Condition assessment of 132/220 kV oil-paper current ... - ac

November / December — Vol. 36, No. 6 21

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Measurements of dielectric response in fre-quency domain greatly assist condition as-sessment of high voltage oil filled current transformers in tropical climates.

IntroductionCurrent transformers (CTs) are extensively used in electrical

switchyards and substations for metering and protection pur-poses [1] and are expected to operate properly for at least 30 years [2]. Normally, aging of CTs under service conditions is relatively slow, but they also may fail prematurely due to vari-ous reasons, such as design faults, inadequate quality during manufacture, lightning strikes, operation beyond rated condi-tions and inadequate maintenance [3]. Compared with other high voltage apparatus, failure of a CT can be violent or even catastrophic, causing damages to the CT itself as well as to nearby located assets and humans [4–9]. Build-up of internal pressure during a failure of a CT results in an instant fire due to burning of oil and explosion of porcelain housing, where porce-lain pieces can spread to a distance up to 100 m [4], [6].

Catastrophic CT failures were reported from different coun-tries, for example Mexico [4], Australia [5], China [6], Canada [7], Indonesia [8] and Sri Lanka [9]. In Mexico several tens of CT failures happened during the period from 1985 to 2006 in their 230 kV and 400 kV transmission networks [4]. In South Australia a CT failure took place in February 1997 during sum-mer time with external temperature increases up to 40°C [5]. In 2015, a CT blast was reported from the Chinese 230 kV sys-tem with spread of porcelain pieces over a large distance [6]. In Canada [7], three 230 kV CT blasts were reported in August 2008. In Sri Lanka several CT failures happened between 2005 and 2018 [9]. By considering the failure circumstances, the ma-jority of them had happened during summer periods under high temperature and high humidity conditions, which accelerated the degradation of the insulation.

The majority of the high voltage CTs have oil and paper/pressboard as their main insulation, as in power transformers. Once the solid insulation deteriorates due to various reasons, the generated moisture and other aging by-products may trans-fer to the oil causing degradation of insulation quality [10]. Therefore, monitoring of oil properties is widely used to assess CT condition and hence to predict possible premature failures [10–12]. Typical chemical properties of the oil include mois-ture content, acidity, viscosity, interfacial tension and dissolved gases. On the other hand, electrical tests of breakdown voltage, dielectric response and loss tangent provide direct information about oil quality [10], [11]. However, unlike in power trans-formers, the number of oil tests that can be performed on a CT is limited by its relatively low volume. Also, oil sampling in the field is very risky and requires strict adherence to safety mea-sures. Another approach for condition assessment is to monitor the whole insulation system, i.e., both oil and paper [13–19] and dielectric spectroscopy, either in time or frequency domain, is one of the possible measurements.

To minimize possible CT failures, the Sri Lankan electricity utility company, Ceylon Electricity Board (CEB), started condi-tion monitoring of CTs in 2005 mainly based on oil tests. Later, in collaboration with the high voltage group of the University of Peradeniya, these activities were extended to dielectric re-sponse measurement on CTs, laboratory aging of oil and CTs. This article summarizes the findings of those activities to share our experiences on CT condition assessment in a tropical cli-mate. Various electrical and chemical tests were performed to assess the condition of 25 field or laboratory aged oil samples. Dielectric response measurements in the frequency range of 1 kHz to 10 mHz were introduced as an effective condition as-sessment method on a fleet of 149 CTs, including new, field aged and laboratory aged units. Finally, based on oil and dielec-tric investigations, a condition assessment strategy is proposed.

Failure CasesAccording to the 2nd international survey conducted among

22 utilities by the CIGRE study committee A3, more than 50%

Condition Assessment of 132/220 kV Oil-Paper Current Transformers in Sri LankaS. Kumara,1 M. Fernando,1 T. N. Aravinda,1 D. S. Daulagala,2 A. P. Bandara,2 K. Bandara,2 P. Nandasena,2 and G. A. Jayantha3

1Department of Electrical and Electronic Engineering, University of Peradeniya, Peradeniya, 20400, Sri Lanka; 2Ceylon Electricity Board, Colombo, Sri Lanka; and 3EnPower Engineering Consultant Pvt Ltd., Sri Lanka

Key words: current transformer, live tank, dead tank, condition assessment, dielectric response, loss tangent, insulating oil

Authorized licensed use limited to: Ramesh Fernando. Downloaded on October 19,2020 at 11:32:23 UTC from IEEE Xplore. Restrictions apply.

