Enhanced measurements for diagnostics of power-system components

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Project abstract

Oil with oil-impregnated pressboard (thick paper) forms the insulation and cooling of transformers. Oil-impregnated paper is still found in many bushings and cables. These are important power-system components, so diagnostic methods for them are of strong interest in industry. Frequency-domain spectroscopy (FDS) measurements provide information about polarization and conduction in an insulation system. FDS results from aged transformer oils reported in [2] show clearly the deviation for measurements below a voltage-dependent frequency threshold. This non-linear phenomenon is called Garton effect [3], which arises when the very limited number of mobile (ionic) charges in liquid parts of the insulation have become trapped at the edges, leaving the effective conductivity of the oil much less than the constant value that would be assumed for higher frequency and lower voltage. The extent of the deviation is influenced by factors such as the electric field, temperature, and geometry of the sample.

The dependence of results on voltage as well as frequency makes it hard to compare the results measured under different conditions. For example, in field tests of a capacitor voltage transformer, the tested loss tangents when tested far below the rated voltage could be judged to exceed the threshold value of the standard, leading to premature discard [4]. The influence of the Garton effect is also noticed in laboratory measurement of oil-paper insulation, causing the measured result to be affected by the applied waveform at some frequencies [5]. The nonlinearity at low frequencies when measuring on oil-impregnated pressboard/paper can be avoided by decreasing the voltage, which is the common practice for e.g. in-situ measurements on oil-insulated power apparatus, for which low-frequency FDS measurements are typically limited to a few volts in order to avoid significant nonlinearity. A disadvantage is that the resulting reduced current will make the measurement more susceptible to disturbance, limiting its accuracy.

This short project-funding will continue and complete a PhD project about improving the measurements for insulation characterization and diagnostics. The particular focus in the funded period is to propose a technique to reduce the variation in results caused by the Garton effect, for use both in the lab and field.

Summary of work

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Event log

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Project reference-group

Francisco Penayo,  HAPG
Hans Edin,  KTH
Nathaniel Taylor,  KTH

Publications by this researcher

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Frequency-Domain Spectroscopy of Oil and Oil-Impregnated Pressboard With DC Bias
Jing Hao,   Nathaniel Taylor,   Yiming Xie.
2022,   IEEE transactions on dielectrics and electrical insulation, vol. 29(2)

DC-biased dielectric measurements using an existing frequency-domain spectroscopy (FDS) instrument and series battery
Nathaniel Taylor,   Jing Hao.
2022,   Nordic Insulation Symposium (NORD-IS 22), Trondheim June 13-15, 2022

Enhanced Dielectric Response Methods for the Characterization of Dielectric Materials
Jing Hao.
2021,   Thesis (PhD), KTH Royal Institute of Technology, TRITA-EECS-AVL 2021:69

Non-contact method to reduce contact problems between sample and electrode in dielectric measurements
Jing Hao,   Xu Xiangdong,   Nathaniel Taylor.
2020,   High Voltage, vol. 5(6)

Non-contact Method for Dielectric Response Measurements
Jing Hao,   X. Xu,   Jialu Cheng,   Nathaniel Taylor.
2020,   7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020, 6 September 2020 through 10 September 2020

Influence of Nonlinear Stress Grading Material on Dielectric Frequency Response of Stator Insulation
Jialu Cheng,   Nathaniel Taylor,   Peter Werelius,   Amar Abideen,   Jing Hao.
2020,   7th IEEE International Conference on High Voltage Engineering and Application, ICHVE 2020, 6 September 2020 through 10 September 2020

An Electrode Setup for Non-contact Dielectric Response Measurement
Jing Hao,   Xu Xiangdong,   Nathaniel Taylor.
2019,   Nordic Insulation Symposium on Materials, Components and Diagnostics

Publication list last updated from DiVA on 2024-01-10 15:21.

Page started: 2021-09-01
Last generated: 2024-01-10