D Session 2004 CIGRÉ. 50 kv. 150 kv. Condition Assessment of High Voltage Power Cables. The Netherlands. E. Gulski * F.J.

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1 21, rue d'artois, F Paris D1-306 Session 2004 CIGRÉ Condition Assessment of High Voltage Power Cables E. Gulski * F.J. Wester Ph. Wester E.R.S. Groot J. W. van Doeland Delft University of Technology Nuon Arnhem The Netherlands InfraCore Alkmaar Pirelli Cables and Systems Delft Abstract From the reliability and availability performance point of view power cables connections of the transmission network are very important assets. Moreover, the liberalization of electricity markets has two effects on the business environment of power utilities. First, the maintenance and investment costs have to be maximally reduced using the maximum service life of the existing transmission power cable networks. Secondly, due to increasing cost of nonavailability a higher reliability in power supply is requested. In this contribution based on experiences made in the Netherlands, for condition assessment of HV power cables systematic approach has been developed. Based on the assumption that there is not one dominant failure process in HV cable networks, PD in the cable insulation cannot be seen as the only messenger for failures: the complexity of cable systems in HV networks is often higher (e.g. oil-filled, gaspressurised cable systems, therefore different approaches have been investigated and implemented in the last fife years. 1. INTRODUCTION It is known, that the insulation failures in a cable network may be caused by lower dielectric strength 50 kv 150 kv Figure 1: Examples of HV cable terminations in the field (The Netherlands). * Delft University of Technology, HV Technology & Management, 2628 CD Delft, Mekelweg 4, The Netherlands 1

2 due to aging processes and by internal defects in the insulation system. To reduce the failures by the aging of the impregnated insulation two types of diagnostic methods are in use: (a) oil analysis e.g. dissolved gas analysis (DGA) (b) assessment of bulk properties of insulation e.g. tan δ measurements [1]. To reduce the failure by internal defects, on-site cable diagnostics can be applied based on quantities related to insulation degradation, as partial discharges. Moreover, to assess the condition of a certain cable type diagnostic packages have been developed. After a survey of all relevant information about the cables in the network, diagnostics are carried out to assess the condition of each cable. Interpretation is done based on criteria for each diagnostic. All results together are used for a classification of the cable into five possible categories. A maintenance program and/or guideline for further operation of the cable is linked to each category. Depending on the category, the condition assessment is repeated once every 3 or 5 years. 2. POWER CABLES DIAGNOSTIC TOOLS Nowadays the following on-site diagnostics are widely accepted and applied in the field. Unlike voltage testing, measurements of the dielectric do give an absolute indicator for the quality level of the cable insulation. The results of these measurements have a direct relation to the average qualitative level of the insulation at the moment of measurement and can thus be applied as a trend- or fingerprint measurement The tan δ measurement is applied for the determination of the loss factor of the insulation material. This factor increases during the ageing process of the cable. The 50 Hz tan δ measurement should be regarded as a diagnostic and/or supporting measurement (figures 2, 13, tables 3, 4). The tan δ value of a cable is strongly influenced by the composition of the connection, the trace, and the deviations in joints and the actual cable temperature. The tan δ measurement is only applicable as trend measurement if composition circumstances of the trace and thermal conditions of successive measurements are virtually identical. The tan δ measurement is not applicable for XLPE cables due to the very low tan δ value. For HV paper insulated cables the tan δ can be an important indicator of possible thermal breakdowns [2, 3]. Figure 2: Dielectric Measurements (The 50Hz tan δ) on a 17.5/30kV paper-oil power cable using 15 kv Mobile Insulation Diagnosis System (MIDAS). Figure 3: Oil analysis mobile test set. An oil analysis determines the gas amount, the type of breakdown voltage and tan δ of the insulating oil applied in pressured oil of cables and joints. From these data aging phenomena, thermal overload and partial discharges can be detected (figure 3, tables 5, 6). The oil analysis is the standard test with which the quality of oil insulated cables is checked. Important for the judgment of the results are the configuration and age of cable/joints, the historical and present load pattern of the connection and the amount of oil added in the past. These factors have an important influence on the results of the oil analysis. Partial discharges are an indication for weak spots in a cable connection (figure 4, table 6). In order to run the measurement partial discharges are ignited in the cable insulation or joints by the application of a test voltage [4]. Due to the physical character of discharge occurrence, such as the PD inception voltage the PD pulse magnitudes, PD patterns and PD mappings for a utility interested in applying PD diagnostics for condition assessment of its power cable networks, a number of technical and economical aspects are of importance: Voltage type: equivalence in PD inception processes among different voltage stresses for solid insulating materials; 2

