Continuous Online Oil Quality Monitoring. Oleg Roizman Collin Feely

Transcription

1 Continuous Online Oil Quality Monitoring By Oleg Roizman Collin Feely

2 SECOND PAGE IS INTENTIONALLY BLANK PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 2 of 20

3 CONTINUOUS ONLINE OIL QUALITY MONITORING Oleg Roizman, IntellPower Collin Feely, PowerCor Abstract The monitoring of transformer oil quality plays a vital role in overall transformer health assessment. Apart from being an insulator and a coolant, oil is also an information carrier. That information could be related to a condition of another critically important component - cellulose, affecting overall transformer performance and its insulation life span. There are some physical and chemical parameters that characterise oil quality. Among these are dielectric loss factor, conductance, resistivity, viscosity, oil chemical composition, colour, acidity, interfacial tension, moisture, and particle content, to name a few. When properly measured these parameters can form the basis for an integrated diagnosis of oil condition. Currently, it is not feasible to monitor all the above mentioned parameters online. The authors of this paper are taking up the challenge of introducing a monitoring solution that offers a continuous online determination of insulating liquid condition in the operating transformer. The method uses an advanced approach to monitoring of moisture in oil, and is based on fundamental properties of water-in-oil solubility. It is well known that the solubility of water in oil changes as the oil deteriorates and becomes service-aged. Thus by measuring water solubility parameters and observing the change, one can relate this change to the oil state and its quality characteristics. The authors of this paper have proposed and implemented a novel method, which allows a determination of changing water solubility characteristics, true absolute water content in mg/kg, oil quality in the form of Oil Quality Index (OQI), and dielectric breakdown voltage, all measured and determined by one single monitor. Some case studies, demonstrating the practical application of the proposed methodology, are presented along with a comparative analysis of the results. Introduction Both international standards, IEC 60422: and IEEE C , offer guidance on the acceptance, supervision and maintenance of the quality of the insulating oil in electrical equipment. These International Standards are applicable to mineral insulating oils in transformers, switchgear and other electrical apparatus where oil sampling is reasonably practicable, and where the normal operating conditions listed in the equipment specifications apply. These International Standards are intended to assist the power equipment operator in evaluating the condition of the oil and maintaining it in a serviceable condition. The standards include recommendations on tests and evaluation procedures, and outline methods for reconditioning and reclaiming oil. Also included are recommended values for the key oil quality parameters. Comparing the two standards, one can see a number of inconsistencies, mostly outlined in a research paper 3. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 3 of 20

4 The authors of the research 3 made the following observation: Notwithstanding the ease of comparison to recommended values, doubts still persist on the validity of the recommended values. There is a lack of statistical backup or explicit information on how those values were determined. It is still an open question as to whether the typical value ranges were formed based on substantial technical arguments, economic reasons or international experience. And further: One thing that can be certain is that wrong classification of transformer condition could induce serious consequences regarding unnecessary maintenance expenses or severe penalty incurred for reduced quality of electricity supply due to transformer failure. There is a long list of questions as to the validity and scientific evidence, or lack of it, in relation to various oil quality parameters, but first let us take a closer look at major oil quality indicators. Oil Quality Characteristics The quality of insulation oil is normally monitored offline by taking a sample and processing it in the laboratory environments per the above mentioned standards 1,2. Measured values are then compared to the limits in Table 1 through Table 4 to interpret the results. Table 1 IEC recommended limits for mineral insulating oil after filling in new electrical equipment as related to oil quality Limits for Highest Voltage for equipment (kv) Voltage range < > 170 Colour (on scale given in ISO 2049) Max. 2.0 Max 2.0 Max. 2.0 Breakdown voltage (kv) 2.5 mm gap >55 >60 >60 Water content (mg/kg) 20 <10 <10 Acidity (mg KOH/g) Max Max Max Dielectric dissipation factor at 90 C and Max Max Max Hz to 60 Hz Interfacial tension (mn/m) Min. 35 Min. 35 Min. 35 Table 2 IEEE recommended limits for mineral Insulating oil after filling in new electrical equipment as related to oil quality Limits for Highest Voltage for equipment (kv) Voltage range < > 230 Colour Max. 1.0 Max 1.0 Max. 0.5 Breakdown voltage (kv) 2 mm gap >45 >55 >60 Water content (mg/kg) max <20 <10 <10 Acidity (mg KOH/g) Max Max Max Dielectric dissipation factor at 100 C and Max. 0.4 Max. 0.4 Max Hz to 60 Hz Interfacial tension (mn/m) Min. 38 Min. 38 Min. 38 Table 3 IEC classification of quality for in-service mineral oil by key indicators PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 4 of 20

