chapter04_switching overvoltage analysis.pdf

8/12/2019 Chapter04_Switching Overvoltage Analysis.pdf

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Chapter 4

Switching Overvoltage Analysis

4.1 Introduction

In the extra high voltage (EHV) transmission line, switching overvoltages are

used to determine the insulation design rather than lightning overvoltages. The

insulation level required to withstand the switching surge overvoltages can had a

significant influence on the cost of the transmission systems. Therefore, an accurate

estimation of the switching overvoltages under various conditions of the operation is

important factor for the design of transmission systems. Switching overvoltages result

from the operation of switching devices, either during normal conditions or as a result

of fault clearings. These transients have durations from ten to thousands of

microseconds. This thesis investigates the switching overvoltages occurring during

the switching of line circuit breaker on each side of the 500 kV transmission line

between Nam Theun 2 and Thailand network at Roi Et 2 substation as shown in

Figure 4.1. The analyses to assess the switching overvoltages in cases are as

following: [4], [5], [16]

- Line energization

- Line re-energization due to single phase to ground and three phases to

ground faults.

Two cases above bring to get the highest overvoltage. In case of line re-

energization, more than 85-90% comes from line to ground faults and the other comes

from three phases to ground faults. However, case of three phases to ground faults hasmore damage than single line to ground fault.

4.2 Line Energization Analysis

4.2.1 Cases of the study

The 500 kV transmission line between Nam Theu 2 and Roi Et 2 had

double circuits. The study of line energization is divided into three cases as following:


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1) Line energization from Nam Theun 2 to Roi Et 2 circuit 1 with open

circuit at the receiving end at RE 2 substation and energizing with load

conditions.

2) Line energization from Nam Theu 2 to Roi Et 2 circuit 2 with open

circuit at the receiving end at RE 2 substation.

3) Line energization from Nam Theun 2 to Roi Et 2 circuit 1 and circuit 2

energizing with load.

Switching overvoltages during line energization of the 500 kV transmission line

between Nam Theun 2 and Thailand network at Rio Et 2 substation is analyzed with a

presence of 444 kV surge arresters at both sides and 355 Mvar shunt reactors at Nam

Theun 2 Power Plant and 255 Mvar at Roi Et 2 substation at both sides terminal. It

was assumed that protection devices switched turning on/off during line energization.

The 200 operations statistical switching are considered for finding that the maximum

overvoltage occurring the transmission lines.

4.2.2 Methodology

All cases of the study, the circuit breaker at bus the sending end is

operating energizing to lines. The line energization overvoltages study during no load,

half load and full load are considered. In case of line energization, it brings to get the

maximum overvoltages and more damage, for example, open circuit breaker at the

receiving end during the energization from the sending end will get the overvoltages

at the receiving end. As well known, switching overvoltage occurred on power

systems due to many factors which have an effect on the value and waveform. The

maximum overvoltage is found out by the statistical method. This method is random

many parameters such as circuit breaker closing time, time scatter between phases,line parameters. It should be note that the closing time plays an important role on the

value of energization overvoltage. First step to study switching energization, we have

to find out the worst closing and the statistical closing time.

4.2.3 Line Energizing from NTN 2- RE2 Circuit 1

Line energization overvoltage study of circuit 1, energizing from the

sending end named NTN 2 to the receiving end named RE 2 as illustrated in Figure

4.1.


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Figure 4.1 Single line diagram of 500 kV transmission line NTN 2 RE 2 substation

circuit 1 energizing.

Before closing the circuit breaker of Nam Theun 2, the generator of power plant

has to be in steady state condition. All line circuit breakers at both sides of these two

circuits are opened and one set of line circuit breaker on the circuit 1 of the double

circuit lines a Nam Theun 2 is operated.

Since one circle of waveform has 20 ms, result in many closing times can apply

for circuit breaker. To find the worst closing time ( mean closing time ), we have

change the closing phase angle and find out the particular closing phase angle which

can cause the highest value. Table: 4.1 shown the results for different closing time

( when the three phases closing at same time ). The highest overvoltage is 1.704 p.u

occurred at the receiving end when the closing time is 15ms.

Table: 4.1. The effect of different closing time on the energization overvoltage

closing 3 poles of circuit breaker at the same time from NTN 2

RE 2 with protection devices terminal.

Maximum overvoltage at Roi Et 2 substation ( 1 p.u = 429 kV )


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( p.u ) ( p.u ) ( p.u ) ( p.u ) ( p.u )

1 1.688 41 1.695 81 1.693 121 1.700 161 1.702

2 1.702 42 1.704 82 1.665 122 1.676 162 1.6943 1.706 43 1.697 83 1.704 123 1.681 163 1.692

4 1.704 44 1.690 84 1.701 124 1.676 164 1.699

5 1.699 45 1.701 85 1.703 125 1.665 165 1.702

6 1.703 46 1.704 86 1.702 126 1.702 166 1.680

7 1.704 47 1.697 87 1.680 127 1.703 167 1.682

8 1.699 48 1.703 88 1.694 128 1.682 168 1.704

9 1.686 49 1.686 89 1.704 129 1.688 169 1.701

10 1.701 50 1.691 90 1.671 130 1.680 170 1.700

11 1.702 51 1.703 91 1.704 131 1.698 171 1.678

12 1.676 52 1.706 92 1.706 132 1.702 172 1.694

13 1.695 53 1.688 93 1.672 133 1.685 173 1.703

14 1.703 54 1.704 94 1.674 134 1.662 174 1.690

15 1.664 55 1.703 95 1.704 135 1.703 175 1.703

16 1.697 56 1.697 96 1.678 136 1.694 176 1.702

17 1.691 57 1.686 97 1.706 137 1.704 177 1.702

18 1.703 58 1.691 98 1.688 138 1.704 178 1.662

19 1.667 59 1.703 99 1.706 139 1.690 179 1.701

20 1.702 60 1.686 100 1.702 140 1.704 180 1.697

21 1.704 61 1.695 101 1.703 141 1.667 181 1.703

22 1.704 62 1.704 102 1.686 142 1.689 182 1.691

23 1.704 63 1.697 103 1.705 143 1.678 183 1.70424 1.703 64 1.690 104 1.676 144 1.704 184 1.671

