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Application of Polarization and Depolarization Current Measurement for Rotating Machine Insulation Analysis
(2021-01-01)
Pattanadech, N.
;
Nimsanong, P.
;
Worthong, T.
Rotating machine is a vital asset of the power plants. For the motors and generators in service, the stator winding insulation is generally operated under thermal, electrical, ambient, and mechanical stresses. The combination of these stresses causes insulation degradation that can lead to early aging or severe damage and, finally, the failure of such machines. The failure of rotating machines may result in immense financial loss and other aspects. Polarization and depolarization current (PDC) measurement has been introduced as one of the time-domain dielectric spectroscopy test techniques applied for insulation condition testing. This paper represents the application of PDC measurement to evaluate the insulation for the stator bars/coil insulation experienced with various kinds of stresses. Moreover, the PDC field test of generators and high voltage motors used in the power plants is introduced. From the experiments, the dielectric parameters obtained from PDC measurements are clearly useful parameters to evaluate the electrical insulation of such rotating machines.
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VLF dielectric response and HF localized dielectric discharge measurement for rotating machine insulation assessment
(2020-08-14)
Nimsanong, P.
;
Pattanadech, N.
This paper represents the very low frequency (VLF) dielectric response and high frequency (HF) localized dielectric discharge measurement for rotating machine insulation assessment. The integral conditions of stator winding insulation, the so-called aging condition, were investigated by the dielectric response measuring technique. The polarization and depolarization currents in the VLF range from 0.0001 to 1 Hz were measured under an external step electric field. The local conditions of stator winding insulation, the so-called weak spot condition, were examined by the partial discharge (PD) measuring technique. The PD pulse currents were detected by a capacitive sensor in a wide-band range, where the bandwidth of the measuring system was set between 30 kHz and 30 MHz. The medium voltage rotating machine rated 6.6 kV and 240 to 2,270 kW under different service conditions, i.e., new stator winding, moisture contamination, dirt contamination as well as thermally and severely aged insulation, was studied. Besides, four case studies on measuring the PD in service rotating machines rated 11–15 kV, 7100 to 211,000 kW as well as the attenuation of the PD pulses were conducted and demonstrated. With several case studies, this paper introduces new dielectric parameters, the so-called charge ratio (QR) and charge difference gradient (QDG), to identify the dielectric mechanism occurring in the stator winding insulation caused by the polarization and conduction processes. It can be concluded that the proposed parameters are a valuable tool for assessing the aging condition. In the case of the PD measurement, it was found that the PD pulse is strongly attenuated in the slot section. This paper also introduces the combination of both the dielectric response and PD measurement results, which can be very useful for assessing a complete insulation condition in the rotating machine. Moreover, the criteria for insulation conditions are suggested in this paper to evaluate the integral and local conditions for the rotating machine insulation. The local discharge in the machine causes electromagnetic waves, which may get released from the non-perfect characteristics of the enclosure. This signal may interfere with the functioning of other nearby electronic devices, especially the communication equipment. Therefore, maintaining the excellent condition of the insulation system by the proposed technique detailed in this paper will support the highly effective operational efficiency of the communication system as well.
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Estimating conductivity and interfacial polarization loss factors of oil-paper insulation for power transformers
(2020-07-01)
Nimsanong, P.
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Maneerot, S.
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Pattanadech, N.
This paper proposes the method for categorizing the estimating conductivity and interfacial polarization loss factors of the oil-paper insulation. The simulated dielectric responses in the time domain of oil-paper insulation with various conditions were studied. Lumped equivalent circuit, so-celled extended Debye model, for modeling the oil-paper insulation obtained from simulated results, were estimated by using ohm's law for conduction current, and a curve fitting technique with exponential functions applied to the depolarization current idep(t). The complex capacitance, conductivity loss factor, and interfacial polarization loss factor of the insulation system in the frequency domain from 0.01 mHz to 1 Hz can be calculated.
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Evaluation of loss factor of mineral oil and alternative fluids with temperature normalization
(2020-07-01)
Maneerot, S.
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Nimsanong, P.
;
Pattanadech, N.
This paper proposes the evaluation of loss factor of mineral oil and alternative fluids the natural ester (FR3) with temperature normalization. The oil samples (i.e., mineral oil, natural ester, and palm oil) were prepared for experiments. The oil samples were dried at 70 °C under 200 mbar in the controlled temperature oven and then cooled down to ambient temperature. The moisture contents of the oil samples were measured according to ASTM D1533. The test cell, according to IEC61620, was employed in these measurements. The polarization currents, ipol(t), of such oil samples under electric field stress of 0.2 kV/mm with a temperature range from 30 to 70 °C were measured, The test results are summarized in this paper. The step response measurement results were analyzed for conductivities, permittivity, and loss factor value. It was found that increasing temperature causes increasing conductivities but decreasing permittivity of oil samples.
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A fast and accurate dielectric response measurement for transformer moisture assessment and remaining life estimation
(2020-07-01)
Nimsanong, P.
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Maneerot, S.
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Pattanadech, N.