5 Oil Test Parameter Voltage Class Condition Classification Good Fair Poor Dielectric Dissipation Factor, DDF (40 60 Hz at 90 C) Breakdown Voltage, BDV (2.5 mm electrode gap) Neutralization Number (Acidity) (mg KOH / g oil) Water (mg H 2 O / kg oil at transformer operating temperature) Interfacial Tension, IFT (mn / m) > 170 kv < > 0.20 < 170 kv < > 0.50 > 170 kv > < kv > < 40 < 72.5 kv > < 30 > 170 kv < > kv < > 0.20 < 72.5 kv < > 0.30 > 170 kv < > kv < > 30 < 72.5 kv < > 40 All (Inhibited) > < 22 All (Uninhibited) > < 20 Colour per ISO 2049 All < 2 > 2 Table 4 IEEE recommended limits for continued use of in-service mineral oil Test and method Dielectric breakdown voltage per ASTM D1816 kv minimum 1 mm gap 2 mm gap Dissipation factor (power factor) ASTM D º C, % maximum Interfacial tension ASTM D971 mn/m minimum Neutralization number (acidity) ASTM D974 mg KOH/g maximum Water content ASTM D1533 mg/kg maximum (ppm) Colour per ASTM D1500 Value for voltage class 69 kv >69 <230 kv 230 kv The IEEE recommendations do not differentiate the limits for in service oil into three classes as is suggested in its IEC counterpart. This implies that values beyond the limits are considered to be unacceptable (not recommended) according to the IEEE standard, while the same parameters could be fair according to IEC. The Dielectric Dissipation Factor per IEEE is in the order of magnitude larger than it is in the IEC standard. IEC does not differentiate IFT for different voltage classes. On the other hand, the IEEE Guide has substantial variations (5 32 mn/m) depending on voltage class. There is a large difference between the limits for oil colour. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 5 of 20

6 According to the IEEE Guide the limit for acidity in the low voltage of HV range equipment is 0.2 mg KOH/g while the IEC limit has a considerably more relaxed value of 0.3 mg KOH/g. Water concentration in oil is clearly made dependent on voltage level, implying that the oil dielectric property such as DBV is affected. It was proven and reported in various research publications 4,5,6 that water concentration (ppm) is not the right parameter to relate moisture in oil to the dielectric integrity of the liquid insulation. Rather water relative saturation is the appropriate parameter for that purpose, although relative water saturation is not even considered in the main body of the documents. Notwithstanding that the IEEE C introduces a relationship between DBV (dielectric breakdown voltage) and %rs (relative saturation) in Annex B, it is only informative leaving WCO as the only indicator for the limit. It appears that there is no consensus among North American and European communities on most of the oil quality parameters. An extensive literature search has not returned any evidence about how these limits were obtained, or what the scientific foundation for these limits is. Water-in-Oil Solubility as Oil Quality Parameter Water-in-oil solubility is not part of the oil quality characteristics specified in the standard tests and oil maintenance guidelines. However, we are going to demonstrate that this is one of the most sensitive indicators revealing signs of deterioration of insulating oil, from the very early stage to its complete degradation. Water-in-oil solubility is the maximum concentration of water that can exist in mineral oil at thermodynamic equilibrium at specified temperature and pressure. This definition is adopted from IUPAC (International Union of Pure and Applied Chemistry) recommendations 7. Mathematically water-in-oil solubility can be approximated by the frequently used formula 8,9 : ln W = A B T or W = exp (A B T ) (1) where W* is the water-in-oil solubility in mg/kg, also known as the water in oil saturation limit, A and B are experimentally determined coefficients, and T is the thermodynamic temperature. It is interesting to note that contrary to popular belief Eq 1 is not an Arrhenius type equation, but a direct integration of Van t Hoff equation ln (W*)/ (1/T) = - H/ R. As will be shown below, this Van t Hoff equation is useful for the determination of enthalpy change as a result of dissolution of water in oil. It has been demonstrated by much research 10 and reported in a CIGRE technical brochure 11 that water-in-oil solubility does not remain constant over the life of a transformer. Its temperature dependent characteristic changes so that the water solubility increases as the oil deteriorates (Figure 1). The fact that water is more soluble in service-aged oil can be explained by the decrease in the heat energy required to dissolve water in oil. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 6 of 20

