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Dielectric properties of stator coil insulation of medium voltage motor
(2019-07-01)
Pattanadech, N.
;
Boonsathitthavorn, S.
;
Phumipunepon, N.
One of the non-destructive methods commonly used to characterize the electrical properties of power devices is polarization and depolarization current (PDC) method. The objective of this paper is first to compare the dielectric properties of the stator coil without overhang insulation, the stator coil after hot-press process, and the stator coil with overhang insulation. The second objective is to compare dielectric properties of newly wound stator coil, the stator coil heated at {\mathrm {60^{\circ}C}}, and the stator coil heated at {\mathrm {90^{\circ}C}} for a specific time. The stator coils in this research were designed for a 6.6 kV 260 kW synchronous motor. For the stator coil without overhang insulation, the slot portion stator coil was wound by Nomex paper, Kremica tape, and conductive tape. For the overhang insulation, the end portion was wound by Filosam tape and polyester tape. Then, the PDC measurement was performed. The parameters from PDC analysis were used to assess dielectric properties. These parameters were composed of the PDC shapes, capacitance ratio, polarization loss and conduction loss. Test results showed that different insulation types applied for each part of the stator coil manufacturing provided different dielectric properties. This point should be considered when PDC measurement is performed with the whole insultion system of the high voltage motors.
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Polarization and depolarization current characteristics of thermally stressed stator bars
(2019-07-01)
Pattanadech, N.
;
Srichuen, N.
;
Wang, C.
;
Kaewdee, N.
;
Poungpat, T.
Polarization and depolarization current (PDC) measurement was used in this research to investigate the insulation integrity of stator bars. This method is non-destructive testing. This paper presents the PDC analysis of thermally stressed stator bars divided into two main groups. The first group was heated at 100^{\circ}C and the second group was heated at 130 ^{\circ}C for 36 hours. After 12, 24 and 36 hours of heating process, PDC measurement of each test specimen was performed. PDC test results including capacitance ratio and dielectric dissipation factor were analyzed and reported.
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The Dissipation Factor (tan δ) Monitoring of A Stator Winding Insulation of A Synchronous Machine
(2018-11-14)
Phloymuk, N.
;
Nimsanong, P.
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Phumipunepon, N.
;
Potivejkul, S.
;
Wiangtong, T.
the aim of this paper is to describe the dielectric loss tangent (tan δ) behaviors of the stator winding insulation of the 14.5 MVA 11kV synchronous machine from 2014-2017. This machine is still operated up to now. The tan δ values at different test voltages was measured and recorded. It was found that the sharp increase in tan δ values gave the sign of a significant degree of contamination and damage on the insulation surface which was proved by inspection. From the investigation the tan δ measurements is one of the effective ways to monitor and evaluate the insulation conditions of the stator insulation. The analysis and discussion of the existed problem of the synchronous machine are also included in this paper.
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Dielectric Properties of Resin Rich Stator Coil of High Voltage Motor during Processing
(2018-11-14)
Boonsathitthavorn, S.
;
Phumipunepon, N.
;
Kitcharoen, P.
;
Pattanadech, N.
One of the non-destructive test methods commonly used to characterize the electrical properties of power equipment is polarization and depolarization current testing. The objective of this paper is to study of the change of dielectric properties during the manufacturing stages of a stator coil used in 6.6 kV 260 kW motor. There were five steps to manufacture the resin rich stator coil. The first step, the copper coil was wound around by NOMEX paper. Then the slot portion of the stator coil was wound by KREMICAL tape as the second process and by the conductive tape as the third process. Then, the insulation and conductive layer of the stator coil were pressed and cured at 160°C for one and a half hour as the fourth process. The pressing and curing will combine the multi insulation to be homogeneous insulation of the stator coil. The final step, the end winding portion was wounded by Filosam tape and polyester tape. The polarization and depolarization currents were measured and recorded after finishing each manufacturing process. From the test results, the polarization currents and depolarization currents obtained from each step were clearly different. Then the polarization and depolarization currents, conduction current and capacitance of the test results were analyzed and reported in this paper.
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Polarization and Depolarization Current Characteristics of Degradation Stator Insulation of A Rotating Machine
(2018-11-14)
Phumipunepon, N.
;
Chaisiri, P.
;
Thungsook, K.
;
Pattanadech, N.
This paper presents the dielectric analysis of the simulated degradation stator bars compared with unmodified stator bars. The stator bars used in the experiments were acquired from the 30 year in-service synchronous machine of a hydro power plant. The simulated degradation stator bars were prepared and comprised of outer corona protection degradation stator bars, partial discharge (PD) stator bars and thermal degradation stator bars. In case of the outer corona protection degradation, the outer corona protection surface was abraded for small damages. For PD degradation bar, the PD existing bars were used for the experiment. In case of thermal degradation stator bars, they were divided into three groups, the first group of stator bars was heated in the oven at 100°C for 12 hours. The second and third group stator bar was heated at 120 and 140 °C respectively for 12 hours as well. After preparing the test objects, the polarization and depolarization current (PDC) were performed with the mentioned stator bars. The PDC test results were recorded. The test results showed that the polarization currents and depolarization currents, the conduction currents and the capacitances of the simulated degradation stator bars were clearly different from these of the unmodified stator bars. Other analysis parts are reported also in the paper. This paper suggests that PDC test technique is one of the effective methods for evaluation of the stator bar insulation characteristics.