3 Non-destructiveness: non-destructiveness of voltage stress during the diagnosis; IEC conformity: in the case of measuring the PD quantity apparent charge of PD pulses in [pc] and [nc] the PD detection methods applied has to fulfil the recommendation of IEC 60270; Sensitivity: immunity for on-site interferences and the level of system background noise; Analysis: possibility to generate advanced diagnostic information to support diagnostic knowledge rules; Efficiency: investment costs, maintenance costs, transportability and operation of the method in different field circumstances; 3. On-Site PD DETECTION HV CABLES Test object: HV power cable up to U 0 = 290 kv 1600 HV Divider Control and data processing unit 2000 Inductor L 250kV solidstate switch Resistor R 250kV HV DC Supply Figure 4: Schematic over-view of the 250 kv Damped AC Voltages Partial Discharge Diagnosis System: 13 MVA, total weight 300 kg; occupied space 1.6m x 3m x 2m. For the on-site detection of PD related defects in power cables, it is necessary to energise the disconnected cable sample for the ignition of the PD sources. The detection equipment is therefore directly connected to the cable conductors (or through the switchgear). In this way, the different phases of the cable circuit can be energised and the PD pulses can be coupled out. The capacitive power P needed to stress on-site the cable insulation is determined by the test frequency f, the cable capacitance C cable and the test voltage U test. In order to decrease the capacitive power demands for energising cables as compared to 50Hz test voltages, different energising methods using specific voltage shaped and frequencies have been introduced for PD diagnostics nowadays [1]. With regard to the on-site application a number of characteristics have been pointed out for mobile HV systems [5]: - lightweights measured with kg/kva specific weight, - compactness versus output voltage, - system assembling and voltage erecting effort, - necessary power demand. At commercially available HV systems the specific weights vary between 1.5 up to 20 kg/mva. In dependence of the rated power the characteristics as mentioned in above may result in a solution with kg weight and higher: large truck(s) solutions. With regard to possibility of dielectric measurements e.g. PD, due to external disturbances till now, by using conventional systems e.g. 50/60 Hz tunable reactor circuits or Hz tunable frequency circuit sensitive PD detection is still difficult. Independent of background noise on-site resonant test sets using tuned frequency needs very dedicated noise suppression techniques if applied for sensitive PD detection using a conventional PD measuring circuit according to IEC Figure 5: Schematic view of a 250kV DAC energizing diagnostics, Oscillating Wave Test System High Voltage. Figure 6: Schematic behaviour of charging and discharging time. In contrast to the situation around XLPE and PILC distribution power cables [1] in the case of HV cables (rated voltage 50kV and higher) the PD diagnostics is due to above mentioned limitations still not systematically used. Considering the above mentioned situation in the field of on-site PD detection for HV power cables it can be concluded that there is still a structural need to explore the possibility of on-site PD diagnosis for HV cables. Therefore on the basis of 4 years of systematic field experiences 3

4 with PD diagnosis of distribution power cables [6] as well as on the base of 2 years of fundamental research the authors discuss in this contribution a new solution for PD diagnosis of transmission power cables. This solution covers the on-site application of damped AC voltages in the range of 50Hz up to 500Hz to energize HV cables and to detect and to locate discharging sites [7]. The off-line PD diagnostic tool as used for the investigations in this paper is based on external energising of a cable circuit by damped AC voltages with a voltage source up to 250kV. Originally, the DAC voltages are introduced as a cost-effective withstand-voltage test for XLPEinsulated HV cables [8]. Nowadays, DAC voltages are more and more used for nondestructive PD diagnosis of distribution power cables [1, 3, 4, and 7]. One of the methods using DAC