Modelling Of 3 Phase Transmission Line Engineering Essay

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Transmission line is a medium to transmit electric energy from one place to another for long distances with the aim is to reduce and economically. Voltage, current, power and power factor are the main point must be considered at the sending end and receiving end. Typically, in Malaysia the overhead transmission line was used because cost and maintenance can be handle easily. As we know, the transmission line produced high strength of electric and magnetic field under the tower. Based on that, this project will modeling transmission line using Finite Element Method (FEM) focus on level voltage 275kV. The result of simulation of the transmission line model will analyze electric and magnetic field under transmission line tower.

2.0 Problem statement

It is well known understand that the Transmission Line for 275kV produced high strength of electric and magnetic field under the tower. In other word, the field strength of electric field may create higher stress to the tower that may also tend to create high risk to the tower as well as to the insulator to be used. Another issue is how much tendency of magnetic field to be effect to the human and environment has be identified wisely. However, the real measurement under 275kV transmission line tower may give high risk. Therefore, the best idea is to carry out the information as mention above is by performing simulation study.

3.0 Objective

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To collect the 275kV Transmission Line specification.

To model the 275kV Transmission Line using Finite Element Method (FEM)

To simulate the 275kV Transmission Line using Finite Element Method (FEM)

To analyze the electric & magnetic field generated by the 275kV Transmission Line model

4.0 Scope

The scope of this project are :-

Specification is based on TenagaNasionalBerhad (TNB) 275kV Transmission Line.

Transmission Line modelling using Finite Element Method (FEM) software.

5.0 Literature survey and project background

An electric power system is a network of electrical components used to supply, transmit and use electric power. The main parts of electric power system are generation, transmission system, distribution system and load. At generation part, to generate an electrical energy on large scale, energy must be generate from the various sources energy such as oil, natural gas and other. Then, the transmission system transmit or carries current that generate from generation and distribution system feeds electric to load such as consumer and industry. This project will discuss further about transmission line system.[1]

5.1 Transmission Line

Transmission line or power line are important part in power network. Other than that, based on theory, transmission line also can be describe as propagation of electric waves along the transmission line. There are many factor must consider to design transmission line. Such as transmission voltage level, types of tower, environment and others. The transmission line also can be constructed in two ways, overhead transmission line and underground transmission line.

5.1.1 Underground Transmission Line

In underground system, the cable must be selective because all conductor must be insulated in this system. Therefore, the voltage level for this system will below 66kV cause difficult to find insulation for high voltage. Underground transmission line usually use at crowded areas because the cable used preferred compare with overhead use bare conductor not suitable at that areas.[1]

5.1.2 Overhead Transmission Line

Overhead transmission line usually use for transmit electric for over long distances. In this system, spacing between the tower and the conductor are very important cause to avoid an electric discharge between the conductors. The appropriate spacing between the conductor will produce insulation between them. This system also expose to fault such as short circuit, breakage of line and lightening. But it easy to troubleshoot and repair compare to underground transmission line. However, it difficult to find exact point of fault cause transmission line are very long. Other than that, between the tower and the conductor must have insulation to make the transmission more safety when do it maintenance. [1]

5.2 Types of Transmission Line

Transmission line be separated two part AC transmission line voltage and High Voltage DC transmission line (HVDC).

5.2.1 High Voltage DC Transmission Line

The main factor affecting the cost of energy increases is the process of transmission lines to transmit the power to the load away from power generation. To overcome this issue that is usually done AC transmission line is using HVDC transmission line.

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The HVDC transmission line requires conversion at two ends, from AC to DC at the sending end and back to AC at the receiving end. The converter are static using high power thyristors connected in series to give the required voltage ratings. The physical process of conversion is such that the same station can switch from rectifier to inverter by simple control action, thus facilitating power reversal.[2]

Figure 5.2.1: Variation of costs with line length[4]

Figure above show the variation of costs of transmission line with distance for AC and DC transmission. Based on figure, before break even distance, cost of AC transmission is reasonable and economical than DC transmission. Before the break even distance point, the distance is around 500 to 800 km, so after that point or longer distance HVDC transmission line more economical than AC transmission.[2]

5.2.2 AC Transmission Line

Transmission line also can be classified into three types such as short transmission line, medium transmission line and long transmission line. For short transmission a length less than 80km, medium transmission between 80km until 240km and long transmission have length more 240km.[] Normally, the power grids also have three level of voltage; High voltage (HV), medium voltage (MV) and low voltage (LV). In Malaysia, based on fact from Tenaga Nasional Berhad (TNB), AC transmission line have standard voltage called National Grid. Below are standard voltage of AC transmission line:-

i) 132kV

ii) 275kV

iii) 500kV

5.3 Modelling Transmission Line

For this project focus on 275kV transmission line modelling. Before go through below some journal refer to this project.

