[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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FIGURE 3.11.1 Conversion of dew point to vapor pressure. (Courtesy of Waukesha Electric Systems.) electricity can build up in the transformer and cause a problem for the assembly crew. A static discharge could cause a crew member to jump or move and lose their balance while assembling parts. Another item is to have all accessories to be assembled set close to the unit, as this eliminates a lot of lost time moving parts closer or from a storage yard. With the contractor setting the accessories close to the unit, you can usually save a day of assembly time. Keep in mind that some transformer manufactures “match-mark” each item. This means that each part has a specific location on the unit. Do not try to interchange the parts. Some manufacturers do not have this requirement, which allows bushings, radiators, and other parts to be assembled at the contractor or customer’s discretion. Weather is a major factor during the assembly of any transformer. Always have an ample supply of dry air flowing through the unit during the assembly. Be ready to seal the unit on positive pressure at the end of the day or if the weather turns bad. If the weather is questionable, keep the openings to a minimum and have everything ready to seal the unit. There are many types of contaminants that can cause a transformer to fail. Foreign objects dropped into the windings, dirt brought into the unit on the assemblers’ shoes, moisture left in the assembled parts, and misplaced or forgotten tools left inside are just a few items that could cause a failure. Take time to caution the assemblers about the preventions of contaminants and to follow good safety procedures. Again, an experienced contractor should have experienced assemblers and good assembly procedures in place. If weather conditions are a problem, there are many other assembly operations that can be done during marginal weather. The following are a few: 1. Uncrate all items. 2. Locate and count all hardware. 3. Clean bushings with denatured alcohol and cover. 4. Count and replace gaskets — if possible. FIGURE 3.11.2 Moisture equilibrium chart (with moisture content in percent of dry weight of insulation). (Courtesy of Waukesha Electric Systems.) Caution: Do not supply power to the control cabinet as it could back-feed into the inside current transformers, which could energize the primary and secondary bushings. A shock from the bushings could cause serious injury. 3.11.1.2 Bushings You need to read the installation manual to understand the correct lifting and assembly methods. There are a variety of bushings so it will save time to have read this information. All bushing surfaces should be cleaned again with denatured alcohol. This also includes the inside tube (draw-through type bushing). During shipment, even though the bushings may be protected, contaminants, such as moisture, could be found inside the bushing tube. The draw-through bushings have a conductive cable, or a rod, that has to be pulled through the bushing while it is being installed. In some cases, the corona shield on HV bushings should be removed and cleaned. There are also bottom connected bushings that require copper bus, a terminal, and hardware to secure the connection to the bushing and winding. © 2004 by CRC Press LLC © 2004 by CRC Press LLC
All connections should be cleaned and free of oxidation or corrosion and then wiped down with denatured alcohol. 3 After the installation of all bushings and all internal connections are made, another inspection should be made for the following: 1. Lead clearances. During the internal assembly work, some leads may have been moved. Check the manufacturer’s installation book for the necessary clearances. The information should include the basic installation level (bil) rating along with the clearances needed. 2. Bolted connections, done by the assemblers, should be inspected for proper clearances. 3. Wipe down and vacuum clean the inside of the unit around the assembly area to remove any dirt or oil smudges. 4. Operate the de-energized tap changer (DETC) and check its mechanical operation. 5. Check for items, such as tools, that may have been left inside during the assembly. 6. Replace man-hole gaskets, if required. Some units have conservators and require gas piping and oil piping connected to the transformer, after the man-hole covers are installed on the transformer and before pressure or vacuum cycles are started. 3.11.1.3 Oil Conservators Conservators are usually mounted on one end of the transformer and well above the cover and bushings. Conservators normally have a rubber bladder inside. This bladder expands or retracts due to the temperature of the oil vs. the ambient temperature. The inside of the bladder is connected to external piping, and then to a silica gel breather. All exposure of the oil to the air is eliminated, yet the bladder can flex. (See Fig. 3.11.3.) The oil supply piping, from the conservator to the transformer, should have at least one valve. The valve(s) must be closed during the vacuum cycle as the vacuum will try to pull the rubber bladder through the piping. The oil piping should have been cleaned prior to installation and the valves inspected. The conservator should have an inspection cover and the inside bladder inspected. While making this inspection, also check the operation of the oil float. (See Fig. 3.11.3.) 3.11.1.4 Gas Monitoring and Piping The piping is used to bring any combustible gases to a monitor. The monitor is usually located on the cover where it is visible from ground level. All gas piping should be cleaned by blowing dry air through them, or cleaning with a rag and denatured alcohol. Gas pipes are usually not connected to the gas monitor until after the vacuum/oil filling. The gas monitor could have tubing running down the side of the unit to allow ground-level sampling or bleeding of the line. There are other types of oil/gas monitors than the one shown in Fig. 3.11.4. 3.11.1.5 Radiators All radiators should be free of moisture and contaminants such as rust. If anything is found, the radiators should be cleaned and oil flushed with new transformer oil. The radiators may have to be replaced with new ones. Take time to inspect each radiator for bent fins or welding defects. If a problem is found, the repair should be made before installation. Touch-up painting, if needed, should be done, as it is difficult to reach all areas after the radiators are installed. During the radiator installation, all of the radiator valves need to be tested on at least 1 kg (2 lb) of pressure, or under oil, for a good seal. Some gaskets for mounting the radiator/valve mounting flange may have to be replaced. Coating the outside of the gasket with petroleum jelly protects the surface of the gasket during the radiator assembly. The radiator surface will then slide without damaging the gasket. 3 Some manufacturers will require all bushing gaskets to be replaced. Others furnish a Buta-N O-Ring that, in most cases, will not need replacing. FIGURE 3.11.3 Outline of typical relay installation on transformer cover. (Courtesy of Waukesha Electric Systems.) FIGURE 3.11.4 Conservator tank construction. (Courtesy of Waukesha Electric Systems.) 3.11.1.6 Coolers Coolers are oil to air heat exchangers which require oil pumps and usually less space around the transformer. Forced oil cooling can be controlled by a top oil or a winding temperature gauge, or both. All pumps, piping, and coolers should be inspected for contaminants before assembly. The correct pump rotation is an important checkpoint. 3.11.1.7 Load Tap Changers (LTC) Some LTCs mounted external to the main tank are shipped full of oil but you may want to make an internal inspection. After removing the oil you can inspect for problems. Check the manufacturer’s © 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
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FIGURE 2.7.22 Equalizer winding inc
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TABLE 2.7.4 Increase in Ampere Load
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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
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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
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V 90 ( X X ) s T (2.9.10a) where,
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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
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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
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References Goosen, P.V. , Transform
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If i 1 is the full-load current rat
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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
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: 29. Degeneff, R.C., Reducing Storag
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 241: TABLE 3.14.13 Relevant Documents fo
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