voltages for detection and localisation of PD in cables is known as Oscillating Wave Test System (OWTS), see figure 5 [6, 7]. For the generation of damped AC (DAC) voltages, the power demand is low due to the charging the cable capacitance with an continuously increasing DC voltage, after which the cable capacitance is switched in series with large inductance, resulting in an oscillating voltage wave with a frequency comparable to power frequencies. Figure 6 shows a scheme of the energising method for damped AC voltages for PD detection in power cables. The cable sample (represented as a capacitance C c ) is linearly charged with a DC power supply in a few seconds to the selected test voltage level (figure 7). As soon as the cable is charged, the DC supply is disconnected and a specially designed solid-state switch connects the cable sample to an air-core inductor in a closure time of less than 1µs. In this way, and LC loop is created and an oscillating voltage wave is applied to test the sample. Due to application to the cable section of a continuously increasing DC voltage supply (figure 6), directly followed by a switching and oscillation period no steady state DC conditions occur [9]. The test frequency of the oscillating voltage wave is approximately the resonant frequency of the circuit. This means that the test frequency of the applied Figure 7: Dependence of the charging time and applied test frequencies of the DAC stress and the power cable capacitance. Figure 8: Dependence of the maximum power cable capacitance and the applied test voltage. 1.6 m 2 m Inductor L 3.5H 250 kv HV divider; PD coupling unit 250 kv solid state switch 15 kω Resistor 250 kv HV DC supply Figure 9: Schematic over-view of the 250 kv Damped AC Voltages Partial Discharge Diagnosis System: 13 MVA, total weight 300kg; occupied space 1.6m x 3m x 2m. DAC voltage is dependent on the cable capacitance, see figure 7. The cable capacitance varies due to length and insulation type. Due to the low loss factor and design of the air-core, the resonant frequency is close to the range of power frequency of the service voltage: 50Hz to 500Hz, e.g.: - cable sample of 300 m ~ 30nF results in an oscillation voltage of ~ 375 Hz; - cable sample of 3km ~ 0.30µF results in an oscillation voltage of ~ 118 Hz; 4

5 - cable sample of 10km ~ 1.0µF results in an oscillation voltage of ~ 85 Hz. The quality factor Q of the resonant circuit remains high depending upon cable (30 to more than 100), as a result of the relative low dissipation factor of power cables. The maximum power cable capacitance which can be tested at DAC stresses using OWTS HV system can be calculated in dependence of maximum voltage applied (figure 8): The energizing system as well as the PD measuring circuit practical solution as proposed by OWTS HV system consists of a number of components (figure 9). As the DAC frequency represents the AC power line frequency, the measurement bandwidth of the PD detection circuit is chosen in accordance with IEC recommendations. For the purpose of PD localisation by travelling waves, the bandwidth of the system amplifier is increased up to 10 MHz combined with a 100 MHz digitiser. The PD activity signals, ignited during one or more oscillating voltage waves, are detected by the system, which can process the signals for two purposes: A phase-resolved PD pattern can be resolved from multiple DAC sequences. In this way, patterns can be obtained which are similar to those recognised under 50(60) Hz conditions (figure 10). Single PD pulses can be analysed for original location by using travelling wave analysis. Statistical evaluation of PD signals obtained after several oscillating waves can be used to evaluate the location of discharge sites in the power cable. A PD mapping is created, which shows the distribution of the detected PD in a cable circuit, as a function of the magnitude or the intensity (figure 11). In contrast to traditional HV test systems this new solution for advanced PD diagnosis for HV power cables up to 250kV uses damped AC voltage stresses in the frequency range of 50Hz 600Hz. Due to the compactness and lightweight of the system (e.g. 300kg to generate 13 MVA, dimension 1.6m x 2 m x 3m) and no large external voltage sources connected to the test cable during PD detection at damped AC voltages, sensitive PD measurement is possible. Using a number of PD quantities as processed by the system advance diagnosis is possible. Unless the facts that this method is fully accepted for distribution power cables, the authors realize that the full acceptance for transmission power cables has to be proved. Therefore in the next time intensive and systematic field measurements on power cables in Dutch transmission grid will be performed to validate this advanced PD diagnostic for HV cables. (a) (b) Figure 10: Examples of DAC voltages as generated using OWTS HV system and PD detected: a) full voltage wave b) zoom of PD patterns as detected during 1 power cycle. Figure 11: Examples PD location mapping as made after DAC voltage stresses. In the graph the PD mapping shows for all three phases the discharge concentration across the cable length. In the table measured PD quantities are extracted for particular cable parts and accessories. 5

