Filters for Three Phase Unbalanced Voltage Systems

A.I. Litchev (Botswana), N.T. Nikolov (Bulgaria), and K.M. Yanev (Botswana)


Unbalanced system, symmetrical components, filter, simulation.


The usual exploitation of power systems requires any three-phase voltage systems to be balanced. Any deviation of this requirement leads to lower efficiency and to deterioration of technical characteristics of the equipments in use. Many standards prescribe the voltage unbalance within 2 % or 3 %, depending on the type of equipment [1, 2, 3]. As known any unbalanced three-phase voltage system could be represented by a set of three symmetrical 3-pase systems having positive, negative and zero sequence. The unbalance is determined by a coefficient representing the ratio between the negative and the positive symmetrical components. These components could be determined experimentally by the use of circuits called filters for symmetrical components. This paper contributes to the theoretical and experimental studies of a filter consisting of star connected resistive, resistive-inductive and capacitive elements. Contribution is also the development of a method to determine the filter element values needed for measurements of the positive and negative voltage components by the use of one filter only. The unbalanced voltage system was simulated and the outcomes matched excellently with the analytical results.

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