPF, he ideal location of the PCC at the main

34

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switchboard could be realized because there is enough space to physically place thepassive filter at the optimal position. The parallel passive filter can then be locailyoptimized at the place determined by the filter placement method discussed M e r n thischapter

This work is concerned with smaller distribution systems, and, in the case ofmaritime coastal vessels, the distribution systems are considered relatively small innature. The passive filter is tuned to the harmonic level that has been determined to be aproblem. The parallel passive filter placement method c m be empirically determinedthrough an exhaustive search pattem in the topology o f the distribution system todetermine the reduction in harmonic content throughout the entire system when the filteris placed at each node in the topology. By using every node in the topology, the resultswill show that there are several locations throughout the distribution where the filter canbe physically placed and still reduce the hamonic distortion. However, the number ofnodes in the s e m h pattern can be reduced by only using nodes where the filtercan bephysicaily placed. Since maritime coastal vessels have very Iittle space where a paraIlelpassive filter of the size required by the IEEEguideline [2] could be installed, it would bebeneficiai to have a scheme to allow a search pattern so that physically realizablepositions for the filter can be obtained. It is to this end that this filter placement schemewas developed.

The method of the placement of the filter requires that the system under study bethroughly understood before the implementation of the filter placement method, includingthe hamonics of concem and the physical collstraiats on the placement of the filter.

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Therefore, the intention of this work is to provide a means to determine where the filtercan be physically placed within the d istribution system and still reduce the hannonicdistortion to an acceptable level. Once the filter location is determined, the filter must beoptirnized for the harmonic component that it was designed to reduce or eliminate.

3.2 System Mode1The first step in the filter placement procedure was to produce a computer

model of the distribution system under study. The computer simulation of the Navyvessels was done using the software called EDSA [24]. EDSA was selected because ofits increased capabilities over Cymharmo and Micro Tran, n that it provides a totalsolution package for designing, simulating, and anaiyzing electrical distribution systemsin a Windows or NT environment. EDSA provides a visual representation of thedistribution whereas Cyrnharmo and Micro Tran have a coded representation of thedistribution As a result of the visual representation of the disrribution, theoperator willhave fewer errors in the development of the system model. To avoid repetition, only theMCDV will be discussed in the following sections; however, the filter placementlocations were determined for both the CPF and MCDV and can be viewed in Chapter 4.Figure 3.1 shows the simplified distributionsystem for the MCDV. The distributionsystemwas simplified to include the areas of harmonic concern.

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PropulsionDIAH Propulsion DIA In Propulsion DIA tl(tbdM) (poflm (PortFM)

Stbd Propulsion

Figure 3.1. MCDV 6V PowerGeneratioo& Distribution System (from 141)

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R e d = cabinet (6-puise. 3-phase. thpnor-coatroned dual coiw#tcr)

1150k W h h ropulricm sep--micdDC motord n q one propeler dxougb r2-DrivecoiiQiirrbon ( h o ahd 'aamh-

Table 3.1. Symbois for the MCDV DistributionSystem (from [JI)The simplified distributionsystem of the MCDV h o w in Figure 3.1 is restricted to the600V, ropulsion support, deck auiliary, and the ship's service switchboard. The power

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generation for the MCDV comprises four 715K W iesel-altematos that supply the mainswitchboard with 600V, phase, 60Hz ower. The items that are not labeled in Figure3.1 were not used in the topology of the distribution system, and the primary focus of thedistribu tion system is Iimited to the items shown n Table 3.1. The auxiliary loads are nots h o w in the diagram but were used in the development of the variable load profilesdiscussed later within this chapter. The oading profiles o f the distribution system arediscussed in Chapter 4. The symbols shown in Figure 3.1 are explained in M e r etailin Table 3.1. The layout of the distribution system is required to produce the topologyused in the filter placement method.

Once the distribution mode1 has been validated by supporting data or by previoussimulations, the topology of the distribution system can be produced. In the case of theCPF and the MCDV, he computer simulation models were validated by previous workcompleted and power quality analysis in [3] and [4] respectively. Within this work, themodels were simulated using the computer software called EDSA. The results of themode1 validation can be viewed in Chapter 4. The next step in the filter placementmethodology is to convert the distribution system into a topology diagram. The topologyfor the MCDV s shown in Figure 3.2.

