[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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circumvent the induction of different EMFs (electromotive force) in the strands due to different loops of strands linking with the leakage flux, which would involve circulating currents and further loss. Different forms of conductor transposition have been devised for this purpose. Ideally, each conductor element should occupy every possible position in the array of strands such that all elements have the same resistance and the same induced EMF. Conductor transposition, however, involves some sacrifice of winding space. If the winding depth is small, one transposition halfway through the winding is sufficient; or in the case of a two-layer winding, the transposition can be located at the junction of the layers. Windings of greater depth need three or more transpositions. An example of a continuously transposed conductor (CTC) cable, shown in Figure 1.10, is widely used in the industry. CTC cables are manufactured using transposing machines and are usually paper-insulated as part of the transposing operation. Stray losses can be a constraint on high-reactance designs. Losses can be controlled by using a combination of magnetic shunts and/or conducting shields to channel the flow of leakage flux external to the windings into low-loss paths. 1.4.4 Short-Circuit Forces Forces exist between current-carrying conductors when they are in an alternating-current field. These forces are determined using Equation 1.15: Thus and therefore B = I (1.16) F I 2 (1.17) Since the leakage flux field is between windings and has a rather high density, the forces under shortcircuit conditions can be quite high. This is a special area of transformer design. Complex computer programs are needed to obtain a reasonable representation of the field in different parts of the windings. Considerable research activity has been directed toward the study of mechanical stresses in the windings and the withstand criteria for different types of conductors and support systems. Between any two windings in a transformer, there are three possible sets of forces: • Radial repulsion forces due to currents flowing in opposition in the two windings • Axial repulsion forces due to currents in opposition when the electromagnetic centers of the two windings are not aligned • Axial compression forces in each winding due to currents flowing in the same direction in adjacent conductors where F = B I sin F = force on conductor B = local leakage flux density = angle between the leakage flux and the load current. In transformers, sin is almost always equal to 1 The most onerous forces are usually radial between windings. Outer windings rarely fail from hoop stress, but inner windings can suffer from one or the other of two failure modes: • Forced buckling, where the conductor between support sticks collapses due to inward bending into the oil-duct space • Free buckling, where the conductors bulge outwards as well as inwards at a few specific points on the circumference of the winding Forced buckling can be prevented by ensuring that the winding is tightly wound and is adequately supported by packing it back to the core. Free buckling can be prevented by ensuring that the winding is of sufficient mechanical strength to be self-supporting, without relying on packing back to the core. 1.4.5 Thermal Considerations The losses in the windings and the core cause temperature rises in the materials. This is another important area in which the temperatures must be limited to the long-term capability of the insulating materials. Refined paper is still used as the primary solid insulation in power transformers. Highly refined mineral oil is still used as the cooling and insulating medium in power transformers. Gases and vapors have been introduced in a limited number of special designs. The temperatures must be limited to the thermal capability of these materials. Again, this subject is quite broad and involved. It includes the calculation of the temperature rise of the cooling medium, the average and hottest-spot rise of the conductors and leads, and accurate specification of the heat-exchanger equipment. 1.4.6 Voltage Considerations A transformer must withstand a number of different normal and abnormal voltage stresses over its expected life. These voltages include: FIGURE 1.10 Continuously transposed conductor cable. • Operating voltages at the rated frequency • Rated-frequency overvoltages • Natural lightning impulses that strike the transformer or transmission lines • Switching surges that result from opening and closing of breakers and switches • Combinations of the above voltages © 2004 by CRC Press LLC © 2004 by CRC Press LLC
• Transient voltages generated due to resonance between the transformer and the network • Fast transient voltages generated by vacuum-switch operations or by the operation of disconnect switches in a gas-insulated bus-bar system This is a very specialized field in which the resulting voltage stresses must be calculated in the windings, and withstand criteria must be established for the different voltages and combinations of voltages. The designer must design the insulation system to withstand all of these stresses. References Kan, H., Problems related to cores of transformers and reactors, Electra, 94, 15–33, 1984. H. Jin Sim Scott H. Digby Waukesha Electric Systems Dudley L. Galloway Galloway Transformer Technology LLC Dan Mulkey Pacific Gas & Electric Company Gustav Preininger Consultant Sheldon P. Kennedy Niagara Transformer Corporation Paulette A. Payne PEPCO Randy Mullikin Kuhlman Electric Corp. Craig A. Colopy Cooper Power Systems Arindam Maitra Anish Gaikwad Arshad Mansoor Douglas Dorr EPRI PEAC Corporation Ralph Ferraro Ferraro, Oliver & Associates Richard F. Dudley Michael Sharp Antonio Castanheira Behdad Biglar Trench Ltd. 2 Equipment Types 2.1 Power Transformers Introduction • Rating and Classifications • Short-Circuit Duty • Efficiency, Losses, and Regulation • Construction • Accessory Equipment • Inrush Current • Transformers Connected Directly to Generators • Modern and Future Developments 2.2 Distribution Transformers Historical Background • Construction • General Transformer Design • Transformer Connections • Operational Concerns • Transformer Locations • Underground Distribution