[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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TABLE 2.8.2 Characteristics of Load Type Used in the Test Measured Load Type Characteristic Resistive Resistive/Inductive Mixed Nonlinear 1 / 2 Load Full Load 1 / 2 Load Full Load 1 / 2 Load Full Load Apparent power, VA 435 953 475 948 603 993 True power factor 1.00 1.00 0.79 0.79 0.99 0.99 Displacement power factor 1.00 1.00 0.80 0.79 1.00 1.00 Output Voltage (Volts) 160 140 120 100 Output Voltage (Volts) 122 118 114 110 122 118 114 110 122 118 Resistive Load Resistive/Inductive Load Half Load Full Load 80 50 55 60 Input Frequency (Hz) FIGURE 2.8.11 Output-voltage amplitude resulting from variations in frequency of the ac input voltage. Distorted Input Ferro Output 65 70 114 Mixed Nonlinear Load 110 96 108 120 132 144 Input Voltage (Volts) FIGURE 2.8.10 Output-voltage regulation with varying input ac voltage. true power factor of 0.99. The amplitude of the ac input voltage was varied from 96 Vac (80% V nominal) to 144 Vac (120% V nominal) in 6-V increments. The input voltage and resulting output voltage of the CVT for each load type are shown in Figure 2.8.10. The ferroresonant transformer effectively reduces or eliminates the effects of several kinds of voltage variations in the electric-service supply. When the amplitude of the input voltage was varied ±20%, the fully loaded transformer had an output voltage well within ANSI-C84.1 limits (from +6% to –13%). 2.8.2.2.2 Performance: Frequency The CVT was half loaded with a purely resistive load. While the input voltage was fixed at 120 V, the frequency of the ac input voltage was varied from 50 Hz to 70 Hz in 1-Hz increments. The output voltage amplitude changed proportionally with the change in input frequency, ranging from 80% V nominal voltage at 50 Hz to 120% V nominal voltage at 70 Hz (see Figure 2.8.11). 2.8.2.2.3 Performance: Harmonics To test the ability of the transformer to filter out harmonics, a distorted input voltage (15.29% V total harmonic distortion [THD]) with 15.1% third-harmonic content was applied. The resulting output harmonic distortion was 2.9%, with mostly fifth-harmonic content (2.3%). The distorted input voltage and the filtered output voltage is shown in Figure 2.8.12. Notched Input Ferro Output FIGURE 2.8.12 Output voltages resulting from distorted and notched input voltages at full load. 2.8.2.2.4 Performance: Notching A notched voltage was applied to the input of the fully loaded transformer. As shown in Figure 2.8.12, the transformer successfully filtered the notched input voltage. 2.8.2.3 Application Considerations — Output Performance under Dynamic Supply Conditions The objective of this application was to characterize the CVT performance during power system disturbances such as momentary interruptions, sags, phase shifts, capacitor switching, and lightning strikes [10]. The CVT was connected to a full, purely resistive load. 2.8.2.3.1 Performance: Voltage Interruption The CVT was subjected to voltage interruptions lasting from 0.5 to 5 cycles and adjusted in 0.5-cycle increments. Switching from the normal supply voltage source to an open circuit created each interruption. The input and output voltages of the transformer during a three-cycle interruption are shown in Figure 2.8.13. During the three-cycle interruption, the CVT dropped out of the regulating mode (refer to jump resonance shown in Figure 2.8.5), and the output voltage decreased as the resonant capacitor in the CVT discharged. When the input voltage returned to normal, an overshoot occurred on the output voltage as the resonant capacitor recharged. Note that the CVT does not act as an uninterruptible power supply, which is designed to eliminate the effect of an interruption on the electric service supply, © 2004 by CRC Press LLC © 2004 by CRC Press LLC
Input with Interruption Ferro Output Input with Oscillating Transient Ferro Output Input with Sag Ferro Output Input with Impulsive Transient Ferro Output FIGURE 2.8.14 Output voltages resulting from oscillating and impulsive transients in the input voltages. Input with Phase Shift Ferro Output FIGURE 2.8.13 Output voltages (labeled ferro-output) resulting from voltage interruption, sag, and phase shift on the input. but it does slightly decrease the effect of an interruption by reducing it to a deep voltage sag. In conclusion, a CVT can moderately mitigate, but not eliminate, the effects of momentary voltage interruptions. 