7 Figure 1 Water-in-oil solubility for new and severely aged oil Water-in-oil solubility is a critical parameter when it comes to the determination of absolute water content as described in Eq. 2. W = rs 100 W, (2) where W is the absolute water content in oil in mg/kg (ppm) and rs is the relative water content as measured by a moisture sensor and expressed in percentage. It can be shown that Eq. (1) is a representation of the fundamental thermodynamic equation (3) ln W = H RT + S R, (3) where ΔH and ΔS are changes in enthalpy and entropy of water dissolving in oil. R is a universal gas constant. The enthalpy here is the heat energy required to dissolve a certain amount of water in a certain amount of oil, and is measured in kj/mol. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 7 of 20

8 Indeed, assuming that ΔH and ΔS are independent of temperature in the transformer operating range and substituting ΔS/R and ΔH/R with A and B respectively, Eq. (3) becomes Eq. (1). The enthalpy of water-in-oil solution can be determined from the well-known Clausius- Clapeyron Equation: a ln a w2 H 1 R T2 T w1 1 1 (4) where a w1 and a w2 are water-in-oil thermodynamic activities at respective temperatures T 1 and T 2. Rearanging Eq. 4 to find ΔH yelds: H a Rln a w1 w2 TT 1 2 T1 T 2 (5) It could be seen from (5) that the four parameters have to be known to determine ΔH. The change in enthalpy of water-in-oil solution is an important parameter as it is directly related to the solubility coefficient B in (1). Therefore, with reference to Figure 2, by continuously calculating the enthalpy per (5) with the assistance of the algorithm, schematically shown in Figure 3, it is possible to trace oil quality online. The water activity is not readily available and can only be determined when a transformer is in a state of thermodynamic equilibrium. This is nearly never the case. However, by continuously estimating water content in two locations as depicted in Figure 2, it becomes possible to determine ΔH by measuring rs and T at the bottom and top oil levels, provided there is a temperature difference between the top and bottom oil levels. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 8 of 20

9 Upper probe W to rsto exp( A B T 100 to ) W bo Lower probe rsbo exp( A B T 100 bo ) Figure 2 Oil Quality Monitor comprising dual probe moisture/temperature sensors As depicted in Figure 2 concentrations at the top and bottom oil levels can be expressed as W to and W bo respectively. Assuming that water content in the lower cooler pipe is equal to water content in the upper cooler pipe for any given moment of time, the solubility coefficient B can be determined by equating W to.to W bo.as: rsto TtoTbo B ln (6) rsbo Tto Tbo This equation is valid for each moment of time including non-equilibrium conditions. Comparing Eq. 6 to Eq. 5 yields: H = B R (7) While R is a gas constant = J mol -1 K -1, the B coefficient is not a constant and will experience change due to a change of oil chemical composition over time. The B coefficient can be found by solving the optimization problem of minimizing a mismatch between two series of top and bottom water content measurements during a prolonged period of time. As it will be shown in the next section, the B coefficient and therefore ΔH can be different from the one obtained in a laboratory with the help of the standard Karl Fischer method following one of the procedures given in 12 or elsewhere. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 9 of 20

10 Figure 3 Determination of Oil Quality using dual probe moisture monitor It follows from Eq. 6 and Eq. 7 that the change in ΔH is not dependent on the second solubility coefficient A, i.e. change in entropy, but it is only dependent on B. Then the Oil Quality Index (OQI) could be calculated as a linear function of B, B max and B min, e.g.: OQI = 1 B max B B max B min, (8) or in terms of ΔH OQI = 1 ΔH max ΔH ΔH max ΔH min, (9) where B max and B min are the highest and lowest values of the solubility coefficient B, which varies from B max, representing a new clean insulating oil, to B min, representing very aged (end of life) liquid. For transformer mineral oil these values are found to be 3900 and 3100 respectively 13. This translates to the range of H = [~25 ~33] kj mol -1. Case Studies In the following section we are going to demonstrate the applicability of the proposed approach for oil quality determination. Table 5 summarises the nameplate parameters of three studied transformers. Table 5 Parameters of three studied transformers Nameplate Trx-A Trx-B Trx-C Power, MVA ~ Voltage, kv 22/4.5 66/22 22/6.6 Oil preservation COPS COPS COPS Oil cooling ONAN/ONAF/OFAF ONAN/ODAF ONAN Age New > 45 years > 55 years PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 10 of 20

