Behrooz Vahidi Ashkan Teymouri Quality Confirmation Tests for Power Transformer Insulation Systems Quality Confirmation Tests for Power Transformer Insulation Systems Behrooz Vahidi Ashkan Teymouri • Quality Confirmation Tests for Power Transformer Insulation Systems 123 Behrooz Vahidi Department of Electrical Engineering Amirkabir University of Technology Tehran, Iran Ashkan Teymouri Department of Electrical Engineering Amirkabir University of Technology Tehran, Iran ISBN 978-3-030-19692-9 ISBN 978-3-030-19693-6 https://doi.org/10.1007/978-3-030-19693-6 (eBook) © Springer Nature Switzerland AG 2019 This work is subject to copyright All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by 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Preface Power transformer insulation is an indispensable part of a power transformer The importance of insulation was increased over the years due to the increase in the voltage rating of transformers Within the last decades, although research on the transformer insulation and diagnosis methods has been improved so much, the insulation of HV transformers remained more or less unchanged and for EHV and UHV transformers, the oil–paper insulation is dominant The book in hand is the first edition and based on the oil–paper insulation The contents of this book are divided into five chapters The first and second chapters explain the oil insulation The third chapter explains the paper insulation The fourth and fifth chapters deal with the tests The authors’ special thanks go to all readers in advance who will give us a feedback on the book Tehran, Iran August 2018 Behrooz Vahidi Ashkan Teymouri v Contents 1 3 9 10 11 In-Service Mineral Insulating Oil 2.1 Introduction 2.2 Oil Monitoring and Purification 2.3 Oil Ageing and Degradation 2.4 Oil Tests 2.4.1 Color and Appearance 2.4.2 Breakdown Voltage 2.4.3 Water Content 2.4.4 Water in the Insulation System 2.4.5 Acidity 2.4.6 Dielectric Dissipation Factor (DDF) and Resistivity 2.4.7 Additives and Oxidation Stability 2.4.8 Sludge and Sediment 2.4.9 Interfacial Tension 2.4.10 Particle Content 2.4.11 FlashPoint 2.4.12 Compatibility of Insulating Oil 2.4.13 Pour Point 13 13 13 14 14 15 15 15 17 19 20 21 22 22 23 23 23 24 Unused Mineral Insulating Oil 1.1 Introduction 1.2 Mineral Oil 1.3 Classification of Mineral Oil Based on Application 1.3.1 Transformers Oil 1.3.2 Switchgear Oil in Low Temperatures 1.4 Additives 1.5 Special Cases 1.6 Analysis of Potentially Corrosive Sulphur 1.7 Oil Contamination References vii viii Contents 2.4.14 Density 2.4.15 Viscosity 2.4.16 PCB 2.4.17 Corrosive Sulphur 2.4.18 Dibenzyl Disulphides (DBDS) 2.4.19 Passivators 2.5 In-Service Oil Monitoring 2.5.1 Uninhibited Oil Monitoring 2.5.2 Inhibited Oil Monitoring 2.6 Time Schedule of Sampling and Testing In-Service Oil 2.7 Available On-Site Tests 2.8 Classification of Operating Oil 2.9 Corrective Actions 2.10 Purification 2.10.1 Physical Purification 2.10.2 Chemical Purification (Refinement) 2.11 Replacing Oil in Electrical Equipment 2.12 Adding Passivators 2.13 Determining Water Concentration in the Oil References 25 25 26 26 27 27 27 28 28 28 29 29 30 30 31 32 34 35 35 36 Chemical Indicators 3.1 Introduction 3.2 Insulation Paper Life Determination 3.3 Cellulose 3.4 Cellulose Molecular Structure 3.5 Cellulosic Insulation 3.6 Degree of Polymerization 3.7 Oil Impregnated Insulation Paper 3.8 Ageing of Oil Impregnated Insulation Paper 3.9 Ageing Mechanism 3.9.1 Pyrolysis 3.9.2 Hydrolysis 3.9.3 Oxidation 3.10 Influence from Acids 3.11 Ageing of Oil 3.12 Oil Oxidation 3.13 Degradation Products in Oil Impregnated Insulation Systems 3.14 Degradation Products from Cellulosic Insulation 3.14.1 Water 3.14.2 Acids 3.14.3 Furans 3.14.4 Carbon Oxides 3.14.5 Hydrocarbons 37 37 37 39 39 40 40 41 42 43 43 44 46 46 47 47 47 48 48 48 49 49 50 Contents ix 3.15 Degradation Products of Oil 3.15.1 Acids 3.15.2 Sludge 3.16 Chemical Indicators 3.17 Furan Compounds 3.17.1 Furans Origin 3.18 The Relationship Between DP and Furans 3.19 Stability 3.20 Furans Disadvantages 3.21 CO2 and CO 3.22 The Combination of CO2 /CO Ratio and 2-Furfural 3.23 Methanol References 50 50 50 50 51 51 52 53 53 54 54 55 62 Dissolved Gas Analysis (DGA) 4.1 Introduction 4.2 Total Flammable