Alleviation of transmission system overloads using fuzzy reasoning

Abstract

Power flows on a large inter-connected power system must be kept within limits to prevent thermal overloading leading to excessive sagging of lines or over-heating of transformers and cables. Flows must also be limited to prevent transient instability. Such control essentially requires the co-ordination of sources of active power and controls of its flow such as quadrature boosters. This paper describes a new approach to this co-ordination problem which utilises a fuzzy expert system. A set of rules is developed to model operators' decisions based on criteria concerning the extent of a limit violation, the sensitivity of a candidate control device, the margin available at the control device, the cost of the required control move and the maximum number of control settings to be moved. Co-ordination of control actions using fuzzy inference and composition is shown to succeed in resolving conflicts while use of fuzzy cardinality enables effective control devices to be ranked. The work is extended to address the duration of overloads so that actions are taken only as and when needed, the scheduling of preventive actions and the meeting of group constraints.