[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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TABLE 2.6.4 Instrument Transformer Standards Country CT Standard VT Standard U.S. IEEE C57.13 IEEE C57.13 Canada CAN-C13-M83 CAN-C13-M83 IEC. 60044-1 (formerly 185) 60044-2 (formerly 186) U.K. BS 3938 BS 3941 Australia AS 1675 AS 1243 Japan JIS C 1731 JIS C 1731 flows out of the X1 terminal, making this polarity subtractive. These terminals are identified on the transformer by name and/or a white dot. 2.6.2.4 Industry Standards In the U.S., the utility industry relies heavily on IEEE C57.13, Requirements for Instrument Transformers. This standard establishes the basis for the test and manufacture of all instrument transformers used in this country. It defines the parameters for insulation class and accuracy class. The burdens listed in Table 2.6.3 are defined in IEEE C57.13. Often, standards for other electrical apparatus that may use instrument transformers have adopted their own criteria based on IEEE C57.13. These standards, along with utility practices and the National Electric Code, are used in conjunction with each other to ensure maximum safety and system reliability. The industrial market may also coordinate with Underwriters Laboratories. As the marketplace becomes global, there is a drive for standard harmonization with the International Electrotechnical Commission (IEC), but we are not quite there yet. It is important to know the international standards in use, and these are listed in Table 2.6.4. Most major countries originally developed their own standards. Today, many are beginning to adopt IEC standards to supersede their own. 2.6.2.5 Accuracy Classes Instrument transformers are rated by performance in conjunction with a secondary burden. As the burden increases, the accuracy class may, in fact, decrease. For revenue-metering use, the coordinates of ratio error and phase error must lie within a prescribed parallelogram, as seen in Figure 2.6.7 and Figure 2.6.8 for VTs and CTs, respectively. This parallelogram is based on a 0.6 system power factor (PF). The ratio error (RE) is converted into a ratio correction factor (RCF), which is simply FIGURE 2.6.7 Accuracy coordinates for VTs. RCF = 1 – (RE/100) (2.6.5) The total-error component is the transformer correction factor (TCF), which is the combined ratio and phase-angle error. The limits of phase-angle error are determined from the following relationship: PA tan TCF RCF 3438 (2.6.6) where TCF = transformer correction factor RCF = ratio correction factor PA = phase-angle error, min = supply-system PF angle + = for VTs only (see Figure 2.6.7) – = for CTs only (see Figure 2.6.8) 3438 = minutes of angle in 1 rad Therefore, using 0.6 system power factor ( = 53) and substituting in Equation 2.6.6, the relationship for VTs is TCF = RCF + (PA/2600) (2.6.7) FIGURE 2.6.8 Accuracy coordinates for CTs. © 2004 by CRC Press LLC © 2004 by CRC Press LLC
and for CTs is TCF = RCF – (PA/2600) (2.6.8) The TCF is mainly applied when the instrument transformer is being used to measure energy usage. From Table 2.6.5, the limits of TCF are also the same as RCF. A negative RE will yield an RCF > 1, while a positive RE will yield an RCF < 1. The “adopted” class in Table 2.6.5 is extrapolated from these relationships and is recognized in industry. The accuracy-class limits of the CT apply to the errors at 100% of rated current up through the rating factor of the CT. At 10% of rated current, the error limits permitted are twice that of the 100% class. There is no defined requirement for the current range between 10% and 100%, nor is there any requirement below 10%. There are certain instances in which the user is concerned about the errors at 5% and will rely on the manufacturer’s guidance. Because of the nonlinearity in the core and the ankle region, the errors at low flux densities are exponential. As the current and flux density increase, the errors become linear up until the core is driven into saturation, at which point the errors increase at a tremendous rate (see Figure 2.6.9). Trends today are driving accuracy classes to 0.15%. Although not yet recognized by IEEE C57.13, manufacturers and utilities are establishing acceptable guidelines that may soon become part of the standard. With much cogeneration, the