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Investigation on dielectric properties of mineral oil by AC and DC method under low electric strength

Investigation on dielectric properties of mineral oil by AC and DC method under low electric strength
Investigation on dielectric properties of mineral oil by AC and DC method under low electric strength
Mineral oil has been widely used in power transformers for its stability at high temperature and excellent electrical insulating properties. Understanding its electrical conduction mechanism will help us get a better view of oil status. In this paper, dielectric spectroscopy and DC conductivity measurement will be combined to investigate the mineral oil with different aging times.
As seen from the dielectric spectroscopy result, the conductivity calculated from dielectric response are almost constant with the frequency, whilst the permittivity reveal an increase at low frequency. It seems the response enter a pure ohmic region at medium frequency range (1Hz-100Hz). If only drift of ions contributes to the total conductivity, initial conductivity observed in DC test should be equal to those obtained in AC test.
A simple charge regeneration model has been proposed to explain the duration time of initial conductivity in both AC and DC test. Based on that model, the charge generating rate is determined by both permittivity and conductivity. Since the aged oil has a higher regenerating rate, its original current would sustain for a longer time when compared with that for fresh oil.
Besides, a new model will be used to simulate the dielectric spectroscopy result. Since the charge around the electrode can attract opposite charge in the electrode by electrical force, the permittivity and conductivity of mineral oil will be affected by this extra current. As the frequency goes low, more charge carriers will accumulate in that area. If the electrical potential shift to the next half circle, the electric stress at the boundary of the electrode and the liquid may not be able to keep the existing charge layer in the liquid attached to the electrode and then a notable displacement current will occur. From the simulation, this model fit the experimental data very well.
10
Zhou, Y
2dd820ca-fb03-496b-8a45-f2a11816c4b5
Hao, M
fb7006e0-07c0-46f5-9279-e30a7d3bd614
Chen, G
3de45a9c-6c9a-4bcb-90c3-d7e26be21819
Wilson, G
25fbd90e-6949-481c-9e75-0d457003c839
Jarman, P
390aafbd-393e-4e20-bace-b4416e0dd456
Zhou, Y
2dd820ca-fb03-496b-8a45-f2a11816c4b5
Hao, M
fb7006e0-07c0-46f5-9279-e30a7d3bd614
Chen, G
3de45a9c-6c9a-4bcb-90c3-d7e26be21819
Wilson, G
25fbd90e-6949-481c-9e75-0d457003c839
Jarman, P
390aafbd-393e-4e20-bace-b4416e0dd456

Zhou, Y, Hao, M, Chen, G, Wilson, G and Jarman, P (2013) Investigation on dielectric properties of mineral oil by AC and DC method under low electric strength. Dielectrics 2013, Reading, United Kingdom. 09 - 11 Apr 2013. p. 10 .

Record type: Conference or Workshop Item (Paper)

Abstract

Mineral oil has been widely used in power transformers for its stability at high temperature and excellent electrical insulating properties. Understanding its electrical conduction mechanism will help us get a better view of oil status. In this paper, dielectric spectroscopy and DC conductivity measurement will be combined to investigate the mineral oil with different aging times.
As seen from the dielectric spectroscopy result, the conductivity calculated from dielectric response are almost constant with the frequency, whilst the permittivity reveal an increase at low frequency. It seems the response enter a pure ohmic region at medium frequency range (1Hz-100Hz). If only drift of ions contributes to the total conductivity, initial conductivity observed in DC test should be equal to those obtained in AC test.
A simple charge regeneration model has been proposed to explain the duration time of initial conductivity in both AC and DC test. Based on that model, the charge generating rate is determined by both permittivity and conductivity. Since the aged oil has a higher regenerating rate, its original current would sustain for a longer time when compared with that for fresh oil.
Besides, a new model will be used to simulate the dielectric spectroscopy result. Since the charge around the electrode can attract opposite charge in the electrode by electrical force, the permittivity and conductivity of mineral oil will be affected by this extra current. As the frequency goes low, more charge carriers will accumulate in that area. If the electrical potential shift to the next half circle, the electric stress at the boundary of the electrode and the liquid may not be able to keep the existing charge layer in the liquid attached to the electrode and then a notable displacement current will occur. From the simulation, this model fit the experimental data very well.

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More information

Published date: 10 April 2013
Venue - Dates: Dielectrics 2013, Reading, United Kingdom, 2013-04-09 - 2013-04-11
Organisations: EEE

Identifiers

Local EPrints ID: 352379
URI: http://eprints.soton.ac.uk/id/eprint/352379
PURE UUID: 19573506-2f35-415f-87f7-9fcc8d436951

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Date deposited: 10 May 2013 14:54
Last modified: 07 Jul 2020 16:51

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