[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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FIGURE 3.3.2 Switching sequence of tap selector — arcing switch. positions a–c). Then the arcing switch transfers the load current from the tap in operation to the preselected tap (Figure 3.3.2, positions c–g). The LTC is operated by means of a drive mechanism. The tap selector is operated by a gearing directly from the drive mechanism. At the same time, a spring energy accumulator is tensioned. This operates the arcing switch — after releasing in a very short time — independently of the motion of the drive mechanism. The gearing ensures that this arcing switch operation always takes place after the tap preselection operation has been finished. With today’s designs, the switching time of an arcing switch lies between 40 and 60 ms. During the arcing switch operation, transition resistors are inserted (Figure 3.3.2, positions d–f), which are loaded for 20 to 30 ms, i.e., the resistors can be designed for short-term loading. The amount of resistor material required is therefore relatively small. The total operation time of an LTC is between 3 and 10 sec, depending on the respective design. An arcing tap switch (Figure 3.3.3) carries out the tap change in one step from the tap in service to the adjacent tap (Figure 3.3.4). The spring energy accumulator, wound up by the drive mechanism actuates the arcing tap switch sharply after releasing. For switching time and resistor loading (Figure 3.3.4, positions b–d), the above statements are valid. The details of switching duty, including phasor diagrams, are described by IEEE (Annex A [IEEE, 1995]) and IEC (Annex A [IEC, 2003]). 3.3.1.2 Reactance-Type Load Tap Changer For reactance-type LTCs, the following types of switching are used (Annex B of [IEEE, 1995 and IEC, 2003]): • Arcing tap switch • Arcing switch with tap selector • Vacuum interrupter with tap selector FIGURE 3.3.3 Design principle — arcing tap switch. FIGURE 3.3.4 Switching sequence of arcing tap switch. © 2004 by CRC Press LLC © 2004 by CRC Press LLC
FIGURE 3.3.5 Reactance-type LTC, inside view showing vacuum interrupter assembly. Today the greater part of arcing tap switches is produced for voltage regulators, whereas the vacuumtype LTC is going to be the state of the art in the field of power transformers. Figure 3.3.5 shows a three-phase vacuum-type LTC with full insulation between phases and to ground (nominal voltage level 69 kV). It consists of an oil compartment containing tap selector and reversing/ coarse change-over selector, vacuum interrupters, and bypass switches. A typical winding layout and the operating sequence of the said LTC is shown in Figure 3.3.6. The operating sequence is divided into three major functions: 1. Current transfer from the tap selector part preselecting the next tap to the part remaining in position by means of the vacuum interrupter in conjunction with the associated bypass switch (Figure 3.3.6b, positions A–C). 2. Selection of the next tap position by the tap selector in proper sequence, with the reclosing of the vacuum interrupter and bypass switch (Figure 3.3.6b, positions C–F). Contrary to resistance-type LTCs, the bridging position—in which the moving selector contacts p1 and p4 are on neighboring fixed selector contacts (in Figure 3.3.6b, contacts 4 and 5, position F)—is a service position, and therefore the preventive autotransformer/reactor (normally produced by the transformer manufacturer) is designed for continuous loading; i.e., the number of tap positions is twice the number of steps of the tap winding. In other words, the preventive autotransformer works as a voltage divider for step voltage of the tap winding in the bridging position. In comparison with the resistance-type LTC, the reactance-type LTC requires only half the number of taps of the tap winding for the equivalent number of service tap positions. 3. Operation of reversing or coarse changeover selector in order to double the number of positions; for this operation, the moving selector contacts p1 and p4 have to be on the fixed selector contact M (Figure 3.3.6a). For more detailed information about switching duty and phasor diagrams, see Annex B (IEEE, 1995 and IEC, 2003). 3.3.1.3 Tap Position Indication There are no general rules for defining the numerals on the tap-position indicator dial. This is a question of the user’s specifications or national standards. Some users are accustomed to designations such as 1 through 33 (or 0 through 32), while other have traditionally known 16L (lower), 15L, 14L, … N (neutral); 1R (raise), 2R … 16R. An additional point of confusion comes about with the selection of the placement of the tap changer on the primary or secondary winding of the transformer. A tap changer on the primary FIGURE 3.3.6 Reactance-type LTC. Top) Typical winding layout, LTC in position 16L; bottom) Switching sequence, position 16L to 15L. is sometimes designated such as 1 through 33, but position #1 may indicate the greatest degree of voltage boost or buck, depending upon the transformer designer. 