Imprecision in power flow analysis is modeled using fuzzy-set theory. Fuzziness on the power generation and loads used in a power flow analysis implies fuzziness on the outputs; a method is suggested for calculating imprecision through informative statements about the system generation data and availability of generation units in the power flow analysiswhich depends on the imprecision of the inputs. In the present paper not only the power generations and loads in the power systems are descri bed by fuzzy set, butthe availability of each generation unit also is presented in fuzzy term. In addi ti on improvement have been made over previous works through eliminating someunpractical assumptions. Tow test cases were preformed to demonstrate thecompatibility of the purposed method with typical electric utility planning programs. Ageneral discussion on the resul ts were made, al ong wi th di scussi on of theadvantages and disadvantages of the approach is given.

كلمات كليدي:

fuzzy set, fuzzy power flow, power system.