| 1. |
- Bollen, Math, et al.
(författare)
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Limits for voltage distortion in the frequency range 2 to 9 kHz
- 2008
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Ingår i: I E E E Transactions on Power Delivery. - I E E E. - 0885-8977. ; 23:3
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- This paper addresses voltage distortion in the frequency range 2 to 9 kHz, above what is normally considered in harmonic studies. By extrapolating the voltage-distortion limits that exist in international standards for distortion up to 2 kHz, it is concluded that 0.5% of nominal voltage per 200-Hz band is a safe limit. This limit is next used to estimate the number of small generator units (1-10 kW) that can be connected to a low-voltage grid. It is concluded that in some cases the connection of one or just a few units already leads to a distortion level above the limit.
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| 2. |
- Gil-de-Castro, A., et al.
(författare)
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LED street lighting a power quality comparison among street light technologies
- 2013
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Ingår i: Lighting Research and Technology. - Sage Science Press (UK). - 1477-1535.
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- High-pressure sodium lamps are currently the main lamps used in public lighting. However, the possibility of using high-power light emitting diode (LEDs) for street lighting is growing continuously due to their greater energy efficiency, robustness, long life and light control. The aim of this paper is to study the power quality of high-power lighting networks based on LED and high-pressure sodium lamps. Both electromagnetic and dimmable electronic ballasts, which can dim the lamp output smoothly and uniformly, have been used connected to high-pressure sodium lamps. High-pressure sodium lamps connected to electronic equipment have been tested with different arc power levels using dimming on a 230 V power supply. The study presented in this paper is completely based on measurements, including harmonic currents in the frequency range up to 150 kHz for all the technologies. The main results show a broadband spectrum in LED lamps which confirms other research in fluorescent lamps powered by high-frequency ballasts. Results also indicate a decrease in the harmonic value with increasing harmonic order, and a decrease in the harmonic value at half load (60%) compared with full load (100%). Although total harmonic distortion of the current is lower with high-pressure sodium lamps connected to electronic rather than electromagnetic ballasts, LED lamps achieved the lowest total harmonic distortion of curren
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| 3. |
- Lundmark, Martin, et al.
(författare)
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Required changes in emission standards for high-frequency noise in power systems
- 2006
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Ingår i: International Journal of Energy Technology and Policy. - Inderscience Publishers. - 1472-8923. ; 4:1-2
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- This paper discusses some recent developments that make the existing standards on the emission of high-frequency noise in power systems need to be reconsidered. It is shown that it is possible for an equipment to remain below the emission limits while at the same time the disturbance level increases beyond what was intended by the standard document. Further, the change from analog to digital communication and the use of communication via the power system, make that the permitted disturbance levels need to be reconsidered. This paper also contains an example of measured high-frequency noise and proposes a framework for re-coordination of emission and immunity levels.
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| 4. |
- Akhter, Tansim, et al.
(författare)
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Changes in the Artery Wall Layer Dimensions in Women with Preeclampsia : an investigation using non-invasive high frequency ultrasound
- 2012
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Ingår i: Acta Obstetricia et Gynecologica Scandinavica. - 0001-6349. ; 91:S159, s. 28-28
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Tidskriftsartikel (övrigt vetenskapligt)abstract
- Background:Preeclampsia (PE) is associated with increased risk for cardiovascular disease later in life. Whether, the artery wall layer dimensions differ between PE and normal pregnancy is unclear. The aim of this study was to estimate if women with PE have different common carotid artery wall layer dimensions than women with normal pregnancy, both during pregnancy and about one year postpartum.Methods:By using high-frequency (22MHz) ultrasound (Collagenoson, Meudt, Germany) separate estimates of the common carotid artery intima and media layers were obtained and the I/M ratio was calculated in women with PE (n=55 during pregnancy and n=48 at postpartum) and with normal pregnancy (n=65 during pregnancy and n=59 at postpartum). Thick intima, thin media and a high intima/media ratio are signs of less healthy artery wall and vice versa.Results:In women with PE, the intima was thicker (0.18 } 0.03 vs. 0.11 } 0.02; p < .001), the media was thinner (0.47 } 0.12 vs. 0.55 } 0.14; p = .001) and the I/M ratio was higher (0.41 } 0.14 vs. 0.20 } 0.05; p < .001) compared to women with normal pregnancy. Further, for changes from pregnancy to postpartum, both for PE and normal pregnancy, the intima and the I/M ratio had improved but still significantly higher in women with PE than in women with normal pregnancy.Conclusion:In women with PE, we found a thicker intima, thinner media and a higher I/M ratio compared to women with normal pregnancy, indicating a more negatively affected artery wall layer dimensions. Persisting negative effects of PE on artery wall at postpartum, despite improvement of artery wall layers compared to values during pregnancy, indicates a permanent damage of the vascular system in this group of women.
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