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Topology For MCDV

Main Bus (1)w I I 1 IStbd Prop Bus (2) Port Prop Bus (3)

De& Aux Bus (4) Service SWBD Bus (5)

SCR Cabinet SCR Cabinet(Sm,6) (Port, 7)

600V/450VTx Bus (8)

Figure 32. Topology for the Distribution System of the MCDV

Thebuses of the distribution system are numbered to provide position numbenfor filter placement, and these nurnbers are referred to as nodes. Each of the powersupplies, main buses, transformers, power panels, or other possible locations of harmonicsources are numbered. The SCR abinets are included in nurnbering for the MCDV

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because of the high harmonic content that is generated at these points. In the case of theCPF, ower panels were included in the numbering.

3.3 Filter Location AlgorithmHarmonic d y s i s provides the ability to calculate and display the impedance

fkequency response of d l buses with respect to a harmonic source at a given bus, and withrespect to positive, zero, and negative sequence networks. EDSA displays the impedancefrequency response graphically or in text format, in ohms or pu, and phase angle indegrees or radians. The impedance fiequency response is based on the fiequency domainanalysis approach, but the results can be displayed in the time domain if desired.

The harmonic analysis isfm camed out for the system without harmonic filtercompensation. The hannonic analysis determineswhat harmonic components need to bereduced in order to reduce the THD to meet the Iimits of the IEEE standard for thedistribution system. Once a specific harmonic component has been identitied as apotential problem basedon the IEEE allowable distortions, a pwive filtercm beselected. Figure 3.2 illustrates possible filter locations. Aftera filter configurationisselected, the filter is designed to meet the requirements of the distribution system inquestion. For example, if the 5" hannonic (which is 300 Hz if the fundamental fiequencyis 60Hz) is excessively high in value, the filter is tuned to a value of siightiy below 300Hz. According to studies carried out byKawann et al [19], the filter shodd be m e d to avalue of approxirnateiy2% lower than the resonant fiequency in order to avoid parallel orseries resonance. For the purposes of this example, the fifterwould be nined for294 Hz

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The derivation of the actual components is d et em he d by this fiequency and the qualityfactor.

The quality factor of aRLC series circuit is defined as the ratio of the reactivepower of either the inductor (L) or the capacitor (C) to the average power of the resistor atresonance. At resonance, the capacitive reactance(X,) s equal to the inductive reactance(Xh,herefore, only the derivation of the inductive reactance will be shown. The qualityfactor for the type 1 filter (seeFigure 3.4 on page 47) is calculated by the followingformula:

whereX, is defined by:X, = 2Rj;L

Ais the resonant tiequency of the filter, and L s the inductance selected. The formulaused to calculate the resonant fiequency is the following:

For the purposes of this work, the quality factor was set at 50. The maximum Q forcommercially available coils can be as hi& as 100 [2], so it is reasonable to assume that avalue of 50 c m be obtained. Dependhg on available components (RLC), he filter cm betuned to 294 Hz to reduce the effectsof the srnharmonie. This thesis restricts the

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components to a pre-detemiined range of filter component values before the op timizationof the filter is carried out. This procedure will be discussed later in this chapter.

Once the components of the filter have been calculated, the filter is placed a t nodenumber one and the harmonic m dy sis is carried out. The calculation m u t be carried outat each new node location because the passive filter alters the overall system impedanceat the new location, and this change in the system's impedance may cause resonanceproblems, as previously discussed. Therefore, this step is repeated at each node untilthere are no major differences in the harmonic levels at nodes or sub-nodes or newham onic problems due to parailel or series resonance. Major differences were arbi tranlychosen to be harmonic distortions greater than 1%, and could be changed as required.Sub-noder are created if there is a difference in the THD of 1% at adjacent nodes. Sub-nodes are placed midway between adjacent nodes. For example, if there was a differenceof 1% between nodes 1 and 2, then a sub node named 1.5 would be created. In the eventthat sub nodes are created then m e r requency scans are carried out until there are nonew sub-nodes created. Figure 3.3 shows the flowchart for the filter placement method.