25 1.678 65 1.701 105 1.686 145 1.705 185 1.702

26 1.688 66 1.704 106 1.706 146 1.672 186 1.702

27 1.704 67 1.697 107 1.704 147 1.693 187 1.683

28 1.702 68 1.703 108 1.693 148 1.704 188 1.705

29 1.696 69 1.686 109 1.697 149 1.704 189 1.704

30 1.678 70 1.691 110 1.699 150 1.674 190 1.674

31 1.687 71 1.703 111 1.703 151 1.704 191 1.665

32 1.694 72 1.706 112 1.683 152 1.702 192 1.702

33 1.680 73 1.688 113 1.706 153 1.681 193 1.676

34 1.701 74 1.704 114 1.704 154 1.684 194 1.694

35 1.704 75 1.703 115 1.693 155 1.703 195 1.669

36 1.704 76 1.697 116 1.684 156 1.686 196 1.678

37 1.676 77 1.686 117 1.671 157 1.702 197 1.704

38 1.705 78 1.691 118 1.680 158 1.702 198 1.697

39 1.691 79 1.703 119 1.691 159 1.703 199 1.703

40 1.704 80 1.686 120 1.700 160 1.700 200 1.702


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From table: 4.2, the 200 operations switching line energization circuit 1 with

protection devices of 500 kV transmission lines Nam Theun 2 to Roi Et 2 substation.

The line energization overvoltage in circuit breakers occurs at the closing time of

14.28 ms. The maximum overvoltage at the receiving end is reach 1.706 p.u. The

minimum overvoltage at the receiving end is 1.662 p.u. The mean of overvoltage at

the receiving end is 1.692 p.u and the standard deviation is 5.056 %. The voltage

waveform is illustrated in Figure 4.2.

Figure 4.2 SOV during line energizing circuit 1 with protection devices.


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Table: 4.3 The 200 statistical calculations for energization overvoltage from

NTN 2 RE 2 circuit 1 without shunt reactor at NTN 2.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 1.701 41 1.708 81 1.706 121 1.715 161 1.721

2 1.721 42 1.722 82 1.684 122 1.697 162 1.714

3 1.721 43 1.710 83 1.722 123 1.703 163 1.705

4 1.722 44 1.711 84 1.720 124 1.689 164 1.712

5 1.718 45 1.714 85 1.721 125 1.684 165 1.721

6 1.721 46 1.722 86 1.718 126 1.721 166 1.701

7 1.722 47 1.710 87 1.693 127 1.720 167 1.695

8 1.712 48 1.720 88 1.707 128 1.695 168 1.722

9 1.699 49 1.699 89 1.719 129 1.701 169 1.71410 1.720 50 1.712 90 1.684 130 1.693 170 1.715

11 1.721 51 1.716 91 1.722 131 1.711 171 1.691

12 1.689 52 1.723 92 1.722 132 1.721 172 1.707

13 1.716 53 1.709 93 1.684 133 1.706 173 1.722

14 1.721 54 1.719 94 1.687 134 1.681 174 1.711

15 1.677 55 1.719 95 1.721 135 1.721 175 1.721

16 1.712 56 1.710 96 1.691 136 1.707 176 1.721

17 1.712 57 1.699 97 1.723 137 1.722 177 1.721

18 1.720 58 1.712 98 1.701 138 1.720 178 1.675

19 1.680 59 1.719 99 1.722 139 1.702 179 1.71720 1.715 60 1.699 100 1.721 140 1.722 180 1.712

21 1.722 61 1.714 101 1.719 141 1.680 181 1.721

22 1.722 62 1.691 102 1.699 142 1.702 182 1.704

23 1.721 63 1.690 103 1.720 143 1.691 183 1.722

24 1.716 64 1.687 104 1.689 144 1.722 184 1.684

25 1.691 65 1.708 105 1.699 145 1.722 185 1.721

26 1.709 66 1.678 106 1.721 146 1.684 186 1.721

27 1.718 67 1.721 107 1.723 147 1.706 187 1.705

28 1.721 68 1.722 108 1.706 148 1.723 188 1.720

29 1.710 69 1.721 109 1.712 149 1.722 189 1.722

30 1.691 70 1.716 110 1.713 150 1.687 190 1.687

31 1.708 71 1.718 111 1.716 151 1.718 191 1.684

32 1.707 72 1.710 112 1.705 152 1.721 192 1.718

33 1.693 73 1.695 113 1.722 153 1.703 193 1.697

34 1.714 74 1.721 114 1.721 154 1.697 194 1.707

35 1.721 75 1.721 115 1.706 155 1.722 195 1.682

36 1.722 76 1.722 116 1.697 156 1.699 196 1.691

37 1.697 77 1.690 117 1.692 157 1.721 197 1.722

38 1.723 78 1.722 118 1.693 158 1.721 198 1.710

39 1.704 79 1.718 119 1.712 159 1.720 199 1.716

40 1.722 80 1.707 120 1.716 160 1.716 200 1.721


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From table: 4.3, the 200 operations switching line energization circuit 1 without

shunt reactors at Nam Theun 2 of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation. The energization overvoltage in circuit breakers closing time is 14.31 ms.

The maximum overvoltage at the receiving end is reach 1.723 p.u. The minimum

overvoltage at the receiving end is 1.675 p.u. The mean of overvoltage at the

receiving end is 1.709 p.u and the standard deviation is 5.582 %. The voltage


Figure 4.3 SOV during line energizing circuit 1 without shunt reactor at NTN 2.


