Proceedings of the 1st Iberic Conference on Theoretical and Experimental Mechanics and Materials /

11th National Congress on Experimental Mechanics. Porto/Portugal 4-7 November 2018.

Ed. J.F. Silva Gomes. INEGI/FEUP (2018); ISBN: 978-989-20-8771-9; pp. 193-198.

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PAPER REF: 7438

DYNAMICAL ANALYSIS OF A 230 kV TRANSMISSION LINE

Nilson Barbieri1,2(*)

, Marcos José Mannala1,3, Lucas de Sant’Anna Vitor Barbieri

1,

Gabriel de Sant’Anna Vitor Barbieri1, Key Fonseca de Lima

1

1Pontifícia Universidade Católica do Paraná (PUCPR), Curitiba, Paraná, Brasil

2Universidade Tecnológica Federal do Paraná (UTFPR), Curitiba, Paraná, Brasil

3Instituto de Pesquisa para o Desenvolvimento (LACTEC), Curitiba, Paraná, Brasil

(*)Email: nilson.barbieri@pucpr.br

ABSTRACT

The current standards applied to construct aerial transmission lines are based outdated components creating a very conservative set of rules that does not extract all potential from current towers, transmission cables and accessories. The main objective of this work is to reassess the current methodologies with focus on the power cables traction, establishing new standards in order to increase the ampacity of future and existing aerial transmission lines. An Experimental Transmission Line (ETL) was constructed in order to determine the cable’s vibrational mechanical behaviour under higher traction. The tests conducted at ETL will elucidate in which conditions the ampacity can be increased, respecting the reliability and safety standards. Three distinct transmission line cables, towers and accessories will be tested under various conditions. Some conditions can be induced and controlled like cables traction and forced vibration using electromechanical shaker. Others results can be obtained from the environment, as temperature and wind. The data from ETL tests will be analysed and compared with tests made at the laboratory with limited and controlled environment. Comparing the information from ETL and laboratory will allow closing the gap between the standards and the real projects. The biggest advantage of this field bench over the laboratory ones is to find out what really happens in real world with the actual components.

Keywords: Experimental transmission line, aluminium conductor cable, aeolian vibration, testing laboratory.

INTRODUCTION

Applying axial tractions above the values prescribed by the Brazilian standard NBR 5422 may be the best alternative to increase the ampacity taking account technical, economic and environmental reasons, reducing the cable sag and keeping the minimal safe distance to the ground. However, adopting higher tractions will demand further investigation to ensure operational conditions and safety.

Simulations and tests are being conducted in dedicated benches at laboratory, which simulate mechanical and electrical components of a transmission and distribution transmission lines, in order to determine the mechanical vibrational behavior of the conductive cables and accessories. However, the space availability for these benches is limited. Due to this fact, the samples performance analysis in cables and accessories tests are approximated to the actual operating condition of the component [1,2].

Another relevant aspect is the determination of how the supporting structures behave when transfer the line components load to the towers foundations, when conductor cables are set to a higher traction.

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The main components of the ETL systems (Figure 1) are:

• Anchor tower foot stress monitoring system: this equipment helps to determine the

foundation stresses due by conductor cables forces during the vibration tests;

• Conductor cable puller driver: at the anchor tower there is an equipment that sets a

specific traction to each conductor cable independently;

• Conductor Shakers: vibrators induce the desired oscilation to each of the condutor

cables indepedently;

• Vibration recorder: measures the conductor cables vibration amplitude, at 88,9 mm

from the suspension clamp;

• Environment: two anemometers, one int the anchor twer and the other in the suspension

tower, colecting wind information and three termocouples measuring conductor cables

temperatures.

Fig. 1 - Measurement equipments at anchor and suspension towers.

The ETL will be assembled with three types of conductor cables, namely, Tern (795 kcmil),

Greeley (923 kcmil) e Phosphorus (823 kcmil). The cable length is 270m (length between

ends). A variety of tests can be conducted, such as modal test, to compare the behavior of the

three cables, taking account the vibrational intensity, force amplitude and mechanical traction.

Stockbridge dampers are also fixed on the cables to evaluate the reduction of the vibration

level in each of the cables.

In this work will be presented modal analyzes of three different cables subject to wind

excitation on different atmospheric conditions (temperature, wind speed, time). The modal

data are obtained through operational modal analysis and the natural frequencies are

compared with numerical values obtained through the computational simulation of a

nonlinear model obtained by the Finite Element Method [3].