2.8.2.3.2 Performance: Voltage Sag To simulate a fault in the load’s electric-service supply, the input voltage to the CVT was decreased to 90%, 70%, and 58% of nominal voltage for one, two, three, four, and five cycles. The variations in the output voltages were measured and recorded for each of the applied voltage sags. Figure 2.8.13 shows the CVT’s input and output voltage waveforms down to 58% nominal voltage for sags lasting three cycles. In general, the input voltage sags produced output voltage sag having approximately the same duration but smaller sag depth. For example, during the nominal voltage sag to 58%, the CVT stayed in the regulation mode and reduced the effect of the sag to approximately 20% of nominal voltage lasting three cycles. Again, the recharging of the resonating capacitor caused an overshoot when the input voltage returned to normal. 2.8.2.3.3 Performance: Voltage Phase Shift To simulate the effects of a large load being switched off near the end of a long electric-service supply feeder, the input voltage of the CVT was shifted forward 10˚ while the input and output voltages were monitored and recorded. The phase shift occurred at the positive peak of the input voltage (see Figure 2.8.13). The resulting phase shift in the input voltage caused the output voltage to briefly swell. The CVT is sensitive to voltage phase shifts in the electric-service supply. 2.8.2.3.4 Performance: Oscillating Transient A transient caused by capacitor switching was simulated with a 500-Hz ring wave with a peak magnitude of 1 per unit and duration of 10 ms. The ring wave was applied to the positive peak of the input voltage. Figure 2.8.14 shows the input voltage with the ring-wave transient and the output voltage with a small impulsive transient. 2.8.2.3.5 Performance: Impulsive Transient To simulate a lightning strike, a 2-kV, 1.2/50-s combination wave (as described in ANSI C62.41-1991) was applied to the positive peak of the input voltage. As shown in Figure 2.8.14, the CVT significantly damped and filtered the surge. 2.8.2.4 Application Considerations — CVT <strong>Electric</strong>al Characteristics during Linear and Nonlinear Loading The objective of this application was to characterize the CVT as a load while the CVT supplied a simple linear load and while it supplied a complex nonlinear load [11]. In the following tests, the CVT was connected first to a simple linear load and then to a complex nonlinear load. An electric-service supply source with an average total harmonic distortion in the voltage of 3% supplied power to the CVT during all tests. 2.8.2.4.1 Performance: Line Current Distortion A resistive linear load consisting of incandescent lamps was connected to the output of the CVT. The load was increased in ten equal increments from 0 to 8.3 A (output current rating of the CVT). Next, a bridge rectifier (such as the type that might be used in electric-vehicle battery chargers) was connected to the CVT. The rectifier and its resistive load (incandescent lamps) were the complex nonlinear load of the CVT. By adding lamps, this complex load was increased in ten equal increments from approximately 0.4 A (rectifier with no lamps connected) to 8.3 A. Figure 2.8.15 and Figure 2.8.16 show the line-current distortion during these tests compared with the line-current distortion for the same loads connected directly to the electric-service supply. At no load, the power consumption of the CVT was approximately 120 W (core losses only). With the full linear load, total losses increased to approximately 134 W (core losses plus load losses); with the full nonlinear load, total losses dropped to approximately 110 W. Notice in Figure 2.8.15 and Figure 2.8.16 that, while the y-axis current-distortion magnitudes are significantly different, the absolute current-distortion values of the CVT’s input current with either linear or nonlinear load is nearly identical. Current distortion at the CVT’s input terminals was practically independent of the type of load connected to the output (approximately 40% at no loading to approximately 5% at full loading). When a linear, low-distortion load was connected to the CVT output, the CVT contributed to the current distortion at its input terminals from the electric-service power source, particularly during low loading. When a nonlinear, high-distortion load was connected, the CVT substantially reduced load-current distortion. When fully loaded, the CVT had relatively small power consumption and an efficiency of 85% to 90%. As opposed to most voltage regulators, the losses of the CVT decreased as the nonlinear load increased. The CVT also significantly affected the power factor of the load. © 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
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: TABLE 2.8.1 Typical Sizing Workshee
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
Page 129 and 130: 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
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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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TABLE 3.14.13 Relevant Documents fo
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[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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