6 4. CONDITION ASSESSMENT AND CLASSIFICATION OF OIL-FILLED CABLE SYSTEMS In order to operate the network with optimal availability against minimal costs good knowledge of the condition of the cable links is required. Four main steps can be distinguished in this process as is shown in figure 12. It is always the complete condition of the cable system that has to be examined to optimise its performance. For example, the insulation of an oil-filled cable can be in good condition, when the hydraulic system of this cable link does not function, a failure will be inevitable. The complexity of a cable system is expressed in the example of an oil-filled cable system in figure 12. For a complete insight into the condition of the cable system, diagnostics are required for every part of the cable system. Depending on the type of cable and the construction of the system a combination of diagnostics is applied. After the fieldwork, the results are processed, stored in databases and compared with reference values to evaluate the condition of the cable system. Referring to figure 12, classification is the next step after the condition assessment. The main goal of classification is to divide the investigated cable systems into categories on which future maintenance and operation can be based. Table 1 gives an example of the categories, which in general are used to classify a group of cables. The listed availability rates, service times and life times are examples and do not automatically apply to every type of cable system. These rates and times can be used as performance indicators in service contracts between grid owners and service providers. The first target of a maintenance program Inventarisation of cable network Maintenance - operation accessories Table 1: Example of cable classification. Cable Description Availabi Expected Expected cat. lity in time for life time service CBM (h/y) (years) A new cable in good >99.9% <24 >30 condition B good condition but >99% <48 >25 extra attention is required C stable situation, but >95% <72 >15 moderate condition D In-stable situation <50% - - E end of life <5% - <3-5 based on the classification is to keep the cable system in the highest category as long as possible against minimal costs of ownership. Maintenance activities comprise, among others, small repairs, replacements, tests and inspections. Depending on the classification and the type of cable, a complete condition assessment is repeated once every 5 or 10 years. For a group of cables of the same type, which have the same classification after the initial condition assessment, the condition of one or two representative cables can be followed to get insight in the ageing of the complete group. If new information becomes available, the classification of a cable or a group of cables can be adjusted. The ageing and development of failures in paper insulated cable systems is a complex process that has been described in numerous publications, for example [10-12]. Every part of a cable system is exposed to ageing under influence of thermal, mechanical and electrical load. Also external factors like excavation damages and environmental changes can be of great influence on ageing and failure processes. In the end, these mechanisms lead to a cable failure, due to an electrical or thermal breakdown. The ageing and failure processes involve: ageing of metallic sheaths due to thermal and mechanical stress or vibrations; changes in the thermal resistance of the soil surrounding the cable; corrosion of contacts in pressure gauges with an alarm function; pollution of terminations; influence of cable construction on ageing, for example the difference between ageing of mineral and synthetic oil. earthing system cable Condition assessment hydraulic system Classification cable environment Figure 12: Maintenance approach of oil-filled cable system. 6