Based on journal titled "Modelling and Analysing of a 275kV HVAC Transmission Line for Power System Transient Studies" written by M. Z. A. Ab Kadir and C. Y Jay. In this journal, it discuss the efficiency and power losses of transmission line via the concept of travelling wave. This case study had be done at Kampung Awah- Paka, Terengganu. This paper was model transmission line using PSCAD/EMTDC software which they want analyze the efficiency between the frequency dependent model and PI-section model.

Before design or model transmission line on simulation, this paper had consider three important parameter such as series resistance, series inductance and shunt capacitor. Based on tower information below, this paper obtained the parameter such as resistance, inductance and capacitance via calculation. From the information are given, Tenaga Nasional Berhad (TNB) such as Table 1, design PI-section model.

Line name

KAWA-PAKA

Tower type

System

Voltage

Frequency

Line length

Conductor diameter

Bundle spacing

Ground to conductor height

Horizontal spacing

Vertical spacing

Double circuit lattice

Three phase

275kV

50Hz

160km

24.16mm

400mm

12630

7300mm

13000mm

Table 5.3: Parameter of 275kV KAWA-PAKA lattice tower[1]

After consider all parameter, this paper construct design PI-section model using PSCAD/EMTDC software for 160km an overhead transmission line. To model 160km an overhead transmission line, this paper used eight identical pi-sections are connected series which each PI-section represent 20km of transmission line. By terminating the surge impedance at the end of transmission line, the efficiency can be measure.

Figure 5.3.1: Line surge impedance using PI-section model [1]

For the frequency dependent model, this project used it as a reference cause it is the most accurate model. From this model also, we can learn the transient or harmonic behaviour of a line. Figure 2 show frequency dependent model.

Figure 5.3.2 : Line surge impedance using frequency dependent model[1]

Both model are carried out using three different test such as, short circuit test, open circuit test and line surge impedance test. Line surge impedance test is a real line with minimum losses and both other are used to demonstrate the behaviour of the travelling wave.

Section

Model

% differences

Pi-section

Freq. Dependent

Pi-section

Freq. Dependent

1

2

3

4

5

6

7

8

273.59

272.72

271.87

271.04

270.24

269.69

268.69

267.95

272.97

271.28

269.32

267.10

264.63

263.55

263.01

262.22

0.33

0.65

0.96

1.26

1.55

1.84

2.11

2.38

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0.56

1.17

1.88

2.69

3.59

3.98

4.18

4.47

Table 5.4 : Summary of Pi-section and Frequency dependent model

Result of output voltage of each 20km section are summarized in Table above. From the Table, result of this project show the output voltage of Pi-section model and Frequency Dependent model are approximately same. In the real transmission line system, we expect voltage level before step up or step down at substation are maintain. Based on Table above, compare the output voltage of the Frequency dependent low than Pi section because the frequency dependent model consider all losses such as hysteresis, corona effect, eddy current losses in nearby ferromagnetic materials and induced losses in nearby short circuited non ferromagnetic material while Pi-section model only consider proximity effect and skin effect. Conclude from that, the efficiency both model are acceptable and approximately same. An efficiency percentage for Pi-section model is 97.6% and Frequency dependent model 95.5%. This project successful in modelled Pi-section model using PSCAD/EDMTC software and analyzed by compare with Frequency dependent model.[3]

Second journal titled "Power Flow Assesment in Transmission Lines using Simulink Model with UPFC" written by Ch. Chengajah and R. V. S.Satyanarayana. This paper discuss about the performance of a single and double transmission line system (6.6/22)kV using UPFC or without UPFC model. UPFC is a Unified Power Flow Controller which it can improve capability of power transfer or in other word to provide comprehensive control of power flow in transmission system.[4]

This paper model the transmission line using Simulink to connected with UPFC model. Figure below show the transmission line model with UPFC device by using Simulink. From the figure show the double circuit 22kV and 6.6kV interconnected with UPFC model. UPFC device function to control voltage profile as the real and reactive power in the transmission line.[4]

Figure5.3.2: Transmission line model with UPFC device[4]

Table below show the result of power flow and voltage profile transmission line model with UPFC and without UPFC.

