advert

JOURNAL OF RESEARCH IN NATIONAL DEVELOPMENT VOLUME 8 NO 2, DECEMBER, 2010   

MAINTENANCE MANAGEMENT OF GAS TURBINE POWER PLANT SYSTEMS

A.A.Fadipe

Engineering Management Department, University of Port Harcourt, Port Harcourt

and 

J.J. Biebuma

Electrical and Electronics Engineering Department, University of Port Harcourt, Port Harcourt,

E-mail: femi.fadipe@gmail.com

 

Abstract

Over the years, electric power generation and supply has not been steady and sufficient in Nigeria. Breakdown of machinery and equipment is being identified as some of the major factors for continuous state of affairs. Given the abundant availability of gas and the significant installed capacity of the electricity from Gas Turbine Power Systems; effective maintenance of Gas Turbine Power Plants in Nigeria could be the panacea for achieving regular power generation and supply. The study identified environmental impact on the machines, economic limitation, government policies, inconsistency in following maintenance procedures and bottlenecks as some of the serious constraints affecting maintenance of Gas Turbine Power Plants in Nigeria. Maintenance models that could be considered in Afam power station are highlighted and analyzed in the context of these constraints. Also necessary recommendations that will improve maintenance and operations of Gas Turbine Power Plants in Nigeria are proposed.

Keywords; Maintenance, gas-turbine, equipment, strategies, optimization, profitability


Introduction

The demand for electricity and an increasingly competitive environment has raised important questions concerning maintenance in the industry power plant systems. The present emphasis on deregulation in the power sector is likely to result in increased competition among the country’s power producers. To survive the competition suppliers have to handle maintenance more efficiently, that is reduce maintenance cost. One way to reduce maintenance cost is to optimize the utilization of maintenance resources. Thus, power plant service continuity is achieved (Duffuaa and Al-Sultan, 1999).

 

Maintenance requires three resources: manpower, materials and equipment Everyone of these resources is crucial component of maintenance management; therefore, the focus of this study is to present how these indices determine the optimum availability and reliability of a power plant (Alfares and Lilly, 2006), while emphasizing on plant equipment.

 

Maintenance management considerations

The maintenance management of a power plant is an engineering function that seeks to coordinate and integrate the activities of the various functional areas of plant operation in order to achieve one singular objective - to ensure the continuous supply of electricity. A balanced scorecard is often used to evaluate the overall performance and reliability of a power plant and its progress towards attaining this objective. A power plant is labeled to be effective, reliable, available and efficient when it continuous to perform to its intended capabilities and function (Dunn, 2002).

Gas turbines regularly undergo a series of scheduled or unscheduled outages during their normal operating lives. It is the function of maintenance management to ensure service continuity during these outages so that there is reduction of the occurrence of unscheduled outages.

The combustion (gas) turbines being installed in many of today's natural-gas-fueled power plants are complex machines, but they basically involve three main sections (DOE, 2008): 1. The Compressor System 2. The Combustion System 3. The Turbine

Maintenance inspection and strategies

Management of maintenance inspection of gas turbines can be broadly classified into as standby, running and disassembly inspections. The standby inspection is performed during off-peak periods when the unit is not operating and includes routine servicing of accessory systems and device calibration. The running inspection is performed by observing key operating parameter while the turbine is running. The disassembly inspection requires opening the turbine for inspection of internal components and is performed in varying degrees. Disassembly inspections progress from the combustion inspection to the hot gas path inspection to the major inspection.


Figure 1 Combustion, Hot Gas Path, and Major Inspection Scope of Work, Balevic and Others (2004)


Gas turbines have dramatically increased in size and complexity due to technological improvement in output and efficiency together with increasingly stringent environmental requirements. Therefore the requirements upon plant maintenance managers/engineers are growing as are the option available at their disposal. The essence to this study is to assess the required techniques for maintenance management of a modern Gas Turbine and evaluate the options available to meet those requirements through by employing these maintenance strategies: 1.Breakdown Maintenance (BdM) 2. Planned Maintenance (PM) 3. Predictive Maintenance (PdM) 4. Reliability Centered Maintenance (RCM)

 

Manpower scheduling

 