Dissolved Gas in the Transformer 4.3 Allowable Concentration of Gases in a Transformer 4.4 Gas Ratio Methods 4.4.1 Dürrenberg Method 4.4.2 Rogers Ratio 4.4.3 IEC Ratio Method 4.5 Duval Triangle Method 4.6 Detection of Partial Discharge Using DGA 4.7 Impact of DGA Accuracy on Fault Detection References 65 65 67 67 67 68 69 69 71 72 72 73 Other Tests 5.1 Introduction 5.2 Partial Discharge (PD) 5.2.1 Corona Discharge 5.2.2 Surface Discharge 5.2.3 Discharge in Composite Insulation Materials 5.2.4 Electric Discharge in Cavities 5.2.5 Electric Treeing 5.3 Partial Discharge Measurement 5.4 Insulation Monitoring by PD Measurement 5.5 Comparison of Electrical and Audio Detection Methods 5.6 Partial Discharge Formation in Transformers 5.7 Dielectric Response Analysis 5.8 Polarization 5.9 Polarization and Depolarization Current 5.10 Insulation Spectroscopy in Time Domain 75 75 76 76 76 78 78 78 78 81 83 84 84 85 85 88 x Contents 5.11 5.12 5.13 5.14 5.15 5.16 5.17 5.18 FDS Test Returning Voltage Method Isothermal Relaxation Current Frequency Response Analysis (FRA) Frequency Response Analysis Theory Application of FRA in Power Transformers FRA Test Features Frequency Response Measurement Methods 5.18.1 Swept Frequency Method (SFM) 5.18.2 Low Voltage Impulse Methods (LVI) 5.19 Comparison of LVI and SFM Methods 5.20 Detectable Defects by FRA References 91 93 94 96 97 97 98 98 98 99 99 101 102 Index 105 Chapter Unused Mineral Insulating Oil 1.1 Introduction The purpose of this chapter is to determine the characteristics and test methods of unused mineral oil containing additives or without additives used in transformers in which oil has been used as the insulator This chapter is written using the standard IEC 60296 [1] and is not applicable to the insulating oil used in cable or capacitor It is important to know that insulating oil is made from refining, reforming or mixing petroleum products and other hydrocarbons It needs to be explained that this chapter is applicable only to the unused mineral insulating oil and it is not applicable to the refined or used oil The characteristics and test methods of the used mineral insulating oil will be presented in Chap as well 1.2 Mineral Oil Transformer oil is a mineral insulating oil used in transformers and similar electrical appliances There are also some other mineral oil types that are designed for the low temperatures which are used in the oil filled switchgears in the very cold climate Mineral insulating oil is obtained through refining, reforming or mixing petroleum products with other hydrocarbons and additives It should be noted that these additives not include esters, silicone fluids and synthetic aromatic chemicals Additives are the chemicals which are added to the mineral oil to improve its specifications For example, antioxidants, metal passivators, electrostatic charging tendency depressant, gas absorbers, pour point depressants, anti-foam compounds and refining processes improver are some additives [1] The definition of these chemicals will be presented in the following: • Antioxidant additives: Compounds added to mineral insulators to improve oxidation stability, including inhibitors, peroxide decomposers and metal passivators [1] © Springer Nature Switzerland AG 2019 B Vahidi and A Teymouri, Quality Confirmation Tests for Power Transformer Insulation Systems, https://doi.org/10.1007/978-3-030-19693-6_1 5.12 Returning Voltage Method 93 Fig 5.16 Capacitance value in cellulosic insulation with different moisture content [13] 5.12 Returning Voltage Method One of the oldest methods for examining the insulation properties is the returning voltage method which is still used today The basis of this method is that a DC voltage (Uc ) is applied to the test device for t1 seconds which has previously been completely discharged Then, for a certain period of time, the test device is shortcircuited and after the short-circuit is disconnected, a returning voltage Ur (t) appears in the terminals of the test device as shown in Fig 5.17 It should be noted that the voltmeter impedance used in this measurement must be very high The origin of the returning voltage is the depolarization current that has not been stable in the insulating material during the short