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    Frequency Domain Spectroscopy Analysis of the Water Tree XLPE Cable
    (2022-01-01)
    Sawatdimongkol, Whichakorn
    ;
    Chancharoensook, Phop
    ;
    Sawatdimongkol, Worachai
    ;
    Taylim, Alisala
    ;
    Luangpol, Amata
    Water tree is one type of insulation deterioration occurring in polymeric cables such as polyethylene, ethylene-propylene rubber, and cross-linked polyethylene (XLPE) caused by the existing impurities in the bulk insulation or imperfection of the semiconductive surface. Moreover, the water tree phenomenon affects the cable's overall lifetime and can be developed into an electrical tree, leading to the failure of the cable. Because of this, the evaluation of water trees becomes one of the most important factors in the condition assessment of the cable. This paper presents the comparison of the dielectric properties of 22 kV XLPE underground cable between aged and new (unused) cables. Furthermore, the water tree was detected in the aged cable. Besides, the evaluation of aged and new cables was performed by frequency-domain spectroscopy (FDS), which measures the insulation's complex capacitance and dissipation factors in the frequency domain. Then, the aged and new cables' complex capacitance and dissipation factor were compared. The test result found that the dissipation factor and imaginary part of the complex capacitance of the aged cable have a higher value than these of the new cable. More or less, the results show that FDS is one of the non-destructive testing methods suitable for assessing the condition of the cable insulation, which deteriorated by water tree.
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    Estimating conductivity and interfacial polarization loss factors of oil-paper insulation for power transformers
    (2020-07-01)
    Nimsanong, P.
    ;
    Maneerot, S.
    ;
    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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    A fast and accurate dielectric response measurement for transformer moisture assessment and remaining life estimation
    (2020-07-01)
    Nimsanong, P.
    ;
    Maneerot, S.
    ;
    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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    The aging of the insulation system of large rotating machines in frequency domains
    (2019-07-01)
    Phloymuk, Natthawut
    ;
    Pattanadech, Norasage
    The insulation of stator winding in a rotating machine consisted of mica and epoxy resin materials. The structure was also composed of junctions, so, a diagnostic monitoring condition of this insulation was taken into consideration. First, the results of the polarisation and depolarisation current measurement (PDC) of the test sample (stator winding rate of 13.8 kV) were investigated, as an experiment in the laboratory. The conditions of the experiment were conducted under different thermal stresses of 25°C and 100°C. The test sample was full stator bar. As found, the trend of the temperature of the winding rise if the current of the polarisation and depolarisation was increased. Second, the results of the PDC were calculated from the time domain to the frequency domain. The aim found that the aging point of the insulation system should take into consideration the results of the calculation of the frequency domain. The aging of the insulation system was a variant by the thermal stress, which was an effect from the complex capacitance and polarisation losses in the insulation winding system. Finally, this identified the phenomenon of the aging of the machine insulation system.
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    The investigation of insulation performance evaluation of the large electrical rotating machine in frequency domain
    (2019-01-01)
    Phloymuk, Natthawut
    ;
    Kando, Masaaki
    ;
    Pattanadech, Norasage
    The insulation structure of winding in a large electrical rotating machine consists of epoxy resin and mica material. The insulation structure is composed of many junctions. The insulation problems generate different kinds of signals, such as 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. Therefore, maintaining an excellent condition of the insulation system of the machine is very important. For a condition monitoring of this insulation as proposed in this research, it is taken into consideration the results of the polarization and depolarization current (PDC) measurement of the test sample, and the stator winding rated 13.8 kV was investigated. The experiments were conducted under different thermal stresses, i.e., 25<sup>◦</sup>C (the room temperature) and 100<sup>◦</sup>C (the operation temperature). The test samples were divided into three types: I. haft-overhang, II. overhang and III. full stator bar. From the PDC measurement data record, the complex capacitance and polarization losses (ion migration polarization, slow relaxation polarization and interfacial polarization) were calculated. It was found that the aging of the insulation related to the complex capacitance and polarization losses can be contributed for research in future wireless technology.
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    Equivalent circuit approximation of transformer insulation by using PDC measurement
    (2008-10-06)
    Roongroj, Ch
    ;
    Pattanadech, N.
    ;
    Praisuwanna, P.
    ;
    Yutthagowith, P.
    ;
    Thongkaemkaew, K.
    This paper represents the insulation model of 3φ, 50 MVA, 132.8/13.8 kV power transformer. This model is developed from the polarization and depolarization current measurement (PDC). The insulation modeling consists of a parallel circuit among C<inf>50</inf> <inf>Hz</inf>, R<inf>0</inf>, R <inf>1</inf> and C<inf>1</inf> in series, R<inf>2</inf> and C<inf>2</inf> in series, R<inf>3</inf> and C<inf>3</inf> in series, and R<inf>4</inf> and C <inf>4</inf> in series. C<inf>50</inf> <inf>Hz</inf> is obtained from the conventional measurement method; whereas, the applied step voltage and the sum of PDC are calculated for R<inf>0</inf>. The individual elements (R<inf>1</inf> and C<inf>1</inf>) are determined from fitting technique employing MATLAB program. From experimental results of the tested transformer, the example of insulation model for Transformer No. 1 (T1) is created with C<inf>50</inf> <inf>Hz</inf> of 3.643 nF, R<inf>0</inf> of 334.8 GΩ. The values of R <inf>1</inf>-R<inf>4</inf> are 86.52, 110.5, 669.5 and 271.0 GΩ respectively; while, the values of C<inf>1</inf>-C<inf>4</inf> are 37.62, 6.047, 0.101 and 0.013 nF respectively. The proposed model is validated by calculating dissipation factor and measuring dissipation factor. The results show that the proposed model and experimental validation are good agreement with each others. © 2008 IEEE.