Manpower is usually the most important and expensive resource of any organization, adequate manpower scheduling is a crucial component of maintenance management. In order to reduce maintenance problems it is required to effectively schedule the maintenance workforce to handle ever-increasing plant maintenance load. Traditionally manpower scheduling is classified into three types (Ernst, 2004):

i. shift, or time-of-day, scheduling

ii. days-off, or days-of-week, scheduling

ii. tour scheduling, combination of the first two

 

Plant maintenance checks are carried out daily by maintenance crews (mechanical, electrical, instrumentation & control, workshop services and planning. The checks involve taking plant parameters like load, compressor inlet temperature, plant evaluated operating hours etc. Apart from the required daily checks, maintenance line crew carry out three types of inspections as described by Alfares and others (2006):

i.        First minor (small) inspection-type A inspection

ii.       Second minor (normal) inspection-type B inspection

iii.    Major inspection-type C inspection

 

The importance of these inspections is to reduce downtime and achieve high production capabilities, through the process of preventive, predictive and corrective maintenance.

 

 The first minor inspection of the plant is carried out every 4,000 evaluated operating hours (EOH). The second minor inspection is carried out every 8,000 EOH. The major inspection is usually carried out every 16,000 EOH. Eight mechanical workers are needed for Type-A inspection on a particular plant, 8-10 workers are needed for type B inspection, while 15 workers are needed for type C inspection. For daily plant checks, only one maintenance worker is needed to handle a plant. As defined by Alfares and others (2006), information from plant daily checks, inspections, and other parameters are used by the planning department to develop an annual maintenance schedule. The three alternative work schedules available to satisfy the labour demands is given in Table 1. The first alternative is to continue with the existing regular time Monday-to-Friday workweek, scheduling workers for the weekend on an overtime basis. The second alternative is to switch to a seven-day workweek schedule for the morning shift only, continuing with the five-day workweek for both the afternoon and night shifts. Therefore, the second alternative would require weekend overtime only for the afternoon and night shifts. The third alternative is to switch to a seven-day workweek schedule for all three shifts. Under the third alternative, weekend overtime would be eliminated.


 

Table 1. Daily maintenance labour demands for three shifts

 

Table 2. Calculation of total pay hours per week for Alternative 1

 


Equipment operation

The compressor, combustion system and the turbine constitute the three main sections of the gas turbine power plant. Within these sections comprises of diverse intricate cross-functional devices and systems such as, close circuit water (CCW), fans (axial and centrifugal), air filters, nozzle, recuperators or heat recovery steam generators (HRSG), water and oil piping to mention a few. In other to forestall unscheduled outages in an operational power plant series of scheduled inspections it is required to maintain high quality of equipment performance. Scheduled outages require one of three types of inspections: a combustion inspection, a hot/gas path inspection, or a major inspection

 

Power plant maintenance optimization

Power plant maintenance optimization is a process that attempts to balance the maintenance requirements (legislative, economic, technical, etc.) and the resources used to carry out the maintenance program (people, spares, consumables, equipment, facilities, etc.). The goal of the maintenance optimization process is to select the appropriate maintenance technique for each piece of equipment within a system and identifying the periodicity that the maintenance technique should be conducted to achieve regulatory requirements, maintenance targets concerning safety, equipment reliability, and system availability/costs. When maintenance optimization is effectively implemented it will:

·         Improve system availability

·         Reduce overall maintenance cost

·         Improve equipment reliability, and

·         Improve system safety

 

A true maintenance optimization process continually monitors and optimizes the current maintenance program to improve its overall efficiency and effectiveness. The effort to initiate the maintenance optimization process can be eliminated over time if additional effort is not taken to sustain the process.

 

The following activities support the sustenance of maintenance optimization process:

·         Removing unnecessary requirements

·         Identifying adverse failure trends

·         Conducting root-cause analysis of component failures resulting in system events

·         Reporting maintenance feedback

·         Conducting predictive maintenance analysis

·         Monitoring system performance

·         Trending preventive maintenance and corrective maintenance historical data

·         Conducting surveillance test optimization studies

·         Introducing equipment design modifications

 

Equipment optimization

Machinery and system are increasingly becoming complex, advance in technology is making more machines obsolete and redundant own to present day innovation that bothers around factors such as automotive control, ruggedness, safety, performance, fast-response, self diagnostic and financial benefits.  Therefore equipment optimization in design, production and maintenance of power plant equipment is a means of ensuring the following:

·         Increase production capacity by optimizing process flows.