3.3.2 Applications of Load Tap Changers 3.3.2.1 Basic Arrangements of Regulating <strong>Transformer</strong>s The following basic arrangements of tap windings are used (Figure 3.3.7). Linear arrang ement (Figure 3.3.7a), is generally used on power transformers with moderate regulating ranges up to a maximum of 20%. With a reversing chang eover selector (Figure 3.3.7b), the tap winding is added to or subtracted from the main winding so that the regulating range can be doubled or the number of taps reduced. During this operation the tap winding is disconnected from the main winding (for a discussion on problems arising from this disconnection, see Section 3.3.5.1 entitled “Voltage Connection of Tap Winding during Changeover Operation”). The greatest copper losses occur, however, in the position with the minimum number of effective turns. This reversing operation is realized with the help of a changeover selector, which is part of the tap selector or of the arcing tap switch. The double reversing chang eover selector (Figure 3.3.7c) avoids the disconnection of tap winding during the changeover operation. In phaseshifting transformers (PST), this apparatus is called an advance-retard switch (ARS). By means of a coarse chang eover selector (Figure 3.3.7d), the tap winding is either connected to the plus or minus tapping of the coarse winding. Also during coarse-selector operation, the tap winding is disconnected from the main winding. (Special winding arrangements can cause the same disconnection © 2004 by CRC Press LLC © 2004 by CRC Press LLC
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ELECTRIC POWER TRANSFORMER ENGINEER
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I wish to recognize the interest of
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Contents 1 Theory and Principles Ch
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1.3 Equivalent Circuit of an Iron-C
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designer starts to make a design fo
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• Transient voltages generated du
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the transformer’s bushings and, m
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% regulation = [(V NL - V FL )/V FL
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In core-form transformers, the wind
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FIGURE 2.1.14 Layer windings (singl
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the transformer design, which may b
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consumer’s service circuit is a d
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FIGURE 2.2.3 Single-phase transform
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is installed so that the tank never
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above which persons might be burned
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FIGURE 2.2.16 Two-bushing subway. (
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carbon steel or the very expensive
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FIGURE 2.2.31 Radial-style dead fro
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FIGURE 2.2.36 Complete transformer
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voltage in each winding simultaneou
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mounted transformers can have arres
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V S + V S I V L Z=R+jX a) V L V S V
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Z = jX (2.3.19) 0.7 Then the curren
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X1 L* X1 S =X1 L X2 L* X3 L* a) S L
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150 V(%) 100 50 0 -50 40 80 T(s) 12
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2.3.8.1.2 Series Connection • The
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A six-pulse single-way transformer
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The degree of coupling also influen
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where I h = current for the hth har
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In the case of liquid-filled transf
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FIGURE 2.4.21 A 36-pulse system mad
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Vacuum-pressure encaps ulated — T
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FIGURE 2.6.1 Typical wiring and sin
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a) H1 b) Ip X2 FLUX H2 LEAKAGE FLUX
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and for CTs is TCF = RCF - (PA/2600
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RCF x Bx Bt RCF t - RCF 0 co
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2000 1000 5% Vex BANDWITH FROM NOMI
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This may be more useful when operat
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also some uncertainty in repeatabil
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FIGURE 2.6.25 Standard two-element
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2.7 Step-Voltage Regulators Craig A