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Figure 33. Filter PlacementMethod

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The results of the parallel filter placement scheme outlined in Figure 3.3 will beshown in chapter 4. This method assumes that the required software is available, and thatthe topology of the distribution system c m be obtained. M e r , the completion of thesteps outlined in Figure 3.3, itmut be detemined where the filter can be placed due tospace restrictions within the vesse1 itself. The location of the parallel passive filter iscritical in the optimization of the filter, as the system irnpedance at that location isconverted into a transfer h c t i o n used in the objective fnction. For the purposes of thiswork, it is assumed that the passive filter can be physically Iocated at the mainswitchboard for both vessels. This location was arbitranly chosen to reduce thecomplexity of the calculations involved in the optimization process by fixing the physicallocation of the passive filter.

3.4 Parrllel Passive FilterOptimization SynthesisP d l e l passive filters are less affected by component drift, due to manufacturing

and environmental changes, than other types of filtering rnethods (19,201. Theoptimization of the passive filter is based on a composite objective function whichfocuses on the following tw o parameters: reduction of the harmonic current of concernand the prevention of paralle1 resonance. As discussed earlier, parallel resonance maycause more problems than the original armonic distortion before the placement of theharrnonic filter itself. The p h a r y goalof the optimization is to maximize the harmoniccurrent that is shunted to ground through the parallel passive filter, while rninimizing hefilter components. The derivation of the objective b c t i o n is discussed later in this

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chapter.Parallel passive filter synthesis includes the type of the specific filter, the

placement of the filter and the optimizationof the filter. The filter optimization iscalculated at the node selected. For the purposes of this work, the location of the parallelfilter was located at the main switchboard. The parallel passive filter is nined to theharmonic component that is to be reduced.

Locations chosen for both of the test systems were the main switchboard as theideal placement of the parallel passive filter; however, this location would normally bedetem ine d via the filter placement methodology previously discussed. The filterplacement scheme is implemented before the optimization in order to maxirnize theeffects of the paraliel passive filter at the point of filter placement. Figure 3.4 shows fourstandard passive filters that EDSA uses and which a re accepted by the IEEE Standard519-1992. Thiswork will show the development of the second order filter (Type 3) forthe MCDV or the placement and optimization of the parailel passive filter. All fourfiltersshown n Figure 3.4 were optimized for the location where the filter could bephysically installed in both vessels, and the reduction of the THD due to these filters areshown in Chapter 4.

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Figure3.4. Standard RLC Passive Fters (from 1241)The optimization of the parallei filter uses the information that EDSA provides

after a fiequency scan and the harmonic analysis simulationsare performed. However,there was a need to use an additional software package to interpret the results producedh m DSA. Matlab was chosen as aid in the extrapolation of the information producedfkom EDSA. The results are translated into a text document to be interpolated by theMatlab tooibox, 'Frequency Domain System Identification Toolbox' [25]. Toolboxeswithin Matab area collection of pre-fabricated programs which are used to implementvarious processes. From the information obtained in the simulations using E D S hMatlab was prognuned to determine the transfer functionof the system impedance andthevarious values of the objective function within the constraints of filter componentvalues that are selected. The caiculated system ransfer function used in the objectivef'unction provides biasing that speeds up the convergenceof the objective function. Table3.2 shows the componentvalues that were selected for the purposes of this work.

The transfer fiinctions for the system and the filter were used in the objective

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functionand are discussed later in this chapter. For the purposes of this work, itwasassumed that the systemwas a balanced three phase system, and that a single phaseanalysis could be used. Figure 3.5 showsthe systemmodel used for the derivation of theobjective hctioa. The objective function is cornprised of the harmonic cunents showin this figure.

(Total Hannonic Current)'htf lter Placementat the SelectedNode of theDistributionSystem 1 Filter lmpedance

Figure 3.5. Passive Filter Synthesis

Zks) represents the filtes irnpedanceand Z&) represents the system irnpedance. InFigure 3.5 oniy the harmonic currents are represented, and a harmonic anaiysis is requiredto determine the values of 1 and 1 The general model used in the determination of thetransfer bction is shown in Figure 3.6 fiom reference [25].