11 Transformer Trx-A Trx-A is a new transformer undergoing a seven day temperature rise test. Similar to Fig. 2, the two moisture probes, installed at the top radiator header and bottom radiator header, were used to determine oil quality per the algorithm outlined in the previous section. a) b) Figure 4 a) Top and Bottom Oil Temperature for New Oil Filled Transformer in C; b) Top and Bottom Water Content in ppm. A = 7.37; B= default solubility coefficients The temperature profile for top and bottom oil is shown in Figure 4a, while absolute water content for top and bottom oil is shown in Figure 4b. As expected for new oil, a good agreement between top and bottom water content was reached over all periods of monitoring. Water content was calculated using default solubility coefficients provided by the sensor manufacturer. The heat of water dissolution in oil (enthalpy change) is calculated from the given B solubility coefficient as ΔH = ln(10) R B = kj mol -1, which is very close to the enthalpy of a new, unused oil. Then Oil Quality Index is calculated using Eq.8. OQI= Also Eq. 9 can be used for OQI calculation which gives the same result. Given that a brand new oil has an OQI =1 the studied oil is classified as new or in GOOD condition, using the terminology of the IEC Guide. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 11 of 20

12 Transformer Trx-B The temperature and relative saturation profile for two weeks of monitoring of Trx-B are shown in Figure 5 and Figure 6. Oil quality data are summarised in Table 6. From the analysis of oil annual samples for the last five years, one can see that the water content was always below the specified limits according to both IEEE and IEC guidelines (see tables 3 and 4). However, examining the data of Figure 7 we can observe that on the 8th of January water content was 45 ppm, well over limit according to both IEEE and IEC. This renders annual oil sampling nearly useless as far as water-in-oil is concerned. Table 6 Oil Quality Data for last 5 years Sample date 8 Jan Jan Jan Feb Apr 2014 Oil Temp, C Moisture bottom, ppm Dielectric breakdown 2mm DDF at 100 C Acid number, mg KOH/g IFT, Colour Acidity is within the norm, but IFT is borderline between fair and poor according to the IEC guide and unacceptable per IEEE. The DBV does not correlate with the age as well, however the value of 29 kv registered on the 7 th of February indicates that the oil is unacceptable and poor by both Guides. The next year it is back to a rather high 60 kv (meaning acceptable and good by both Guides). The colour is progressively getting worse. Having a value of 2.5 indicates that oil approaches an unacceptable level per both IEEE and IEC Guides. Indication of getting close to unacceptable is also supported by the IFT value approaching 22 mn / m. A comparison of top and bottom calculated values for WCO is shown in Figure 7. These two series theoretically must agree, having the same value of ppm for top and bottom oil. Also shown (Fig 7) the residuals (a difference of top and bottom oil ppm at any given moment of time). One can notice that the average residual is approximately 2.5 ppm and the max is 6 ppm. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 12 of 20

13 Top oil T, C Bottom oil T, C Figure 5 Top and bottom temperature recorded for Trx B during two week period Bottom oil rs Top oil rs Figure 6 Top and bottom relative water saturation recorded for Trx B PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 13 of 20

14 ppm Top ppm Bottom ppm Δ ppm Figure 7 Top, bottom and residual water content recorded for Trx B A = 7.37; B= built in coefficients The calculated top and bottom ppm are also shown in Figure 8. This time the calculation is based on a laboratory determination of solubility coefficients A and B. There is an even larger difference between top and bottom oil ppm. This observation supports an expert opinion that calibration of moisture sensors by KF method is not a valid approach for service aged oils Top ppm Bottom ppm Jan-15 0:00 8-Jan-15 0:00 10-Jan-15 0:00 12-Jan-15 0:00 14-Jan-15 0:00 16-Jan-15 0:00 18-Jan-15 0:00 20-Jan-15 0:00 22-Jan-15 0:00-10 PPM top! PPM bot! Delta PPM! Figure 8 Top, bottom and residual water content recorded for Trx B: A = 6.6; B = by KF lab method PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 14 of 20