Transformers • Pad-Mounted Distribution Transformers • Transformer Losses • Transformer Performance Model • Transformer Loading • Transformer Testing • Transformer Protection • Economic Application 2.3 Phase-Shifting Transformers Introduction • Basic Principle of Application • Load Diagram of a PST • Total Power Transfer • Types of Phase-Shifting Transformers • Details of Transformer Design • Details of On- Load Tap-Changer Application • Other Aspects 2.4 Rectifier Transformers Background and Historical Perspective • New Terminology and Definitions • Rectifier Circuits • Commutating Impedance • Secondary Coupling • Generation of Harmonics • Harmonic Spectrum • Effects of Harmonic Currents on Transformers • Thermal Tests • Harmonic Cancellation • DC Current Content • Transformers Energized from a Converter/Inverter • Electrostatic Ground Shield • Load Conditions • Interphase Transformers 2.5 Dry-Type Transformers Transformer Taps • Cooling Classes for Dry-Type Transformers • Winding Insulation System • Application • Enclosures • Operating Conditions • Limits of Temperature Rise • Accessories • Surge Protection 2.6 Instrument Transformers Overview • Transformer Basics • Voltage Transformer • Current Transformer 2.7 Step-Voltage Regulators Introduction • Power Systems Applications • Ratings • Theory • Auto-Booster • Three-Phase Regulators • Regulator Control • Unique Applications 2.8 Constant-Voltage Transformers Background • Applications • Procurement Considerations • Typical Service, Storage, and Shipment Conditions • Nameplate Data and Nomenclature • New Technology Advancements • Addendum © 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: designer starts to make a design fo
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 and 46: Z = jX (2.3.19) 0.7 Then the curren
Page 47 and 48: X1 L* X1 S =X1 L X2 L* X3 L* a) S L
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
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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
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FIGURE 2.7.22 Equalizer winding inc
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TABLE 2.7.4 Increase in Ampere Load
Page 91 and 92:
References IEEE, Standard Requireme
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300% FIGURE 2.8.4 Schematic of a co
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TABLE 2.8.1 Typical Sizing Workshee
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Input with Interruption Ferro Outpu
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FIGURE 2.8.20A Performance of a rid
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• Input frequency or frequency ra
Page 103 and 104:
References 1. Sola/Hevi-Duty Corp.,
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FIGURE 2.9.5 Typical phase-reactor
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FIGURE 2.9.10 Two generator arrange
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• Overloading of lines • Increa
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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 = (
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ate of rise of transient-recovery v
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the LLCR is provided in IEEE Std. C
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aluminum shielding, i.e., an oil-im
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Leo J. Savio ADAPT Corporation Ted
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3.1.2.2.2 Heat Dissipation A second
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FIGURE 3.2.1 Solid-type bushing. ma
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1.6 cm. This means that most of the
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where HS = steady-state bushing ho
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the conductivity of the water-solub
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of 178 ohm-m, and a test duration o
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2. Easley, J.K. and Stockum, F.R.,
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FIGURE 3.3.5 Reactance-type LTC, in
Page 141 and 142:
FIGURE 3.3.10 LTC with delta connec
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3.3.5 Selection of Load Tap Changer
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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
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3.5.4 Three-Phase Transformer Conne
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FIGURE 3.5.4 Interconnected star-gr
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3.6.1.1 Standards ANSI standards fo
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ANSI standards. LTC control setting
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FIGURE 3.6.7 Discharging the capaci
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FIGURE 3.6.10 Standard switching-im
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voltage of the excited winding, rea
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FIGURE 3.6.18 Current, voltage, and
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TABLE 3.6.3 Transformer Short-Circu
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FIGURE 3.7.3 Control for voltage re
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FIGURE 3.7.6A Feeder with power-fac
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3. Circulating current (current bal
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FIGURE 3.7.10 Control block diagram
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Primary Current (Amps) 60 40 20 0 -
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current transformer having two prim
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87R1 87BL1 (A) Independent Harmonic
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Winding 1 Secondary Currents Data A
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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.,
Page 193 and 194:
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
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
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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
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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