A probabilistic method for comprehensive voltage sag management in power distribution systems

OF DOCTORAL THESIS Helsinki University of Technology P.O.Box 1000, FIN-02015 HUT http://www.hut.fi/ Author: Pasi Pohjanheimo Name of the thesis: A probabilistic method for comprehensive voltage sag management in power distribution systems Date of dissertation: October 20, 2003 Type of thesis: Monograph Department: Department of Electrical and Communications Engineering Laboratory: Power Systems Laboratory Field of research: Power Quality Opponents: Dr. Jovica V. Milanovic & Dr. Anssi Seppala Pre-examiners: Prof. Kimmo Kauhaniemi & Dr. Anssi Seppala Supervisor: Prof. Matti Lehtonen Abstract: Voltage sags, their technical and economic impact and the means of their mitigation have become popular topics for discussion, publication and R&D projects within the power engineering society. However, a tool including and combining analysis of all these fields in a simple yet mathematically exact way has not been proposed. This thesis outlines a probabilistic method for comprehensive voltage sag management named Prob-A-Sag. All quantities are processed as probabilistic two-dimensional arrays. Multiplying the arrays cell by cell gives the total annual sag related cost. Further, the optimal type and rating of a mitigation device can be assessed. Remaining voltage and sag duration are the variables considered in the arrays. Array resolution and thus the procedure accuracy are freely selectable. Increasing the number of dimensions allows for additional sag features, e.g. unbalance and phase-angle jump could be included in a future enhancement of the method. A probabilistic approach, one of the key features of the method, is essential when assessing the performance of multiple similar sag sensitive components connected together. It also proved useful in cases where specific device sensitivity tests cannot be carried out but instead, generalised data from previously prepared libraries has to be used to assess the entire process sensitivity. In addition to this method, the thesis provides sag sensitivity test results for contactors, personal computers and gas discharge lamps. Discussion and calculations on the feasibility and network requirements of custom power technology are also included.