Power System Operation Risk Assessment Based on Credibility Theory Part Two Theory Fundament

The encountered new problems in real studies are the traditional statistical reliability index of overhead lines can not exactly express the fault possibility of field running lines, and it is impossible to complete the operating risk assessment of the whole system by purely adopting the reliability theory. In fact, the uncertainty of power systems includes both aspects of probability and fuzziness. Since probability theory and fuzzy theory belong to independent branches of mathematics, and used to be computed separately in power system research. Till 2004 the credibility theory is completed as one of the mathematic branches in mathematic field to give the axiomatic foundation of fuzzy theory based on measure theory, and provide the rigorous mathematic foundation of probability and fuzziness evaluations. In this paper the reason why credibility theory adopted in operation risk assessment is presented first. Then the main principles of credibility theory are introduced, which include axioms, credibility measure, expected value of fuzzy variable and random fuzzy variable etc. These theories mentioned above are very important for risk assessment based on credibility theory.