Study On The Under Frequency Load Shedding Based On Power Shortage Tracing

Frequency as a key index reflecting the balance between the supply anddemand of the active power, meanwhile, it’s also an important content of the powersystem safe and stable operation research. With the development of electricalindustry and the trend of interconnected large power system, large capacity unit,UHV transmission and the parallel in of new energy, the dynamic frequencycharacteristic of the power system becomes more and more complicated. The usingof wide-area measurement system (WAMS) has greatly enriched observableinformation quantity of power system automation equipment. By the means of theabundant wide area measurement information, the under-frequency load shedding(UFLS) device, which is the third defensive line of power system, can realize therapidity, reliability and selectivity of the load shedding action, protect electricalequipment and prevent frequency collapse. Therefore, the study in this area hasbecome one of the most important issues urgent to be conducted.Base on the analysis of the superiority and drawback of current UFLS scheme,a method is discussed by tracing the power shortage to deal with the large-scalepower flow transferring after the UFLS action. Then an algorithm research for theelectrical dissecting theory is proposed, Depth First Search (DFS) of directed graphtheory is used to obtain dissecting sub-path relation sets, electrical dissectingprogram is created using C#language, and the equivalence of dissecting theory isdemonstrated by the example analyzing. Furthermore, a tracing method for activepower shortage at fault time is proposed according to sub-path “power”superposition of the electrical dissecting theory, which is used in the distribution ofthe load reduction. Finally, power shortage tracing results and corresponding loadreduction distribution scheme can be illustrated from a simulating example. In thispaper, the effectiveness of the proposed scheme in solving large-scale power flow transferring is verified by the comparative analysis of the simulation results and thecontrast scheme.