[James_H._Harlow]_Electric_Power_Transformer_Engin(BookSee.org)

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FIGURE 3.13.9 Sample differential-temperature measurement. The top trace is the main-tank top-oil temperature, and the bottom trace is the LTC compartment temperature. FIGURE 3.13.7 Load-tap-changer motor current during a tap-changing event. FIGURE 3.13.8 Sample motor-current-index curve. 3.13.3.4.2 Thermal Diagnostics for On-Load Tap Changers A variety of diagnostic algorithms for on-load tap changers can be implemented using temperature data. The heat-transfer pattern resulting from energy losses results in a temperature profile that is easily measured with external temperature sensors. Temperature profiles are normally influenced by weather conditions, cooling-bank status, and electrical load. However, abnormal sources of energy (losses) also impact the temperature profile, thus providing a method of detection. The following four electrical/ thermal parameters can be monitored on-line. [ 3.13.3.4.2.1 Temperature — The simplest temperature-related diagnostic involves monitoring the temperature level. Load-tap-changer temperature in excess of a certain level may be an indication of equipment trouble. However, there are also many factors that normally influence temperature level. One LTCmonitoring system measures the temperature of the diverter-switch oil and the main-tank oil temperature as a way to estimate the overload capacity of the tap changer. 3.13.3.4.2.2 Simple Differential Temperature — Another simple algorithm involves monitoring the temperature difference between the main tank and load-tap-changer compartment for those tap-changer designs in which the tap changer is in a compartment separate from the main tank. Under normal operating conditions, the main-tank temperature is higher than the tap-changer compartment temperature. This result is expected, given the energy losses in the main tank and general flow of thermal energy from that point to other regions of the equipment. Differential temperature is most effective on external tap-changer designs because this arrangement naturally results in larger temperature differences. Smaller differences are expected on tap changers that are physically located inside the main tank. Many factors influence differential temperature. Excessive losses caused by bad contacts in the tap changer are detectable. However, load-tap-changer temperature can exceed main-tank temperature periodically under normal conditions. Short-term (hourly) variations in electrical load, weather conditions, and cooling-bank activation can result in main-tank temperatures below the tap changer. Reliable diagnostic algorithms must account for these normal variations in some way. Figure 3.13.9 is a graphical representation of the top-oil temperature in the main tank and of the LTC compartment temperature. 3.13.3.4.2.3 Differential Temperature with Trending — Trending is one method used to distinguish between normal and abnormal differential temperature. When the load-tap-changer temperature exceeds the main-tank temperature, the temperature trends are examined. If the tap-changer temperature is decreasing, this is deemed a normal condition. However, if the tap changer temperature exceeds the main-tank temperature and is increasing, an equipment problem may be indicated. 3.13.3.4.2.4 Temperature Index — Another method used to examine temperature differential involves computing the area between the two temperature curves over a rolling window of time (usually one week). This quantity is called the temperature index and is usually expressed in units of degree-hours. Normal temperature difference (main tank above tap changer) is counted as “negative” area, and the reverse is “positive” area. Therefore, over a period of seven days, the index reflects the general relationship between the two measurements without changing significantly due to normal daily variations in © 2004 by CRC Press LLC © 2004 by CRC Press LLC
temperature. Under abnormal conditions, the index will exhibit an increasing trend as the load tap changer tends to run hotter relative to the main tank. This method eliminates false alarms associated with simple differential monitoring, but it responds slowly to abnormal conditions. A change in tapchanger temperature characteristics that takes place over the course of several hours will require several days to be reflected in the index. This response time is usually adequate, as the problem developing within the LTC normally requires an extended period to progress to the point where maintenance is required. 3.13.3.4.3 Vibro-Acoustic Monitoring The vibrations caused by various mechanical movements during a tap-changing operation can be recorded and analyzed for signs of deterioration. This provides continuous control of the transition time as well as an indication of contact wear and detection of sudden mechanical-rupture faults (Bengtsson et al., 1998). Acoustic monitoring of on-load tap changers has been under development. The LTC operation can be analyzed by recording the acoustic signature and comparing it with the running average representative of recent operations. The signal is analyzed in distinct frequency bands, which facilitates the distinction between problems with electrical causes and those with mechanical causes. Every operation of the tap changer produces a characteristic acoustic wave, which propagates through the oil and structure of the transformer. Field measurements show that in the case of a properly functioning tap changer, this vibration pattern proves to be very repeatable over time for a given operation. The acoustic signal is split into two frequency bands. Experience has shown that electrical problems (arcing when there should not be any, notably as for the case of a vacuum-switch-assist LTC) are detected in a higher frequency band than those mechanical in nature (excessive wear or ruptured springs). This system has the intelligence to distinguish imminent failure conditions and normal wear of the LTC to allow for just-in-time maintenance (Foata et al., 1999). 