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  • 1.
    Taylor, Nathaniel
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Hao, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    DC-biased dielectric measurements using an existing frequency-domain spectroscopy (FDS) instrument and series battery2022In: Proceedings of the 27th Nordic Insulation Symposium, Trondheim: Norwegian University of Science and Technology (NTNU) Library , 2022, Vol. 27Conference paper (Refereed)
    Abstract [en]

    We present a simple method for adding DC bias to frequency-domain spectroscopy (FDS) measurements by inserting a battery in series in the `high' lead to the specimen. An instrument designed for FDS measurements with pure AC can be used in this way without modification, even for DC voltages above the instrument's AC range. Issues and limitations of the method are discussed, along with some alternative methods. Experimental results from FDS measurements on well defined linear specimens are compared with/without the DC bias, to check that the measurement is not disturbed by the DC source. The only detected difference was the expected effect of including the battery impedance in series with the specimen in the measurement. This effect was negligible for typical lab-specimen capacitances, around and below power frequency. The nature of battery impedance is further described, as multiple small batteries in series can strongly affect the results for large specimens and at high frequencies.

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    dc_biased_fds__Taylor_Hao__NORD-IS_2022.pdf
  • 2.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xie, Yiming
    Wuhan Univ, Sch Elect Engn & Automat, Wuhan 430072, Peoples R China..
    Frequency-Domain Spectroscopy of Oil and Oil-Impregnated Pressboard With DC Bias2022In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, no 2, p. 370-377Article in journal (Refereed)
    Abstract [en]

    Dielectric response measurement is widely used to characterize oil/oil-impregnated pressboards in order to evaluate the condition of transformer insulation. Insulation systems with oil can exhibit voltage dependence at low frequencies. This is due to the limited number of mobile charges in the liquid, rather than to the dielectric relaxation processes that may, in some cases, be of more interest to study. This work investigates the voltage-dependent properties of oil/oil-impregnated pressboards under ac voltages with regard to the complex permittivities. Frequency-domain spectroscopy (FDS) measurements are made with a dc voltage added to the ac voltage stimulus. Considered influences are the voltage amplitudes and polarity as well as the dependence on temperature. Properties of the space-charge polarization in the oil and oil-impregnated pressboard are calculated and discussed based on the dc-biased measurements. It is seen that using the dc bias in the FDS measurements of oil/oil-impregnated pressboard can significantly decrease the voltage dependence of the results that are caused by ion drift and consequent depletion of ions from the bulk liquid. Based on the dc-biased measurements, the complex permittivity due to the linear and nonlinear polarization can be separated.

  • 3.
    Hao, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Enhanced Dielectric Response Methods for the Characterization of Dielectric Materials2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dielectric response measurement is widely used for condition assessment of high voltage equipment and for characterizing candidate materials. Measurement with high accuracy and reliability is important in all stages of the lifetime of high voltage equipment, from manufacture to replacement decision. However, several deficiencies in the commonly used measurement methods may affect the reproducibility and accuracy of results. This thesis focuses on two issues: the contact problems between the surfaces of sample and electrode in the measurement of solid insulation samples, and the non-linear phenomenon of voltage-dependent permittivity occurring in measurements on insulating liquids such as oil and oil-paper insulation.

    For reducing the contact problems, this thesis introduces an easily realized electrode arrangement for non-contact measurements. The performance of the electrode arrangement is evaluated in terms of the edge effect and the measure-guard capacitance that can influence results if there is deviation of the potentials of the guard and measure electrodes. The non-contact and contact methods are compared based on the error-sensitivity analysis and experimental data from frequency-domain spectroscopy (FDS). The differences are investigated further, with attention to contact pressure. By using the non-contact method, the contact problems can be reduced, although error sensitivity is likely to be higher. In addition, the non-contact method can decrease the influence of the pressure applied by the electrode compared with the contact measurement. Therefore, the non-contact method can be an alternative to improve the accuracy and reliability of FDS measurements.

    Regarding FDS measurements of oil and oil-impregnated pressboards, the non-linear phenomenon has been studied using combined AC and DC voltages as stimuli. The complex permittivities are compared between the cases with and without the DC bias, considering the influence of the voltage amplitude and polarity and the temperature. It is seen that using the DC bias in the FDS measurements of oil and oil-impregnated pressboard can significantly decrease the voltage dependence of the complex permittivities caused by the limited numbers of ions in the liquid being blocked at boundaries. Properties of the space-charge polarization in the oil are calculated and discussed based on the DC-biased measurements. A numerical calculation of space charge polarization is done to analyze the experimental results and explain the permittivity change in terms of ion transport. It is concluded that using combined AC and DC voltages can reduce misinterpretation of results because of the voltage dependence caused by the ion movements, and can also provide a method to obtain the contribution of complex permittivities due to the space charge polarization in the oil.