circuit Various experiments show that the size and shape of the returning voltage are strongly dependent on the amplitude of Uc and its duration (t1 ), as well as the short-circuit duration [14–16] The depolarization process has decreasing and uniform nature and therefore, these types of functions can be expressed as a sum of exponential functions In the simplest modeling, this summation can be obtained through parallelizing several branches in each branch, one resistor with a serial capacitor These parallel branches, with a high frequency capacity and an insulating resistance, complete the equivalent circuit of the test device Using this test circuit shown in Fig 5.18, one can simulate the depolarization current and also perform an RVM test 94 Other Tests Fig 5.17 Returning voltage test Fig 5.18 Modeling the dielectric response of multilayer insulation [13] The initial slope of the returning voltage is proportional to the active depolarization current at the moment t2 and therefore, the initial slope is proportional to the intensity of the depolarization process at this moment It should be noted that, if the test device is a combination of several different parts of various insulating materials, the application of this method is not feasible for any of the sections and this is a fundamental disadvantage for the RVM method 5.13 Isothermal Relaxation Current It is another monitoring method which was first used to assess the insulation status of cables The basis of this method is the depolarization current In this method, a voltage of 1000 V is applied to the device at a time interval of 1800 s Then the equipment is short-circuited for s Then, the depolarization current is measured and multiplied by the time (t) elapsed from the moment of the start of the measurement Finally, the IRC curve is plotted in a logarithmic form This diagram is then used as an 5.13 Isothermal Relaxation Current 95 indicator for evaluating insulation Since the depolarization current has a decreasing nature, so it is approximately the same as an exponential function Therefore, the IRC curve is in the form of a bell that is completely different from the shape of the depolarization current curve Figure 5.19 shows the depolarization current diagram in each phase of a three phase of XLPE cable The IRC charts are also calculated for each of the three phases and plotted in Fig 5.20 As could be seen, phase C insulation condition is inappropriate compared to the other phases [17] Fig 5.19 The depolarization current diagrams of all three phases of an XLPE cable [17] Fig 5.20 The calculated IRC curves of all three phases of an XLPE cable [17] 96 Other Tests It needs to be explained that all tests mentioned including spectroscopy in the time domain or frequency domain, the returning voltage (RVM) method or the IRC method, are for measuring the moisture concentration of paper insulation Due to the fact that direct paper sampling measurement is impossible in some equipment including transformers and also because of the importance of the moisture concentration in the paper, these tests are very important The measurement of the dielectric response (DR) in the frequency domain or in the time domain contains important information about the insulation condition Therefore, analysis dielectric response results is considered as one of the monitoring methods for transformers and more surveys are being performed about these tests Also, it has been shown in this chapter that different types of methods have the same result, but they are different in the way of measurement Each method has also its own advantages and disadvantages 5.14 Frequency Response Analysis (FRA) The transfer function analysis method, commonly known as the frequency response analysis (FRA) in the industry, is one of the fundamental techniques for troubleshooting transformers Based on this method, the transformer transfer function or the ratio of the input current or input voltage to the output voltage or the output current is measured over a wide range of frequencies Then, the measurement result is compared with the reference transfer function Frequency response analysis technology has been widely considered and used worldwide in recent decades The purpose of this test is