Influence of Short-Circuit Duration on Dynamic Stresses in Substations
The short-circuit peak current and the electromagnetic short-circuit peak force appear at about 10 ms after the short-circuit inception. However, the maximum value of dynamic stress due to the electromagnetic forces may occur much later and depends on the fundamental frequency of the structure. A decrease in dynamic stress can be obtained even if the short-circuit duration is much longer than 10 ms. In the presentwork, the dynamic stress on stiff conductors and insulators during the short-circuit, as well as, the subsequent free oscillation after fault clearing, are analytically determined and the influence of short-circuit duration on the dynamic stress in certain cases of busbar structures is investigated. Furthermore, the shortest short-circuit durationwhichresults in maximum dynamic stress is given for the entire range of the relevant mechanical fundamental frequencies.
Dynamische Kurzschlußbeanspruchung in Gleichstromanlagen
ÜbersichtDie Zeitverläufe der Kurzschlußströme und daher auch der elektromagnetischen Kurzschlußkräfte in Gleichstromanlagen sind sehr vielfältig und können nur mit einer größeren Anzahl von Parametern beschrieben werden. Für jeden dieser Verläufe kann eine einfache Ersatzfunktion — Rechteck oder Sinusquadrat — bestimmt werden, die annähernd den gleichen maximalen Momentanwert der mechanischen Beanspruchung wie die ursprüngliche elektromagnetische Kraft verursacht, wenn die Kurzschlußdauer kleiner als die halbe mechanische Periodendauer ist. Nach geeigneter Modifikation kann das Ersatzrechteck auch dann verwendet werden, wenn die Kurzschlußdauer größer ist als die halbe mechanische Periodendauer.ContentsThe time patterns of short-circuit currents and therefore of the electromagnetic short-circuit forces in DC bus systems are very manifold; they only can be expressed by use of several parameters. For each of these patterns a substitute time function can be determined (rectangle or sinussquare) which causes about the same maximum instantaneous value of mechanical strength, like the original electromagnetic force, if the short-circuit duration is less than the half period of the mechanical oscillation. After suitable modification the rectangle function can also be used if the short-circuit duration is greater than the half period of the mechanical oscillation.
Digital Computation of Short-Circuit Bus Stresses
A digital computer program has been developed for the purpose of checking the adequacy of generator and substation bus designs in withstanding mechanical stresses due to short circuits. Experience with the program to date shows that the computer carries out the required calculations in about 1/100 of the time needed by a trained engineer and provides a reduction in calculating cost of four to one. It is expected that the computer program will contribute to better engineered and more economical station design by making comprehensive bus stress analyses easier and less time consuming.