1,324 research outputs found
Power Quality
Electrical power is becoming one of the most dominant factors in our society. Power
generation, transmission, distribution and usage are undergoing signifi cant changes
that will aff ect the electrical quality and performance needs of our 21st century industry.
One major aspect of electrical power is its quality and stability – or so called Power
Quality.
The view on Power Quality did change over the past few years. It seems that Power
Quality is becoming a more important term in the academic world dealing with electrical
power, and it is becoming more visible in all areas of commerce and industry, because
of the ever increasing industry automation using sensitive electrical equipment
on one hand and due to the dramatic change of our global electrical infrastructure on
the other.
For the past century, grid stability was maintained with a limited amount of major
generators that have a large amount of rotational inertia. And the rate of change of
phase angle is slow. Unfortunately, this does not work anymore with renewable energy
sources adding their share to the grid like wind turbines or PV modules. Although the
basic idea to use renewable energies is great and will be our path into the next century,
it comes with a curse for the power grid as power fl ow stability will suff er.
It is not only the source side that is about to change. We have also seen signifi cant
changes on the load side as well. Industry is using machines and electrical products
such as AC drives or PLCs that are sensitive to the slightest change of power quality,
and we at home use more and more electrical products with switching power supplies
or starting to plug in our electric cars to charge batt eries. In addition, many of us
have begun installing our own distributed generation systems on our rooft ops using
the latest solar panels. So we did look for a way to address this severe impact on our
distribution network. To match supply and demand, we are about to create a new, intelligent
and self-healing electric power infrastructure. The Smart Grid. The basic idea
is to maintain the necessary balance between generators and loads on a grid. In other
words, to make sure we have a good grid balance at all times. But the key question that
you should ask yourself is: Does it also improve Power Quality? Probably not!
Further on, the way how Power Quality is measured is going to be changed. Traditionally,
each country had its own Power Quality standards and defi ned its own power
quality instrument requirements. But more and more international harmonization efforts
can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures
that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and
even directly embedded into sensitive loads. But work still has to be done. We still use
Power Quality standards that have been writt en decades ago and don’t match today’s
technology any more, such as fl icker standards that use parameters that have been defi
ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct.
Almost all experts are in agreement - although we will see an improvement in metering
and control of the power fl ow, Power Quality will suff er. This book will give an
overview of how power quality might impact our lives today and tomorrow, introduce
new ways to monitor power quality and inform us about interesting possibilities to
mitigate power quality problems.
Regardless of any enhancements of the power grid, “Power Quality is just compatibility”
like my good old friend and teacher Alex McEachern used to say.
Power Quality will always remain an economic compromise between supply and load.
The power available on the grid must be suffi ciently clean for the loads to operate correctly,
and the loads must be suffi ciently strong to tolerate normal disturbances on the
grid
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The Nazis in Mexico : Mexico and the Reich in the prewar period, 1936-1939
There are three main reasons for undertaking a survey of the relations between Germany and Mexico on the eve of World War II. First, only one specific work exists on the topic, and it was published in Germany. All other publications, whether in Spanish, English, French or German deal very limitedly or indirectly with the relationship between the two countries in the prewar period. These secondary sources fail to describe and analyze properly the political and economic implications of both sides' foreign policy. The second reason is the geographical location of Mexico. It represents the Achilles' heel of the United States and thus the topic involves more than bilateral relations. Hence external political influences and trade agreements with Mexico naturally drew the interest of the United States. Its interference must be seen on two levels: first, the business interest, in particular by the oil companies before and after the expropriation in 1938; and secondly in the political realm of the Good Neighbor policy. Thus it is desirable to look at a complex set of foreign relations, especially in the triangle formed between Washington, Mexico City and Berlin. Finally, there was and is a good deal of rhetoric on the subject. While the German trade inroads in Latin America were at least rationalized by some critics in order to curb them, German political and ideological penetration by propaganda aroused uneasiness and more often fear. This psychological component was often treated emotional and irrational, and on both sides of the Rio Grande writers and political observers tended to express their anxieties about the 'Fifth Column' in exaggerated, sometimes even paranoid fashions. Of course, as we will see, these antagonists of National Socialism found evidence of German agitation in Mexico. They failed, however, to put this evidence in context of the political reality, meaning that the perceived German threat was harmless vis a vis its counter forces. For this reason, the thesis will attempt to show that the degree of German propaganda was clearly outweighed by the political success of the Cardenas administration and thus was doomed to insignificance. One might add that the Reich did not even perceive any intention to a 'spiritual conquest of Latin America' - as Franco imagined it after winning the Spanish Civil War. The only goal Germany might have aimed at, was a dissolution of the western hemisphere solidarity.Histor
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Regional market integration in East Africa: local but no regional effects?
We investigate the spatial impact of the establishment of a regional economic community between Kenya, Tanzania, and Uganda in 2001. Measuring economic activity using satellite imagery of lights emanating from Earth at night, we demonstrate that cities near the community's internal borders expanded more than cities further away. The growth effect is temporary and highly localized: only cities less than 90 min of travel from the border experienced an acceleration in growth rates; after four years growth rates revert to their pre-treatment level. We show that this is consistent with an asymmetric reduction in trade costs for two types of trade modalities that co-exist in many parts of sub-Saharan Africa, local small-scale trade and regional large-scale trade, with a larger reduction in costs of the former. Yet, while local effects are relatively large, equivalent to a 5% higher GDP for cities near the EAC's internal borders, region-wide effects are non-significant
Klippel-Feil syndrom: a duplicated thumb
A 71-year-old woman was admitted to our hospital because of vertigo. At clinical examination a duplicated right thumb was noticed. The Patient revealed that she was suffering from Klippel-Feil Syndrom (KFS). KFS is a rare skeletal disease where a mutation of the GDF6 and GDF3 genes can be found. It is characterized by congenital fusion of any of the 7 cervical vertebrae. There can be associations with other malformations such as congenital elevation of the scapula (Sprengel’s deformity), spina bifida, scoliosis, cleft palate, malformations of the heart, head, face, arms, legs and fingers. Because of these heterogeneous medical conditions treatment for KFS is symptomatic and can include surgery
Ölpreis, Strompreis – welche Auswirkungen haben die gestiegenen Energiekosten, und sollten energieintensive Branchen entlastet werden?
Der Streit um die stark angestiegenen Energiepreise hält an. Kritik üben nicht nur Verbraucherverbände, auch mittelständische Unternehmen, energieintensive Industriebranchen und die Politik klagen über die Preisentwicklung und befürchten Standortnachteile für die deutsche Wirtschaft. Sollte der Staat regulierend eingreifen?
Experimental and numerical investigation of edge tones
We study both, by experimental and numerical means the fluid dynamical phenomenon of so-called edge tones. Of particular interest is the clarification of certain scaling laws relating the frequency ƒ to geometrical quantities, namely 푑, the height of the jet, 푤, the stand-off distance and the velocity of the jet. We conclude that the Strouhal number S푑 is given by S푑 = C · (푑/푤)푛 with 푛 ≈ 1 in our case. Moreover, the constant C of the experiment agrees within 10-15% with the result of the simulation. As for the frequency dependence on the geometry and on the jet velocity there is a very good agreement of experimental and numerical results
Геохимия твердой фазы снежного покрова в окрестностях цементного завода (на примере г. Топки Кемеровской области)
Dress A, RUCH E, TRIESCH E. Extremals of the cone of norms and the cohomology of c3-stratifications. Advances in Applied Mathematics. 1992;13(1):1-47
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