ON THE DETERMINATION OF CHARACTERISTIC TEMPERATURES IN POWER OIL TRANSFORMERS DURING TRANSIENT STATES

Under usual assumptions the equations describing thermal phenomena in a transformer are established. Without neglecting any substantially important factor, algorithms are developed for predicting the temperatures in critical spots in non-stationary states occurring either in practice or in load/time diagrams. This paper suggests the determinaton of conductances dependent on temperature and constant capacitances of equivalent thermal circuits of a transformer. They are based on a small number of experiments (as simple as possible) and on a parameter estimation procedure. In such a way the temperatures of transformer parts in different transient states can be determined by computer simulation established on equivalent circuits, so the operators in power and sub-stations will be able to load their transformers close to the permitted limit. It is felt that this paper may give a stimulation for a possible revision of IEC rules.