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2.2.4 Induction Motor Starting High current demand of an induction motor during start up has been a problem since late 70s when the induction motor usage started to increase. This surge current causes voltage dips and flicker in a power system and exceeds the disturbance limits defined by the electricity authorities. To prevent these results, many methods are developed. Among these methods, the most considerable one is the switched shunt capacitor since the rest of them requires a decrease in starting torque. Using a switched shunt capacitor in medium and large size motor starting is a well-known practice with proven benefits over years. In this application, mechanical switches are preferable over semiconductor-based ones since the switching occurs only a couple of times in one start up. In addition, large motors are not stopped often as its inertia requires a vast amount of real power each time it is started. However, the reliability of semiconductor technology and maintenance-free operation make the semiconductor switches such as thyristors preferable every time. Besides, its cost is reduced due to the developing technology, so the only drawback is eliminated. Therefore, TSC is a suitable and effective solution for reducing the voltage disturbances in the induction motor starting. The total capacitance is divided into several equal capacitor branches to ensure that the voltage stays stable as much as possible and smooth transitions occur during the entire motor acceleration. Each stage is turned on and off one by one whenever the motor reaches the speed which doesn’t cause a higher voltage disturbance than expected. In [33], it is claimed that the entire capacitor banks are turned on until the current speed reaches 87% of the rated speed. Due to the economical considerations, in motor starting applications, capacitors are involved to work under stress. The rated voltage is chosen to be suitable for a phase to ground connection, however they are installed to the network phase to phase. Since an increase in rated voltage is proportional to the square of the effective power, it takes only 1/3 as many units as necessary to obtain the same reactive power. Capacitors can withstand this overstress as it lasts only 24
a couple of cycles. However, at least 5 minutes should pass before reenergizing the capacitors to ensure that they are fully discharged [34]. This application directly restricts the frequent switching of a motor during start-up. In addition, it requires a controllable switching to ensure that the overstressed capacitors do not get damaged by a high inrush current component. 2.3 Switching Performance of TSC The key parameter in TSC design is the transient-free switching concept. It means that switching occurs without any distortion or oscillation in current and voltage waveforms. This could be true only for the ideal system which does not include any inductance and whose single phase consists of a capacitor parallel with an anti-parallel connected thyristor pair. However under practical circumstances with several parallel stages on a phase, the capacitor/thyristor combination draws extremely high inrush current component. This situation is illustrated in Figure 2.10. When the last stage (the branch consisting of C 1 as capacitor and S 1 switch as thyristor pairs) is turned on, it draws current from other branches that are already charged and still conducting as well as the supply. As a result, the amplitude of initial current becomes too high to damage the semiconductor switches. According to [36], the peak value of overcurrents because of these switching transients should not exceed 100I N (I N is the rated rms capacitor bank current). It is also stated that the inrush transient current can be calculated as: Iˆ S = U√ 2 √ , (2.9) XC X L where X C = 3U 2 ( 1 Q 1 + 1 Q 2 ) × 10 −6 . (2.10) Here, 25
Page 1 and 2: DESIGN AND IMPLEMENTATION OF THYRIS
Page 3 and 4: I hereby declare that all informati
Page 5 and 6: ÖZ TRİSTÖR ANAHTARLAMALI ŞÖNT
Page 7 and 8: ACKNOWLEDGMENTS I would like to exp
Page 9 and 10: 2.3 Switching Performance of TSC .