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Figure 3.6. Mode1 used to determine of the system transfer functioa (from [25))

The system tnuisfer function is represented by Matlab as the following: H(Q),where !Q =F ~ = 2zfin the Laplace domain. For the purposes of this work, H(Q) isequivalent to YJs) and is used in the objective hinction. The excitation signal hascomplex amplitudes X at preselected h m o n i c fiequencieshw, and the response of thesystem at the placement of the filter is Y. The measured input and output complexamplitudesare compted by noises N, and N,. The erroa are assumed to be Gaussian,which means that the signals are uncorrelated between input and output. The unknownparameters of the system transfer function are termed the vector P, and the complexinputs and outputs amplitudes are vecton X and Y respectively. The equation used in thedetermination of the tr a d e r fiinction by Matiab's toolbox is the following:

whereM is the number of zeros, nd is the nurnber of poles, andT, s the sampliag period.49

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The spnipling penod will be used in the starting iteration and will determine time requiredfor miriirhization of the transfer f'unction. It is recornmended to keep this value between Oand 1 by the author of the toolbox [26]. As the order of the tramfer f ic ti o n is increased,the accuWy of this b c t i o n increases, but so too, does the computation time required forMatlab ta converge on a solution. For the purposes of this work, it is assumed that thetransfer b c t io n obtained using the 5" order forM and nd, fiom Equation 3.3, is vaiid,and will be referred to as Y,(s). The system transfer function obtained at the mainswitchbogd for the MCDV s the following:

The riextpart of the objective function is the transfer function of the filter itself.Figure 3.7 represents one of the parallel filters used in this work. This figure indicates thecomponents with their s-space values to determine the transfer function.

Type 3

Figure 3.7. PassiveHarmonic Filter (from [24))

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The developrnent of the transfer f'unction is shown with the following formulae:

The transfer fnction for a Type 3 filter is simplified by the following equation:.

The values of RLC were determined when the objective function retumed specificvalues der optimization. The objective function is the total h m o n i c current, and is acombination of the rem ainhg system harmonic curen t and the harmonic current forwhich the passive filter is tuned. The objective h c t i o n begins with Kirchoff s currentlaw applied at the filter placement location, except only the harmonic currents are used.

The generai objective function used in the determination of the passive filtercomponents begins with the following equation:

= G, 8) +W)

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where equation 3.7 is derived fiom Figure 3.5 with the following formula:lh I~~ rh (3.8)

where Ihf is the filter's harmonic current and 1, is the remaining system's harmoniccurrent.

12, s) =-, s)substituting equations 3.10 and 3.1 1 into 3.9 yields the following formulae:4,=&(Y,(s)+ Y/&!) (3.12)

rearranging 3.12 in terms of Vhyields the following formulae:

to eiiminateV, the following terms are used:

by substituting the terms h m .l4, the following equationsare derived:

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With equations 3.15 and 3.16, the following ratio of currents can be represented in termsof the filter transfer fiuiction, YXs), and the system transfer huiction, Y&), in order toobtain the objective function shown in equation 3.7.

where G,(s) represents the ratio of system harmonic current to the total harmonic currentat the filter placement location,G,(s) represents the ratio of filter's current to the totalharmonic cunent., I',-is the harmonic current of the specified fkquency for the filter, I, isthe harmonic current of the specified fiequency for the syaem, nd 1,is the total harmoniccurrent. The ratios of hannonic currents were used in equation 3.7 in order that theequationwas represented in terms of the transfer functionof the system and filter. As aresultof normalizing equation 3.7 when the harmonic current ratios were used, theequation iscoaseained too aiways being equal to one. This ensures that oniy the filterpanuneterswill be the oniy variables in the optimization of the objective function.

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The objective function is derived by the substitution of s=jo into Equation 3.7 and theansposing the equation into the following summation:

Subject to:ph R I

cm" CI m"where:N epresents the highest order of discrete harmonic fiequencies under study, k representsthe harmonic order o f the filter, ando epresents the 2-x-f in this thesis, f = 60Hz). Forexample, if one of the discrete fiequencies of concem is the 5" harmonic, then o will beequal to h ( 3 0 0 )andN will be equd to 5.

Within Matiab's Optimization toolbox, there aremany different optimizationtechniques that codd be used to solve the optimized filter's parameten. Equation 3.19was constructed to have the harmonic current of the filter and the remaining harmoniccurrent seen by the system at the selected filter placement node. Since the filterparameters and the selected harmonic fiequency are the constraints of the objectivefnction, the problem of optimization could be transformed into an easier problem. Itwas to this end, that the objective h c t i o n dealt with the filter and system transferfiinctions. The optimization of the objective function could now be solved with the useof theminllnax fiiactionwithin the optimization toolbox.