15 OQI ppm And finally, Figure 9 depicts a comparison of estimated top and bottom ppm based on the proposed method. Here we can see that a satisfactory agreement between the two trends is reached with a high level of accuracy. When compared, the estimated online solubility coefficients A = 6.96; B= are different from the default values, being A = 7.37; B= The B coefficient converts into ΔH = 29.2 kj/mol. 50 Top and Bottom PPM determinjed online by OQM Jan-15 0:00 8-Jan-15 0:00 10-Jan-15 0:00 12-Jan-15 0:00 14-Jan-15 0:00 16-Jan-15 0:00 18-Jan-15 0:00 20-Jan-15 0:00 22-Jan-15 0:00-10 PPM top! PPM bot! Delta PPM! Figure 9 Top, bottom and residual water content recorded for Trx B: A = 6.96; B= determined by OQM method. The Oil Quality Index (OQI) = 0.52, representing a 50% deterioration as compared to new oil. There is not yet an established scale for OQI, but based on the results with the studied transformers we could offer diagnostic classes as depicted in Figure OQI = F(ΔH) Good Fair Poor ΔH, kj/mol Figure 10 OQI based oil condition diagnostic The same classification approach was applied to another transformer, labelled Trx-C. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 15 of 20

16 Transformer Trx-C This is a 10 MVA 22/6.6 kv underground transformer, 55 years in operation, ONAN, free breathing conservator. Its oil test data are presented in Table 7. Table 7 Oil Quality Parameters for Trx C No Oil Quality Parameter Top Bottom 1 Oil Sample Temperature, ºC Moisture (Karl Fischer), ppm Breakdown Voltage, kv DDF at 25 C, % Resistivity (90 C), GOhm.m Acidity, mgkoh/g Interfacial Tension (IFT), mn/m Colour Particles 5-15 µm 17,305 68, Particles µm 590 2, Particles µm Particles µm 0 30 Surprisingly, at a time of sampling the breakdown voltage obtained in the laboratory for the top oil was much lower than that for the bottom oil, despite the fact that resistivity and DDF did not support the trend (see Table 7). Given that the relative saturation of the top oil was lower than that at the bottom, and the particle counts at the top were lower than at the bottom, there was no explanation for the discrepancy observed between the top and bottom oil breakdown voltages of 44 and 63 kv. The acidity level of , and the IFT level of indicate an extremely deteriorated oil condition. The top and bottom ppm series for two months are shown in Figure 11 using default water solubility coefficients. Estimated solubility coefficients, using the proposed method, are: A = 6.54; B= There is a larger disagreement between traditional (using default A and B) and the proposed estimation of top and bottom ppm than was the case with Trx-B. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 16 of 20

17 WCO, ppm ppm Sep 20-Sep 30-Sep 10-Oct 20-Oct 30-Oct 9-Nov 19-Nov ppm1 ppm2 Figure 11 Top, bottom and residual water content recorded for Trx C A = 7.37; B= built in coefficients Sep 20-Sep 30-Sep 10-Oct 20-Oct 30-Oct 9-Nov 19-Nov ppm1! ppm2! Figure 12 Top, bottom and residual water content recorded for Trx C: A = 6.54; B= by OQM method The A and B coefficients are considerably different from the ones of Trx-B respectively. The enthalpy of water solution for Trx-C is ΔH = 26.5 kj/mol. The OQI and red / yellow / green diagnostic is shown in Figure 13. The estimated oil quality index (OQI = 0.1) indicates that the Trx-C's oil is heavily deteriorated, which is also supported by IFT and NN (acidity) diagnosis. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 17 of 20