7 Table 2: Diagnostics. No Description Result On- Applicability per cable type site Oilfillepregnatesurised Mass-im- Gas pres- a) measurement of dielectric loss angle indication of condition cable yes yes yes yes insulation b) partial discharge measurement detection of local faults yes yes yes yes c) oil analysis: dissolved gas analysis, AC electric condition of the oil and yes yes no no strength, dielectric dissipation factor indication for ageing and defects in insulation d) paper analysis (destructive): visual inspection, condition of paper insulation no yes yes yes magenta test, foam test, water content e) DC sheath test condition of non-metallic outer yes yes yes no sheath f) lead sheath analysis (destructive) condition and life expectancy no yes yes yes of lead sheath g) visual inspection of accessories detection of pollution, ageing yes yes yes yes and damages h) Inspection of earthing system check of layout and resistances yes yes yes yes i) Inspection of hydraulic system check on leakages, working of yes yes no yes pressure gauges and alarm settings j) determination of impregnation coefficient presence of free gas in the yes yes no no cable insulation k) g-value measurement thermal resistance of soil yes yes yes yes around cable l) HV tests on cable samples (destructive) condition of cable and life time no yes yes yes assessment Table 3: 50Hz off-line method interpretation rules for combination of tan δ and PD diagnosis to assess and classify the condition of power cables. Cable category PD at U 0 [pc] tan δ at U 0 [x10-4 ] remarks A PD 250 & 30 - B PD 1000 & 50 - C PD 1000 or PD no localization & tan δ > 50 tan δ 80 Follow trend D PD > localization & tan δ 80 Inspect/replace PD location E PD > no localization &/or tan δ > 80 Think about cable replacement For HV paper insulated cable systems several diagnostic tools are available to get a good impression of the condition [4]. Table 2 lists a number of these diagnostics, together with: the result after applying the diagnostic in the third column; the on-site applicability in the fourth column; the applicability per cable type in the last three columns. In table 3 schematic example of interpretation rules for off-line PD measurements on power cables are shown. These are rules of thumbs supporting the analysis of the measurement results from a cable section tan(d) Tan(d) to Voltage Test Voltage (kv) Cable 1 (XLPE) Cable 2 (XLPE) Cable 3 (Paper/Oil) Cable 4 (Paper/Oil) Cable 5 (P/O) 2.5 Uo Figure 13: MIDAS diagnostic data( tan δ in function of the test voltage as obtained for different power cables. 7

8 Most diagnostics can be applied in the field, especially for this purpose mobile test sets have been developed for on-site measurements. Some diagnostics (d, f and l) take place in the laboratory and are destructive; this means that a cable sample is needed to carry out the tests and analyses. The advantage of laboratory tests is weighting factor for long term assessment 1 l a b 0,5 f c,d,h diagnostics corresponding to table 2 e,g,h,i 0,5 1 weighting factor for short term assessmen Figure 14: Contribution of diagnostics (table 2) to short and/or long term condition assessment. Table 5: Reference values and criteria for oil analysis. AC electric Good > 50 kv/2,5 mm Decreased < 30 kv/2,5mm strength tan δ Good Increase 40 C < > C < > C < > C < > DGA Good Increase H 2 < 658 µl/l > 1093 µl/l CO < 50 µl/l > 78 µl/l CH 4 < 19 µl/l > 32 µl/l C 2 H 6 < 10 µl/l > 17 µl/l C 2 H 4 < 5 µl/l > 8 µl/l C 2 H 2 < 5 µl/l > 8 µl/l C 3 H 8 < 12 µl/l > 20 µl/l C 3 H 6 < 3 µl/l > 5 µl/l iso-c 4 H 10 < 2 µl/l > 3 µl/l n-c 4 H 10 < 34 µl/l > 63 µl/l CO 2 < 416 µl/l > 577 µl/l j Figure 15: Test on service aged 50 kv massimpregnated cables in the high voltage laboratory. that more and longer tests and measurements can be applied, which can be used for residual lifetime estimations and the development of criteria for on-site diagnostics. Each single diagnostic provides information about the condition of (a part of) the cable system on short and/or long term. Figure 14 gives an idea of which diagnostics contribute to short and/or long term condition assessment. With good knowledge of the cable network (inventarisation) a balanced package of diagnostics can be applied to all cables for a complete condition assessment. Both availability on short term and life expectancy on long term can be determined. Table 5 shows an example of criteria for interpretation of oil analysis. Despite current developments on on-site diagnostics, the need for further research on cable samples in the laboratory still exists, and even seems to grow (figure 15). These diagnostics contain both material analyses as HV tests on cable samples. These laboratory diagnostics give a powerful contribution to on-site diagnostics and vice versa. This contribution is attained by a good integration of these diagnostics if old cable is replaced, or a cable sample comes available due to a cable fault, this cable can be tested in the laboratory. Depending on the cable type, different test programs are applied, for example: - measurement of the dielectric dissipation factor at different voltages and temperatures with an example of a test on a service aged mass-impregnated cable) in the laboratory gives information about the thermal behaviour of the cable insulation and can be used as reference for on-site diagnostics and as guideline for future operation of the cable. - measurement of dielectric dissipation factor and partial discharges and performing oil-analysis while conditioning a piece of oil-filled cable at different temperatures and voltages gives information of ageing processes in this kind of cable; during these tests the temperature is measured with an integrated optical fiber. - measurement of the dielectric dissipation factor of a piece of gas pressurised cable under different conditions gives information about the relaxation time after refilling the system. Metallurgic analysis of the condition of the lead sheath gives an indication of the condition of this sheath. Especially for oil-filled and gas-pressured cables a good condition of the lead sheath is essential. Analysis on the paper insulation-material gives information on the condition of the insulation and the progress of ageing processes. 8