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NTN 2 RE 2 circuit 1 without shunt reactor at RE 2.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 1.708 41 1.718 81 1.713 121 1.724 161 1.729

2 1.729 42 1.730 82 1.691 122 1.704 162 1.722

3 1.730 43 1.717 83 1.730 123 1.710 163 1.715

4 1.730 44 1.718 84 1.728 124 1.696 164 1.720

5 1.726 45 1.722 85 1.730 125 1.691 165 1.729

6 1.730 46 1.731 86 1.727 126 1.729 166 1.709

7 1.730 47 1.717 87 1.700 127 1.728 167 1.702

8 1.720 48 1.728 88 1.716 128 1.702 168 1.731

9 1.707 49 1.706 89 1.728 129 1.708 169 1.72210 1.728 50 1.720 90 1.691 130 1.700 170 1.724

11 1.729 51 1.725 91 1.731 131 1.718 171 1.698

12 1.696 52 1.731 92 1.731 132 1.729 172 1.716

13 1.723 53 1.717 93 1.692 133 1.714 173 1.730

14 1.730 54 1.728 94 1.694 134 1.688 174 1.718

15 1.685 55 1.728 95 1.730 135 1.730 175 1.730

16 1.721 56 1.717 96 1.698 136 1.716 176 1.729

17 1.720 57 1.707 97 1.731 137 1.731 177 1.729

18 1.728 58 1.720 98 1.709 138 1.729 178 1.682

19 1.687 59 1.728 99 1.731 139 1.710 179 1.72620 1.724 60 1.706 100 1.729 140 1.731 180 1.721

21 1.731 61 1.722 101 1.728 141 1.687 181 1.730

22 1.730 62 1.698 102 1.706 142 1.711 182 1.711

23 1.730 63 1.696 103 1.729 143 1.698 183 1.730

24 1.726 64 1.694 104 1.696 144 1.731 184 1.691

25 1.698 65 1.718 105 1.707 145 1.731 185 1.729

26 1.717 66 1.685 106 1.730 146 1.692 186 1.729

27 1.727 67 1.730 107 1.731 147 1.713 187 1.712

28 1.729 68 1.731 108 1.713 148 1.731 188 1.729

29 1.720 69 1.729 109 1.721 149 1.730 189 1.730

30 1.698 70 1.725 110 1.722 150 1.694 190 1.694

31 1.715 71 1.726 111 1.726 151 1.727 191 1.691

32 1.714 72 1.720 112 1.712 152 1.729 192 1.727

33 1.700 73 1.702 113 1.731 153 1.710 193 1.704

34 1.722 74 1.729 114 1.730 154 1.704 194 1.714

35 1.730 75 1.729 115 1.713 155 1.730 195 1.689

36 1.731 76 1.730 116 1.704 156 1.706 196 1.698

37 1.704 77 1.696 117 1.699 157 1.729 197 1.730

38 1.731 78 1.730 118 1.700 158 1.729 198 1.717

39 1.711 79 1.727 119 1.720 159 1.728 199 1.725

40 1.730 80 1.716 120 1.725 160 1.725 200 1.729


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shunt reactors at Roi Et 2 of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation. The energization overvoltage in circuit breakers closing time is 14.31 ms.

The maximum overvoltage at the receiving end is reach 1.731 p.u. The minimum

overvoltage at the receiving end is 1.682 p.u. The mean of overvoltage at the

receiving end is 1.717 p.u and the standard deviation is 5.835 %. The voltage


Figure 4.4 SOV during line energizing circuit 1 without shunt reactor at RE 2.


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NTN 2 RE 2 circuit 1 without arrester at NTN 2.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 1.693 41 1.705 81 1.698 121 1.710 161 1.713

2 1.713 42 1.716 82 1.673 122 1.685 162 1.705

3 1.715 43 1.703 83 1.715 123 1.691 163 1.702

4 1.714 44 1.700 84 1.711 124 1.681 164 1.706

5 1.709 45 1.709 85 1.714 125 1.673 165 1.713

6 1.714 46 1.715 86 1.713 126 1.713 166 1.689

7 1.715 47 1.703 87 1.686 127 1.714 167 1.688

8 1.706 48 1.714 88 1.703 128 1.690 168 1.715

9 1.695 49 1.691 89 1.714 129 1.693 169 1.70910 1.711 50 1.702 90 1.677 130 1.686 170 1.710

11 1.713 51 1.711 91 1.715 131 1.705 171 1.686

12 1.681 52 1.716 92 1.716 132 1.713 172 1.703

13 1.706 53 1.699 93 1.679 133 1.695 173 1.714

14 1.714 54 1.714 94 1.679 134 1.670 174 1.700

15 1.671 55 1.713 95 1.715 135 1.714 175 1.714

16 1.708 56 1.703 96 1.684 136 1.703 176 1.713

17 1.702 57 1.695 97 1.716 137 1.715 177 1.713

18 1.714 58 1.702 98 1.696 138 1.715 178 1.668

19 1.674 59 1.713 99 1.716 139 1.695 179 1.71220 1.710 60 1.691 100 1.713 140 1.715 180 1.708

21 1.715 61 1.709 101 1.713 141 1.674 181 1.714

22 1.715 62 1.684 102 1.691 142 1.698 182 1.697

23 1.715 63 1.678 103 1.715 143 1.684 183 1.714

24 1.712 64 1.681 104 1.684 144 1.715 184 1.677

25 1.684 65 1.705 105 1.695 145 1.716 185 1.713

26 1.699 66 1.667 106 1.715 146 1.679 186 1.713

27 1.713 67 1.714 107 1.716 147 1.698 187 1.693

28 1.713 68 1.716 108 1.698 148 1.716 188 1.715

29 1.706 69 1.713 109 1.708 149 1.716 189 1.715

30 1.684 70 1.711 110 1.709 150 1.681 190 1.681

31 1.697 71 1.709 111 1.712 151 1.713 191 1.673

32 1.700 72 1.706 112 1.693 152 1.713 192 1.713

33 1.688 73 1.690 113 1.716 153 1.691 193 1.685

34 1.709 74 1.713 114 1.715 154 1.692 194 1.700

35 1.715 75 1.713 115 1.698 155 1.714 195 1.676

36 1.715 76 1.715 116 1.690 156 1.691 196 1.684

37 1.685 77 1.678 117 1.681 157 1.713 197 1.715

38 1.716 78 1.715 118 1.688 158 1.713 198 1.703

39 1.697 79 1.713 119 1.702 159 1.714 199 1.711

40 1.714 80 1.698 120 1.711 160 1.711 200 1.713


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arresters at Nam Theun 2 of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation. The line energization overvoltage closing time is 14.28 ms. The maximum