22 IEEE Electrical Insulation Magazine

of major CT failures were found to be caused by design faults or inadequate quality during manufacturing [3]. In addition, 47% of failures, out of 2636 cases, occurred prematurely within the first 10 years of service. A premature failure is often a rela-tively fast process caused by localized degradation as compared with normal failures caused by slow aging of the bulk insula-tion system [10]. Such localized degradation can be initiated by the presence of weak spots due to manufacturing defects (e.g., by metallic particles, bubbles, sharp points, blockage of oil flow path) and/or local field enhancement due to over stress or fast transients. Also, the presence of moisture is a key factor that leads to failure of degraded oil-paper insulation system in a CT [10], [18], [20]. When CTs operate at temperatures close to their rated limits, moisture in the paper insulation is dissolved in the oil. After cooling down, due to a reduction of moisture solubility in oil, the dissolved water can turn into free water and form water vapor bubbles concentrating in micro pores of the paper insulation in the vicinity of the high voltage conductor. As a result, discharge activity starts, which may further develop into a catastrophic failure. In some cases, the final failure of paper-oil insulated equipment may also yield a quick build-up of excessive pressure in the porcelain housing, resulting in an explosion and fire.

Within the period between 2005 and 2018, CEB had experi-enced 10 explosions of CTs in 132 kV and 220 kV switchyards belonging to its hydro power generation division. This division

has altogether 110 and 173 CT units, respectively operating at voltage levels of 220 kV and 132 kV. It was found that all the failed CTs were 132 kV live tank type [9]. Details related to those failure events are summarized in Table 1 and some of the photos taken after the failures are shown in Figure 1. Out of 10, seven of the CTs failed prematurely, within 15 years of service. Many of these cases resulted in explosions with splitters of the porcelain housings traveling a distance longer than 50 m away from the original location, causing damage to assets in their vicinity. These failures also caused line or plant outages. The most severe repercussion was a loss of human life during a CT explosion at power station B in 2011.

Oil InvestigationsSamples and Conducted Tests

Details on tested oil samples, aging method and parameters are summarized in Table 2. Field aged oil samples were col-lected from 16 CTs in three power stations located in the wet and hot climatic zone of Sri Lanka. These CTs were in service for 25–50 years. In parallel, eight artificially aged mineral oil (BS:148 1998 class 1) samples (0.5 - 1.1 L each) were prepared in the laboratory as (i) slow thermally aged dry and wet samples prepared under sealed and unsealed conditions, (ii) accelerated thermally aged samples prepared under unsealed conditions and

Table 1. CT failures at 132 kV switchyards in Sri Lanka during 2005–2018

Location Failure date

No. of units failed

Age at failure

(in years) Repercussion

132 kV switchyard at power station A 2005–2007 4 15 Damages to nearby assets, plant outage132 kV switchyard at power station B February 2011 1 25 Fatal – one employee died132 kV switchyard at power station C 2013 2 10 Damages to nearby assets, plant outage

April 2014 1 0.5 Damages to nearby assets132 kV switchyard at power station D November 2016 1 ~30 Damages to nearby assets, line outage

May 2017 1 ~30 Major damages to nearby assets, line outage

Figure 1. Photos taken after failures of 132 kV CTs. Failed CT at power station C in 2013. Failed new CT at power station C in 2014. Fire due to failure of a new CT at power station C in 2014.



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(iii) electro-thermally aged samples under unsealed conditions. These aging conditions were selected to simulate the types of aging behavior appearing in the field. Different concentrations (in g/l) of Cu (2.5), Al (0.5), Fe (2.5) and Zn (0.5) were added to each of those samples to mimic the catalytic effect of the metals used in real transformers. In addition, pieces of pressboard (100 g/l) were added to wet samples [21]. The thermal aging was conducted inside an air circulated oven with cyclic aging and resting, i.e., respectively for 8 and 16 h per day. The conducted tests were visual inspection (VI), interfacial tension (IFT), acid-ity level (AC), moisture content (MC), dissolved gas analysis (DGA), breakdown voltage (BD) and frequency dielectric spec-troscopy (FDS). Detail description of the test procedures can be found in our earlier publications [21], [22].