to detect the transformer windings structure damages It is very difficult to detect the deformation of power transformer windings using the traditional methods such as turns ratio measurements, impedance and inductance measurements However, the deformation of the windings can cause minor changes in the values of the inductance and the capacitance of the windings On the other hand, the removal of the transformer from the service and disassembling the transformer for the purpose of examining such imperfections are not rational and economical Therefore, Frequency response analysis (FRA) is used to investigate the deformation of the windings in power transformers This method can detect deformation defects without disassembling the transformer The methods of measuring the transfer function have certain principles, but there is a need for practical experience to carry out a successful measurement and interpreting the results correctly [18–21] FRA test is a very sensitive test and can be performed on a transformer several times 5.15 Frequency Response Analysis Theory 97 5.15 Frequency Response Analysis Theory The basis of the transfer function method is the bipolar network theory In this model, the transformer is assumed to be a linear, coherent and passive network This theory allows the user to apply an input signal and obtain different output signals Each defined output signal produces a function as follows: U Au ( f ) Voltage transfer function UE ( f ) I Au ( f ) Current transfer function T FAi,V ( f ) = UE ( f ) T FAu,V ( f ) = (5.1) (5.2) UAu (f): Output voltage FFT IAu (f): Output current FFT UE (f): Input voltage FFT In addition to the above transfer functions, several other transfer functions can also be defined In fact, by dividing the voltage or current of an arbitrary terminal over another desired voltage or current, a transfer function or conversion function is obtained It is noteworthy that the sensitivity of the transfer functions to the changes and defects occurring inside the transformer is different [22] 5.16 Application of FRA in Power Transformers During the lifetime of a transformer, severe short circuit currents caused by various faults occurring in the power system networks may pass through the transformer The forces generated by these short circuit currents are capable of displacement or mechanical deformation of the windings depend on the fault severity In practice, the mechanical strength of windings’ cellulosic insulation is also reduced due to these forces and thus the insulator’s vulnerability increases Transformer transportation is also another cause of the mechanical damages inside the transformers [23] However, in most cases, the mechanical displacement or mechanical deformation of the windings does not prevent the transmission of energy in the system, but there is a risk that the mechanical damage to the insulation may lead to an insulation failure ultimately Therefore, identification of the displacement and various defects of the windings are very important The FRA test calculates the values of the frequency dependent variables of transformer windings such as inductance and capacitance of the coils These parameters change when the windings are short-circuited, open circuited or deformed [23–26] 98 Other Tests 5.17 FRA Test Features Power transformers are very important and valuable equipment in power system networks Therefore, many advanced techniques have been developed in recent years to improve fault diagnosis technics The main objectives of this test are as follows: Checking the status of a specific transformer in order to prevent the electrical breakdown inside the transformer Deciding whether to carry out the repairs Today, the use of frequency response analysis test (FRA) has been expanded considerably for the following reasons: • The existence of a direct relationship between the geometry of the windings and the core of the transformer with a distributed network of resistors, inductance and capacitors that models the transformer [27] • The above RLC distributed network can be specified by the frequency dependent transfer function Therefore, FRA test is very useful for detecting any faults inside the transformers The main concern in the FRA test is interpreting