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  • 4.
    Cheng, Jialu
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Werelius, Peter
    Abideen, Amar
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Hao, Jing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Influence of Nonlinear Stress Grading Material on Dielectric Frequency Response of Stator Insulation2020In: 7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2020Conference paper (Refereed)
    Abstract [en]

    Aging of high voltage generators and motors lead to changes in the dielectric properties of the stator winding insulation system. Research on the relation between aging and dielectric response has been going on for decades. A particular challenge is that the coil insulation consists of several materials: two that strongly affect the dielectric response are the ground-wall insulation and the stress grading shield (end-corona protection, ECP), which exhibit quite different properties. The influence of the ECP on the overall dielectric response of the insulation system might dwarf the condition change of the ground-wall insulation. In this paper, we introduce a test system that can measure the dielectric response in both time and frequency domain from low to rated voltage. Measurement results of two types of custom-designed, commercial standard stator winding coils are presented, and the influence of the ECP can be observed. The validity of time-frequency domain transformation of this nonlinear system is discussed. This paper acts as a basis for the application of dielectric diagnostic testing in the field.

  • 5.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xu, X.
    Cheng, Jialu
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Non-contact Method for Dielectric Response Measurements2020In: 7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2020Conference paper (Refereed)
    Abstract [en]

    The dielectric response measurement is an important technique to assess the properties of insulation materials. However, the widely used approach with contact between samples and electrodes can in some cases limit the accuracy of the measurement. In this paper, an easily fabricated design is introduced and used to perform non-contact measurements. Air-reference measurements, comparing the sample to an air-gap for improved calibration, are used for all measurements. Results obtained by contact and non-contact methods, and with the feedback of electrometer locked and unlocked are compared. The effect of the pressure applied by the electrode is also investigated for both non-contact and contact measurements. Results show that the non-contact method can be an alternative to reduce contact problems between the sample and electrodes. For air-reference measurements, the impedance measurement instrument should be forced to use the same reference component for the air and sample measurements. Results obtained by the non-contact measurements are less sensitive to the pressure compared to that by contact measurements. 

  • 6.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xiangdong, Xu
    Chalmers Univ Technol, Elect Power Engn, S-41296 Gothenburg, Sweden.
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Non-contact method to reduce contact problems between sample and electrode in dielectric measurements2020In: High Voltage, ISSN 2397-7264, Vol. 5, no 6, p. 753-761Article in journal (Refereed)
    Abstract [en]

    Dielectric response measurement is a widely used technique for characterising dielectric materials in terms of theircapacitance and dielectric loss. However, the widely used approach with contact between samples and electrodes can in somecases limit the accuracy of the measurement. The authors introduce an easily realised electrode arrangement for non-contactmeasurements, which avoids these contact problems. The performance of the electrode arrangement in terms of the edge effectis assessed. The non-contact and contact methods are compared based on error-sensitivity analysis and experimental results.Differences are studied further, with attention to contact pressure. The non-contact method is also compared experimentally withthe one-sided non-contact method. Air-reference measurements, comparing the sample to an air-gap for improved calibration,are used for all measurements. The results show that the non-contact method can be an alternative to reduce contact problemsbetween the sample and electrodes, although error sensitivity can be higher when the non-contact method is used. The non-contact method can decrease the influence of the pressure applied to the sample compared to the contact method, and can alsoreduce the problem of poor contact that can arise from the absence of pressure in the one-sided non-contact method

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  • 7.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Xiangdong, Xu
    Taylor, Nathaniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    An Electrode Setup for Non-contact Dielectric Response Measurement2019In: Proceedings of the 26th Nordic Insulation Symposium, Tampere, June 2019, Norwegian University of Science and Technology (NTNU) Library , 2019Conference paper (Refereed)
    Abstract [en]

    The dielectric response measurement is a widely used technique for characterizing dielectric materials. However, the contact problems between samples and electrodes existing in the use of conventional electrode setup limit the accuracy of the measurement. In this paper, a type of electrode arrangement is introduced for avoiding direct contacts of the sample with both the bottom and the top electrode. The edge effect of this arrangement is calculated by the FEM model. The equations to derive the complex permittivity is presented. The measurement instrument is described and the influence of the potential difference between two terminals of the IDAX input is analyzed. Furthermore, the error sensitivities are compared between the non-contact and contact methods. The results show that this electrode arrangement can be used to perform non-contact measurements, and the edge effect of it is not significant. The potential between the two terminals of the IDAX is not an obstacle to obtain results with high accuracy. Overall, the non-contact electrode arrangement combined with the IDAX 300 can potentially improve the accuracy of dielectric response measurements although the non-contact methods can increase the sensitivities to errors.

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    fulltext
  • 8.
    Hao, Jing
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Yiming, Xie
    Nathaniel, Taylor
    Frequency-domain Spectroscopy of Oil and Oil-impregnated Pressboard with DC BiasManuscript (preprint) (Other (popular science, discussion, etc.))
1 - 8 of 8
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