| 1. |
- Johansson, Anette, 1977, et al.
(författare)
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A Versatile System for Electrical Treeing Tests under AC and DC Stress Using Wire Electrodes
- 2011
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Ingår i: 8th International Conference on Insulated Power Cables, Jicable’11, 19 – 23 June 2011, Versailles - France.
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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.
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| 2. |
- Johansson, Anette, 1977, et al.
(författare)
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Wire-Plane Electrode System for Electrical Tree Initiation Exposed to AC and DC Voltage Stress
- 2011
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Ingår i: The Proceedings of 17th International Symposium on High Voltage Engineering, s. C-025. - 9783800733644
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Electrical treeing in XLPE exposed to DC (of both polarities) and 50 Hz AC voltages has been analysed in a wire-plane electrode geometry using real-time optical detection and microscopic observations. It has been found that treeing mechanisms differ between AC and DC stresses. For AC voltage, the tree initiation and growth is easily observable in real time during the testing. In the case of DC stress a complete breakdown of the XLPE occurs before electrical trees can be discerned with the use of CCD camera. However, in the microscopic observations of the specimens, very fine tree structures can be distinguished. The effect of voltage ramping rate was also analysed. For AC stress, the faster ramping results in a higher tree inception voltage. The opposite trend is true for DC stress, where the faster ramp results in a lower breakdown voltage level. When comparing the effect on polarity of the DC breakdown voltage, negative polarity results in higher voltage levels than positive polarity.
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| 3. |
- Nilsson, Susanne, 1981, et al.
(författare)
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Influence of Morphology Effects on Electrical Properties in XLPE
- 2011
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 121:6, s. 3483-3494
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Tidskriftsartikel (refereegranskat)abstract
- This study elucidates the influence of differences in crosslink structure and crosslink density on water tree growth, electrical tree growth, and electrical breakdown strength. One reference LDPE was compared with a LDPE containing a higher number of vinyl groups, introduced via the copolymerisation with a diene. Because of the chemical difference, the initially formed crosslink structure will be different for the materials. A range of various crosslink densities was considered for the two materials. It was found that along with a noticeable change in morphology after crosslinking, significant changes in particularly water tree growth, electrical tree growth, and electrical breakdown strength could be observed.
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| 4. |
- Sonerud, Björn, 1979, et al.
(författare)
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Dielectric response measurements during electrical treeing in sub-picofarad samples
- 2011
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Ingår i: Polymer Testing. - : Elsevier BV. - 0142-9418. ; 30:1, s. 43-49
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Tidskriftsartikel (refereegranskat)abstract
- A technique called Arbitrary Waveform Impedance Spectroscopy (AWIS) developed for measuring dielectric properties in insulating materials has been used to study capacitance and dielectric loss changes during electrical tree growth in LDPE samples. The sample capacitance is small, in the range of 0.1–0.15 pF, placing high demands on the measurement system. Simulations in FEM-software show that the measured capacitance is in agreement with simulated values and can be used to estimate tree growth rate. It also seems to be possible to differentiate between different regions of tree growth by analyzing changes in capacitance and loss of the studied samples.
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| 5. |
- Sonerud, Björn, 1979, et al.
(författare)
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Noise and Aliasing Aspects in a Multiharmonic-Dielectric-Response-Measurement System
- 2011
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 60:13, s. 3875-3882
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Konferensbidrag (refereegranskat)abstract
- Dielectric-response measurements are commonly performed with frequency-domain spectroscopy, polarization/depolarization-current measurements, or return-voltage measurements. These techniques operate in a frequency or time domain, and all have high requirements on the voltage source in order to acquire accurate results. This limits dielectric-response measurements to offline applications. A new technique, which is called arbitrary-waveform- impedance spectroscopy, has been developed, which makes use of the harmonics of any voltage waveform to perform dielectric-response measurements. The technique provides possibilities for online measurements facilitating the monitoring of materials and components in high-voltage applications. Here, the different aspects of the measurement system are presented, including circuit modeling, normalization, and discussions on aliasing and noise; all of them are necessary to control in order to perform accurate measurements. © 2011 IEEE.
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