The minima minimizes the worst-case value of a set of multivariable fitnctionsstarting at an initial estimate. The value was subjected to the constraints of fiter

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parameters and the harmonic fiequency that the parallel passive filterwas tuned for. Theminimax fnction within Matlab generates the optimization of the objective function withthe following equation:

minyy(~;x)) + G(X)< Or;;where x is a vector and F(x) and G(x) are b c t i o n s that retum vector values. F,(x) is thevalue of the i element of the vector returned by F(x). G(x) represents the equalityconstraints imposed on the objective f'unction. Table 3.2 shows the equality constraintsfor the pararneters (RLC) for the passive filter under study.

Table 3.2. Range of Component Values for the Passive FilterThe values o f RLC depend on component availability. The cornponent values werecontinuously constrauied in the optimization of Equation 3.1 9. It should be noted thatthe optimization cannot guarantee a global minimum is found; however, it will yield alocal minimum.

A global minimum would be the ideal value obtained; however, there is no realmethod that ensures that this value is obtained with a complex problem s h o w inEquation 3.19. The constrained objective function simplifies the optimmizationrocess todlow for convergence of the h c t i o n to aminimum value. Whether this value is a local

R (9)Min100

Max500

c (PF) L Hl 1Min1

MinO. 1

Max30

Max ,0.3

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minimum or a globalminimum ca nw t be guaranteed. The scope of this thesis was toshow that the parallel passive filter's h c t i o n could be improved after optimization.Therefore, only one method of optimization was used within this work and the only onetechnique was implemented to ensure that a global minimum value was achieved. Thistechnique was the selection of the initial estimates were selected below, above and withhthe consfraints shown in Table 3.2. The various initial estimates confumed that the sarneminimum is achieved. Obtaining same minimum does not prove that the minimum is aglobal value; however, it is a good indication that the minimum could be a global value.For the purposes of this work, the value obtained from the optimization was assurned tobe a global minimum.

M e r he optimization of Equation 3.7, the specific values of the objectivefunction are obtained. Subsequently, al1 of the combinations possible with the valuesfrom Table 3.1 can be extrapolated from the results of the Optimization process. Thefilter values are updated with the minimal values obtained fiom the optimization process.The new component values will ensure that the minimum impedance of the filter isobtained allowing the maximum value of the harmonic current to be shunted to ground.

Afier the values of the filter are detemiined, the filter data is upiiated and thehamionic analysis is niaagain. The resuits in Chapter 4 show that d e r optimization ofthe filter, theTHD or both the CPF and MCDV decrease in harmonic content by as muchas 50%.

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3.5 SummatyIn the preceding chapter, the filter placement method has been illustrated, and

optimization o f the passive filter has been outlined. With a combination of the filterplacement method, and subsequent optunization, the passive filter becomes a viableoption for harmonic reduction.

The next chapter will show the results of the passive filter placement method andoptimization.

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Chapter4Evaluation and Validation4.1 HarmonicAnalysis and Mode1Validation

The previous chapter outlined the proposed filter placement method andsubsequent optimization of the passive filter. This chapter provides the results of systemmodeling, and shows the results obtained using the new rnethod.

4.1.1 CPF ValidationThe fm step in the validation of theCPF mode1was to simulate the vessel under

the same loading conditions as in the previous work. The CPF mode1 was sirnulatedwith the 43 harmonic sources that were identified as being potential harmonic problemareas within the distribution system. The harmonic sources are comprised of 10 staticfiequency converters and 33 unitemiptible power supplies(UPS). The static fiequencyconverters(SFC) re basically an inverter, that produces an output frequency differentfiom 60 Hz. In the case of the CPF, he SFC produces power at 400 HZ which is usedfor the combat systems on the vessel. The 33 UPS's on the CPF provide backup powerin the event of power failures. Figure 4.1 illustrates the ladder diagram for the 43h m o n i c sources pre-detemined and their comection scheme within the CFF'sdistribution system. The Iadder diagram shows how the forward and after switchboardscm be connected to provide redundant power supplies for the vessel. Table 4.1 showsthe load profiles that were used in the validation of the previous work on the CPF, oensure that the program EDSA was providing res dts sllnilar to the given load model.