TESTS AND RESULTS

Figure 2 shows the schematic position of the accelerometers disposed along the cables.

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Fig. 2 - Schematic position of the accelerometers.

Two measurement data (Table 1) was chosen to obtain the experimental modal parameters.

Table 1 - Testing parameters.

Parameter

Data 1 Data2

Tern Greeley Phosphorus Tern Greeley Phosphorus

Wind speed

(m/s)- Tower

1

1.732 4.212

Wind speed

(m/s)- Tower

2

1.893 3.355

Mechanical

load (kN) 16.065 15.680 25.501 15.891 15.495 25.152

Temperature

(oC)

18.305 18.463 18.139 21.240 20.110 20.893

The numeric modal parameters were obtained using the nonlinear FEM model presented in

[3]. Table 2 shows the values of the natural frequency (Hz) for the two data of Table 1. Note

that there are small variations between the values of the natural frequencies. This fact was

expected since there were only small variations in the parameters of the two tests. A smaller

increase is observed between the frequencies of the first modes characterizing the system as

non-linear.

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Table 2 - Natural frequencies (Hz).

Mode Data 1 Data2

Tern Greeley Phosphorus Tern Greeley Phosphorus

1 0.4053 0.4318 0.4315 0.4030 0.4292 0.4339

2 0.5116 0.5058 0.5191 0.5124 0.5081 0.5156

3 0.6811 0.6937 0.7905 0.6820 0.6926 0.7857

4 0.8126 0.8654 1.0400 0.8082 0.8602 1.0320

5 1.0246 1.0882 1.3019 1.0194 1.0820 1.2931

6 1.2199 1.2990 1.5602 1.2133 1.2913 1.5495

7 1.4263 1.5180 1.8216 1.4187 1.5091 1.8092

8 1.6280 1.7330 2.0820 1.6190 1.7230 2.0670

9 1.8332 1.9517 2.3432 1.8233 1.9402 2.3272

10 2.0365 2.1685 2.6043 2.0255 2.1557 2.5865

Figures 3 and 4 show the stabilization diagrams for the three cables and for the two tests. Note

that some modes are more excited than others depending on the different wind and

temperature conditions. In the first test the excitation of some modes alone is predominant,

while for the second test, low-frequency modes (less than 1 Hz) are excited.

(a)

(b)

(c)

Fig. 3 - Stabilization diagram for the three different cables: Tern (a), Greeley (b) and Phosphorus

(c) using testing parameters of data1.

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(a)

(b)

(c)

Fig. 4 - Stabilization diagram for the three different cables:Tern (a), Greeley (b) and Phosphorus

(c) using testing parameters of data2.

CONCLUSIONS

In this work, preliminary data of a dynamic analysis of cables of electric transmission lines

are presented. The analyzes involved the acquisition of vibratory data from an experimental

line of cable tests with sample length of 270m and subject to atmospheric conditions

(temperature, humidity, wind, rain, etc.).

In a first step a numerical analysis was made through the computational simulation of a

numerical nonlinear model obtained by the finite element method. It was noted that the

natural frequencies for the three types of cables are close since the mechanical load normally

used in electric transmission lines was used.

In a later stage we used stabilization diagrams to verify the feasibility of use and operational

modal analysis for experimental modal identification. It was noticed that depending on the

speed and intensity of the wind some modes are more excited than others. It is expected that

with constant monitoring and obtaining data with adverse atmospheric conditions (wind,

rainfall, temperature changes) it is possible to make a database for the analysis of the dynamic

behavior of electric transmission lines.

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REFERENCES

[1]-Transmission and Distribution Committee of the IEEE Power Engineering Society, IEEE

Guide for Laboratory Measurement of the Power Dissipation Characteristics of Aeolian

Vibration Dampers for Single Conductors, IEEE Std 664-1993;

[2]-IEEE Power Engineering Society. IEEE Guide for aeolian vibration field measurements of

overhead condutors. 35. New York, NY, USA, 2006.

[3]-R. Barbieri, N. Barbieri, O. H. Souza Jr., Dynamical analysis of transmission line cables.

Part 3 - Nonlinear theory, Mechanical Systems and Signal Processing 22(4): 992-1007, 2008.