the test results whether a fault occurs inside the transformer or there is the possibility for a fault to occur inside the transformer [28, 29] 5.18 Frequency Response Measurement Methods The measurements needed to determine a transfer function could be done both in the time domain and the frequency domain Research in [30] shows that the accuracy of both methods is the same 5.18.1 Swept Frequency Method (SFM) In this method, a sinusoidal voltage with a predetermined domain in a wide range of frequency is applied continuously to the winding by devices such as FRA Analyzer or the Network Analyzer, then the output is measured The results of the measurements are displayed as the domain and phase The domain and phase of the transfer function are expressed as follows [31]: K = 20 × log10 φ = arctan T R T R (5.3) (5.4) 5.18 Frequency Response Measurement Methods 99 where K = Transfer function domain Ø = Transfer function phase T = Output signal R = Input signal Also, for example, an FRA Analyzer device manufactured by OMICRON is shown in Fig 5.21 The FRAnalyzer device shown in Fig 5.21 is connected to a computer by a USB port and its software, called FRAnalyzer 2.2 is specially designed to present the transformer transfer function as a graphical chart and in a table to the user A view of the software is shown in Fig 5.22 In Fig 5.22, the domain and phase of the transfer function are shown In this measurement, the transfer function domain is measured in dB and the phase of the transfer function is measured in degrees and in the range of MHz 5.18.2 Low Voltage Impulse Methods (LVI) In this method, measurements are carried out in the time domain and the test device is stimulated with an impulse voltage and then the corresponding response is measured In the LVI method, the impulse domain is usually between 100 and 2000 V and the front time is in the range of 200 ns to μs and the half-value time is in the range of 40–200 μs [32] The measured signals after noise cancellation and sampling are stored as data in time domain Then these data are transmitted using the Fourier transform to the frequency domain and then the transfer function of the transformer will be calculated 5.19 Comparison of LVI and SFM Methods Each of these methods has its own advantages and disadvantages The LVI method has the following disadvantages [33]: • Fixed frequency accuracy (faults detection at low frequencies is difficult) • It’s difficult to filter the white noise • Multiple measurement equipment is required The advantages of the LVI method include the following: • Different transfer functions (admittance, impedance, voltage, etc.) could be measured simultaneously • The time required for each measurement is about a few minutes 100 Fig 5.21 a OMICRON FRAnalyzer device, b equipment specifications Other Tests 5.19 Comparison of LVI and SFM Methods 101 Fig 5.22 View of FRAnalyzer 2.2 software The disadvantages of the SFM are as follows: • Only a transfer function can be measured at each measurement • The required time for each measurement is longer The advantages of the SFM method are as follows: • The signal-to-noise ratio is high (suitable white noise filtering) • The Scan is performed at a wide frequency range • Good frequency accuracy at low frequencies 5.20 Detectable Defects by FRA There are various methods for detecting defects in transformers; each one is used to detect some defects FRA detectable faults are mostly the faults that lead to a change in the physical, geometric or insulation structure of the transformer It is also important to note that there are some special methods in some papers to detect defects of windings insulation in transformers [34, 35] Table 5.1 shows the detectable faults by the FRA test 102 Other Tests Table 5.1 The FRA test ability to detect some defects [33] Defects Detection capability Windings axial displacement Easily Windings holder loosen Easily Windings deformation Easily Deformation of core sheets Easily Windings loop short circuit Easily Poor tank connection to the ground Easily No connection between core and ground Indiscoverable The presence of a closed loop in the tank (Circulating current) Detectable Weak connections Easily Extra loops in windings Easily Several grounding