58

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Figure 4.1. CFP ladder distributionsystem (from 131)

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30 Fonvwd EngincRwm (FER) 2 KWL

3 1 FonvardEnginc Room (FER) 2 KW32 FonvrvdCommunication Rwm (FCR) 2 KW

1

Table 4.1 Lord profdes used to validate previous work (from 131)

29 1 ForwnrdEnginc Room (FER) 2 KW I

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The mode1 shown in Figure 4.1 provides the general layout of the CPF'sdistribution system. The point of validating the distribution system was to ensure that theparameters entered into the software prognim were providing adequate resuits, beforeproceeding to the proposed work The estimated design data for the Static FrequencyConverter is s h o w in Table 4.2.

Table 4.2. Static frequency current injection (from (31)As seen in Figure 4.1, the locations of the static fiequency converters are shown

by the numbers in the square symbois within the ladder diagram. The components wereassumed to be running at full load (19.7 Arnps) and have the same conditions as theprevious work. Values fiom Table 4.2 were used in lieu of the UPS cunent injections.EDSA allows for distortion values to be entered as a text file so this was easy toimplement. Table 4.3 indicates the loading conditions used in the validation o f the CPF.

Static fiequency current injectionsHarmonic Component

1

1Percentage Distortion

O

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1 Location 1 Load 1

Table 4.3. Load Profile for440V Power Panels (from [31)The load profiles given in Table 4.3 indicate the static load conditions of the CPF.

The power panels split into different feeders having static loads, static frequency

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converters, or UPS. With the static load profiles for the different power panels and thestatic converter information, the CPF model was consucted. A fiequency scan, loadflow and harmonic analysis were carried out to validate the CPF model. The results ofthe previous work in Table 4.4were obtained usingCymhamio (fiom [3]).

Table 4.4. Cornparison behveenCymharmo and EDSA harmonic distortions

_

Theredts CPF show nTable 4.4 shows hat the models in both the CymharmoandEDSA programs give results that are within 3%. Having validated the CPF model

Location

Total DistortionsL

F483F459

I

F4681

F434F440.F428

1

F432F427F417F424

I

F4441

F42F431

THDO%Cymharmo

8.320.3490.3630.3430.3520.3530.3600.3800.3840.3890.3800.3600.4400.356

THD 1)Cymharmo

12.3090.560.2670.2270.7900.3660.6030.6250.4351 .O300.566O 4421.9500.244

EDSA8.290.3490.3590.3390.3510.350.3490.3760.3890.3950.3940.3570.4450.356

%EDSA12.7070.60.3

0.2290.90.40.620.6250.4461 O

0.630.431.960.25

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using EDSA, variable load profiles were used instead of the static loads in order tocompare their affects to that of the static load profiles used in the previous work for theCPF.

4.1.2 MCDV ValidationThe first step in the validation of the MCDV mode1 was to simulate the vesse1

mder the same loading conditions fiom the previous work. The distribution systemwaspreviously reduced to investigate the major sources of harmonies. Figure 4.2 representsthe reduced distribution used in the previous work on the MCDV 4].

Figure 4.2. Reduced distribution system for theMCDV (from (41)

The load profiles for the reduced distribution system inFigure 4.2 are s h o w inTable 4.5.

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1 2 1 Prop D/A #2 1 83 3 kW 1Number

1

1 9 1 Ship Service Alternator 1 300 kW 1

NameProp DIA #1

56

r 13 1 Lube Oil Pump 1 2.24kW 1

Power833 kW

1 14 1 Hydrauiic Pump 1 30 kW 1

Main Prop via SCR 1Main Prop via SCR #2

1 15 1 Cooling Pump 1 15 k W 1

1150kW1150kW

1 18 1 Cooling Fan 1 I l kW 1

1 21 1 Lube Oil Pump 1 2.24 kW319

1 25 1 Supply Fan 1 22.4kW 1

Survey ContainerCooling Fan

2224

Table 4.5. Loading profile for distribution system for the MCDV (from [41)

53 k W1

t l k W

The entire load profile for the MCDV can be viewed in reference [4]. Previously,the MCDV was simulated,with the main harmonic sources that were identifiedasbeingpotentiai hannonic problems using Micro Tm. o vaiidate the previous work on theMCDV, he reduced distribution system was simulated using EDSA, and Table 4.6 showsthe cornparison between the Micro Tran and EDSA models, where theMicro T m esults

Hydraulic PumpCooling Pump

30kW1 5 k W

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are fiom the previous work and the EDSA results arefiom the present work.