·         Avoid downtime by using virtual simulation for troubleshooting process issues.

·         Accurately determine causes of failure and vibration issues.

·         Enable optimum decision making for replacement of damaged equipment through fitness for service analysis.

·         Ensure compliance with industry regulations.

 

Workforce optimization

To achieve optimum delivery in operation and maintenance of Afam power plant is on a large scale dependent on the nature of the workforce assigned to manage every other task in the facility. Advance in technology and gas turbine power plant engineering has indeed necessitated that operators are also increasing in competence levels to meet the challenges of the technicalities and dynamics of a present day power plant operation. To achieve this, the following is required:

i. Manpower training: A purposeful training schedule is required for supervisors, operators and craftsmen to ensure cross-functional competences through the plant and to keep workforce abreast with current trends, innovation, technical modification and process on the gas power plant systems.

ii. Enabling environment: Under the health, safety and environment (HSE) policies; the environment in which an employee perform duties overall affects production and service delivery. Provision of a suitable working condition around the facility will ultimately enhance proactive in the maintenance crew, as a result ensure continuity in operation. Under this are the following:

·         Create a proper chain of command, stating clearly defined roles and responsibilities of employees.

·         Creation of an environmentally friendly work area, provision of water, canteen, rest rooms, better workstations

·         Provision of personal protective equipment (PPE) to employees, ensuring safety in the facility through provision fire extinguishers to designated areas, quick assess ways, proper illumination; and maintain zero tolerance of risk and hazards.

·         Provision of life-insurance, better remuneration and good working condition.

·         Provision of tools and equipment (reduce human effort to the barest minimum).

·         Accessibility to other fringe benefits of the organization.

 

Planning for the future of Afam power station

 

Planning is the process of setting goals and choosing the means to achieve these goals. Without plans managers cannot know how to organize people and resources effectively. They may not even have a clear idea of what they need to organize. Stoner and others (1995) deduce that without a plan, they cannot lead with confidence to expect others to follow them. And without a plan, managers and their followers have little chance of achieving their goals or knowing when they stray from their path.

 

The challenges facing gas powered stations in Nigeria’s power project tend to put a hitch to the enormous amount of resources the Federal Government commits to the projects to ensure their smooth operations; owning to environmental factors such as militancy, gas shortages and transportation, global prizes, corruption and expertise shortages. Other technical factor that may affect gas turbine performance includes: air-temperature and site elevation, humidity, inlet and exhaust losses and type of fuels.

In other to achieve the goals set for Afam power station, that is to ensure an all-year-round optimal, efficient and effective performance, for the purpose of planning it is required for power plant managers to major on the following goals.

i. Sense of direction

Without a goal, individuals and their organizations tend to muddle along, reacting to environmental changes without a clear sense of what they really want to achieve. By setting goals, people and their organization bolster their motivation and gain a source of inspiration that helps them overcome the inevitable obstacles they encounter.

ii. Focus efforts

In every organization they are limited resources and wide range of possible ways to use them. By setting goals, priorities are established and commitments about the way to use the scarce resources are maintained. This is especially important where managers must coordinate the actions of many individuals.

iii. Plans and decisions

Power plant managers must make decisions that necessitate growth and development in the different sections, by classifying short-term and long-term plans as a means of moving the organization towards it sets goals.

iv. Evaluate progress

A clearly stated, measurable goal with a specific deadline becomes a standard of performance that lets individuals and managers alike evaluate their progress. Thus, goals are the an essential part of ‘controlling-the process of making sure that actions are in keeping with goals and the plans created to achieve them.

 

Implementation of organizational profitability system (ops) in Afam

Sound maintenance management decisions of Afam are based on a thorough understanding of profitability dynamics. In the implementation of a total profitability measurement process, analysis of the gas-turbine power plant profitability helps management measure performance in a department-by-department context that is consistent with its inherent view of the institution.