Page 11 and 12: LIST OF TABLES TABLES Table 1.1 Cur
Page 13 and 14: Figure 2.9 (a) Equivalent circuit r
Page 15 and 16: Figure 4.8 Resultant line-to-line v
Page 17 and 18: Figure 4.38 3 Phase current wavefor
Page 19 and 20: CHAPTER 1 INTRODUCTION 1.1 Power Qu
Page 21 and 22: this disturbance since they do not
Page 23 and 24: driving algorithm and it has to wit
Page 25 and 26: how to improve the transient respon
Page 27 and 28: From the practical view, the less t
Page 29 and 30: CHAPTER 2 PROBLEM DEFINITION AND PR
Page 31 and 32: as switching devices instead of ant
Page 33 and 34: Directly Connected Clients 35 33 30
Page 35 and 36: 2.2.2 Harmonic Filtration A pure si
Page 37 and 38: components dramatically. The follow
Page 39 and 40: 20A 20A 15A 15A Line Current 10A Li
Page 41: VS RS XS VL Source Load IL Ic Compe
Page 45 and 46: i + + VT - T1 T2 V + VC - L C Figur
Page 47 and 48: 2.15 shows that there are some comp
Page 49 and 50: waveform directly follows the sourc
Page 51 and 52: is known as copper loss of the tran
Page 53 and 54: components parallel to the thyristo
Page 55 and 56: Ls Coupling Transformer V TCR TSC L
Page 57 and 58: +1.0 Reactive Power, Q (pu) Inducti
Page 59 and 60: V V max V max = voltage limit I Cma
Page 61 and 62: power system. Voltage source conver
Page 63 and 64: timing of switching must be when th
Page 65 and 66: Table 3.1: Type of the excavators a
Page 67 and 68: 3.3 Selection Criterion of Capacito
Page 69 and 70: minutes should be given to self-dis
Page 71 and 72: possible in order to achieve a tran
Page 73 and 74: advantage. It is not affected by th
Page 75 and 76: (a) (b) Figure 3.7: PSCAD model of
Page 77 and 78: this value is at least twice of the
Page 79 and 80: of the reverse recovery current and
Page 81 and 82: curve in its datasheet should be ta
Page 83 and 84: Figure 3.13: The current distributi
Page 85 and 86: stays in inductive or capacitive re
Page 87 and 88: ”ENB A, ENB B and ENB C” are co
Page 89 and 90: 3.7 Key Points in Design of TSC Cab
Page 91 and 92: chapter, some basic calculations to
Page 93 and 94:
CHAPTER 4 EXPERIMENTAL RESULTS 4.1
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(a) Contactor Switched Plain Capaci
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ated capacitor current. This inrush
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current. Line-to-line voltage is al
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(a) Three phase current waveform at
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4.2.2 Contactor Switched Shunt Filt
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to high inrush current causes a con
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(a) Voltage Waveform across the cap
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Page 111 and 112:
This transient has also negligible
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(a) Three phase current waveform at
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Figure 4.17: Resultant 3φ Capacito
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Figure 4.21: Resultant line-to-line
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Figure 4.24: Firing pulses, voltage
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566 uF 2x6.0 MVA TM 34.5 kV 500 / 5
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Experimental results will be presen
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+1.6 +0.66 Thyristor Voltage (kV) -
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+1.5 +1.0 Capacitor Voltage (kV) +0
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+1.5 +1.0 Capacitor Voltage (kV) +0
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increase in current can be approxim
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would be given to the supply voltag
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250 1 cycle transient fft 200 I Pha
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4.4 TSC Cabinet Interior Equipment
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4.5 Discussion In contactor or thyr
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• Delta-connected TSC topology is
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[13] Tabandeh, M., Alavi, M.H., Mar
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[38] Bilgin, H.F., “Design and Im
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Since the roots of this equation ar
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APPENDIX B DISTINCTIVE CURVES OF TH
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135 Figure B.2: Stored charge and r
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APPENDIX C DETAILS OF THE CONTROL C
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139 Figure C.2: P-CAD 2002 Schemati
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Page 161 and 162:
Page 163 and 164:
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147 Figure C.10: P-CAD 2002 Schemat
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149 Figure D.1: General view of the
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APPENDIX E APPLICATION MODEL OF THE
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153 Figure E.2: 3 dimensional plot
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155 Figure F.1: Installed SVC syste
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157 Figure F.3: Installed SVC syste
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