overvoltage at receiving end is reach 1.716 p.u. The minimum overvoltage at

receiving end is 1.667 p.u. The mean of overvoltage at receiving end is 1.702 p.u and

the standard deviation is 5.787 %. The voltage waveform is illustrated in Figure 4.5.

Figure 4.5 SOV during line energizing circuit 1 without Arrester at NTN 2.


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arresters at Rio Et 2 of 500 kV transmission lines Nam Theun 2 to Roi Et 2 substation,

for energization overvoltage closing time is 17.47ms. The maximum overvoltage atreceiving end is 2.023 p.u. The minimum overvoltage at receiving end is 1.855 p.u.

The mean of overvoltage at receiving end is 1.980 p.u and the standard deviation is

18.524 %. The voltage waveform is illustrated in Figure 4.6.

Figure 4.6 SOV during line energizing circuit 1 without Arrester at RE 2.


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Table 4.7 The 200 statistical calculations for energization overvoltage from

NTN 2 RE 2 circuit 1 without shunt reactor at both sides.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 1.723 41 1.736 81 1.728 121 1.742 161 1.749

2 1.749 42 1.749 82 1.708 122 1.723 162 1.746

3 1.748 43 1.733 83 1.750 123 1.732 163 1.731

4 1.750 44 1.743 84 1.749 124 1.711 164 1.736

5 1.748 45 1.740 85 1.749 125 1.708 165 1.749

6 1.749 46 1.750 86 1.745 126 1.749 166 1.729

7 1.750 47 1.733 87 1.716 127 1.747 167 1.718

8 1.736 48 1.747 88 1.734 128 1.718 168 1.750

9 1.721 49 1.722 89 1.746 129 1.723 169 1.74010 1.749 50 1.744 90 1.707 130 1.716 170 1.742

11 1.749 51 1.743 91 1.750 131 1.734 171 1.714

12 1.711 52 1.750 92 1.749 132 1.749 172 1.734

13 1.746 53 1.741 93 1.707 133 1.737 173 1.749

14 1.749 54 1.746 94 1.709 134 1.705 174 1.743

15 1.701 55 1.746 95 1.748 135 1.749 175 1.749

16 1.740 56 1.733 96 1.714 136 1.734 176 1.749

17 1.744 57 1.721 97 1.750 137 1.750 177 1.749

18 1.747 58 1.744 98 1.724 138 1.747 178 1.698

19 1.703 59 1.746 99 1.749 139 1.725 179 1.74420 1.742 60 1.722 100 1.749 140 1.750 180 1.740

21 1.750 61 1.740 101 1.746 141 1.703 181 1.749

22 1.750 62 1.714 102 1.722 142 1.726 182 1.727

23 1.748 63 1.714 103 1.747 143 1.714 183 1.750

24 1.744 64 1.709 104 1.711 144 1.750 184 1.707

25 1.714 65 1.736 105 1.721 145 1.749 185 1.749

26 1.741 66 1.701 106 1.748 146 1.707 186 1.749

27 1.745 67 1.749 107 1.750 147 1.728 187 1.734

28 1.750 68 1.749 108 1.728 148 1.750 188 1.747

29 1.738 69 1.749 109 1.740 149 1.749 189 1.750

30 1.714 70 1.743 110 1.741 150 1.709 190 1.709

31 1.739 71 1.748 111 1.744 151 1.745 191 1.708

32 1.730 72 1.738 112 1.734 152 1.749 192 1.745

33 1.716 73 1.718 113 1.749 153 1.732 193 1.723

34 1.740 74 1.749 114 1.748 154 1.720 194 1.730

35 1.748 75 1.749 115 1.728 155 1.749 195 1.705

36 1.750 76 1.750 116 1.720 156 1.722 196 1.714

37 1.723 77 1.714 117 1.717 157 1.749 197 1.750

38 1.750 78 1.748 118 1.716 158 1.749 198 1.733

39 1.727 79 1.745 119 1.744 159 1.747 199 1.743

40 1.750 80 1.734 120 1.743 160 1.743 200 1.749


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shunt reactors at both sides of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation, for energization overvoltage closing time is 14.31ms. The maximum




Figure 4.7 SOV during line energizing circuit 1 without Shunt reactor at both sides.


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NTN 2 RE 2 circuit 1 without arrester at both sides.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 2.121 41 2.183 81 2.139 121 2.188 161 2.068

2 2.068 42 2.157 82 2.094 122 2.058 162 2.016

3 2.151 43 2.154 83 2.099 123 2.044 163 2.176

4 2.096 44 2.025 84 2.055 124 2.103 164 2.161

5 2.044 45 2.165 85 2.078 125 2.094 165 2.068

6 2.078 46 2.109 86 2.183 126 2.068 166 2.047

7 2.114 47 2.154 87 2.106 127 2.177 167 2.106

8 2.161 48 2.177 88 2.180 128 2.146 168 2.119

9 2.158 49 2.115 89 2.163 129 2.121 169 2.16510 2.055 50 2.019 90 2.102 130 2.106 170 2.188