EDSACurrent

Distortion

Harmonic No. Micro TranVoltage

Distortion

EDSAVoltage

Distortion

Micro TranCurrent

Distortion

Fundamental

THD (%)

Table 4.6. MCDV 600 V Bus Harmonic Content: Micro Tran versus EDSAThe results fiom the previous work and the presentwork are very close in

agreement. The validation of the MCDV mode1 using EDSA was determined to beacceptable, and therefore the variable load profiles were used instead of the static loads inorder to compare the effectsof the variable load profile to that of the static load profiles.

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4.1.3 Assessrnent of ModelsThe models for the CPF andMCDV ave produced simi1a.r results to the results

fiom previous work. It is reasonable to expand both models to the full distributionsystems and fbrther the investigation of the harmonic content and subsequent filterplacement and optimization techniques using variable Ioad profiles s h o w Iater in thisChapter.

4.2 Variable venus Static Load ModelsThe variable load model has become the preferred model (over the static load) in

harmonic studies and there has been significant work in this area [17,18]. For thepurposes of this work, the method of dynamic load modeling produced by Chikhani et al[14] was implemented, where the load profile for the four seasons were normalized over atwenty-four hour period. In the case of the CPF and the MCDV, the three sailingconditions of at anchor, peacetime sailing , nd emergency conditions were normalizedover a twenty-four period. The various sailing conditions determine the arnount of poweravailable and the equipment that is brought on line. The highest requirernent for powerand Ioads is the emergency sailing condition.

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Figures 4.3 to 4.5 shows the variable load profiles for the three types of sailing conditionsfor the CPF and theMCDV. --CPFMCDV Variable Load Profile

(Emergency Levels)

Normr l iz rdLoad Current

Figure 4.3. Variable load profde in emergency conditions

-- -- * - - - - - -- --- - - -- -CPFIMCDV Variable LoadProfile(PeaceTime Sailing)

Figure4.4. Variable load pronle for normal sailing conditions

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CPFIMCDVVhriable LoadProfile

LordCumnt 0.4 -1 - 1

Figure 4.5. Variable loadprofile at anchor

It was necessary to assign load profiles to actual system loads. Loads on thesystem are those shown in Figure 3.1 for the MCDV, nd Figure 4.1 for the CPF. Totalsystem generating capacity for the CPF s 3200 kVA, with a peak demand of 1625 kW.Therefore the load at each load point, i, a particular instant in time , , is assigned as:

where the load(time) is the load profile information given as a f i c t i o n of the. Thesevalues have been normalized to reach amaximum value at 1 .O. Equation 4.1 is used forthe MCDV except that the value of (l62Y32OO) s replaced with (1450/2860). The loadprofiles were obtained h m he ships load profiles referenced in [3] and [4] respectively.Table 4.7 shows the results for variable load profiles in lieu o f the static load for the CPF,and Table 4.8shows the redts for the MCDV. Each of the variable load pronles

69

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obtained were used with the system models to provide more realistic results in the overallaveragedTHD naiysis.

Table 4.7. Averaged variable load verses the static load profile for the CPF

1

Table 4.8. Averaged variable load verses the static load profile for the MCDV

Static Load

Static LoadProfile

THDvL

Emergency

EmergencySa ilhg Load

ProfileTHDI THDv

8.3 1 12.7

Peacetime SaingProfile 1 Sailing Load

THD,

Peacetime SaTngLoad Profile

At Anchor Load

1 9.3 1 14.0m v

LoadProfile

TH&7.1

1

THDI

At Anchor LoadProfile

Profile

THDv7.2

THD,29.8

Profile

8.3 1 12.8THDv

TH&6.7

THDI30.4

THDv7.4

r THDI

I

THD,1

28.2THDI31.2

1 7.9 1 11.6

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4.2.1 AssessrnentFor both the CPF and the MCDV the THD changed with the variable load

profiles. nierewere similar results when the sailingcondition closely matched the sta ticload profile for both vessels. The THD for both vessels increased with the increasedvariable load profile in the emergencysailing condition and decreased with the ut anchorcondition. Tbese results are similar to results found in a paper written by Lin et al [15],and can be attributed to the increased hmon i c loads that were in use during theseconditions. Where the auth oa detemillied that the variable load model will give moreprecise calculations of the power system under study. These results are supported byother studieswhich can be viewed in [16.17]. It has been demonstrated with the systemmode