New approach in thermal monitoring of large power transformers applied on a 350 MVA odaf-cooled unit

Large power transformers belong to the most valuable and important assets in electrical power systems. The ageing of the used oil/paper-insulation primarily depends on the hot-spot temperature of the solid insulation system. Hence it is the dominant factor limiting the lifetime of the transformer. Therefore in 1996 a prototype of a stand alone thermal monitoring system was developed and installed on a 350 MVA transformer to observe the hot-spot temperature. The experiences of successfully operation during the last years encouraged us to update the system to the newest stage. The paper describes the state-of-the-art of the thermal transformer monitoring system based on new field bus technology. The advantages of a networked system and the usage of a centrally managed data base shared between multiple monitoring systems are exposed. The intention to implement new features exceeding the conventional monitoring system philosophy is discussed on an intelligent multifunction criteria Fuzzy algorithm for the control of fans of the heat exchanger units. It permits a more cost-effective long-time transformer operation management.