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Source Bypass Switch Source Bypass
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2.7.4 Theory A step-voltage regulat
Page 87 and 88: FIGURE 2.7.22 Equalizer winding inc
Page 89 and 90: TABLE 2.7.4 Increase in Ampere Load
Page 91 and 92: References IEEE, Standard Requireme
Page 93 and 94: 300% FIGURE 2.8.4 Schematic of a co
Page 95 and 96: TABLE 2.8.1 Typical Sizing Workshee
Page 97 and 98: Input with Interruption Ferro Outpu
Page 99 and 100: FIGURE 2.8.20A Performance of a rid
Page 101 and 102: • Input frequency or frequency ra
Page 103 and 104: References 1. Sola/Hevi-Duty Corp.,
Page 105 and 106: FIGURE 2.9.5 Typical phase-reactor
Page 107 and 108: FIGURE 2.9.10 Two generator arrange
Page 109 and 110: • Overloading of lines • Increa
Page 111 and 112: FIGURE 2.9.23 34-kV, 25-MVAR (per p
Page 113 and 114: V 90 ( X X ) s T (2.9.10a) where,
Page 115 and 116: Therefore, Line reactive losses = (
Page 117 and 118: ate of rise of transient-recovery v
Page 119 and 120: the LLCR is provided in IEEE Std. C
Page 121 and 122: aluminum shielding, i.e., an oil-im
Page 123 and 124: Leo J. Savio ADAPT Corporation Ted
Page 125 and 126: 3.1.2.2.2 Heat Dissipation A second
Page 127 and 128: FIGURE 3.2.1 Solid-type bushing. ma
Page 129 and 130: 1.6 cm. This means that most of the
Page 131 and 132: where HS = steady-state bushing ho
Page 133 and 134: the conductivity of the water-solub
Page 135 and 136: of 178 ohm-m, and a test duration o
Page 137: 2. Easley, J.K. and Stockum, F.R.,
Page 141 and 142: FIGURE 3.3.10 LTC with delta connec
Page 143 and 144: 3.3.5 Selection of Load Tap Changer
Page 145 and 146: FIGURE 3.3.19 Effect of the leakage
Page 147 and 148: References Goosen, P.V. , Transform
Page 149 and 150: If i 1 is the full-load current rat
Page 151 and 152: TABLE 3.4.1 Loading Recommendations
Page 153 and 154: 3.5.4 Three-Phase Transformer Conne
Page 155 and 156: FIGURE 3.5.4 Interconnected star-gr
Page 157 and 158: 3.6.1.1 Standards ANSI standards fo
Page 159 and 160: ANSI standards. LTC control setting
Page 161 and 162: FIGURE 3.6.7 Discharging the capaci
Page 163 and 164: FIGURE 3.6.10 Standard switching-im
Page 165 and 166: voltage of the excited winding, rea
Page 167 and 168: FIGURE 3.6.18 Current, voltage, and
Page 169 and 170: TABLE 3.6.3 Transformer Short-Circu
Page 171 and 172: FIGURE 3.7.3 Control for voltage re
Page 173 and 174: FIGURE 3.7.6A Feeder with power-fac
Page 175 and 176: 3. Circulating current (current bal
Page 177 and 178: FIGURE 3.7.10 Control block diagram
Page 179 and 180: Primary Current (Amps) 60 40 20 0 -
Page 181 and 182: current transformer having two prim
Page 183 and 184: 87R1 87BL1 (A) Independent Harmonic
Page 185 and 186: Winding 1 Secondary Currents Data A
Page 187 and 188: Y Y 20 18 3 rd Harmonic CTR1=40 CTR
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230 kV 3 180 MVA 138 kV 5 CTR1 = 2
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29. Concordia, C. and Rothe, F.S.,
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FIGURE 3.9.1 Measurement of pressur
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H 2m 1. Vertical Forced Air 2. Prin
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Gade, S., Sound Intensity Instrumen
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nected. This steady-state voltage d
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where [A] = state matrix [B] = inpu
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where C = capacitance between the t
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L ijo = N i N j ijo (3.10.31) 1.4
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% VOLTAGE % VOLTAGE 100 BIL 90 50 3
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29. Degeneff, R.C., Reducing Storag
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All connections should be cleaned a
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6. Costs to set up and use a mobile
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Records of relay operation must be
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• Has heating occurred as the res
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a reference value) of the currents
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The next data-processing step is to
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temperature. As the transformer coo
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3.13.3.2 Instrument Transformers Th
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FIGURE 3.13.5 Analysis of bushing s
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temperature. Under abnormal conditi
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3.14.1.2 Accredited Standards Commi
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FIGURE 3.14.4 IEC technical-committ
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TABLE 3.14.2 Relevant Documents for
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TABLE 3.14.13 Relevant Documents fo
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