need to meter at extremely low currents with the same CT used TABLE 2.6.5 Accuracy Classes Accuracy Class RCF Range Phase Range, min TCF Range New 0.15 1.0015–0.9985 ± 7.8 1.0015–0.9985 IEEE C57.13 0.3 1.003–0.997 ± 15.6 1.003–0.997 IEEE C57.13 0.6 1.006–0.994 ± 31.2 1.006–0.994 IEEE C57.13 1.2 1.012–0.988 ± 62.4 1.012–0.988 IEEE C57.13 2.4 1.024–0.976 ± 124.8 1.024–0.976 Adopted 4.8 1.048–0.952 ± 249.6 1.048–0.952 for regular loads has forced extended-range performance to be constant from rating factor down to 1% of rated current. This is quite a deviation from the traditional class. In the case of the VT, the accuracy-class range is between 90% and 110% of rated voltage for each designated burden. Unlike the CT, the accuracy class is maintained throughout the entire range. The manufacturer will provide test data at 100% rated voltage, but it can furnish test data at other levels if required by the end user. The response is somewhat linear over a long range below 90%. Since the normal operating flux densities are much higher than in the CT, saturation will occur much sooner at voltages above 110%, depending on the overvoltage rating. Protection, or relay class, is based on the instrument transformer’s performance at some defined fault level. In VTs it may also be associated with an under- and overvoltage condition. In this case, the VT may have errors as high as 5% at levels as low as 5% of rated voltage and at the VT overvoltage rating. In CTs, the accuracy is based on a terminal voltage developed at 20 times nominal rated current. The limits of RCF are 0.90 to 1.10, or 10% RE from nominal through 20 times nominal. This applies to rated burden or any burden less than rated burden. 2.6.2.6 Insulation Systems The insulation system is one of the most important features of the instrument transformer, establishing its construction, the insulation medium, and the unit’s overall physical size. The insulation system is determined by three major criteria: dielectric requirements, thermal requirements, and environmental requirements. Dielectric requirements are based on the source voltage to which the instrument transformer will be connected. This source will define voltage-withstand levels and basic impulse-insulation levels (BIL). In some cases, the instrument transformer may have to satisfy higher levels, depending on the equipment with which they are used. Equipment such as power switchgear and isolated-phase bus, for instance, use instrument transformers within their assembly, but they have test requirements that differ from the instrument-transformer standard. It is not uncommon to require a higher BIL class for use in a highly polluted environment. See Table 2.6.6A and Table 2.6.6B. TABLE 2.6.6A Low- and Medium-Voltage Dielectric Requirements Class, kV Instrument Transformers (IEEE C57.13) Other Equipment Standards a BIL, kV Withstand Voltage, kV BIL, kV Withstand Voltage, kV 0.6 10 4 — 2.2 1.2 30 10 — — 2.4 45 15 — — 5.0 60 19 60 19 8.7 75 26 75/95 26/36 15.0 95/110 34 95/110 36/50 25.0 125/150 40/50 125/150 60 34.5 200 70 150 80 46 250 95 — — 69 350 140 350 160 a IEEE C37.06, C37.20.1, C37.20.2,C37.20.3, C37.23. TABLE 2.6.6B High-Voltage Dielectric Requirements FIGURE 2.6.9 CT RCF characteristic curve. Class, kV Instrument Transformers (IEEE C57.13) Other Equipment Standards (IEEE C37.06) BIL, kV Withstand Voltage, kV BIL, kV Withstand Voltage, kV 115 450/550 185/230 550 215/260 138 650 275 650 310 161 750 325 750 365 230 900/1050 395/460 900 425 345 1300 575 1300 555 500 1675/1800 750/800 1800 860 765 2050 920 2050 960 © 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
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
Page 65 and 66: FIGURE 2.6.1 Typical wiring and sin
Page 67: a) H1 b) Ip X2 FLUX H2 LEAKAGE FLUX
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
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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
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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.,
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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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Page 239 and 240:
Page 241:
TABLE 3.14.13 Relevant Documents fo
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