                       

When these packages of corporate profitability measurement and performance management solutions are provided, OPS in Afam it will necessitate proven performance through the following:

i. Cost management

Gas-turbine power plant profitability system will increase the visibility of all costs within Afam. Because general ledger systems view the power plant as a whole, reporting is useful only for measuring overall performance. Even general ledger systems that support responsibility center definition and reporting are usually limited to direct expenses with no allocation capability for indirect expenses. Without a mechanism for distributing all costs to specific profit centers, individual expenditures are blurred. Ultimately, even though the Nigerian government is spending too much money on the power plant, the reason why and knowing where it ends up is achieved through OPS.

ii. Department-to-department allocation

The department-to-department allocation engine in OPS defines and executes allocations in a precise and documented manner; the open approach to defining assignment techniques enables virtually the unlimited allocation of alternatives. The flexibility and power of OPS also enable management to create allocation rules for actual and budget, resulting in a fully allocated budget. Multiple passes provide a framework for logical assignment of expenses and intermediate review of allocations.

 

Employing stategic management to achieve the federal government of Nigeria’s goal on power generation

The Federal Government of Nigeria through its Ministry of Power has sets specific goals for its power industry that is to generate 10000 megawatts of power by December 2011. To attain this goal, the aspect of ensuring a worthwhile plan cannot be over emphasized. As mentioned by Thompson and Martin, (2005), the essence of strategic management (when employed) in the course of planning, serving as baseline and scorecard in evaluating the process progress and the achievement of goals, through:

i. Strategic Formulation

Strategy formulation refers to the process of determining where the Afam power station is now, determining where it wants to go, and then determining how to get there. These three questions are the essence of ‘strategic planning’; achieved through the performance of situation analysis, self-evaluation and competitor analysis.

ii. Strategic implementation

In this process, allocation and management of resources (financial, personnel, time, and technology support) is done. While establishing a chain of command or some alternative structure; this involves managing the process by monitoring results, comparing to benchmarks and best practices, evaluating the efficacy and efficiency of the process, controlling the variances and making adjustments to the process as necessary. Therefore when implementing organizational specific programs it involves acquiring the requisite resources, developing the process, training, process testing, documentation and integration with legacy processes.

ii. Strategic evaluation

Measuring the effectiveness of attaining the generating capacity of Afam gas-turbine power station is a strategy that is core to the survival of power station. It is extremely important to conduct an analysis to figure out the strengths, weaknesses, opportunities and threats (SWOT) -both internal and external of the entity in question. This may require to take certain precautionary measures or even to change the entire strategy.  This can be achieved by evaluating strategic options against three key success criteria.

·         Suitability (would it work?)

·         Feasibility (can it be made to work?)

·         Acceptability (will they work it?)

 

Conclusions

Many organizations have tried to address their maintenance scheduling woes by introducing new and sometimes very advanced technologies. The reality is that trying to automate something that’s broken will cause even more frustration and finger-pointing.

 

The attempts to balance maintenance optimization requirements (legislative, economic, technical, etc.) and the resources used to carry out the maintenance program (people, spares, consumables, equipment, facilities, etc.) and the potential benefits of maintenance planning/scheduling are best achieved by first establishing a sound communication foundation that supports maintenance business processes. By sticking to these basics; (1) improve system availability, (2) reduce overall maintenance costs, (3) improve equipment reliability, and (4) improve system safety, most organizations can achieve significant improvements in their maintenance scheduling capabilities.

 

While attaining 100% maintenance schedule compliance may seem as difficult as pushing string uphill, it should still remain an ultimate goal. It all starts by putting together an effective maintenance management/planning program with cross-functional communication – so everyone is in the loop. By moving closer to this goal, organizations will become more proactive in their approach to maintenance.

 

The operators/technicians/engineers should have the ability to assess maintenance and reliability data to determine the optimum time for replacement of components before failure. The use Reliability Centered Maintenance (RCM) techniques as specified by Eti, Ogaji and Probert (2004) to determine the optimal mix of applicable and effective maintenance activities needed to sustain the desired level of operational reliability of systems and equipment while ensuring their safe and economical operation and support is to be applied. Whether optimizing maintenance before or after the design is fielded the technical crew must have the experience and expertise to ensure the proper mix of corrective and preventive maintenance is identified for any defense or commercial product.