11 2.068 51 2.166 91 2.119 131 2.158 171 2.133

12 2.103 52 2.134 92 2.146 132 2.068 172 2.180

13 2.023 53 2.030 93 2.125 133 2.037 173 2.089

14 2.078 54 2.163 94 2.104 134 2.099 174 2.025

15 2.114 55 2.181 95 2.169 135 2.078 175 2.078

16 2.187 56 2.154 96 2.105 136 2.180 176 2.068

17 2.019 57 2.158 97 2.127 137 2.109 177 2.068

18 2.177 58 2.019 98 2.164 138 2.174 178 2.109

19 2.117 59 2.181 99 2.146 139 2.128 179 2.18520 2.166 60 2.115 100 2.068 140 2.109 180 2.187

21 2.119 61 2.165 101 2.181 141 2.117 181 2.078

22 2.099 62 2.105 102 2.115 142 2.169 182 2.133

23 2.169 63 2.081 103 2.160 143 2.105 183 2.106

24 2.166 64 2.129 104 2.132 144 2.109 184 2.102

25 2.105 65 2.183 105 2.158 145 2.150 185 2.068

26 2.030 66 2.104 106 2.151 146 2.125 186 2.068

27 2.165 67 2.078 107 2.129 147 2.139 187 2.041

28 2.066 68 2.146 108 2.139 148 2.129 188 2.160

29 2.186 69 2.068 109 2.187 149 2.157 189 2.099

30 2.105 70 2.187 110 2.186 150 2.129 190 2.129

31 2.033 71 2.044 111 2.166 151 2.165 191 2.094

32 2.145 72 2.186 112 2.041 152 2.068 192 2.183

33 2.138 73 2.146 113 2.146 153 2.044 193 2.058

34 2.165 74 2.068 114 2.169 154 2.150 194 2.145

35 2.169 75 2.068 115 2.139 155 2.089 195 2.121

36 2.109 76 2.114 116 2.110 156 2.115 196 2.105

37 2.058 77 2.081 117 2.074 157 2.068 197 2.099

38 2.137 78 2.164 118 2.138 158 2.068 198 2.154

39 2.133 79 2.165 119 2.019 159 2.177 199 2.166

40 2.106 80 2.180 120 2.187 160 2.187 200 2.068


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arresters at both sides of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation, for energization overvoltage closing time is 17.05 ms. The maximum




Figure 4.8 SOV during line energizing circuit 1 without arrester at both sides.


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Table: 4.9 The 200 statistical calculations for energization overvoltage from NTN 2

RE 2 circuit 1 without any protection at both sides.

No.Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )No.

Voltage

( p.u )

1 2.362 41 2.365 81 2.369 121 2.364 161 2.320

2 2.320 42 2.352 82 2.262 122 2.236 162 2.265

3 2.359 43 2.373 83 2.334 123 2.224 163 2.363

4 2.335 44 2.237 84 2.310 124 2.334 164 2.373

5 2.297 45 2.370 85 2.326 125 2.262 165 2.320

6 2.326 46 2.339 86 2.357 126 2.320 166 2.229

7 2.349 47 2.373 87 2.345 127 2.352 167 2.350

8 2.373 48 2.352 88 2.365 128 2.345 168 2.342

9 2.353 49 2.358 89 2.359 129 2.362 169 2.37010 2.310 50 2.247 90 2.321 130 2.345 170 2.364

11 2.320 51 2.366 91 2.342 131 2.373 171 2.335

12 2.334 52 2.355 92 2.358 132 2.320 172 2.365

13 2.273 53 2.227 93 2.317 133 2.220 173 2.330

14 2.326 54 2.359 94 2.327 134 2.271 174 2.237

15 2.296 55 2.355 95 2.353 135 2.326 175 2.326

16 2.366 56 2.373 96 2.339 136 2.365 176 2.320

17 2.247 57 2.353 97 2.352 137 2.339 177 2.320

18 2.352 58 2.247 98 2.356 138 2.353 178 2.288

19 2.303 59 2.355 99 2.358 139 2.365 179 2.36020 2.368 60 2.358 100 2.320 140 2.339 180 2.366

21 2.342 61 2.370 101 2.355 141 2.303 181 2.326

22 2.334 62 2.339 102 2.358 142 2.359 182 2.368

23 2.353 63 2.247 103 2.359 143 2.339 183 2.339

24 2.363 64 2.324 104 2.330 144 2.339 184 2.321

25 2.339 65 2.365 105 2.353 145 2.351 185 2.320

26 2.227 66 2.280 106 2.359 146 2.317 186 2.320

27 2.360 67 2.326 107 2.345 147 2.369 187 2.222

28 2.322 68 2.358 108 2.369 148 2.345 188 2.359

29 2.366 69 2.320 109 2.366 149 2.352 189 2.334

30 2.339 70 2.362 110 2.365 150 2.324 190 2.324

31 2.218 71 2.297 111 2.363 151 2.360 191 2.262

32 2.371 72 2.366 112 2.222 152 2.320 192 2.357

33 2.341 73 2.345 113 2.358 153 2.224 193 2.236

34 2.370 74 2.320 114 2.353 154 2.349 194 2.371

35 2.353 75 2.320 115 2.369 155 2.330 195 2.311

36 2.339 76 2.349 116 2.354 156 2.358 196 2.339

37 2.236 77 2.247 117 2.244 157 2.320 197 2.334

38 2.347 78 2.353 118 2.341 158 2.320 198 2.373

39 2.368 79 2.360 119 2.247 159 2.352 199 2.366

40 2.339 80 2.365 120 2.362 160 2.362 200 2.320


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arresters at both sides of 500 kV transmission lines Nam Theun 2 to Roi Et 2

substation, for energization overvoltage closing time is 13.85 ms. The maximum




Figure 4.9 SOV during line energizing circuit 1 without protection devices at both

sides.