18 OQI 1 OQI = f(δh) ΔH, kj/mol Conclusion Figure 13. OQI based oil condition diagnostic Mineral oil is one of the most important and critical natural protective mediums in transformers. It serves many purposes including defending a transformer from dielectric stresses, thermal overheating, and electrical partial discharges and arcing. It also serves as an information carrier. Thus timely monitoring of transformer oil quality has become one of the emerging requirements of a modern diagnostic and monitoring system. A new method for continuous online oil quality assessment has been described and several case studies applying this new method have been discussed. It was demonstrated that annual oil sampling is not adequate for tracing moisture content. The error may lead to wrong diagnosis, which in turn creates the real need for an online oil quality assessment. It was also demonstrated that with periodic sampling it is difficult to see any trends in the degradation of the dielectric strength and oil acidity before the oil reaches a condition of severe deterioration. The proposed Oil Quality Index is an integral indicator of oil deterioration, and correlates well with both late oil life acidity and IFT. OQI has a solid physicochemical basis and is very sensitive to change in oil conditions. One of the benefits of a proposed method is eliminating the need for manual oil sampling, thus saving resources on laboratory analytical services. Another benefit of the proposed method is the simplicity of measuring oil quality with wellregarded and time proven monitoring means such as moisture sensors. It is believed that a new approach to electrical insulation liquid quality assessment will lay a foundation for new analytical techniques, and instruments for more accurate and reliable determination of water in oil parameters, and its effects on the quality of electrical insulating liquids. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 18 of 20

19 Acknowledgements The authors wish to thank a team of R&D scientists led by Senja Leivo of Vaisala for significant contribution to the development of oil quality monitoring solutions and case studies presented in the paper. References 1. IEC 60422:2013. Mineral insulating oils in electrical equipment - Supervision and maintenance guidance, International Electrotechnical Commission, IEEE C57.106:2015-Draft. Guide for Acceptance and Maintenance of Insulating Mineral Oil in Electrical Equipment, S. Tee, Q. Liu and Z.D. Wang, Prognosis of Transformer Health through Oil Data Analysis, TechCon Euro, H. Azizian, J.A. Proskurnicki and J.G. Lackey Relative Saturation Versus Moisture Content of Insulating Oil and Its Application in Monitoring Electrical Equipment Doble Client Conference, Boston, Miners, K., Particles and Moisture Effect on Dielectric Strength of Transformer Oil Using VDE 13 Electrodes, IEEE Transactions on Power Apparatus and Systems, Vol. PAS-101, No. 3 March 1982, 14 pp Vaisala, The Effect of Moisture on the Breakdown Voltage of Transformer Oil, White paper, Glossary of Terms Related to Solubility (IUPAC Recommendations 2008), Pure Appl. Chem., Vol. 80, No. 2, pp , Oommen T.V. Moisture Equilibrium In Paper-Oil Insulation Systems, Proceedings of the 16th Electrical Insulation Conference, Chicago, October 3-6, 1983, pp P. J. Griffin, C. M. Bruce, and J. D. Christie, Comparison of water equilibrium in silicone and mineral oil transformers, Minutes of the Fifty-Fifth Annual. Int. Conf. Doble Clients, sec , Arakelian, V.G.; Fofana, I., "Water in Oil-Filled, High-Voltage Equipment, Part I: States, Solubility, and Equilibrium in Insulating Materials," in Electrical Insulation Magazine, IEEE, vol.23, no.4, pp.15-27, July-Aug CIGRE Technical Brochure 349. Moisture Equilibrium And Moisture Migration Within Transformer Insulation System, Du, Y.; Mamishev, A.V.; Lesieutre, B.C.; Zahn, M.; Kang, S.H., "Moisture solubility for differently conditioned transformer oils," in Dielectrics and Electrical Insulation, IEEE Transactions on, vol.8, no.5, pp , Oct EPRI study on moisture assessment of power transformers PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 19 of 20

20 Biography Oleg Roizman is founder and managing director of IntellPower Pty. Ltd. in Australia, an engineering consulting and services company with an emphasis on continuous online monitoring and diagnostics of power transformers. Prior to forming IntellPower in 2000, Dr. Roizman was employed by Monash University in Australia as an R&D scientist. He was involved in developing analytics in areas of power system stability, power quality, monitoring and diagnostics of electrical plant. Dr. Roizman is an author of many technical papers and an active member of various working groups within IEEE PES Transformers Committee and CIGRE. Colin Feely is an Asset Strategy Engineer with Powercor Australia Ltd, a privatised distribution company operating in Victoria, Australia. Colin has had over 30 years of engineering and management experience in the electrical industry in Victoria and a 12 month consulting assignment in South Sumatra. Colin holds an Electrical Engineering Diploma from the Gippsland Institute of Advanced Education. His preferred job description is to have fun playing with Plant. PROCEEDINGS OF TECHCON ASIA PACIFIC 2016 Page 20 of 20