[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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FIGURE 2.2.23 Six-bushing horizontal. (By permission of Pacific Gas & Electric Company, San Francisco, CA.) FIGURE 2.2.21 Four-bushing horizontal installed. (By permission of Pacific Gas & Electric Company, San Francisco, CA.) FIGURE 2.2.24 Three-phase submersible. (By permission of Pacific Gas & Electric Company, San Francisco, CA.) FIGURE 2.2.22 Four-bushing horizontal. (By permission of Pacific Gas & Electric Company, San Francisco, CA.) or concrete. Installations have been made with and without a solid bottom. Those without a solid bottom simply rest on a gravel base. 2.2.7.2.2 Single-Phase Horizontal Submersible Functionally, these are the same as the round single-phase. However, they are designed to be installed in a rectangular enclosure, as shown in Figure 2.2.21. Three low-voltage cable leads are provided through 100 kVA, while the 167-kVA size has six. They are manufactured in both four-primary-bushing designs (Figure 2.2.22) and in six-primary-bushing designs (Fig. 2.2.23). As well as the normal single-phase versions, there is also a duplex version. This is used to supply four-wire, three-phase, 120/240-V services from two core-coil assemblies connected open-delta on the secondary side. The primary can be either open-delta or open-wye. Horizontal transformers also have been in use since the early 1960s. These units are not specifically covered by a national standard. The enclosures used have included treated plywood, fiberglass, and concrete. The plywood and fiberglass enclosures are typically bottomless, with the transformer resting on a gravel base. 2.2.7.2.3 Three-Phase Submersible The three-phase surface-operable units are detailed in C57.12.24 (ANSI, 2000b). Typical application for these transformers is to serve three-phase commercial loads from loop-feed primary underground cables. Primary voltages are available from 2,400 through 34,500 V. The standard three-phase kVA ratings from 75 to 1000 kVA are available with secondary voltage of 208Y/120 V. With a 480Y/277-V secondary, the available sizes are 75 to 2500 kVA. Figure 2.2.24 depicts a three-phase submersible. Protection options include: • Dry-well current-limiting fuses with an interlocked switch to prevent the fuses from being removed while energized • Submersible bayonet fuses with backup, under-oil, partial-range, current-limiting fuses, or with backup internal nonreplaceable primary-expulsion fuse elements. These are commonly installed in concrete rectangular boxes with removable cover sections. 2.2.7.3 Vault and Subsurface Common Elements 2.2.7.3.1 Tank Material The substrate and coating should meet the requirements detailed in C57.12.32 (ANSI, 2002a). The smaller units can be constructed out of 400-series or 300-series stainless steels or out of mild carbon steel. In general, 300-series stainless steel outperforms 400-series stainless steel, which significantly outperforms mild carbon steel. Most of the small units are manufactured out of 400-series stainless steel, since it is significantly less expensive than 300-series. Stainless steels from the 400-series with a good coating have been found to give satisfactory field performance. Due to lack of material availability, many of the larger units cannot be manufactured from 400-series stainless. With the choice then being limited to mild © 2004 by CRC Press LLC © 2004 by CRC Press LLC
carbon steel or the very expensive 300-series stainless, most of the large units are constructed out of mild carbon steel. 2.2.7.3.2 Temperature Rating Kilovoltampere ratings are based on not exceeding an average winding temperature rise of 55C and a hottest-spot temperature rise of 70C. However, they are constructed with the same 65C rise insulation systems used in overhead and pad-mounted transformers. This allows for continuous operation at rated kVA provided that the enclosure ambient air temperature does not exceed 50C and the average temperature does not exceed 40C. Utilities commonly restrict loading on underground units to a lower limit than they do with pad-mounted or overhead units. 2.2.7.3.3 Siting Subsurface units should not be installed if any of the following conditions apply: • Soil is severely corrosive. • Heavy soil erosion occurs. • High water table causes repeated flooding of the enclosures. • Heavy snowfall occurs. • A severe mosquito problem exists. 2.2.7.3.4 Maintenance Maintenance mainly consists of keeping the enclosure and the air vents free of foreign material. Dirt allowed to stay packed against the tank can lead to accelerated anaerobic corrosion, resulting in tank puncture and loss of mineral oil. 2.2.7.4 Emerging Issues 2.2.7.4.1 Water Pumping Pumping of water from subsurface enclosures has been increasingly regulated. In some areas, water with any oily residue or turbidity must be collected for hazardous-waste disposal. Subsurface and vault enclosures are often subject to runoff water from streets. This water can include oily residue from vehicles. So even without a leak from the equipment, water collected in the enclosure may be judged a hazardous waste. 