Security analysis is an important task in the operation of an electricity network. In the case of a systematic analysis of single or even double contingencies, the combined nature of the problem requires a longer calculation time than is available for real-time analysis. Amongst the recent approaches proposed in scientific publications, some make reference to the use of artificial intelligence and more particularly expert systems. A new modular expert system detailed in the article is the result of the application of these techniques to the security analysis of electricity transmission networks