Switching overvoltages during line energization in circuit 1 with different load

condition such as: no load or light load, half load and full load are considered. The

study was set line circuit breakers at sending end circuit 1 operated and breakers at

receiving end connected with load conditions as illustrated in Figure 4.1. The 200

switching operated in circuit 1 with turning on and off protection devices at both

sides. The switching overvoltages during line energization with different loads

conditions, no load or light load system made the maximum transient overvoltages, is

illustrated in table 4.10 and voltage waveform is illustrated in Figure 4.10 Fiure

4.12.


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NTN 2 RE 2 circuit 1 during energizing with differrent loads

conditions and turning on/off protection devices terminal.

Max. Overvoltage ( p.u )

No.

Shunt

Reactor

NTN 2

Shunt

Reactor

RE 2

Arrester

NTN 2

Arrester

RE 2No load

Half

load

Full

load

1 yes yes yes yes 1.706 1.397 1.146

2 no yes yes yes 1.723 1.423 1.186

3 yes no yes yes 1.731 1.436 1.191

4 yes yes no yes 1.716 1.401 1.160

5 yes yes yes no 2.023 1.408 1.1796 no no yes yes 1.750 1.491 1.235

7 yes yes no no 2.188 1.419 1.196

8 no no no no 2.373 1.645 1.301

Figure 4.10 SOV during line energization with no load condition.

Figure 4.11 SOV during line energization with half load condition.


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Figure 4.13 Single line diagram of 500 kV transmission line NTN 2 RE 2 substation

circuit 2 energizing.


NTN 2 RE 2 circuit 2 turning on/off protection devices terminal.

No.Shunt Reactor

NTN 2

Shunt Reactor

RE 2

Arrester

NTN 2

Arrester

RE 2

Overvoltage

receiving

end ( p.u )

1 yes yes yes yes 1.707

2 no yes yes yes 1.724

3 yes no yes yes 1.7334 yes yes no yes 1.719

5 yes yes yes no 2.024

6 no no yes yes 1.750

7 yes yes no no 2.189

8 no no no no 2.376

4.2.5 Line Energizing from NTN 2- RE2 Circuit 1 during Circuit 2

Energization with Load

In this case, circuit 2 is closed and connected with load while circuit 1 isopen at the receiving end and energized from Nam Theun 2 as illustrated in Figure

4.14. Base on the statistical analysis, the program is run 200 times per case to find out

the maximum overvoltage. Table 4.12 shows the various cases (shunt reactor and

arrester of both sides are closed or opened) for running the program and the maximum

overvoltages.


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Figure 4.14 Single line diagram of 500 kV transmission line NTN 2 - RE 2 substation

circuit 1 energizing during circuit 2 energizing with load.


NTN 2 RE 2 circuit 1 during circuit 2 energizing with light load

turning on/off protection devices terminal.

No.Shunt Reactor

NTN 2

Shunt Reactor

RE 2

Arrester

NTN 2

Arrester

RE 2

Overvoltage

receiving

end ( p.u )

1 yes yes yes yes 1.6972 no yes yes yes 1.708

3 yes no yes yes 1.717

4 yes yes no yes 1.706

5 yes yes yes no 1.947

6 no no yes yes 1.730

7 yes yes no no 1.988

8 no no no no 2.175

4.3 Line Re-energization Analysis

4.3.1 Case of the Study

The 500 kV transmission line between Nam Theun 2 and Roi Et 2 has

double circuits. The study of line re-energization during single line to ground fault

and three phases to ground fault, the step of fault is divided into six, the distance each

step approximately 50 km from sending end as following:

- Line re-energization during single line to ground fault and three phases to

ground fault in circuit 1, energizing from Nam Theun 2 sending end to Roi

Et 2 receiving end.


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ground fault in circuit 1 at energizing with different load conditions.


ground fault in circuit 1 at circuit 2 energizing with different load conditions.


ground fault in circuit 2 at energizing with different load conditions.

4.3.2 Methodology

The cases of line re-energization during single line to ground fault and

three phases to ground fault with different load (no load, half load and full load) are

considered. The distance between Nam Theun 2 to Roi Et 2 is divided into 6 parts (50

km per part) to find out the maximum overvoltage occurred in the transmission line.

4.3.3 Line Re-energizing during Single Line to Ground Fault Circuit 1

The case of single line to ground fault with re-energization operation is

examined, the studied according to the variation of fault position from sending

end to receiving end in step different location fault approximately 50 km as

illustrated in Figure 4.15. The simultaneous fault clearing case of single line to

ground fault in circuit 1 and changing phase fault from A, B and C, is selected in

determine the maximum overvoltage. During single line to ground fault is applied

at time t = 1 ms. Cleared time at t = 5 ms and re-energized at time t = 10 ms at

different load condition.

Figure 4.15 Single line diagram NTN 2- RE 2 line re-energizing during fault.


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The maximum overvoltage from line reclosing during single line to ground fault

during phase A to ground clearing fault is 1.748 p.u as illustrated Figure 4.16, phase B

to ground clearing fault is 1.749 p.u as illustrated in Figure 4.17, Phase C to ground

clearing fault is 1.750 p.u as illustrate in Figure 4.18 in the no load condition. The

highest maximum overvoltage during single line to ground fault is set switched on/off

protection devices. The maximum overvoltage without arrester at both sides is 2.782

p.u, higher than without shunt reactor as illustrated in Figure 4.19 and Figure 4.20.

Overvoltage without any protection devices during single line to ground fault is reach

3.265 p.u as illustrated in Figure 4.21.

Figure 4.16 Re-energization overvoltage during phase A to ground fault.

Figure 4.17 Reclosing overvoltage during phase B to ground fault.


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Figure 4.18 Reclosing overvoltage during Phase C to ground fault.

Figure 4.19 Reclosing overvoltages during phase C to ground fault without shunt

reactors at both sides.

Figure 4.20 Reclosing overvoltage during phase C to ground without arresters at both

sides.


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Figure 4.21 Reclosing overvoltage during Phase C to ground fault without any

protection devices.