3.13.3.4.4 Dissolved-Gas Analysis Analysis of gases dissolved in the oil in the load-tap-changer compartment is proving to be a useful diagnostic. Key gases for this analysis include acetylene and ethylene. However, any conclusions to be drawn from a correlation of measured dissolved-gas concentrations with certain types of faults are not yet well documented. The study is complicated by the fact that the basic design and the materials used in the particular tap changer are found to significantly affect the DGA results. References Bengtsson, C., Status and trends in transformer monitoring, IEEE Trans. Power Delivery, 11, 1379–1384, 1996. Bengtsson, T., Kols, H., Foata, M., and Leonard, F., Monitoring Tap Changer Operations, Paper 12.209, presented at CIGRE Int. Conf. Large High Voltage Electric Syst., CIGRE, Paris, 1998. Bengtsson, T., Kols, H., and Jönsson, B., Transformer PD Diagnosis Using Acoustic Emission Technique, in Proc. 10th ISH, Montréal, 1997. Bengtsson, T., Leijon, M., and Ming L., Acoustic Frequencies Emitted by Partial Discharges in Oil, Paper No. 63.10, in Proc. 7th ISH, Dresden, 1993. Boisseau, C. and Tantin, P., Evaluation of Monitoring Methods Applied to Instrument Transformers, presented at Doble Conference, 1993. Boisseau, C., Tantin, P., Despiney, P., and Hasler, M., Instrument Transformers Monitoring, Paper 110- 13, presented at CIGRE Diagnostics and Maintenance Techniques Symposium, Berlin, 1993. Canadian Electricity Association, On-Line Condition Monitoring of Substation Power Equipment and Utility Needs, CEA No. 485 T 1049, Canadian Electricity Association, 1996. Chu, D., El Badaly, H., and Slemon, C., Development of an Automated Transformer Oil Monitor, presented at EPRI 2nd Conf. Substation Diagnostics, 1993. Chu, D., El Badaly, H., and Slemon, C., Status Report on the Automated Transformer Oil Monitor, EPRI 3rd Conf. Substation Diagnostics, 1994. CIGRE Working Group 05, An international survey on failures in large power transformers in service, Electra, 88, 1983. Cummings, H.B. et al., Continuous, on-line monitoring of freestanding, oil-filled current transformers to predict an imminent failure, IEEE Trans. Power Delivery, 3, 1776–1783, 1988. Domun, M.K., Condition Monitoring of Power Transformers by Oil Analysis Techniques, presented at Science, Education and Technology Division Colloquium on Condition Monitoring and Remanent Life Assessment in Power Transformers, IEE Colloquium (digest), no. 075, March 22, 1994. Duval, M. and Lamarre, C., The characterization of electrical insulating oils by high performance liquid chromatography, IEEE Trans. Electrical Insulation, 12, 1977. Eleftherion, P., Partial discharge XXI: acoustic emission-based PD source location in transformers, IEEE Electrical Insulation Mag., 11, 22, 1995. Eriksson, T., Leijon, M., and Bengtsson, C., PD On-Line Monitoring of Power Transformers, Paper SPT HV 03-08-0682, presented at Stockholm Power Tech 1995, p. 101.0. Feser, K., Maier, H.A., Freund, H., Rosenow, U., Baur, A., and Mieske, H., On-Line Diagnostic System for Monitoring the Thermal Behaviour of Transformers, Paper 110-08, presented at CIGRE Diagnostics and Maintenance Techniques Symposium, Berlin, 1993. Foata, M., Aubin, J., and Rajotte, C., Field Experience with Acoustic Monitoring of On Load Tap Changers, in 1999 Proc. Sixty Sixth Annu. Int. Conf. Doble Clients, 1999. Fox, R.J., Measurement of peak temperatures along an optical fiber, Appl. Opt., 22, 1983. Fruth, B. and Fuhr, J., Partial Discharge Pattern Recognition — A Tool for Diagnostics and Monitoring of Aging, Paper 15/33-12, presented at CIGRE International Conference on Large High Voltage Electric Systems, 1990. Glodjo, A., A Field Experience with Multi-Gas On-Line Monitors, in 1998 Proc. Sixty Fifth Annu. Int. Conf. Doble Clients, 1998. Griffin, P., Continuous Condition Assessment and Rating of Transformers, in 1999 Proc. Sixty Sixth Annu. Int. Conf. Doble Clients, 1999, p. 8-8.1. Harrold, R.T., Acoustic waveguides for sensing and locating electric discharges within high voltage power transformers and other apparatus, IEEE Trans. Power Appar. Syst., 102, 1983. IEEE, Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers, IEEE Std. C57.104, Institute of Electrical and Electronics Engineers, Piscataway, NJ. IEEE, Guide for Loading Mineral-Oil-Immersed Transformers, IEEE Std. C57.91-1995, Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1995. Lachman, M.F., On-line diagnostics of high-voltage bushings and current transformers using the sum current method, PE-471-PWRD-0-02-1999, IEEE Trans. Power Delivery, 1999. Leibfried, T., Knorr, W., Viereck, D., Dohnal, D., Kosmata, A., Sundermann, U., and Breitenbauch, B., On-Line Monitoring of Power Transformers — Trends, New Developments, and First Experiences, Paper 12.211, presented at CIGRE Int. Conf. Large High Voltage Electric Syst., 1998. Lemke, E., A New Procedure for Partial Discharge Measurements on the Basis of an Electromagnetic Sensor, Paper 41.02, in Proc. 5th ISH, Braunschweig, 1987. Morshuis, P.H.F., Partial discharge mechanisms in voids related to dielectric degradation, IEE Proc.-Sci. Meas. Technol., 142, 62, 1995. Myers, S.D., Kelly, J.J., and Parrish, R.H., A Guide to Transformer Maintenance, Transformer Maintenance Institute, Akron, OH, 1981. Oommen, T.V., On-Line Moisture Sensing in Transformers, in Proc. 20th Electrical/Electronics Insulation Conf., Boston, 1991, pp. 236–241. Oommen, T.V., Further Experimentation on Bubble Generation during Transformer Overload, Report EL-7291, Electric Power Research Institute, Palo Alto, CA, 1992. Oommen, T.V., On-Line Moisture Monitoring in Transformers and Oil Processing Systems, Paper 110- 03, presented at CIGRE Diagnostics and Maintenance Techniques Symposium, Berlin, 1993. Sokolov, V.V. and Vanin, B.V., In-Service Assessment of Water Content in Power Transformers, presented at Doble Conference, 1995. © 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
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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
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 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
Page 227: FIGURE 3.13.5 Analysis of bushing s
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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