ResultsFigure 2 shows the multi-correlation coefficient matrix of

the tested parameters covering electrical tests (breakdown volt-age, loss tangent at 50 Hz and permittivity at 1 kHz based on FDS measurements) as well as chemical and physical tests

(color, acidity, interfacial tension and moisture content). In a correlation between two variables, a positive correlation co-efficient indicates that both variables either increase or de-crease together, whereas a negative coefficient indicates that one variable decreases while the other one increases or vice versa. Accordingly, two electrical parameters: loss tangent and permittivity (both estimated by FDS measurements) strongly correlated to each other with a correlation coefficient of 82%. However, their correlations with breakdown voltage (BD) was poor (below 40%). The four chemical and physical test pa-rameters also did not show a good correlation (below 70%). However, there is a moderate correlation (63%) between color and acidity indicating the possibility of excluding the acidity test, when color of the oil is recorded. On the other hand, no correlations were indicated between chemical and electrical test parameters (below 40%).

Table 3 shows a classification of oil condition with respect to different test parameters according to IEC 60422:2013 [11]. The laboratory aged samples showed comparatively higher degradation compared with the field aging, despite the cyclic

Table 2. Laboratory aged and field aged oil samples

Sample Name Oil Aging method Aging condition Tests

Non aged virgin oil — — VI, IFT, AC, MC, DGA, BD, FDS at 70°C and at ambient temperature (~27°C)

Laboratoryaged(8 samples)

unsealed wet oil slow thermal aging first 200 h at 120°Canother 440 h at 110°C–130°Cunsealed dry oil

sealed wet oil slow thermal aging 1176 h at 120°Csealed dry oilunsealed wet oil accelerated thermal aging 8 h at 170°C FDS at ambient temperature

(~27°C)2 h at 200°Celectrical aging 8 h under partial discharges

40 breakdown eventsField aged(16 samples)

CT at 220 kV switchyard 1 CT in service for 26 years VI, IFT, AC, MC, DGA, BD, FDS at 70°C and at ambient temperature (~27°C)

CTs at 132 kV switchyard3 CTs in service for 34 years6 CTs in service for 35 years

3 CTs in service for 33 years

CTs at 33 kV switchyard 2 CTs in service for 26 yearsCT at 33 kV switchyard 1 CT in service for 49 years

Figure 2. Correlation coefficients between chemical and electrical parameters of tested oil samples.



aging and resting procedure that was adopted to simulate the typical daily loading pattern of the transmission network opera-tion [23]. By comparing the parameter performances, the labo-ratory samples aged for about 1200 h (equivalent to 50 d) under sealed conditions showed similar changes as the samples aged in the field for about 49 years.

The DGA results of the tested field aged oil samples indi-cated a possibility of having different types of faults, such as partial discharges (PD), low and high energy discharges (D1, D2) and thermal faults below 300°C (T1), according to IEC 60599–1999 and IEEE 57.104–2009. However, reasonable cor-relations could not be established among the predicted fault types and the tested parameters (see Table 3). In general, for a good oil, we may expect a lower color level, a high break-down voltage, a low moisture content, a low acidity level, a high IFT value and a low loss tangent value. IEC 60422:2013 [11], by introducing different performance indicators for pa-rameter ranges, supports asset managers and engineers in the judgment of tested oil condition. However, when the number of tested parameters increases, it is natural that some disparity may arise among them. For example, the loss tangent values are usually affected by the moisture content and/or the oil acidity and majority of the results of loss tangent and moisture content in Table 3 indicate “good” level of oil samples. In contrast, the acidity levels designate it as “poor.” Such results suggest a ne-cessity for limiting the number of test parameters, being also supported by the difficulty of testing all types of parameters periodically in a sealed type CTs. After careful consideration, we suggest that DGA and color analyses allow to predict the condition of field aged oils.