Figure 4.22 to Figure 4. 24 presents that in case of single line during Phase A, B

and C, The approximately 50 km of faults in circuit 1. The magnitude voltage level is

similar in each phase and step of fault. The maximum overvoltage in phase C is 1.750

p.u. at no load condition, distance of fault is set 100 km from sending end NTN 2

Power Plant.

Reclosing during Ph. A to ground fault

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

50 km 100 km 150 km 200 km 250 km 300 km

Fault location from sending end [km]

Maximumo

vervoltage[p.u

]

No load

Half load

Full load

Figure 4.22 Reclosing during phase A to ground of location fault.


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Reclosing during Ph. B to ground fault

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

50 km 100 km 150 km 200 km 250 km 300 km


Maximumovervoltage[p.u

]

No load

Half load

Full load

Figure 4.23 Reclosing during phase B to ground of location fault.

Reclosing during Ph. C to ground fault

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

50 km 100 km 150 km 200 km 250 km 300 km


Maximum

overvoltage[p.u

]

No load

Half load

Full load

Figure 4.24 Reclosing during phase C to ground of location fault.


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4.3.4 Line Re-energizing during Three Phases to Ground Fault Circuit 1

Switching overvoltages during three phases to ground faults are re-

energization at different load condition. It is finding that the highest overvoltage when

energizing from Nam Theun 2 Power Plant Roi Et 2 substation in circuit 1. The

three phases to ground fault is studied according to the variation of fault position from

sending end to receiving end in step approximately 50 km as illustrated in Figure

4.15. The simultaneous fault clearing case of three phases to ground fault is applied at

time 1 ms. Cleared time 5 ms and re-energized 1 ms at the different load condition.

The maximum overvoltage re-energized after three phases to ground fault at receiving

end is 1.784 p.u as illustrated in Figure 4.25, three phases to ground fault with

protection devices put in service. Reclosing overvoltage is 3.379 p.u during three

phases to ground without arresters at the both sides. The maximum overvoltage is

4.069 p.u without any protection. After arresters put in services, the voltage is reduces

to 1.786 p.u. The voltage waveform is illustrated in Figure 26 to Figure 28. The

simulation results from re-energized during three phases to ground fault, with

different load condition as illustrated in Figure 4.29.

Figure 4.25 Reclosing overvoltage during three phases to ground fault with protection

devices.


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Figure 4.26 Reclosing overvoltages during three phases to ground fault without shunt

reactors at both sides.

Figure 4.27 Reclosing during three phases to ground fault without arresters at both

sides.

Figure 4.28 Reclosing during three phases to ground fault without protection devices.


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Reclosing during three phases to groud fault

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

50 km 100 km 150 km 200 km 250 km 300 km


Maxim

umovervoltage[p.u

]

No load

Half load

Full load

Figure 4.29 Reclosing overvoltages during three phases to ground of location fault.

The summarized simulation from cases line re-energization during single to

ground fault and three phases to ground fault in circuit 1, circuit 2 and fault in circuit

1 due to circuit 2 energizing with load condition as shown in table 4.13 to table 4.15.

It is realized that, in case of having double circuits of 500 kV transmission line

between Nam Theun 2 and Roi Et 2 substation. Reclosing overvoltages during single

line to ground fault and three phases to ground fault level is similar at circuit 1 and

circuit 2. Reclosing overvoltage during three phases to ground fault is always higher

than single line to ground fault. In case of no load condition, the maximum

overvoltage is higher than those of half load and full load.The highest overvoltage

during three phases to ground fault is 1.784 p.u in circuit 1 and single line to ground

fault is 1.750 p.u in circuit 1 at no load condition.


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Table: 4.13 Maximum overvoltages during single phase to ground fault and

three phases to ground fault circuit 1 energizing with different load

condition.

Load condition Fault type

Fault location

from sending

end (NTN2)

Max. SOV at

receiving end

RE 2[ p.u ]

Max. SOV at

sending end

NTN 2 [ p.u ]

50 km 1.748 1.566

100 km 1.750 1.551

150 km 1.749 1.540

200 km 1.747 1.547

250 km 1.748 1.488

Single

phase

300 km 1.747 1.50350 km 1.777 1.642

100 km 1.784 1.656

150 km 1.781 1.649

200 km 1.779 1.657

250 km 1.764 1.572

No load

Three phase

300 km 1.755 1.569

50 km 1.318 1.160

100 km 1.316 1.154

150 km 1.314 1.145

200 km 1.316 1.137

250 km 1.312 1.138

Single

phase

300 km 1.315 1.150

50 km 1.414 1.156

100 km 1.313 1.175

150 km 1.307 1.314

200 km 1.311 1.422

250 km 1.309 1.429

Half load

Three phase

300 km 1.285 1.376

50 km 1.017 1.024100 km 1.018 1.026

150 km 1.017 1.034

200 km 1.019 1.038

250 km 1.018 1.034

Single

phase

300 km 1.019 1.031

50 km 1.026 1.045

100 km 1.027 1.098

150 km 1.026 1.217

200 km 1.027 1.302

250 km 1.025 1.290

Full load

Three phase

300 km 1.028 1.264


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three phases to ground fault circuit 1, circuit 2 energizing.

Load

conditionFault type

Fault location

from sending

end (NTN2)

Max. SOV at

receiving end

RE 2[ p.u ]

Max. SOV at

sending end

NTN 2 [ p.u ]

50 km 1.650 1.426

100 km 1.662 1.346

150 km 1.549 1.346

200 km 1.561 1.416

250 km 1.598 1.460

Single phase

300 km 1.682 1.568

50 km 1.686 1.514100 km 1.688 1.519

150 km 1.686 1.509

200 km 1.680 1.497

250 km 1.683 1.498

Light load

Three phase

300 km 1.682 1.496

50 km 1.603 1.269

100 km 1.600 1.268

150 km 1.652 1.258

200 km 1.560 1.260

250 km 1.595 1.260

Single phase

300 km 1.556 1.246

50 km 1.602 1.270

100 km 1.605 1.271

150 km 1.551 1.259

200 km 1.549 1.259

250 km 1.534 1.255

Half load

Three phase

300 km 1.549 1.251

50 km 1.414 1.178

100 km 1.345 1.177

150 km 1.446 1.195

200 km 1.444 1.196

250 km 1.339 1.173

Single phase

300 km 1.325 1.172

50 km 1.491 1.212

100 km 1.482 1.210

150 km 1.455 1.204

200 km 1.452 1.204

250 km 1.447 1.202

Full load

Three phase

300 km 1.440 1.199


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three phases to ground fault circuit 2 energizing.

