[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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2 2 VL Q0 * X VLa VS * VL * 2 2 ( P * X) ( V Q * X) 0 2 P0 * X VLr VS * VL * 2 2 ( P * X) ( V Q * X) 0 L L 0 0 2 2 (2.3.28) (2.3.29) V V* 2* sin / 2 (2.3.35) V V * cos / 2* 3 (2.3.36) and with I S = I L = I, the part of the current that is transferred to the exciting winding becomes 2.3.5 Types of Phase-Shifting <strong>Transformer</strong>s L (2.3.30) 2.3.5.1 General Aspects The general principle to obtain a phase shift is based on the connection of a segment of one phase with another phase. To obtain a 90˚ additional voltage V, the use of delta-connected winding offers the simplest solution. Figure 2.3.8 shows a possible arrangement and is used to introduce a few basic definitions. The secondary winding of phase V 2 – V 3 is split up into two halves and is connected in series with phase V 1 . By designing this winding as a regulating winding and using on-load tap changers (OLTC), V and the phase-shift angle can be changed under load. The phasor diagram has been plotted for noload conditions, i.e., without considering the voltage drop in the unit. It also should be noted that the currents in the two halves of the series winding are not in phase. This is different from normal power transformers and has consequences with respect to the internal stray field. From the connection diagram (Figure 2.3.8a), the following equations can be derived: From the phasor diagram (Figure 2.3.8b) follows (V S1 = V L1 = V): S I S1 V 30 FIGURE 2.3.8 Single core symmetrical PST. P * X arctan ( P * X) ( V Q * X) ,V 1 V 10 V 20 V, 0 0 2 2 L 0 2 V S1 = V 10 + (V 1 /2) (2.3.31) V L1 = V 10 –(V 1 /2) (2.3.32) V 1 = V S1 – V L1 (2.3.33) V V* cos / 0 2 L I L1 V L1 V S1 V 10 ,V 1 I L1 I S1 = I , V 30 V 20 a) b) (2.3.34) The throughput power can be calculated from I V 2 * I* cos / 2 I* * sin / 2 V 3 P 3* V * I SYS and the rated design power, which determines the size of the PST, becomes P 3* V* I P * 2* sin / 2 T (2.3.37) (2.3.38) (2.3.39) A third kind of power (P ) is the power that is transferred into the secondary circuit. This power is different from P T because a part of the primary current is compensated between the two parts of the series winding itself. In two-core designs (see Equation 2.3.33), this power determines also the necessary breaking capability of the OLTC. 1 P V * I * P SYS * sin (2.3.40) 3 In addition to the transferred power, the phase-shift angle is also important. A phase-shift angle of 20˚ means that the PST has to be designed for 34.8% of the throughput power, and an angle of 40˚ would require 68.4%. In this respect, it has to be considered that the effective phase-shift angle under load is smaller than the no-load phase-shift angle. In the optimum case when the load power factor is close to 1, a PST impedance of 15% would reduce the load phase-shift angle by 8.5˚ (Equations 2.3.14 and 2.3.16). In practice, various solutions are possible to design a PST. The major factors influencing the choice are: • Throughput power and phase-shift angle requirement • Rated voltage • Short-circuit capability of the connected systems • Shipping limitations • Load tap-changer performance specification In addition, preferences of a manufacturer as to the type of transformer (core or shell) or type of windings and other design characteristics may also play a role. Depending on the rating, single- or two-core designs are used. Two-core designs may require either a one-tank or a two-tank design. 2.3.5.2 Single-Core Design Symmetrical conditions are obtained with the design outlined in Figure 2.3.8a. Figure 2.3.9a and Figure 2.3.9b show the general connection diagrams with more details of the regulating circuit. The advantage of the single-core design is simplicity and economy. But there are also a number of disadvantages. The OLTCs are connected to the system and directly exposed to all overvoltages and through faults. The voltage per OLTC step and the current are determined by the specification and do not always permit an optimal economical choice of the OLTC. The short-circuit impedance of the PST varies between a maximum and zero. Therefore, it can not be planned that the PST will contribute to the limitation of fault currents in the system. SYS © 2004 by CRC Press LLC © 2004 by CRC Press LLC