Parameter

6.6kV Line

22kV Line

Without UPFC

With UPFC

Without UPFC

With UPFC

Voltage magnitude(kV)

2.926

2.961

9.754

5.162

Real Power(MW)

0.274

0.281

3.050

0.854

Reactive Power(Mvar)

0.205

0.210

2.280

0.639

Table 5.5: Result power flow and voltage profile[4]

Based on table above, this paper compare three parameter such as voltage magnitude, real power and reactive power. From that, an improvement can see for both transmission line when interconnect with UPFC. From that, this paper suggest improvement in transmission line system.[4]

5.5 Summary

Based on both journal discussed different step to model transmission line. For first journal, using PSCAD software, the paper make comparison efficiency between PI-section model and Frequency Dependent model. The paper construct by consider parameter such as resistance, inductance and capacitor to model transmission line. Then, PI-section model had been construct which each PI-model represent 20km. The simulation had be done not like real transmission line system but result at end of experiment approximately same.

Figure 5.3.1: Line surge impedance using PI-section model [3]

For second journal, it use MATLAB/SIMULINK software to model transmission line. This paper discuss about function Unified Power Flow Controller (UPFC) in transmission system to improve voltage and power profile. This paper also consider value parameter such as resistance, inductance and capacitor to construct the model.

Figure 5.5 22kV Transmission Line Simulink Model[2]

Figure 5.5 above show example 22kV transmission line simulink model. At this end of this paper show result comparison between transmission line system with and without Unified Power Flow Controller (UPFC).

Therefore, this project propose to use Finite Element Method(FEM) to model transmission line. This project will model transmission line like a real transmission line using specification Tenaga Nasional Berhad (TNB). This project focus on 275kV HVAC transmission line and will model like real tower for 275kV transmission line. Besides that, significant of this project also can see electric and magnetic field at transmission line. From that, this project analyze further about effect electric field and magnetic field to human and environment.

6.0 Methodology

Start

Collect the 275kV Transmission Line specification.

Model the 275kV Transmission Line using Finite Element Method (FEM)

Troubleshooting simulation

Simulate the 275kV Transmission Line using Finite Element Method (FEM)

Results - Electric field and magnetic field

Analyze the electric & magnetic field generated by the 275kV Transmission Line model

End

Figure 6.0: Flow chart of Final Year Project

6.1 Collect the 275kV Transmission Line specification.

In this process, the specification of data of 275kV tower in Malaysia is needed to be collect from TNB (Tenaga Nasional Berhad). The data that need to be collect is the tower height from ground level, the distance between phase to ground, the distance between phase to phase, and distance between ground wire to phase. Other than that, types and size conductor that used for 275kV also need to collect.

6.2 Model the 275kV Transmission Line using Finite Element Method (FEM)

Based on data collection, model transmission lines tower with the conductor such as specification that used by TNB using Finite Element Method (FEM).

6.3 Simulate the 275kV Transmission Line using Finite Element Method (FEM).

For this step, simulate the model transmission line 275kV that construct before using Finite Element Method (FEM).

6.4 Results - Electric field and magnetic field

The expected result are to modelling transmission lines using new method using FEM. Other than that, this project also expected to produce electric field and magnetic field at transmission lines from one point to next point.

6.5 Analyze the electric & magnetic field generated by the 275kV Transmission Line

Analyze the electric& magnetic field around transmission line 275kV model based on display from simulation.

7.0 Expected Results/Benefit

The result of this project should be able to design transmission line model using Finite Element Method (FEM) where the model must satisfied 275kV transmission line specification from Tenaga Nasional Berhad (TNB). The model are include electric field and magnetic field. From that, analyze the result based on electric field and magnetic field around the transmission line model. This project will develop new method and new software to model transmission line with electric field and magnetic field by using Finite Element Method (FEM) from ANSYS Maxwell.

8.0 Milestones

Task

Date expectation

Complete literature review on the design of Three Phase Transmission Line including the characteristic needed in design modeling.

Nov 2012

Complete search and collect data of 275kV transmission line

Jan 2013

Complete analyze the function of Finite Element Method to calculate the magnetic field and electric field.

March 2013

Complete design optimization

April 2013

Complete testing model with different parameter and analyze

May 2013

Final report writing (including paper/journal writing) and presentation

June 2013