 

 


References                 

Alfares, H.K., Lilly, M.T and Imovon, I (2007): “Maintenance Staff Scheduling at Afam Power Station”, IEMS, Vol. 6, pp.22-27.

 

Alfred, I. (2009): Personal Communication, Department of Engineering, AFAM VI, Port  Harcourt, Rivers State.

 

Balevic, D., Burger, R and Forry, D (2004): “Heavy-Duty Turbine Operating and Maintenance Considerations”, GE Company, pp. 1-60.

Brooks, F.J (2000): “GE Gas Turbines Performance Characteristics”, GE Power Systems GER-3567h, pp. 1-16.

Clark, A, (2003): “Thermographic Imaging Inspections” Ecolibrium, pp. 24-27.

Eti, M.C, Ogaji, S.O.T and Probert, S.D (2004): “Reliability of the Afam Electric Power Generating Station”, Applied Energy, Vol. 77, Issue 3, pp. 309-

Johnston, J.R (2000): Performance and Reliability Improvements for Heavy-Duty                    Gas Turbines , New-York :GE Power Systems.

Leppakoski , J., Oksanen, J. and Jaatinen, E.(2003): “Maintenance Optimization, Metso Automation Energy, pp. 7-9.

 

Pallos, K.J. (2001): “Gas Turine Repair Technology” GE Power System, pp. 1-5.

 

Pope, E (2006): “Combined Cycle Power Plants”, TM-5-811-6, chapter 8, pp. 1-3

 

Rudd, M (2005): Management Strategies International Profit Associates, pp. 1.

 

Stoner, J.A. and Freeman, R.E. (2007): Management Prentice-Hall.

 

Thompson, J. and Martin, F. (2005): Strategic Management, Thomson Learning, 5th Edition.

 

 

 

 

 

 

 

 

 

 


The helical antenna,  first introduced by Kraus (1946), has been subject of extensive investigations during the past five decades. Many modifications to the basic helix geometry have been proposed with the aim of improving the gain, bandwidth, axial ratio, and VSWR. More recently, the possibility of size reduction, while maintaining the radiation characteristics, has been explored . In this paper, an improved performance antenna with a  helical geometry is introduced.

A helical antenna is an antenna consisting of a conducting wire wound in the form of a helix. In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one of two principal modes: normal (broadside) mode or axial(or endfire) mode.The antenna then falls under the class of waveguide antennas, and produces true circular polarization. These antennas are best suited for space craft tracking and space communication, where the orientation of the sender and receiver can be easily controlled.

 

Helical antenna structure

This antenna, referred to as Helical Antenna is made of a primary helix wound on a cylinder of larger diameter. An important advantage of this antenna is that it can be conveniently constructed.


                         

           Figure 1: A typical structure of helical antenna


The helical antenna can be fully described by five parameters. The influence of these parameters on radiation properties are examined in order to find their optimum values.

 

Optimum parameters

The effects of the helix parameters on radiation characteristics such as gain, input impedance, axial ratio, and bandwidth have been studied extensively. A brief discussion of optimum parameters is presented below. shows the effect of circumference on gain. The influence of pitch angle on gain at different frequencies. Clearly, a pitch angle of 12.50 provides the maximum gain . Kraus has developed empirical formulae for gain, input impedance, axial ratio, and half power beamwidth . The empirical gain formula is given as

  ---------------------------------------------------------------------------------------1.1

Modification by( King and Wong,1989) expressed Gain as


Figure 2 : Cyclical Helix


The Gain of helical Antenna can be approximated using the formula below.

HG = ------------------1.2

HD = diameter of helix, C = circumference of helix = pD

S = spacing between turns , α= pitch angle = tan-1 (S/pD)

For the half-power beamwidth, an earlier empirical expression by Kraus and, a few decades later, a more accurate formula by King and Wong (1989) were developed. The results are

 ---------------------------------------1.3

 

Methodology

Computer simulation or a computer program that attempts to model a real-life or hypothetical situation on a computer, so that it can be studied to see how the system works. By changing the variables, predictions may be made about the behavior of the system. A good example of the usefulness of using computer to simulate can be found in the field of antenna simulation. In such simulation, the model behavior will change each simulation according to the set of initial parameters assumed for the environment. Originally, the formal modeling of systems has been through a mathematical model which attempts to find analytical solutions enabling the prediction of the behavior from set of parameters and initial conditions and Matlab technical computing were used.