Dielectric Response Measurements on Field Installed CTsSamples and Conducted Tests

In this investigation, the dielectric spectroscopy (FDS) mea-surements were performed on 149 oil filled CTs installed in power station switchyards. Information about the CTs is sum-marized in Table 4. Out of these, 114 units were dead tank type covering the transmission voltage levels of Sri Lanka - 55 units at 132 kV and 59 units at 220 kV. The group of 132 kV CTs in-cluded 35 new units originating from two different manufactur-

Table 4. CTs used for the dielectric spectroscopy study

Test Set

Tank Type Voltage Condition

Numberof CTs

1 Dead 132 kV new CTs from manufacturer 1 112 Dead 132 kV new CTs from manufacturer 2 243 Dead 132 kV field aged for 5 - 7 years 144 Dead 132 kV field aged for 29 - 30 years 65 Dead 220 kV new CTs from manufacturer 2 156 Dead 220 kV new CTs from manufacturer 3 247 Dead 220 kV field aged for 27–35 years 208 Live 132 kV new CTs from manufacturer 4 29 Live 132 kV field aged for 12years 310 Live 132 kV field aged for 24 years 311 Live 132 kV sister units to a failed CT 2412 Live 132 kV laboratory aged 3

Table 3. Classification of oil condition based on various tests according to IEC 60422–2013

Oil sampleAgein years DGA Color

Breakdown Voltage

Moisture content Acidity IFT

Loss tangent at 90°C

Field aged, 220 kV 26 T1 Good Poor Poor Poor Good PoorField aged, 132 kV 33 T1 Good Fair Good Poor Good Good

33 T1 Good Good Good Poor Poor Good33 — Good Good Good Poor Good Good34 — Good Fair Good Poor Poor Good34 T1 Good Poor Good Poor — Good34 T1 Poor Poor Good Poor Poor Good35 — Poor Fair Fair Poor — Good35 — Poor Good Fair Poor Good Fair35 T1 Poor Good Good Poor Good Good35 — Good Good Good Poor poor Good35 PD Good Fair Good Poor Fair Good35 — Good Poor Good Poor Fair Good26 D1 Poor Poor Good Poor Poor Fair

Field aged, 33 kV 26 D2 Poor Fair Good Poor Poor Good49 T1 Poor Poor Fair Poor Fair Good

Lab aged: unsealed, wet Slow thermalaging

— Poor Poor — Poor Poor GoodLab aged: unsealed, dry — Poor Poor — Poor Poor FairLab aged: sealed, wet — Poor Poor — Poor Fair GoodLab aged: sealed, dry — Poor Poor — Poor Fair Good



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ers (marked as set 1 and set 2), 14 field aged CTs with less than 10 years in service (set 3) and 6 field aged CTs of 29–30 years in service (set 4). The group of 220 kV CTs was composed of 35 new CTs from two manufacturers (set 5 and set 6) and 20 field aged CTs with service times between 27 to 35 years (set 7). The investigated 35 live tank type CTs were all rated 132 kV. Out of them, two units were new (set 8), 30 CTs were field aged (set 9, set 10 and set 11) and 3 CTs were laboratory aged (set 12). Out of the field aged CTs, 24 were sister units of the failed CTs (set 11). Two new CTs in set 8 were not energized due to poor manufacturing quality. All most all the new CTs used in this study are of dead tank type (74 out of 76). Figure 3 shows photos of some of these CTs taken during testing; Figure 3a shows FDS measurements on a new dead tank type CT, Figure 3b shows three live tank CTs in the laboratory during thermal aging, and Figure 3c shows a thermal image taken before FDS measurement on a dead tank CT in a switchyard.

CT set 12 was electro-thermally aged in a cyclic manner by letting the insulation to be overheated by injecting twice the rated current to the windings [24]. Current of 10 A was injected into the secondary winding while short circuiting the primary winding, so that a current of 800 A flowed through the primary side (see Figure 3b). The CTs were electrically stressed dur-ing a day for 8 h and allowed thereafter to rest during the re-maining 16 h. This procedure was repeated for 840 h until the safety valve of one of the CTs opened due to pressure build up. Condition of the oil samples was tested by performing DGA tests after the safety valve opened. More detail related to the laboratory aging can be found in our earlier publication [25].

The FDS measurements were performed by means of two commercially available insulation diagnostic analyzers: IDA200 [26] and DIRANA [27]. In IDA200 instrument, the frequency of the applied AC voltage varied from 1 kHz to 1 mHz, whereas in DIRANA instrument (see Figure 3a), it varied from 1 kHz to 10 mHz. In both instruments, the applied volt-

ages were 200 Vpeak. The instrument terminals were connected between the primary winding (HV electrode) and short-circuit-ed secondary winding (LV electrode) and the tank (guard elec-trode). As preliminary work, a new and an aged CTs were tested by both IDA200 and DIRANA to check whether measurement results were comparable, and it was found that loss tangent val-ues measured by the two instruments at low frequencies (<1 Hz) matched each other well [25].