points in the core Easily The presence of foreign particles in the tank Indiscoverable References C.L Wadhwa, High Voltage Engineering, 2nd edn (New Age International Publishers) Å Carlson, A.B.B Zürich, Testing of Power Transformers: Routine Tests, Type Tests and Special Tests, 1st edn (Pro Print, 2003), ISBN 3-00-010400-3 E Grossmann, Akustische Teilentladungsmessung zur Überwachung und Diagnose von ÖlPapier-isolierten Hochspannungsgeräten (Shaker, 2002) G Wang, W Zhou, Optical character of partial discharge in transformer oil, in 10th International Symposium on High Voltage Engineering, Montreal, Canada, Aug 1997 J Haema, R Phadungthin, Power Transformer Condition Evaluation by the Analysis of DGA Methods Department of Electronics Engineering Technology college of Industrial Technology King Mongkut’s University of Technology North Bangkok, Thailand, Power and Energy Engineering Conference (APPEEC), 2012 IEEE T.S Ramu, H.N Nagamani, Partial Discharge Based Condition Monitoring of High Voltage Equipment (New Age International Publishers, Delhi, 2010) IEEE Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems (Gold Book) IEEE Std 493-1997 [IEEE Gold Book], pp 1–464, 31 Aug 1998 https:// doi.org/10.1109/ieeestd.1998.89291 B Vahidi, S.J Hosseini, Partial discharge simulation in solid insulation at AC Voltage on MATLAB-SIMULINK for educational purposes Int Rev Modell Simul 4(4) (2011) E Goodarzy, B Vahidi, Hole location determination in insulation by using ultrasonic Int Rev Modell Simul 5(2) (2012) 10 E Grossmann, Empfindlichkeit der akustischen TE-Messung bei Transformatoren im Labor und vor Ort im Vergleich zur elektrischen TE-Messung (IEC 60270), in Haefely Symposioum, Stuttgart, 11–12 Oktober 2000 11 H Borsi, Dielectric behavior of silicone and ester fluids for use in distribution transformers IEEE Trans Electr Insul 26(4), 755–762 (1991) 12 S.M Gubanski et al., Dielectric response methods for diagnostics of power transformers IEEE Electr Insul Mag 19(3), 12–18 (2003) 13 I Fofana et al., On the frequency domain dielectric response of oil-paper insulation at low temperatures IEEE Trans Dielectr Electr Insul 17(3), 799–807 (2010) References 103 14 B Gross, On after-effects in solid dielectrics Phys Rev 57, 57–59 (1940) 15 G.M Urbani, R.S Brooks, Using the recovery voltage method to evaluate aging in oilpaper insulation, in IEEE International Conference on Conduction and Breakdown in Solid Dielectrics, Vasteras, Sweden, 22–25 June 1998, pp 93–97 16 T.K Saha, P Purkait, F Muller, Driving an equivalent circuit of transformers insulation for understanding the dielectric response measurements IEEE Trans Power Delivery 20(1), 149–157 (2005) 17 J Wu et al., The condition assessment system of XLPE cables using the isothermal relaxation current technique, in IEEE 9th International Conference on the Properties and Applications of Dielectric Materials, ICPADM 2009 IEEE (2009) 18 R.H Harner, Distribution system recovery voltage characteristics: I - transformer secondaryfault recovery voltage investigation IEEE Trans Power Apparatus Syst PAS-87(2), 463–487 (1968) 19 R.H Harner, J Rodriguez, Transient recovery voltages associated with power-system, threephase transformer secondary faults IEEE Trans Power Apparatus Syst PAS-91(5), 1887–1896 (1972) 20 Transient Recovery Voltage Conditions to be Expected when Interrupting Short-circuit Currents Limited by Transformers, CIGRE Report 13-07 (1970) 21 M Eslamian, B Vahidi, New equivalent circuit of transformer winding for the calculation of resonance transients considering frequency-dependent losses IEEE Trans Power Delivery 30(4), 1743–1751 (2015) 22 K Feser, J Christian, C Neumann, U Sundermann, T Leibfried, A Kachler, M Loppacher, The transfer function method for detection of winding placements on power transformers after transport, short circuit or 30 years of service, in CIGRE 2000 23 T Leibfried, E Kirchenmayer, W Knorr, Stoßkurzschlußprüfung eines 125-MVATransformers Elektrizitätswirtschaft, Jahrgang 97 (1998), Heft 10, S 24–38 24 C Sweetser, T McGrail, Sweep Frequency Response Analysis Transformer Applications: A Technical Paper from Doble Engineering, Version 1.0, 27 Jan 2003 25 M de Nigris, R Passaglia, R Berti, L Bergonzi, R Maggi, Application of