 

Numerical analysis of the model

It is now clear that a helical antenna can be fully described by five parameters—two radii( a and a1), two pitch angles ( and ), and the number of larger turns (N) on the cylinder of radius a.

In order to facilitate the numerical analysis of the helical antenna, a set of equations describing its geometry are needed. With the availability of these equations, the coordinates of an arbitrary point on the helical structure are readily determined in terms of the parameters a,a1, and an axial dimension  zA .Before embarking upon the derivation of equations for the helical geometry, we first examine the parametric equations for a simple cylindrical helix, such as the primary helix with radius a1and pitch angle  shown in Figure 2. Furthermore, we use two sets of coordinates: namely the primed Cartesian coordinates x1,y1,z1 and cylindrical coordinates

  for the geometry of the primary helix, and the unprimed coordinates

(x , y ,z) and z)for describing the geometry of the doubly helical structure.

The parametric equations of the primary helix are expressed as

-----------------------------------------------------------------------------2.1a

-----------------------------------------------------------------------------2.1b

------------------------------------------------------------------------2.1c


 

 

Figure 3: coordinates for (a) primary helix, (b) helical geometry


Once the primary helix is wound on a cylinder of radius a with a pitch angle as in

Figure 3a, the z1 -axis assumes a helical shape of radius (a+a1).  The parametric equations of the helically-shaped z1 -axis, in analogy with (2b), are expressed as

-------------------------2.2a

-------------------------2.2b

---------------------2.2c

  

------------------2.3
----------------------------2.4

zA varies in the range 0 A A z  z , where zA max is the height of the helical antenna.

It is related to the number of turns N (turns with the mean radius( a+a1) according to the following relationship

-----------------------2.5

Equations (2.3) to (2.4) fully describe the geometry of helical antennas. These

equations are used to generate coordinates of discrete points on the antenna which are then used as part of the input data to the Matlab software ( Balanis ,1997)

 

Designing flowchart of helical antenna

The flow chart shows the design procedures using Rao-Wilton-Glisson (RWG) boundary element for modeling Helical wire antenna because it has the potential to avoid the development and programming of two separate algorithms. This greatly simplifies the underlying mathematics and Matlab source codes for Helical antenna. This text explains how to use the standard matlab package in order to simulate antenna and microwave structures (Makarov ,2002 )


Figure 4 : flowchart of scattering Algorithm of Matlab directory

 


Matlab codes for structural design of helical antenna

clear;

disp('To Run the simulation of the Helix Antenna')

meth=input('default values, type 1 and press Enter or type 2 and press enter to specify your values : ');

if meth==1

a=30; ap=0.01;

alph=10*pi/180; alpha=2.5*pi/180;

length=500; inc=0.03; begin=1500; last=2500;

rad=0.005; intrvl=50;

elseif meth==2

 a=input('Type in the Helix radius a:');

ap=input('Type in the Helix radius prime ap:');

alph=input('Type in the pitch angle 1 in degrees:')

alph*10*pi/180;

alpha=input('Type in the pitch angle 2 in degrees:')

alpha*2.5*pi/180;

length=input('Type in the length of helix:');

inc=input('Type in the increment for length:');

begin=input('Type in the beginning frequency in MHz:');

last=input('Type in the last frequency in MHz:');

rad=input('Type in the radius of the wire:');

intrvl=input('Type in the frequency interval in Hz:');

else

    clear;     helixant;

end

t=num2str(length/inc);

sym='_'; for freq=begin:intrvl:last

%simulation information

f= num2str(freq/10);

rad1=num2str(a); rad2=num2str(ap);

pitch1=num2str(a); pitch2=num2str(ap); radius=num2str(rad);

filename=strcat(t,sym,f,pitch1,'.dat'); fid=fopen(filename,'w');