This paper proposes a fast dielectric response measurement for transformer moisture assessment and remaining life estimation. The dielectric response measurements in the time domain for in-service transformers with various insulation conditions categorized into four levels, i.e., excellent, good, fair, and poor conditions, were investigated. The dielectric response measurements were investigated by polarization and depolarization time for 100, 500, 1000, and 3000 seconds. For the dielectric response of oil-paper insulation of such a transformer, the conductivity of oil in ducts and moisture content in paper can be estimated by using the curve fitting technique in advanced evaluation tool in PDC-Analyzer-1MOD. Besides, significant parameters, i.e., dc resistance, insulation resistance, polarization index, tan δ of oil, complex capacitance, conductivity and interfacial polarization loss factors in the low-frequency range, the paper remaining life time, and bubbling inception temperature were evaluated with a single dielectric response measurement result. To confirm the PDC measurement test results, other insulation test techniques were performed. The dielectric response results obtained from PDC measurement were compared with the results from the other mentioned techniques. It was found that the polarization time for 3000 seconds and depolarization time for 500 seconds is suitable for assessing the moisture content in paper and other dielectric parameters comparatively.
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Condition assessment of MV motor based on charge difference and charge ratio analysis
(2019-07-01)
Nimsanong, P.
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Boonsaner, N.
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Pattanadech, N.
Insulation resistance and polarization index tests have been conducted in utility companies as one of the major tools for evaluating the integrity of stator winding insulation of medium voltage motor. Unfortunately, the information obtained from the measurement results are the combination of the electrical problem and polarization problem in the insulation system not separated from each other. This paper presents a new approach so-called charge difference analysis (QDA) and charge ratio analysis (QRA) to identify the problem in stator winding insulation occurred from conduction mechanism or/and polarization mechanism. Moreover, proposed parameters which are QD, QG and QR have been conducted on field motors in the following case studies: The first group (A) consists of two motors of which one is new motor and the other one is severely aged motor, the second group (B) consists of two motors of which one is lightly loaded motor and the other one is thermally aged motor, and the third group (C) consists of a single motor, on which PDC measurements have been carried out after maintenance in 2014 and 2016 respectively. From experiments, it was found that proposed parameters are able to provide useful information about the condition of stator insulation, i.e. contamination or/and degradation.
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Polarization and depolarization current measurement applied for investigation of underground cable system problems
(2019-07-01)
Pattanadech, N.
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Phongsirichairojna, T.
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Navapittayaratana, N.
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Nimsanong, P.
;
Jirathipchaisakul, T.
This research investigates the problems in XLPE cables system. The 12/20(24) kV underground cable with the cross section area of 240 mm<sup>2</sup> was used in the experiment. Two 3 meter long cables were connected by a cable joint where the defect was simulated on. The dielectric investigation of XLPE cable system by polarization and depolarization current (PDC) measurement was performed comparatively among four different cases: a healthy cable with healthy heat shrinkable joint (case1), a cable joint with an incision on XLPE surface (case2), a cable joint contaminated with 20 micron iron powder on XLPE surface (case3) and a cable joint contaminated with 20 micron copper powder on XLPE surface (case4). Diagnostic parameters, PDC shapes, dielectric dissipation factor (DDF) and conduction current, derived from PDC test results for analyzing the dielectric response are proposed in this paper.
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Dielectric Properties Analysis of Gas Turbine Synchronous Generator by Polarization and Depolarization Current Measuremen
(2018-11-14)
Phloymuk, N.
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Nimsanong, P.
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Phumipunepon, N.
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Kittiratsatcha, S.
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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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Studies of Electrical and Thermal Characteristics of Natural Ester Immersed Transformer Compared with Mineral Oil Immersed and Palm Oil Immersed Transformer
(2018-11-14)
Maneerot, S.
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Jariyanurat, K.
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Nimsanong, P.
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Bunlaksananusor, C.
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Kunakorn, A.
This paper represents studies of electrical and thermal characteristics of natural ester immersed transformer compared with mineral oil immersed and palm oil immersed transformer by designing and constructing three single-phase transformers with rated 400/1000V 10kVA, the first transformer used mineral oil, the second transformer used natural ester, and the last one used palm oil, for studying about electrical properties, thermal properties and chemical properties under different types of liquid insulation in each transformer. First of all, three types of liquid insulation were tested with many item such as dielectric breakdown strength according to IEC 60156, dielectric dissipation factor following to ASTM D924-99. Besides, dielectric breakdown strength of impregnated pressboard were also investigated following to IEC 60243-1. Moreover, the chemical properties of the insulations were tested for some properties such as moisture content in accordance with ASTM D1533-00, interfacial tension according to ASTM D0971-99, acidity according to ASTM D974-02. After that, transformers were operated at 100 % of designed rated with inductor load for four months by which the temperature, current, and voltage were recorded every hour. Every two months, the liquid insulation was sampling from each transformer to be investigated. From the test results, they can concluded that natural ester are the alternative liquid insulation for using instead of mineral oil. In part of palm oil, it has good properties but it has the weak points about dielectric dissipation factor and acidity which are higher than the others.
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The Dissipation Factor (tan δ) Monitoring of A Stator Winding Insulation of A Synchronous Machine
(2018-11-14)
Phloymuk, N.
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Nimsanong, P.
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Phumipunepon, N.
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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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