| 1. |
- Bergman, Anders, et al.
(författare)
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Influence of coaxial cable on response of high-voltage resisitive dividers
- 2017
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Konferensbidrag (refereegranskat)abstract
- An effort is pursued by several European National Measurement Institutes to lower the uncertainties in calibration of UHV measuring systems for lightning impulse. To this end, several reference dividers are investigated as regards their accuracy both for amplitude and for time parameters. During these investigations a deterioration of step response was identified when longer coaxial cables were inserted in the measuring circuit. The measured front time T1 was also affected, in one observed case by 2.5 % elongation of front time as another 25 m cable was inserted. Compared to the intention to calibrate front time measurement to better than 5 % uncertainty for front time, this contribution must be well known, or preferably be eliminated. This paper presents the experimental findings from these investigations. The investigated cables included selected coaxial, tri-axial, and cables with a corrugated screen. The effect of cable length was also studied. The influence was first discovered when applying a very fast step (rise-time < 4 ns) to the high voltage arm of a resistive divider and convolution of this step with the time derivative of an ideal lightning impulse with 0.84/60 µs impulse. The calculated output was analysed with IEC 61083 compliant software to evaluate the front time. Subsequently, these analyses have been augmented by additional comparative measurements where two reference dividers were connected to the same impulse generator, and varying the cable length of one of them. The summarized changes in front time calculated for different combinations of cable and impulse voltage dividers are shown and discussed. It is noted that a change in T1 error depends both on length of cable and its type. The results show that non-negligible front time errors may be introduced when the cable length is increased. To support these findings, further tests have been carried out with two reference impulse dividers connected in standard calibration configuration in accordance with IEC 60060-2. One divider was used as reference, while the cable for the other was varied. In this way, the change of error between configurations could be measured. A theoretical study has also been performed, calculating the distortion of a lightning impulse on a coaxial cable. The results agree qualitatively with experiments, but the detailed results show discrepancies that need further investigation.
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| 2. |
- Bergman, Anders, et al.
(författare)
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Metrology for high voltage direct current
- 2010
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Ingår i: CPEM Digest (Conference on Precision Electromagnetic Measurements). - 9781424467952 ; , s. 669-670
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Konferensbidrag (refereegranskat)abstract
- HVDC energy transmission is crucial for a successful uptake of renewable energy sources in the grid. A research program is described, intended to provide metrology support for the needs of HVDC energy transmission. This program will provide improvements for the present HVDC metrology infrastructure: accurate measurement of HVDC, determination of losses in HVDC systems, on-site power quality measurements at HVDC substations, and DC metering. It is a combined effort of 7 European national metrology institutes, one university and one industrial partner. © 2010 IEEE.
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| 3. |
- Elg, Alf Peter, et al.
(författare)
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Research project EMPIR 19ENG02 future energy
- 2020
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Ingår i: VDE High Voltage Technology 2020. - : VDE Verlag GmbH. - 9783800753550 ; , s. 252-257
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Konferensbidrag (refereegranskat)abstract
- Society's increasing demand for electrical energy, along with the increased integration of remote renewable generation has driven transmission levels to ever higher voltages in order to maintain (or improve) grid efficiency. Consequently, high voltage testing and monitoring beyond voltage levels covered by presently available metrology infrastructures are needed to secure availability and quality of supply. Calibration services for Ultra-High Voltage Direct Current (UHVDC) presently are only available up to 1000 kV. There is a need to extend the DC calibration capabilities for voltage instrument transformers up to 1200 kV and for factory component testing capabilities up to 2000 kV. Also, methods for linear extension of lightning impulse calibration, for dielectric testing of UHV grid equipment, urgently need revision. Recent research has raised questions regarding the validity of the current linearity extension methods for voltages beyond 2500 kV. Furthermore, new methods for calibration are needed for the 0.2 class HVAC voltage instrument transformers for system voltages up to 1200 kV. The current methods used for determination of the voltage dependence are very time consuming, raising the need for methods allowing faster assessment. Finally, with new HVDC transmission grids and associated components, novel methods are needed for detection, classification and localisation of partial discharge (PD) under DC stress. The industry needs methods for reliable monitoring of critical components such as cables, for both HVAC and HVDC, and gas insulated substations (GIS), and techniques for addressing new challenges introduced by HVDC technologies, such as the ability to distinguish PD signals from switching transients in converters and other sources of noise.
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| 4. |
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| 5. |
- Larzelere, W, et al.
(författare)
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MEASUREMENT OF THE INTERNAL INDUCTANCE OF IMPULSEVOLTAGE GENERATORS AND THE LIMITS OF LI FRONT TIMES
- 2017
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Konferensbidrag (refereegranskat)abstract
- The recent push to higher testing voltages for research and production tests onUHV system components rated above 800kV class has led to difficulties in achieving thestandard waveshapes as required by IEC60060 Parts 1 and 2 and other existing IEC,IEEE/ANSI and other standards. One of the limiting components in achieving themaximum capacitive loading on an impulse generator for standard lightning impulse fronttimes is the inductance of the circuit. The total inductance of the circuit is comprised ofthe internal inductance of the impulse generator and the inductance of the loop toconnect to the load. The higher the voltage class of test objects, the larger the loop,yielding more inductance that in turn, reduces the test capacitance that can be connectedand still remain inside the overshoot requirements of the standards. The internalinductance of the impulse generator is comprised of the wiring of the stages and thestage capacitor inductance and/or the inductance of the waveshaping resistors. Thispaper shows the results of methods to measure and calculate the internal inductance ofseveral impulse generators and we review the formulas for calculating the maximum loadof an impulse generator with a given internal inductance. We believe these methods givemore realistic values than adding up nameplate inductance values from an impulsegenerator. The paper also reviews the pros and cons of higher stage capacitances inimpulse generators to test larger loads that are ultimately limited by the circuit inductancevalue. The intent of this paper is to assist in the revision of future IEC and IEEE standardsfor impulse testing apparatus in the UHV range
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| 6. |
- Bergman, Anders, et al.