FDS measurements were performed at temperatures be-tween 23 and 35°C in the case of field aged CTs. Thermal im-ages were taken before each FDS measurement in the field for checking whether the temperature distribution inside the CT was relatively uniform (e.g., in Figure 3c temperature is within 31 - 32.2°C). It is claimed, according to the analyses present-ed in CIGRE TB 394 [3], that loss tangent of CT insulation is weakly sensitive to temperature variations between 15 and 40°C. Therefore, low frequency loss tangent values measured in the field were compared with each other without adjustments for temperature variations (i.e., 23 - 35°C). In case of labora-tory aged CTs the measurement temperature interval was much narrower 24 - 28°C.

Results

Comparison of Laboratory and Field Aging: Figure 4 shows a comparison of loss tangent measured on field aged and laboratory aged 132 kV live tank type CTs. In case of field aged CTs only 4 representative units, one from set 10 (24 years old) and 3 from set 11 (sister units to a failed CT) are presented. The initial FDS result from the laboratory aged unit shows the lowest level. During the laboratory aging, the loss tangent in-creased within the measured frequency span. The topmost curve indicating highest loss tangent values was taken after comple-tion of the aging by the safety valve opening. The loss tangent spectrum of all the field aged samples including the sister units

Figure 3. Photos taken during various stage testing of CTs. (a) testing of a new dead tank CTs at stor-age facility of a switchyard. (b) thermal aging of live tank CTs at laboratory. (c) thermal image taken before FDS measurements on a field aged CT.



to failed CTs lie within the initial and final spectrum of labora-tory aged CT.

The FDS results for laboratory aged CTs are plotted in the figure down to 1 mHz. One should notice that the loss tangent variation between 10 mHz and 1 mHz follows similar increas-ing trend and it is thus reasonable to assume that 10 mHz mea-surement limit is enough to estimate the condition of CTs. In return, the testing time reduces significantly from about 1.5 h to about 10 min, encouraging the utility engineers to use FDS measurements as a condition assessment tool in the field.

The results of FDS test obtained from the laboratory aged CTs were simulated by means of Havriliak-Negami (HN) gen-eral response model [28], which provided an accurate fit of the measured data over the entire frequency range for all the tested cases. Characteristic relaxation time (τ), which is one of the 5 parameters in the HN model, was estimated by fitting measured dielectric response at different aging conditions. As shown in Figure 5, the characteristic relaxation time strongly decreases with the aging time.

Condition Assessment Based on Loss Tangent at 10 mHz:Figure 6 shows frequency spectra of loss tangent for selected

dead and live tank type 132 kV CTs. The spectra of new dead tank CTs (Figure 6a) originating from two different manufac-tures lie as minimum and maximum boundaries, whereas the curves of aged CTs fall between them. In the case of live tank CTs (Figure 6b) the new, 12 years old and the 24 years old, CTs have lower loss tangent levels as compared with the sister units of failed CTs, indicating severe aging of the latter. For both types of CTs, the differences among loss tangent values are bet-ter visible at 10 mHz as at power frequency (50 Hz) or higher frequencies e.g., 1 kHz, similarly as earlier proposed by other researchers [17–19].

Figure 7 presents loss tangent values at 10 mHz for each tested CT set (see Table 4). They are grouped as: (a) live tank

units 132 kV, (b) live tank 220 kV units, (c) dead tank 132 kV units and (d) laboratory aged units. The results indicate that loss tangent values of live tank units are, in general, higher than those of dead tank type. Among live tank type, the sister units showed the highest level, but still below the results of the ones from the laboratory aging. The dotted lines show the general tendency of increasing loss tangent values with respect to aging condition, for example sets 2, 3 and 4 of 132 kV dead tank CTs. It can also be noted that the two sets of new CTs, namely set 1 and set 8, show higher losses, deviating from this tendency. These deviations are related to a poor manufacturing quality. Based on the loss tangent values presented in Figure 7, a condi-tion assessment strategy based on 10 mHz loss tangent value is proposed in Table 5. Action limits were selected in such a way that the condition of CT can be classified in to three catego-ries: good, fair and poor, similarly to the categories used for oil

Figure 4. Comparison of dielectric response results of field aged and lab aged 132 kV live tank CTs.

