Assessment of circuit capability and preparation of rating sheets

The need to work power systems harder using the best knowledge of its capability is central to the objectives of the National Grid Company (NGC) Technology and Science Division (UK). This objective must be balanced by appropriate work on the impact of loading regimes on the life expectancy and maintenance requirements of the power system. This paper describes the development of a unified circuit rating process allowing for the separate characteristics of every power system item in the circuit and the automation of that process using a Critical Unit Program (CUP) written in LOTUS 123. The program is being used to create circuit rating sheets which were previously manually produced in less consistent formats. An example of the output of the CUP system is given. The intention of this work is to enable NGC to operate its power systems harder within the limits set by normal design temperatures. Operators also require guidance on fault current ratings