Text2=strcat('CE',t,sym,pitch1,'.cav'); fprintf(fid,text1); fprintf(fid,'\r'); fprintf(fid,'\n');

c=1;  lam=.02*(3*10^8/(freq*10^6));

 x1(1)=0;     y1(1)=0;     z1(1)=lam;

end

S=11.02*lam;

[X,Y]=meshgrid(linspace(-S,S,20),linspace(-S,S,20));

Z=zeros(size(X)); f= begin:intrvl:last;

f=f/10^6; m=max(size(f));

for i=1:m

end

figure(1);

plot3(x1,y1,z1,'b')

title('The Shape of The Helix Antenna')

Xlabel('X-Axis') Ylabel('Y-Axis') Zlabel('Z-Axis')

hold

q=size(z1); q1=q(1)*q(2); qx=[0,-4*x1(q1)]; qy=[0,-12*y1(q1)];

oo=[0,0] ;mesh(X,Y,Z)

plot(qx,oo,'y');  plot(oo,qy,'m');

plot3([0,0],[0,0],[0,qz],'r');

grid on.

 

Simulation  results analysis

 Modeling and simulations are better summarized in three different perspective :

i).  The shapes modeling based on different parameters of Helical antenna.

ii). The graphical representation of High Gain based on modeled helical antenna parameters.

iii). How to obtained high gain based on the calculation using simulation helix parameters.


 

 

 

Helical antenna structures with varying parameters

(a) The true shape (1500 – 2500) MHz. (b) The shape  frequency interval to 5000 Hz.

 

 

 

(c)The shape freq.(15000 – 25000)MHz  (d) The shape Radius of Helix at 35 mm

 

  (e)The shape of pitch angle of  200        (f) The shape lambda = 0.06

 

 Figure 5: Helical Antenna structures with varying parameters from (a – f)

 

 The graphical explanation of high gain parameters

 

(a)    The graph of Gain against                (b) The graph of Gain against Number of    

       Circumference (mm)                         Turns

 

    

    (e) The graph of Gain against  frequency   (f) The graph of Gain against peak

     (MHz)                                                       Wavelength(mm)

  Figure 5 (a – f) : The graph of High Gain parameter of Helical Antenna

 


High gain calculation  using simulation parameters

The following are simulation parameters using in obtaining the high gain of the helical antenna.

i). Radius/Diameter (a)=31.83mm/63.66 mm .

ii). Spacing between turns(s) = S=1.102 x 40 = 44.34 mm.

iii).  Wavelength (lambda) =  0.02 x3x108/1500 x106 = 0.04 m =40mm.

iv). Number of Helix turns = 11.

v). Circumference of Helix (C) = 2 a=2x3.142x31.83=200.011  mm.

vi).Pitch angle of the Helix (  = .

vii). Axial length or Height of Helix = NS =  = NS= 11x44.34= 487.74 mm.

viii). Total length of wire used in helical coil =  

         = 11  mm.

xi). The  Hhh    Gain G =

G =

G  = 10.8+10log10(25.002)(11)(1.1085)(1.658) = 35.6 dB.

 

The effects on high gain values due to variation of parameters 

The variation on gain can be summarized by calculation of gain based on  helical antenna parameters used in the simulation.

(a) figure 4 a :The gain obtained here are basically due to the default setting ,therefore these the following parameters are responsible for high gain of 35.6 dB which include axial length ,frequency range, radius of helix, Number of turns ,spacing between turns.

(b) figure 5 b :With the interval of frequency increase to 5000Hz , which changes with increase in Number of Turns and reduction in diameter of the helix, both parameters contribute to high gain .

(c) figure 5 c :It is believe that with increase in the radius of the helix will result to High gain ,the high gain computation with of 35 mm is 36,46 dB. The value obtained shows clearly that increase in the radius of helix is a great contribution of high gain.       

(d) figure 5 d :Modeling at this high frequencies between (15000 – 25000)MHz, a high value of Gain is 65.64 dB is obtained, although the number of turns of the helix is reduced.

(e) figure 5e :The variation of the pitch angle with increase to 200 has a retrogressive effects on the gain. The computed values of the gain using the simulation parameter revealed that the gain is 32.06 dB. That at very higher pitch angle the gain collapses.