(författare)
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Design of a wideband HVDC reference divider
- 2012
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Ingår i: Conference on Precision Electromagnetic Measurements, CPEM 2012. - : IEEE. ; , s. 207-208
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Konferensbidrag (refereegranskat)
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| 7. |
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| 8. |
- Hällström, J, et al.
(författare)
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International comparison of software for calculation of lightning impulse parameters based on a new processing algorithm
- 2007
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Konferensbidrag (refereegranskat)abstract
- A new algorithm has been proposed to calculate the parameters of full lightning voltage impulses. The new algorithm enables the application of the test voltage factor (also referred to as k-factor in some literatures) for calculation of the equivalent test voltage of impulses with superimposed oscillations/overshoots. The new algorithm at the same time provides a robust procedure for obtaining time parameters of the impulses from not only smooth waveforms but also waveforms with varying degrees of distortions in the front part of the impulses. These distortions include oscillations on the impulse front and overshoots in the peak region. A critical part of the new algorithm is a 4-parameter fitting procedure to obtain the base curve, which is used for calculation of the test voltage curve. Another important part of the algorithm is applying a filtering procedure in the calculation of the test voltage curve. The new algorithm was tested in different laboratories using different programming languages and different techniques for realising the fitting and filtering routines. The paper reports the results obtained from the participating laboratories using the proposed algorithm. The results obtained by the participating laboratories using existing software based on the requirement of IEC 60060-1: 1989 were also compared. It is anticipated that the results can serve as a part of the basis for a new procedure for determination of lightning impulse parameters in the revised IEC 60060-1.
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| 9. |
- Högberg, G, et al.
(författare)
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Treatment of post-traumatic stress disorder with eye movement desensitization and reprocessing: Outcome is stable in 35-month follow-up
- 2008
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Ingår i: Psychiatry Research. - : Elsevier BV. - 0165-1781 .- 1872-7123. ; 159:1-2, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- Post-traumatic stress disorder (PTSD) is an anxiety disorder that may follow major psychological trauma. The disorder is longstanding, even chronic, and there is a need for effective treatment. The most effective short-term treatments are cognitive behavioural therapy and eye movement desensitization and reprocessing (EMDR). Twenty subjects with chronic PTSD following occupational health hazards from "person under train" accidents or assault at work were treated with five sessions of EMDR. They were assessed with psychometric scales and diagnostic interviews before treatment, directly after treatment, at 8 months, and at 35 months after the end of Therapy. The primary outcome variable was full diagnosis of PTSD according to the DSM-IV diagnostic criteria. Results from interview-based and self-evaluation psychometric scales were used as secondary outcome variables. Immediately following treatment, the patients were divided up into two groups, initial remitters (12 of 20) and non-remitters (8 of 20). There were no drop-outs during therapy, but three patients withdrew during follow-up. The initial result was maintained at the 35-month follow-up. The secondary outcome variables also showed a significant immediate change towards normality that was stable during the long-term follow-up. After 3
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| 10. |
- Martín, Ricardo, et al.
(författare)
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Final report on supplementary comparison EURAMET.EM-S29 : Traceability of DC high voltage reference measuring systems up to 200 kV
- 2012
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Ingår i: Metrologia. - 0026-1394 .- 1681-7575. ; 49, s. 1001-
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the EURAMET supplementary comparison EURAMET.EM-S29 was to compare the calibration and measurement capabilities of the participating institutes. The pilot laboratory was the Laboratorio Central Oficial de Electrotecnia (LCOE, Madrid, Spain), and the other participants were the following other six EURAMET national metrology institutes: BIM (Bulgaria), MIKES (Finland), PTB (Germany), SP (Sweden), UME (Turkey) and VSL (The Netherlands), and the COOMET national institute VNIIMS (Russia). A 200 kV DC reference measuring system provided by LCOE was used as a travelling reference measuring system (TRMS). The comparison measurements were carried out between November 2007 and April 2010. According to the technical protocol, two different types of measurements had to be made: determination of the assigned scale factor of the TRMS between 1 kV and 200 kV, positive and negative polarity, and short-term stability of the measuring systems used. For each voltage level and polarity, a comparison reference value was calculated. Compatibility of each participant with the corresponding comparison reference values and between any pair of laboratories was also obtained. Results of the comparison offered a good opportunity to check the calibration and measurement capabilities of the participants in the field of high voltage DC measurement. The reported results also demonstrate the importance of taking care in order to cancel the influence of the self-heating of the TRMS. Main text. To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/EM/S29/EURAMET.EM-S29.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
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