Figure 5. Variation of relaxation time of laboratory aged CT.



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classification according to IEC 60422:2013. Depending on the condition category and age of the CT, it is recommended either to: (a) continue service, (b) replace CT, or (c) perform oil tests (oil color and DGA) to determine continuation of service and repeat annual testing.

ConclusionsThe failures of live tank type CTs are mostly violent and

catastrophic in nature. CT failures experienced in the wet and tropical climate in Sri Lanka were all related to live tank type units and 70% of them failed prematurely. A necessity has thus

arisen to monitor condition of CTs by laboratory investigations of oil quality or by testing whole units.

The oil investigations showed that the field aging could be simulated by laboratory tests of thermally stressed oil. Accordingly, properties of 49 years field aged oil appeared like those of 50 d laboratory aged samples. The oil properties were investigated by means of chemical, physical and electrical tests. However, use of numerous parameters and classifying them ac-cording to IEC 60422:2013 may sometimes yield ambiguity in result interpretation. It has, therefore, been suggested to con-centrate on the evaluation of oil color and dissolved gas analy-sis, as performance indicators of the condition of the oil.

Figure 6. Selected loss tangent frequency spectra of new and field aged 132 kV CTs. (a) Dead tank CTs. (b) Live tank CTs.



Results of dielectric spectroscopy response measurements on the insulation system of whole CT units show that the technique provides an alternative route for the condition as-sessment. The variations of frequency dependent loss tangent show a general increasing tendency with aging time. It was also found that the loss tangent variations for dead tank type CTs are comparatively lower than those for live tank type. It is thus suggested that the loss tangent value at 10 mHz should be used together with results of oil color test and dissolved gas analysis as performance indicators for condition assessment of CTs, es-pecially for the live tank type.

AcknowledgmentsAuthors would like to acknowledge Ceylon Electricity

Board for facilitating field measurements and providing cur-rent transformers for laboratory testing. Special thanks go to the engineers of Ceylon Electricity Board and students of the Department of Electrical and Electronic Engineering,

University of Peradeniya who were involved in the presented research activities.

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Table 5. Condition assessment criteria based on loss tangent level at 10 mHz

Condition Category

Loss tangent at 10 mHz

Good Fair Poor

Recommendedaction

Age is less than25 years

continue service Oil tests (color and DGA) to determine continuation; test annually

replace the CT

Age is morethan 25 years

Oil tests (color and DGA) to determine continuation; test annually

replace the CT

Action limits Dead tank, 132 kV <1.5% 3–10% >10%Dead tank, 220 kV <1.5% 1.5–7% >7%Live tank, 132 kV <10% 10–40% >40%

Figure 7. Comparison of loss tangent data of field aged and laboratory aged live tank CTs; dotted lines show variations of average value.



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tures: electrical properties and modeling”, IEEE Tran. on Diel. and Elect,” Insu., vol. 9, no. 5, pp. 809–828, 2002.

Sarath Kumara (M’13, SM’17) was born in Ratnapura, Sri Lanka in 1979. He received the B.Sc. Eng. (Hons) degree in Electrical and Electronic Engineering in 2004 and M.Phil. de-gree in 2007, both from the University of Peradeniya (UOP) Sri Lanka. He obtained his Tec. Lic and PhD in 2009 and 2012 from Chalmers University of Technology, Gothenburg, Sweden. Currently he is a senior lecturer in the Department of Electrical and

Electronic Engineering, University of Peradeniya. He is a senior mem-ber of IEEE and an associate member of IESL. His research interests include high voltage insulation materials, condition monitoring, gas discharge simulations, high voltage testing and power system model-ling.

Manjula Fernando (M’07, SM’10) was born in Colombo, Sri Lanka in 1966. He received the B.Sc. Eng. degree from the University of Peradeniya, Sri Lanka in 1993, the Tech. Lic., degree from the Royal Institute of Technology, Stockholm, Sweden in 1997 and the Ph.D. de-gree from the Chalmers University, Gothenburg, Sweden in 1999. At present, he is a senior Professor and head of Department of Electrical and Electronic Engineering. He is a

chartered Engineer, an International Professional engineer and fellow of Institution of Engineers Sri Lanka. He was the founder chair of IEEE Sri Lanka Power and Energy Society Chapter in 2010, the gen-eral chair of IEEE fourth International Conference on Industrial and Information Systems in 2009 and the chair of IEEE Sri Lanka central region subsection in 2009/2010. His research interests include condi-



tion monitoring, alternative insulation and problems related to outdoor insulation.