(f) figure 5 f : The effect of peak wavelength(λ) reduces drastically the gain , when λ=0.06,the gain is 21.32 dB, revealing that with increase in peak wavelength reduces gain.

 

Graphical interpretation results

The basic Matlab command used in plotting the graphs is” ezplot with hold on and hold off codes” ,the fundamental information for designing the antenna is given by Kraus , who has derived an approximate expression modified by king and Wong .The important results of the investigation of helical antenna with respect to High Gain are summarized below:

(i) The peak gain occurs when the outer circumference 2 (a +2a1) is about 0.96 . For a conventional helix of comparable gain, this peak occurs at a circumference of about 1.2 ; Figures 5(a) and 5(d)

(ii) High gains and wide axial-ratio based bandwidths are obtained when the pitch angle is about  100 to 120 shown in figure 5 (c) .The maximum gain, however, occurs when = 12.50.  (iii)The gain increases with the number of turns, but the overall gain is reduced; Figure 5(b). (vi) The wavelength values has great significance on the diameter of the Helix in figure 5 (a).

 

The applications of high gain on improved performance

The modeled high gain of helical antenna has physical attributes on the antenna in general with these simulation results were validated by comparing theoretical and empirical formula, the following can be deducted.

(a) Signal to noise ratio(snr) : modeling at the microwave frequency of 2.5 GHz , with such a high gain the signal to noise ratio is moderated as such noise minimum and clear or filtered signal received or transmitted for helical antenna.

(b) Sensitivity : sensitivity of receiving helical antenna is the ability to pick up and reproduce weak signal . it is determined by the value of microwave frequency and because high gain for improved performance, the higher sensitivity is achieved , thereby reducing the order of distortion transmitting or receiving signal and reduced interference.

(c) Range of reception : the requirement of the transmitter or receiver helical antenna demands that the gain property is capable of being sending or receiving signal within such range of microwave nature of frequencies  and selectivity  within the frequency range which may be microwave frequency results of high gain attribute of the antenna.

(e) Directivity : is a figure of merit for an helical antenna , it’s the power density of actual antenna radiation in the direction of its strongest emission. It also indicating how much of the total energy from the source is radiating in a particular direction,with high gain directivity is very efficient from modeling characteristic and high directivity of energy high directivity of energy to a source or from a source.

 

Conclusions

The helix antenna has been used as an example to demonstrate the improvement found when using the matlab code . As a secondary goal of this paper, the matlab code is used to analyze some interesting properties of the helix..A comprehensive numerical analysis of helical antenna has been carried out using the Matlab codes. Gain-characteristics have been computed for numerous cases ,Several helical antennas were created. Generally.

 

Great advantage of model this antenna and the  accurate data. In an actual design, the helix as simulated may be acceptable for the application; if not, one at least is aware that a redesign is likely to be advisable, without even the need first to build a prototype.

 

  References

Balanis C. A.(1997) ,“Antenna Theory: Analysis and Design, 2nd ed., New York: John Wiley  

    and Sons.

 

Barts R.M and Stutzman W. L.(1977), “ A Reduced Size Helical Antenna,” Proc.   IEEE Antennas and Propagat. Soc. Int. Symp., vol. 3.

 

Cardoso J.C and Safaai-Jazi C.(1993),“Spherical Helical Antenna with Circular  Polarization Over a Broad Beam”, Electronics Letters, vol. 29, pp. 325-326.

 

David B. D.(2005),” Computational Electromagnetics for RF & Microwave Engineering”, Cambridge University Press.

 

Fox N.D.(1988) , “A detailed analysis of the helical array as a high performance portable ground station antenna,” Master’s Thesis, Virginia Tech.

 

Glasser. O.J and Kraus J.D(1948) ,“Measured Impedances of Helical Antennas”,   App.Phys., vol. 19,  pp. 193-197.

 

King H.E. and Wong J.L.(1982) , “Empirical helix antenna design,” Proc. IEEE antenna Propagat. Int. Symp., pp. 366-368.

 

Kraus J.D.(1988),” Antennas for All Applications”, 2nd ed., New York : McGraw Hill.

 

 Makarov n. Sergey (2002) ,”Antenna & EM Modeling with Matlab” New York: John Wiley and Sons.