2.2.7.4.2 Solid Insulation Transformers with solid insulation are commercially available for subsurface distribution applications (see Figure 2.2.25) with ratings up 167 kVA single-phase and 500 kVA three-phase. The total encapsulation of what is essentially a dry-type transformer allows it to be applied in a subsurface environment (direct buried or in a subsurface vault). The solid insulation distribution transformer addresses problems often associated with underground and direct buried transformers. See Sections 2.2.6.2 and 2.2.6.3. Such installations can be out of sight, below grade, and not subject to corrosion and contamination. Padmounted and pole-mounted versions are also available. 2.2.8 Pad-Mounted Distribution Transformers Pad-mounted transformers are the most commonly used type of transformer for serving loads from underground distribution systems. They offer many advantages over subsurface, vault, or subway transformers. • Installation: less expensive to purchase and easier to install • Maintenance: easier to maintain • Operability: easier to find, less time to open and operate • Loading: utilities often assign higher loading limits to pad-mounted transformers as opposed to surface-operable or vault units. FIGURE 2.2.25 Solid-insulation distribution transformer. (By permission of ABB Inc., Quebec.) Many users and suppliers break distribution transformers into just two major categories – overhead and underground, with pad-mounted transformers included in the underground category. The IEEE standards, however, divide distribution transformers into three categories – overhead, underground, and pad-mounted. Pad-mounted transformers are manufactured as either: • Single-phase or three-phase units: Single-phase units are designed to transform only one phase. Three-phase units transform all three phases. Most three-phase transformers use a single-, three-, four-, or five-legged core structure, although duplex or triplex construction is used on occasion. • Loop or radial units: Loop-style units have the capability of terminating two primary conductors per phase. Radial-style units can only terminate one primary cable per phase. The primary must end at a radial-style unit, but from a loop style it can continue on to serve other units. • Live-front or dead-front units: Live-front units have the primary cables terminated in a stress cone supported by a bushing. Thus the primary has exposed energized metal, or “live,” parts. Deadfront units use primary cables that are terminated with high-voltage separable insulated connectors. Thus the primary has all “dead” parts — no exposed energized metal. 2.2.8.1 Single-Phase Pad-Mounted Transformers Single-phase pad-mounted transformers are usually applied to serve residential subdivisions. Most singlephase transformers are manufactured as clamshell, dead-front, loop-type with an internal 200-A primary bus designed to allow the primary to loop through and continue on to feed the next transformer. These are detailed in the IEEE Standard C57.12.25 (ANSI, 1990). The standard assumes that the residential subdivision is served by a one-wire primary extension. It details two terminal arrangements for loopfeed systems: Type 1 (Figure 2.2.26) and Type 2 (Figure 2.2.27). Both have two primary bushings and three secondary bushings. The primary is always on the left facing the transformer bushings with the cabinet hood open, and the secondary is on the right. There is no barrier or division between the primary and secondary. In the Type 1 units, both primary and secondary cables rise directly up from the pad. In Type 2 units, the primary rises from the right and crosses the secondary cables that rise from the left. Type 2 units can be shorter than the Type 1 units, since the crossed cable configuration gives enough free cable length to operate the elbow without requiring the bushing to be placed as high. Although not detailed in the national standard, there are units built with four and with six primary bushings. The four-bushing unit is used for single-phase lines, with the transformers connected phase-to-phase. The six-primary-bushing units are used to supply single-phase loads from three-phase taps. Terminating all of the phases in the transformer allows all of the phases to be sectionalized at the same location. The internal single-phase transformer can be connected either phase-to-phase or phase-to-ground. The © 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: FIGURE 2.2.16 Two-bushing subway. (
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
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
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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.,
Page 105 and 106:
FIGURE 2.9.5 Typical phase-reactor
Page 107 and 108:
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 = (
Page 117 and 118:
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
Page 131 and 132:
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
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
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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
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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
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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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