[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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FIGURE 2.7.24 Voltage regulation on the source side (Type B). FIGURE 2.7.26 Connection of three-phase regulator regulating a three-phase, four-wire, multigrounded wye circuit. FIGURE 2.7.25 Single-phase Auto-Booster® four-step voltage regulator. 2.7.5 Auto-Booster ® Another type of voltage regulator available in the industry, in addition to the 32-step single phase, is the Auto-Booster® single-phase four-step voltage regulator. This voltage-regulating device, shown in Figure 2.7.25, is mainly used for boosting voltage on laterals off the distribution system feeders. The voltage ratings range from 2,400 to 19,920, while the ampere ratings are either 50 A or 100 A. The design is a 65º winding rise Type B construction providing 10% or +6% regulation in four steps of 2 1 / 2% or 1 1 / 2%, respectively. The tap changer incorporates resistors to provide the impedance during the switching cycle. 2.7.6 Three-Phase Regulators If feeders have similar load characteristics and load-center voltage requirements — and if the incoming supply voltage is balanced — then the distribution side of the substation bus can be regulated by a threephase regulator. The choice of using a three-phase or three single-phase regulators depends on several factors, including cost and the need for unbalance correction. With a three-phase unit there is no capability to correct for voltage imbalances caused by unequal loading. If the load is predominantly threephase, or consistently balanced, a three-phase unit may be the better choice. However, most rural distribution systems contain only a small percentage of balanced three-phase loads. Therefore threephase regulators are less common in the industry than the single-phase step-voltage regulators. Chief among the benefits of single-phase regulation is the ability of the single-phase voltage regulators to correct system unbalance. Each phase is regulated to a given set point, irrespective of what is going on with the other two phases. Basic theory behind the design of three-phase regulators is similar to single-phase regulators. Essentially, three single-phase regulators are located in the same tank with their tap changers ganged together and being operated and monitored by one control. The three-phase regulator has only one of its phases monitored to provide a current and voltage supply to the control. Thus all three phases are regulated based on the monitoring of one phase. This is fine for a system that has balanced loads on all three phases. Figure 2.7.26 shows a three-phase regulator connected to a four-wire system. The phasor diagram is similar to the one shown in Figure 2.7.5. The three-phase voltage regulators, up to 13.8 kV, inclusive, with a continuous-current rating of 668 A and below, can be loaded in excess of their rated ampere load if the range of voltage regulation is limited at a value less than the normal 10% value. Table 2.7.4 shows the percent increase in ampere load permitted on each three-phase step-voltage regulator when the percent regulation range is limited to values of 10%, 8_%, 7_%, 6_%, and 5%. Three-phase voltage regulators are available in the common ratings shown in Table 2.7.5. 2.7.7 Regulator Control The purpose of the regulator control is to provide an output action as a result of changing input conditions, in accordance with preset values that are selected by the regulator user. The output action is the energization of the motorized tap changer to change taps to maintain the correct regulator output voltage. The changing input is the output-load voltage and current from an internal voltage transformer © 2004 by CRC Press LLC © 2004 by CRC Press LLC
TABLE 2.7.4 Increase in Ampere Load Permitted on Each Three-Phase Step- Voltage Regulator at Five Levels of Voltage Regulation Range of Voltage Regulation, % Continuous Current Rating, % 10.0 100 8.75 108 7.5 115 6.25 120 5.0 130 TABLE 2.7.5 Common Ratings for Three-Phase Voltage Regulators Rated Volts BIL, kV Rated kVA Load Current, A 7,620/13,200 wye 95 500 219 750 328 1000 437 1500 656 2000 874 2500 1093 3000 1312 19,920/34,500 wye 150 500 84 750 126 1000 167 1500 251 2000 335 2500 418 3000 502 or control winding and current transformer, as shown previously in Figure 2.7.23 and Figure 2.7.24, respectively. The preset values are the values the regulator user has selected as control parameters for the regulated voltage. Basic regulator control settings are: • Set voltage • Bandwidth • Time delay • Line-drop resistive and reactive compensation 2.7.7.1 Set Voltage The control set voltage is dependent upon the regulator rating and the system voltage on which it is installed. The regulator nameplate shows the voltage transformer or shunt winding/control ratio that corresponds to the system voltage. The regulator load voltage is the product of this ratio and the control set voltage. If the winding ratio of the internal voltage transformer of the step-voltage regulator is the same as that of a typical distribution transformer on the system, the voltage level is simply the desired voltage, given on a 120-V base. However, the regulator voltage-transformer ratio is not always the same, and it may be necessary to calculate an equivalent value that corresponds to 120 V on the distribution transformer secondary. Equation 2.7.3 can be used to find this equivalent voltage value. 63.5 V 60 120 127 V (2.7.4) Normally the operator sets the voltage level at a minimum value that is required at the location, which is usually above the optimum level, e.g., 122 V. 2.7.7.2 Bandwidth The bandwidth is the total voltage range around the set-voltage value, which the control will consider as a satisfied condition. For example, a 2-V bandwidth on a 120-V setting means that the control will not activate a tap change until the voltage is above 121 V or below 119 V. The bandwidth is generally kept quite narrow in order to keep the voltage as close as possible to the desired level. Increasing the bandwidth may reduce the number of tap-change operations, but at the expense of voltage quality. The regulators in a substation or on a main feeder tend to have their bandwidths set at a smaller setting than units located on laterals that feed isolated loads. A minimum bandwidth of two times the volts per tap (5/8% or 0.75 V) of the regulator is recommended; this correlates to 1.5 V on most regulators. 2.7.7.3 Time Delay The time delay is the period of time in seconds that the control waits from the time the voltage goes out of band to when power is applied to the tap-changer motor to make a tap change. Many voltage fluctuations are temporary in nature, such as those resulting from motor starting, or even from fault conditions. It is not desirable to have the step-voltage regulator change taps for these momentary voltage swings. By specifying a time-delay value of 15 or 30 sec, for example, the regulator will ignore the vast majority of these temporary voltage swings and only operate when the voltage change is more long term, such as from adding or subtracting load. A general recommendation is a minimum time delay of 15 sec. This length of time covers the vast majority of temporary voltage swings due to equipment starting, coldload pickup, etc. The time-delay setting also has another important benefit when attempting to coordinate two or more regulators in series along the line. One common situation would be to have a regulator bank at the substation providing whole-feeder regulation, with a line regulator out on the feeder to regulate a specific load. The substation regulators should be the first to respond to voltage changes on the system, with the line regulator adjusting as needed for its individual area. By setting the time delay of the line regulator higher that of the substation bank, the substation bank will respond first and regulate the voltage as best it can. If the substation regulation is sufficient to return the feeder voltage to within the bandwidth of the line regulator, that regulator will not need to operate. The suggested minimum time-delay difference between banks of regulators is 15 sec. This coordination between cascading banks of regulators, as shown in Figure 2.7.27, eliminates unnecessary hunting, thus improving efficiency. Distribution <strong>Transformer</strong> Ratio V 120 Regulator PT Ratio (2.7.3) For example, if the distribution transformers are connected 7620/120, this gives a ratio of 63.5:1. If the regulator voltage-transformer ratio is 60:1, the equivalent voltage-level setting, from Equation 2.7.3, is found to be: FIGURE 2.7.27 Cascading single-phase voltage regulators. © 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
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: FIGURE 2.7.22 Equalizer winding inc
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
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.,
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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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TABLE 3.14.13 Relevant Documents fo
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