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Dielectric Properties Analysis of Gas Turbine Synchronous Generator by Polarization and Depolarization Current Measuremen
(2018-11-14)
Phloymuk, N.
;
Nimsanong, P.
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Phumipunepon, N.
;
Kittiratsatcha, S.
;
Pattanadech, N.
Insulation of stator winding in large electric rotating machines mostly consists of mica and epoxy resins with a number of junctions inside the insulation. The diagnostic test method for monitoring the insulation condition of these machines every specified period of operation is very important. The polarization and depolarization current (PDC) test method is one of the potential test techniques that can be used to evaluate the polarization process of the insulation by measuring the charging and the discharge currents of the insulation under the DC high voltage test. The PDC test experiments was done with the stator winding insulations of four identical gas turbine synchronous generators rated at 58,824 kVA 11 kV and 3,000 rpm (manufactured in 1997). From the results, it was found that increase in ambient relative humidity and operation winding temperatures increased the polarization and depolarization currents of the stator winding insulation. Besides, the in-serviced operation hour of the investigated machine had an effect on the tan δ. The tan δ increased with increase in the degree of insulating deterioration and the in-service operation hour also. Increasing of tan δ is associated with increasing of imaginary capacitance of the tested insulation. The analyzed parameters can be taken into account for evaluating the aging and deterioration conditions of the insulating material of the synchronous machine which are useful for a maintenance strategy of the rotating machines.
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Polarization and depolarization currents of the degraded stator insulation of the synchronous machine for hydro power plant
(2018-06-29)
Phumipunepon, N.
;
Phloymuk, N.
;
Pattanadech, N.
The aim of this paper is to investigate the polarization and depolarization current (PDC) characteristics of the simulated degradation stator bars compared with that of the unmodified 30 year in-servicestator bars. The stator bars used in this experiment were obtained from the 30 year in-service synchronous machine for hydro power plant. These bars were divided into two groups. The first group was the unmodified 30 year in-service stator bars. The second group was composed of the unmodified stator bars with the additional thermal stress and the unmodified stator bars with simulated cavities. The coil side stator bars with the length of 30 centimeters and the width of 7 centimeters were prepared for the investigation. Conductive tape at the both ends of the test specimen was removed and replaced by the guard rings for separating the leakage current existing during performing the experiment. The experiment started with PDC measurement of the unmodified 30 year in-service stator bars. Then the PDC measurement of the simulated degradation stator bars were performed. In case of the unmodified stator bars with the additional thermal stress, the test specimen was divided into two groups. The former group was heated in the oven at 100 degree Celsius for 12 hours. The latter group was heated at 120 degree Celsius for 12 hours also. For the unmodified stator bars with simulated cavities, four air cavities with the dimension of 0.1×5×14 cm were simulated in the insulation layer of the stator bars. Besides, four water-cavities as the same dimension and positions with the air-cavity were also simulated in the insulation layer of the stator bar. After completely preparing the test samples, the experiments were performed. A DC voltage was applied to the test specimen for a specified period for polarization current measurement and then suddenly stop DC supplied voltage to short circuit the test specimen for depolarization current measurement. The test results showed that the polarization and depolarization current of the simulated degradation stator bars were clearly different from that of the unmodified stator bars. The insulation characteristics of the investigated stator bars were also analyzed.
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Partial discharge behaviors of a surface discharge problem of the stator insulation for a synchronous machine
(2018-06-29)
Phloymuk, N.
;
Phumipunepon, N.
;
Pattanadech, N.
This paper presents the partial discharge (PD) behaviors of the stator winding insulation focusing on a surface discharge problem of the11kV, 14.5 MVA synchronous machine. This synchronous machine has been installed in 2004 and still operated up to now. The offline PD measurement has been continuously performed during 2014-2017. The PD activities comprising of the magnitude of the highest PD pulse, Qm, at different test voltages and the PD patterns at the rated phase voltage were analyzed. The investigated synchronous machine was stopped for least 12 hours prior to running the off-line PD test in order to cool down so that the winding temperature did not exceed 40 °C during performing the experiment. In accordance with the industry practice guide the voltage applied to the tested stator winding insulation was increased in step with 0.5 kV per step for the duration of 1 minute from 0.5 to 6.3 kV (phase voltage) for monitoring the PD activities. The experiment was made with one phase to ground of the stator winding insulation at a time, with the other two phases grounded. Then two times re-tested as mentioned above were done to ascertain the PD activities measured. After that other two phases of the stator winding insulation were tested as the same manner. The test results show that the change in Q<inf>m</inf> value recorded in 2014 - 2016 were nearly constant respect to the applied voltage. The Q<inf>m</inf> was a strong tendency increase in 2017. The sharp increase in Qm gave the sign of a significant degree of contamination on the insulation surface. Besides, the PD patterns measured were sensitive to the progress of discharges. After that this machine was inspected. The contamination and defects at the surfaces of the stator insulations were detected. From the investigation, the PD measurement is one of the effective ways to monitor and evaluate the insulation conditions of the stator insulation.

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