Thanuja N. Aravinda was born in Colombo, Sri Lanka in 1989. He received the B.Sc. Eng. (Hons) degree in Electrical and Electronic Engineering in 2013 and M.Sc. Eng., degree in 2019, both from the University of Peradeniya (UOP), Sri Lanka. He has worked as Electrical Engineer for LTL Projects Pvt Limited (Presently known as Ceylax Engineering), Sri Lanka and Ceylon Electricity Board, Sri Lanka. Currently he is reading for the Ph.D. degree at

University, Queensland, Australia.

Dileepa S. Daulagala obtained the degree in Bachelor of Science in Electrical and Electronic Engineering (1st Class Hons) from the University of Peradeniya, Sri Lanka in 2009. He joined Ceylon Electricity Board in 2010 as an electrical engineer and worked as a project Engineer in Ukuwela hydro power station reha-bilitation project till 2011. In 2011, he joined the Asset Management Hydro Electrical Branch. He is a chartered engineer from the

Institution of Engineers, Sri Lanka (IESL) and currently seeking to complete his degree in Master of Engineering at the University of Peradeniya. He has 9 years of experience in the field of condition mon-itoring of major power plant assets including generators, transformers and other main switch-yard equipment like circuit breakers and instru-ment transformers.

Asanka P. Bandara was born in Ratnapura, Sri Lanka in 1986. He received the B.Sc. Eng. (Hons) degree and M.Sc. Eng. degrees from University of Peradeniya, Sri Lanka in 2010 and 2013. He became a chartered engineer in 2016. He started his career as an instructor in the University of Peradeniya in 2010 and later worked as an operations engineer in the Kotmale Hydro Power Station during 2011-2015. He is currently working as an operations

engineer in the Samanalawewa hydro power station, Sri Lanka. His main research interests are condition monitoring and identification of faults of power and current transformers using different methods.

Kapila Bandara was born in Kandy, Sri Lanka in 1979. He received the B.Sc. Eng. degree from the University of Peradeniya, Sri Lanka in 2004, M.Sc. Eng., degree from the University of Peradeniya, Sri Lanka in 2009 and the Ph.D. degree from the University, Queensland Australia in 2016. At present he is an electrical engineer of Ceylon Electricity Board and IET chartered Engineer. His research interests in-clude condition monitoring, Power transform-

ers, hydro generators alternative insulation.

Pradeep Nandasena was born in Colombo, Sri Lanka in 1973. He received the B.Sc. Eng. de-gree in Electrical Engineering from the University of Moratuwa, Sri Lanka in 1999, M.Eng. degree in Electrical Engineering from the University of Moratuwa, Sri Lanka in 2005 and PG. Dip. in Business Administration spe-cialized in Management of Technology from the University of Moratuwa, Sri Lanka in 2009. At present, he works as a Chief Engineer in

Asset Management Hydro Electrical Branch, Ceylon Electricity Board, Sri Lanka, involving of condition monitoring of generators, transformers, circuit breakers, surge arresters and battery banks of hydro power stations in Sri Lanka. He is a chartered engineer of The Institution of Engineers, Sri Lanka (IESL) and member of IET. His research interests include condition monitoring and failure prediction of high voltage insulation.

Gawasinghe A. Jayantha was born in Matara, Sri Lanka in 1959.He received B.Sc. Eng. de-gree in Electrical and Electronic engineering from the University of Peradeniya, Sri Lanka in 1983. He is a charted electrical engineer and retired in February 2019 as an Additional General Manager of Ceylon Electricity Board after 34 years of service. Presently he is work-ing as a principal resource engineer for EnPower Engineering Consultants Pvt Ltd., Sri

Lanka. He specialized in electrical power generation including condi-tion monitoring and testing of high voltage equipment, project specifi-cation, contract negotiation, design review, supervision and commis-sioning testing of new and refurbishment of hydro plants.


Condition assessment of 132/220 kV oil-paper current ... - ac

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