| 1. |
- Johansson, Anette, 1977, et al.
(författare)
-
A Versatile System for Electrical Treeing Tests under AC and DC Stress Using Wire Electrodes
- 2011
-
Ingår i: 8th International Conference on Insulated Power Cables, Jicable’11, 19 – 23 June 2011, Versailles - France.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An alternative method to evaluate electrical treeing in solid dielectric materials is presented. Here the test sample utilises a wire electrode for creating the necessary high divergent electric field. This introduces a different preparation method and several of the disadvantages with the traditional needle sample can be avoided. Together with the test object a versatile test setup for both AC and DC measurements is illustrated. This alternative method has proven successful and an evaluation thereof as well as a comparative study between the two electrode systems is included.
|
|
| 2. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Computation of Parameters of Power Transformer Windings for Use in Frequency Response Analysis
- 2007
-
Ingår i: IEEE Transactions on Magnetics. - 0018-9464. ; 43:5, s. 1983-1990
-
Tidskriftsartikel (refereegranskat)abstract
- We present a 3-D model for calculating magnetic fields in a power transformer and the effective parameters (inductance and resistance)of its windings. The transformer is representative of large transformers with power ratings ranging from hundreds of kilovolt amperes to hundreds of megavolt amperes. The model accounts for anisotropic frequency-dependent properties of the laminated transformercore and eddy currents in the steel sheets. We discuss the results of the calculations performed in the frequency range 10 Hz–10 MHz, and show that the largest variations of both the magnetic field and parameters of the windings take place at frequencies below 10 kHz and, at frequencies higher than 1 MHz, the magnetic core does not significantly affect the variation of the effective parameters.
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Effects of the Insulation Quality on the Frequency Response of Power
- 2006
-
Ingår i: KIEE Journal of Electrical Engineering & Technology. ; 1:4, s. 534-542
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents results of frequency domain spectroscopy (FDS) measurements on oilimpregnatedpressboard insulation, their analyses and use of the data for modeling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responseswere parameterized with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarization mechanisms and they were thereafter used to model the FRA response of a three-phase transformer.
|
|
| 6. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Exploring Possibilities for Characterization of POwer Transformer Insulation by Frequency Response Analysis (FRA)
- 2006
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 21:3, s. 1375-1382
-
Tidskriftsartikel (refereegranskat)abstract
- This paper explores the possibility for using frequencyresponse analysis (FRA) technique to characterize thequality of transformer insulation. For this purpose, a single-phase and a three-phase lumped parameter circuit models were developed.The single-phase model represents a transformer without a laminated core, whereas the three-phase model represents a real transformer with core. Calculations of frequency dependent circuit parameters are presented and the effects imparted on the frequency response by different loss mechanisms (in insulation, inwindings and in core) are discussed. The simulations are compared with results of measurements on real objects. It is shown that FRA could be used for insulation diagnostics if the measurements were of high enough quality.
|
|
| 7. |
|
|
| 8. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
High-frequency modeling of power transformers for use in frequency response analysis (FRA)
- 2008
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 23:4, s. 2042-2049
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an advanced model of the frequencyresponse of a three-phase power transformer for usein conjunction with diagnostic measurements by the method offrequency response analysis (FRA). The model includes high frequency behavior of the laminated core and the insulationthrough taking into account the frequency dependencies of the complex permittivity of insulation materials (paper, pressboard, and oil) and of the anisotropic complex permeability of magnetic core and conductors. A lumped parameter circuit model is used to simulate the frequency response of open-circuit impedance,short-circuit impedance, and impedance between primary and secondary windings, in which the characteristics of circuit elements are calculated by means of the finite-element method. Theeffect of correct representation of each circuit element on the FRA response is analyzed and discussed in comparison to measurement results on a real transformer.
|
|
| 9. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Infuence of Core Characteristics on Inductance Calculations for Modeling of Power Transformers
- 2006
-
Ingår i: Industrial and Information Systems, 2006. ICIIS 2006. International Conference. ; , s. 24-29
-
Konferensbidrag (refereegranskat)abstract
- Calculations of effective parameters (inductance and resistance) of transformer windings, including core characteristics, are presented in this paper. Both anisotropic nature of the core and eddy currents in the electrical steel sheets are accounted for. A 3D model is developed and used to find out the inductance and resistance of transformer windings in the frequency range from 10 Hz to 10 MHz. It is shown that strongest variations of the magnetic field inside the core and of the effective parameters occur below ~ 10 kHz, whereas the effect of the magnetic core is negligible above 1 MHz.
|
|
| 10. |
- Abeywickrama, Nilanga, 1976, et al.
(författare)
-
Model Based Frequency Response Analysis for Characterization of Transformer Insulation
- 2005
-
Ingår i: Nordic Insulation Symposium NORDIS'05. ; , s. 27-30
-
Konferensbidrag (refereegranskat)abstract
- This paper presents investigations on the possibility ofcharacterizing the transformer insulation by frequencyresponse analysis (FRA) technique. A lumped parameter circuit model was built for a single winding and for a model transformer. The proposed model was used to predict the effects of different characteristics of insulation on the frequency response of winding impedance. The simulated and measured responses of the model transformer are presented and discussed.
|
|