Load

conditionFault type

Fault location

from sending

end (NTN2)

Max. SOV at

receiving end

RE 2[ p.u ]

Max. SOV at

sending end

NTN 2 [ p.u ]

50 km 1.750 1.554

100 km 1.748 1.545

150 km 1.747 1.560

200 km 1.749 1.555

250 km 1.748 1.550

Single phase

300 km 1.747 1.547

50 km 1.776 1.640100 km 1.782 1.655

150 km 1.780 1.645

200 km 1.779 1.656

250 km 1.758 1.571

No load

Three phase

300 km 1.756 1.570

50 km 1.312 1.150

100 km 1.317 1.156

150 km 1.312 1.153

200 km 1.317 1.156

250 km 1.312 1.148

Single phase

300 km 1.414 1.150

50 km 1.313 1.152

100 km 1.312 1.178

150 km 1.309 1.314

200 km 1.310 1.421

250 km 1.308 1.429

Half load

Three phase

300 km 1.287 1.375

50 km 1.041 1.040

100 km 1.016 1.026

150 km 1.017 1.043

200 km 1.015 1.024

250 km 1.017 1.029

Single phase

300 km 1.016 1.036

50 km 1.026 1.053

100 km 1.023 1.098

150 km 1.026 1.216

200 km 1.025 1.301

250 km 1.027 1.290

Full load

Three phase

300 km 1.029 1.267


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4.4 Conclusion of Switching Overvoltages Analysis

Switching overvoltages during line energization and re-energization duringsingle line to ground fault and three phases to ground faults on the 500 kV

transmission line between Nam Theun 2 substation and Roi Et 2 substation were

analyzed for the cases by PSCAD/EMTDC program, the conclusion can be draw as

following:

1). Line energization overvoltage

The maximum overvoltage during line energization circuit 1, the 200

operations statistical switching is 1.706 p.u at receiving end. The maximum

overvoltage during line energization circuit 2 is 1.707 p. The maximum overvoltage

during line enerzation circuit 1 with circuit 2 energizing during light load or no load is

1.697 p.u. Line energization are considered from Nam Theun 2 to Roi Et 2 substation

with protection devices. When the transmission line without any protection at both

sides, the maximum overvoltage are too high, the overvoltage is reach to 2.376 p.u in

circuit 2 at no load condition.

2). Line energization overvoltage due to different load condition

The maximum overvoltage during line energization circuit 1 is quite low,

when the load condition is considered. The 200 operations statistical switching is

tested; three conditions of loading are studied: no load, half load and full load. The

maximum overvoltage during no load is 1.706 p.u. The maximum overvoltage line

energization during half load is 1.397 p.u. Which is energized during full load

conditions is 1.146 p.u. The results shown the behavior of the system under switching

conditions and the switching overvoltage investigations are usually made with no load

represented on the system. The switching operations on unloaded system will produce

the most severe transient overvoltages.

3). Line energization in circuit 1 and circuit 2 energizing with load during turn

on/off protection devices

Line energization during turn on/off protection devices circuit 1 and circuit

2 energized with load conditions. The 200 operations statistical switching is tested

with load. The maximum overvoltage during line energization without any protection

at both sides is 2.175 p.u. When the transmission line put in protection devices in


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services, the overvoltage could be also reduced to 1.697 p.u at no load condition. The

overvoltage is lower than line energization in circuit 1 and circuit 2.

4). Line re-energization overvoltage during single line to ground faults

The maximum overvoltage due to line re-energization overvoltage during

single line to ground fault is set in the step of fault approximately 50 km from sending

end. The maximum overvoltage is 1.748 p.u during phase A to ground fault. The

overvoltage in phase B to ground fault is 1.749 p.u and phase C to ground fault the

maximum overvotlae is reach to 1.750 p.u energizes with protection devices. When

energized without arresters the maximum overvoltage during phase C to ground fault

is 2.782 p.u and without any protection devices in services the voltage is reach 3.265

p.u.

5). Line re-energization overvoltage during three phase to ground faults

The maximum overvoltage line re-energization overvoltage during three

phases to ground fault was set in the step of faults approximately 50 km from sending

end. The maximum overvoltage is 1.784 p.u at location fault from sending 100 km

( Nam Theun 2 Power Plant ). The maximum overvoltage during three phases to

ground fault without arresters at the both sides is 3.379 p.u and without any protection

devices the overvoltage is reach 4.069 p.u at the receiving end Roi Et 2.

Extensive electromagnetic transient study has been performed for a guide line

for operation and expansion the 500 kV transmission line in Lao PDR. In light of

these study results following main conclusions could be drawn:

- The simulation results line energization with 200 operations statistical

switching from table: 4.9 table: 4.11 in each case, can be concluded that the

maximum overvoltage occurred the transmission lines is 1.196 p.u energized with fullload condition and 2.188 p.u energized without arresters at both sides, no load

condition. When the line put in protection devices in service, the maximum

overvoltage is 1.706 p.u at no load condition and 1.146 p.u at full load condition. It is

found that switching overvoltage on the no load system make produce the most severe

transient overvoltage.

- The simulation results line re-energization during single phase to ground fault

and three phases to ground fault. Three conditions of loading were considered such as:

No load, half load and full load and step of fault approximately 50 km form sending


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