X1 L* X1 S =X1 L X2 L* X3 L* a) S L H1 H2 H3 H0 Change-over Selector H1 K Tap Selector K Diverter Switch H3 H2 X1 X2 X3 X0 X3 S =X3 L b) L X2 S =X1 L S V L ,V V S FIGURE 2.3.10 Regulating transformer with PST effect. K S1 S2 S3 L1 L2 L3 S1 L1* FIGURE 2.3.9 (a) Single-core symmetrical PST (b) Single-core unsymmetrical PST. L3* S2 The advantage of the symmetrical design (Figure 2.3.9a) is that the phase-shift angle is the only parameter that influences the power flow. The design needs two single-phase OLTCs (for low ratings, one two-phase OLTC may be used instead) per phase or two three-phase OLTCs. Figure 2.3.9b shows an unsymmetrical solution. Only one-half of the regulating windings is used. The number of necessary OLTCs is reduced, but the ratio between source voltage and load voltage changes with the phase-shift angle and additionally influences the power flow. A solution that often is used for transformers interconnecting two systems is shown in Figure 2.3.10. The tap winding of a regulating transformer can be connected to a different phase, causing a voltage shift between the regulated winding and the other windings of the unit. The regulated winding normally is connected to the source side, but indirect regulation of the load-side is also possible. The change from the normal regulating transformer state to the phase-shifting state is possible in the middle position of the OLTC without the need to switch off the unit. Another solution of a symmetrical PST, the delta-hexagonal phase-shifting transformer, is shown in Figure 2.3.11. 2.3.5.3 Two-Core Design The most commonly used circuit for a two-core design is shown in Figure 2.3.12. This configuration consists of a series unit and a main unit. For smaller ratings and lower voltages, two-core PSTs can be built into a single tank, while larger ratings and higher-voltage PSTs require a two-tank design. The advantage of a two-core design is the flexibility in selecting the step voltage and the current of the regulating winding. These can be optimized in line with the voltage and current ratings of the OLTC. FIGURE 2.3.11 Delta-hexagonal PST. Since OLTCs have limited current ratings and step voltages per phase as well as limited switching capacity, they are the main limiting features for the maximum possible rating of PSTs. More than one OLTC per phase may have to be utilized for very large ratings. Up to a certain rating, three-pole OLTCs can be used; for higher ratings, three single-pole OLTCs are necessary. The OLTC insulation level is independent of the system voltage and can be kept low. The short-circuit impedance is the sum of the impedances of the main and series transformers. Because the impedance of the series unit is constant and independent from the phase angle, the unit can be designed to be self-protecting, and the variation of the impedance with the phase-shift angle can be kept small when the impedance of the main unit is kept low. 2.3.5.4 Quadrature Booster <strong>Transformer</strong>s Quadrature booster transformers are a combination of a regulating power- or auto-transformer with a phase-shifting transformer. The PST, which can be a single- or two-core design, is supplied from the regulated side of the power transformer (Figure 2.3.13). By this method, the output voltage can be adjusted in a four-quadrant (magnitude and phase) relationship. S3 Retard Position L2* © 2004 by CRC Press LLC © 2004 by CRC Press LLC
Page 1 and 2: ELECTRIC POWER TRANSFORMER ENGINEER