Modern Techniques for the Condition Assessment of Power Transformers, CIGRE Session 2004, Paris, Paper A2207 26 A Ashrafian, B Vahidi, M Mirsalim, Time-time-transform application to fault diagnosis of power transformers IET Gener Transm Distrib 8(6), 1156–1167 (2014) 27 M Eslamian, B Vahidi, Computation of self-impedance and mutual impedance of transformer winding considering the frequency-dependent losses of the iron core Electric Power Compon Syst 44(11), 1236–1247 (2016) 28 J Pleite, E Olias, A Barrado, A Lazaro, J Vazpuez, Modeling the Transformer Frequency Response to Develop Advanced Maintenance Techniques, Paper 4, Session 13, 14th PSCC, Sevilla, 24–28 June 2002 29 M Thein, H Toda, M Hikita, H Ikeda, E Haginomori, T Koshiduka, Investigation of transformer impedance for transformer limited fault condition by using FRA monitoring technique, in The International Conference on Condition Monitoring and Diagnosis 2010 (CMD 2010), paper A7-2, pp 197–200, Shibaura Institute of Technology, Japan, 6–11 Sept 2010 30 T Leibfried, Die Analyse der Übertragungsfunktion als Methode zur Überwachung des Isolationszustandes von Großtransformatoren, Dissertation, Universität Stuttgart (1996) 31 S Tenbohlen, S Ryder, Making frequency response analysis measurement: a comparison of the swept frequency and impulse response methods, in Proceedings of 13th International Symposium on High Voltage Engineering, Delft, Netherlands (2003) 32 C Sweeter, T Grail, Sweep Frequency Response Analysis for Transformer Applications, Technical paper, Doble Engineering Company 33 S.A Ryder, Transformer diagnosis using frequency response analysis: results from fault simulations, in IEEE Power Engineering Society Summer Meeting, vol (Chicago, IL, USA, 2002), pp 399–404 104 Other Tests 34 M Rahmatian, B Vahidi, A Ghanizadeh, G Gharehpetian, H Alehosseini, Insulation failure detection in transformer winding using cross-correlation technique with ANN and k-NN regression method during impulse test Int J Electr Power Energy Syst 53, 209–218 (2013) 35 M Davari, B Vahidi, A new analysis of VFTO on transformers based on DM: considering frequency variable losses, in Modern Power Systems (MPS), Romania, Nov 2008 Index A Acetic acid, 46 Acetylene, 47, 65, 66, 81 Acidity, 3, 6, 9, 19, 26, 29, 32, 35, 46, 50, 53 Acoustic detection, 82 Active part, 17, 18, 41, 42 Additives, 1, 3, 8–10, 21, 24, 31, 33 Ageing, 13–15, 19, 22, 24, 33, 37, 38, 42–54, 62, 76, 81, 84, 85, 91 Alpha cellulose, 39, 40 Amorphous, 39, 46 Antenna, 80, 81 Anti-foam, Antioxidants, 1, 3, 8, 22 Aromatic compounds, 6, 7, 65 Aromatics, 4, Assessment, 19, 27–30 ASTM, 26 B Benzotriazole, Bipolar, 16, 85, 97 Breakdown voltage, 3, 4, 7, 15, 17, 23, 29 Broad band, 80 C Cable, 1, 84, 94, 95 Capacitive sensors, 16, 81 Capacitor, 1, 80, 82, 93, 98 Carbon dioxide, 43, 46, 49, 81 Carbon monoxide, 46 Cavities, 76, 78 Cellulose, 9, 17, 37–52, 54, 65, 75, 91 Centrifuge, 31, 32 Chain, 39, 43, 46, 49 Charges, 27, 85 Chemical detection, 81 Chendong, 52, 55, 57, 58, 60 Circulation, 4, 14, 27 Contact method, 33 Contaminants, 4, 14, 15, 19, 20, 32, 34, 91 Copper, 6, 8, 9, 21, 26, 27, 43 Corona discharge, 76, 77 Corrosive, 3, 6–8, 10, 26, 27 CO2/CO ratio, 50, 54, 55 Cotton fibers, 39 Cylindrical sensor, 81 D DBP, 2, 8, 22 DBPC, 2, 22 Decomposition, 42, 43, 47, 52–54, 65, 67, 69, 70, 72 Degradation, 8, 13–15, 20, 22, 25, 27, 28, 30, 42, 43, 46–55, 66, 67, 69 Degree of Polymerization (DP), 40–43, 45, 46, 49, 50, 52, 53, 55, 57, 60, 75 Dehumidification, 44 Density, 3, 7, 25 De Pablo, 52 Depolarization, 85, 93–95 Deterioration, 23, 43, 47, 50, 51, 62, 91 Dibenzyldisulphide (DBDS), 6–8, 10, 26 Dielectric Dissipation Factor (DDF), 4, 9, 20, 21, 28 Dielectric losses, Dielectric Response (DR), 85, 96 Dielectric strength, 37 © Springer Nature Switzerland AG 2019 B Vahidi and A Teymouri, Quality Confirmation Tests for Power Transformer Insulation Systems, https://doi.org/10.1007/978-3-030-19693-6 105 106 DIN, 26 Dipole, 85 Dissolved Gas Analysis (DGA), 7, 50, 53, 54, 72, 75, 81 Dürrenberg method, 68 Duval triangle method, 71, 72 E Elastic motion, 85 Electrical detection, 81–83 Electrical fault, 7, 27, 66 Electric field, 15, 40, 85, 87, 91 Electric treeing, 78, 79 Electrodes, 6, 76, 78, 85, 88, 91 