9 5. CONCLUSIONS The measurement of the dielectric dissipation factor (available up to and including 400 kv) gives a good indication for the ageing of the cable insulation and provides also important information for (re)calculating the maximum load capacity of a cable. The measurement of partial discharges detects local defects in the cable insulation or in accessories, for analysing the results, knowledge of the relation between discharge patterns on one hand and different defects and noise sources on the other hand is essential. The oil analysis gives an indication for ageing and defects in the cable insulation; a mobile test set containing equipment for measuring the AC electric strength, the dielectric dissipation factor and the concentrations of dissolved gasses was developed to enable a quick response in emergency cases. The DC sheath test gives information about the condition of the non-metallic outer sheath, but can also be used for testing the complete earthing system in for example a cable system with cross-bonded metallic sheaths. The determination of the impregnation coefficient tells if free gas is present in an oil-filled cable system or not, the presence of free gas is of direct danger to the operation of the cable. The measurements of the thermal properties of the soil (g-value) give valuable information to calculate the thermal resistance of the soil around the cable; this is used for (re)calculating the current-carrying-capacity of a cable. The recommended maintenance program for HV cables strongly depends on the type, age and load history of the cable involved. Moreover the maintenance measurement of pressured oil and gas insulated cable systems is very complex. A responsible diagnostic maintenance program demands a thorough inventory of the connection. Table 6 shows a selection of diagnostics that could be part of a maintenance program. Depending on the status of the system (from A to E: from young to old) diagnostics should be applied at different time intervals. 6. REFERENCES Table 6: Program of diagnostics for HV cables Maintenance frequency [n/yr] Diagnostic A B C D E Check oil pressures * 12* 12* Measure saturation factor 0,2 1 1* 1* 1* (existence of gas) Oil measurement (dissolved gas, breakdown voltage, tan δ) 0,2 0,5 1* 1* 1* Check hydraulic system ( leakage) Visual inspection cable terminals On-site tan δ and PD 0,1 0,2 0,2-1 0,2-1 0,2-1 Inspection lead mantle - ** ** ** ** Paper quality - ** ** ** ** * special circumstances can lead to higher frequencies. ** destructive research in case of diversions or disturbances. [1] WG 21.05, Diagnostic Methods for HV Paper Cables and Accessories, Electra No. 176, February 1998 [2] Popma J. and Pellis J.'Diagnostics for high voltage cable systems' Proceedings ERA conference on High Voltage plant life extension.laborelec, Linkebeek, Belgium, November, 2000 [3] Harrewijn R., Doeland W. van, Weerd P. van de 'On-site tan delta measurements as function of the temperature on a 150 kv gas pressurised cable system' Proceedings ERA conference on High Voltage plant life extension. Laborelec, Linkebeek, Belgium, November, 2000 [4] E. Gulski, F.J. Wester, W. Boone, N. van Schaik, E.F. Steennis, E.R.S. Groot, J. Pellis, B.J. Grotenhuis, Knowledge Rules Support for CBM of Power Cable Circuits Cigre Paris 2002, SC 15 paper 104 [5] W. Hauschild, W. Schufft, R. Plath, K. Polster, "The Technique of AC On-Site Testing of HV Cables by Frequency-Tuned Resonant Test Systems", CIGRE 2002, paper [6] E. Gulski, F.J. Wester, J.J. Smit, P.N. Seitz and M. Turner Advanced PD diagnostic of MV power cable system using oscillating wave test system, IEEE Electrical Insulation Magazine, 16, 2, 2000, p [7] E. Gulski, F.J. Wester, J.J. Smit, E.R.S. Groot, Ph. Wester, P.N. Seitz, Transmission Power Cables PD Detection at Damped AC Voltages, Jicable 2003 [8] F. Farneti, F. Ombello, E. Bertani and W. Mosca, Generation of oscillating waves for after-laying test of HV extruded cable links, CIGRE Session [9] F.H. Kreuger, Industrial High DC Voltage, Delft University Press, 1995 [10] Head J.G., et al. Ageing of oil-filled cable insulation CIGRÉ 1982, paper [11] Robinson G. Power engineering journal, March 1990, p [12] Anelli P., et al. Diagnostic methods for HV paper cables and accessories ÉLECTRA No. 176, February 1998, p CIGRÉ 9