Page 3 and 4: I wish to recognize the interest of
Page 5 and 6: Contents 1 Theory and Principles Ch
Page 7 and 8: 1.3 Equivalent Circuit of an Iron-C
Page 9 and 10: designer starts to make a design fo
Page 11 and 12: • Transient voltages generated du
Page 13 and 14: the transformer’s bushings and, m
Page 15 and 16: % regulation = [(V NL - V FL )/V FL
Page 17 and 18: In core-form transformers, the wind
Page 19 and 20: FIGURE 2.1.14 Layer windings (singl
Page 21 and 22: the transformer design, which may b
Page 23 and 24: consumer’s service circuit is a d
Page 25 and 26: FIGURE 2.2.3 Single-phase transform
Page 27 and 28: is installed so that the tank never
Page 29 and 30: above which persons might be burned
Page 31 and 32: FIGURE 2.2.16 Two-bushing subway. (
Page 33 and 34: carbon steel or the very expensive
Page 35 and 36: FIGURE 2.2.31 Radial-style dead fro
Page 37 and 38: FIGURE 2.2.36 Complete transformer
Page 39 and 40: voltage in each winding simultaneou
Page 41 and 42: mounted transformers can have arres
Page 43 and 44: V S + V S I V L Z=R+jX a) V L V S V
Page 45: Z = jX (2.3.19) 0.7 Then the curren
Page 49 and 50: 150 V(%) 100 50 0 -50 40 80 T(s) 12
Page 51 and 52: 2.3.8.1.2 Series Connection • The
Page 53 and 54: A six-pulse single-way transformer
Page 55 and 56: The degree of coupling also influen
Page 57 and 58: where I h = current for the hth har
Page 59 and 60: In the case of liquid-filled transf
Page 61 and 62: FIGURE 2.4.21 A 36-pulse system mad
Page 63 and 64: Vacuum-pressure encaps ulated — T
Page 65 and 66: FIGURE 2.6.1 Typical wiring and sin
Page 67 and 68: a) H1 b) Ip X2 FLUX H2 LEAKAGE FLUX
Page 69 and 70: and for CTs is TCF = RCF - (PA/2600
Page 71 and 72: RCF x Bx Bt RCF t - RCF 0 co
Page 73 and 74: 2000 1000 5% Vex BANDWITH FROM NOMI
Page 75 and 76: This may be more useful when operat
Page 77 and 78: also some uncertainty in repeatabil
Page 79 and 80: FIGURE 2.6.25 Standard two-element
Page 81 and 82: 2.7 Step-Voltage Regulators Craig A
Page 83 and 84: Source Bypass Switch Source Bypass
Page 85 and 86: 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
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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 and 138:
2. Easley, J.K. and Stockum, F.R.,
Page 139 and 140:
FIGURE 3.3.5 Reactance-type LTC, in
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
Page 189 and 190:
230 kV 3 180 MVA 138 kV 5 CTR1 = 2
Page 191 and 192:
29. Concordia, C. and Rothe, F.S.,
Page 193 and 194:
FIGURE 3.9.1 Measurement of pressur
Page 195 and 196:
H 2m 1. Vertical Forced Air 2. Prin
Page 197 and 198:
Gade, S., Sound Intensity Instrumen
Page 199 and 200:
nected. This steady-state voltage d
Page 201 and 202:
where [A] = state matrix [B] = inpu
Page 203 and 204:
where C = capacitance between the t
Page 205 and 206:
L ijo = N i N j ijo (3.10.31) 1.4
Page 207 and 208:
% VOLTAGE % VOLTAGE 100 BIL 90 50 3
Page 209 and 210:
29. Degeneff, R.C., Reducing Storag
Page 211 and 212:
All connections should be cleaned a
Page 213 and 214:
6. Costs to set up and use a mobile
Page 215 and 216:
Records of relay operation must be
Page 217 and 218:
• Has heating occurred as the res
Page 219 and 220:
a reference value) of the currents
Page 221 and 222:
The next data-processing step is to
Page 223 and 224:
temperature. As the transformer coo
Page 225 and 226:
3.13.3.2 Instrument Transformers Th
Page 227 and 228:
FIGURE 3.13.5 Analysis of bushing s
Page 229 and 230:
temperature. Under abnormal conditi
Page 231 and 232:
3.14.1.2 Accredited Standards Commi
Page 233 and 234:
FIGURE 3.14.4 IEC technical-committ
Page 235 and 236:
TABLE 3.14.2 Relevant Documents for
Page 237 and 238:
Page 239 and 240:
Page 241:
TABLE 3.14.13 Relevant Documents fo
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[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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