Electromagnetic detection, 81 Electrostatic Charging Tendency (ECT), 4, 6, Emsley, 43, 52, 53 Epoxy resin, 78 Esters, Ethane, 47, 65, 81 Ethylene, 47, 65, 66, 81 F Filtration, 23, 31 Flammable gases, 67 Flash point, 4, 23, 25 Formic acid, 46, 48 Fourier, 99 Frequency Domain Spectroscopy (FDS), 85, 91 Frequency Response Analysis (FRA), 96 Furans, 31, 49 Furnace, 17, 41 G Gas absorption, Glucose, 40, 43, 45, 46, 49 H Hemicellulose, 41, 51 High molecular weight acids, 46, 50 Hydrocarbons, 1, 6, 7, 23, 26, 47, 50 Hydrogen, 7, 39, 43, 47, 65, 66, 81 Hydrolysis, 44, 48, 84 I IECratio method, 4, 69 IEC 60296, 1, 4, 10, 13, 19, 23, 27, 32, 47 Indicator, 6, 20, 38, 42, 43, 48, 54, 55 Inhibitors, 2, 19 Interfacial Tension (IFT), 3, 6, 22, 27–29 Intermolecular, 39 Index Ionic, 85, 86 IRC curve, 96 Iron, 43 Isothermal relaxation current, 94, 96 K Kraft, 38, 40 L LCSET, 3, Leakage, 13, 23, 30, 35, 54 Levulinicacid, 46, 48 Life, 6, 9, 21, 27, 29, 40, 42–45, 47, 50, 52, 62, 72, 75, 97 Life time, 14, 32, 37, 42, 45, 47, 50, 52–54 Lignin, 39, 40 Low molecular weight acids, 50 Low Voltage Impulse methods (LVI), 99 M Mechanical stress, 37 Metal passivators, 1, 6, 8, 10, 26, 27, 33, 35 Methane, 47, 66, 81 Methanol, 57, 62 Micro fibrils, 39 Mineral, 1–3, 6–8, 10, 13, 23, 27, 31, 35, 41, 47, 65, 72, 82 Mixing, Moisture, 15, 17, 41, 45, 46, 48, 49, 52, 53, 87, 91, 96 Monomers, 45 Monosaccharide, 39 N Naphthenic acid, 46 Narrow band, 80 Noise, 80, 82, 83, 101 Non-homogeneous materials, 85 O OFAF, 16 Off-site, 33 Oil, 1–4, 6–10, 13–17, 19, 20, 22–35, 37, 38, 40, 42, 43, 45, 46, 48–54, 66–69, 72, 75, 81, 82, 84, 91 Oil-filled, 13, 16 ONAN, 16 On-site, 29, 33, 82 Oommen chart, 45 Optical detection, 81 Orientation, 85, 86 Index Oscilloscope, 82 Oxidation, 1, 2, 4, 6, 8, 10, 14, 16, 19, 21, 22, 25–29, 32, 43, 50, 54, 69 P Pahlavanpour, 52 Paper, 6, 8, 10, 15, 17, 19, 26, 35, 40–42, 44, 45, 47, 49–51, 53, 54, 62, 65, 66, 72, 75, 88, 96, 101 Paper insulation, 15 Paper loss, 37 Partial Discharge (PD), 78, 80, 84 Particle content, 7, 23 PDC, 75, 85, 87–90 Percolation method, 32 Peroxide, Petroleum products, Phenolic, 2, 22 Piezoelectric sensors, 82 Polar, 4, 14, 20, 22, 32, 33, 50 Polarization, 50, 75, 85–87 Polychlorinated Biphenyls (PCB), 2, 4, 13, 26, 27, 30, 33 Polycyclic Aromatics (PCA), 4, Polymethacrylates, Polynaphthalenes, Polysaccharide, 39 Pour point, 1, 3, 24 Pressboards, 40 Pressure, 34, 37, 41, 47, 66 Pulses, 78, 80–82 Pumps, Purification, 4, 10, 13, 14, 19, 20, 30, 32–34 Pyrolysis, 43, 51 R Refining, 1, 6, 22, 26, 47 Reforming, Regeneration, 14 Relative humidity, 16 Reservoir oil tank, 23, 32 Resistivity, 20, 21 Return voltage, 75 Return Voltage Method (RVM), 85, 93, 96 Risk, 13, 27, 29, 30, 47 Rogers’s ratio, 69 107 S Scholnick, 52 Sediment, 22 Silicone, Sinusoidal voltage, 98 Sludge, 6, 14, 22, 23, 26, 28, 31, 50 Spectroscopy, 75 Spraying, 34 Stability, 2, 3, 6, 9, 21, 22, 26–28, 32, 40, 41, 49, 54 Stearic acid, 46 Sugars, 39 Sulphur, 2, 3, 6, 8–10, 26, 27 Surface discharge, 7, 78, 81 Swept Frequency Method (SFM), 101 Switchgears, 1, 3, 4, 13, 26, 34 T Tan delta, 20 Tap changer, 4, 23, 31, 67, 69 Temperature, 1, 4, 6, 9, 14–17, 19, 20, 23, 24, 26, 28, 31, 35, 43–45, 47, 49, 52, 54, 55, 57, 62, 66, 69, 75, 81, 85, 91 Tensile strength, 38, 39 Thermodynamic equilibrium, 17 Transfer functions, 96, 99 Transformers, 3, 6, 7, 9, 13, 17, 21, 27, 28, 32, 33, 35, 37, 40, 42, 43, 47, 52–54, 66–68, 75, 78, 81–84, 88, 96–99 U UHF sensors, 81 Uninhibited oil, 7, 23, 28 Unused, 1, 2, 6, 7, 10, 16, 23, 26, 32, 35 V Vacuum, 17, 18, 31, 32, 34, 41, 84 Vacuum furnace, 17, 18 Viscosity, 3, 4, 25 W Water, 3–5, 7, 14, 15, 45, 48, 49 Wood, 39 X XLPE, 95 .. .Quality Confirmation Tests for Power Transformer Insulation Systems Behrooz Vahidi Ashkan Teymouri • Quality Confirmation Tests for Power Transformer Insulation Systems 123 Behrooz... Preface Power transformer insulation is an indispensable part of a power transformer The importance of insulation was increased over the years due to the increase in the voltage rating of transformers... the transformer insulation and diagnosis methods has been improved so much, the insulation of HV transformers remained more or less unchanged and for EHV and UHV transformers, the oil–paper insulation