Estimation of transformer winding temperatures and coolant flows using a general network method

The windings of large modern transformers are generally cooled by pumping oil through a network of ducts in the winding. The resulting value of the hottest conductor temperature and the position it occurs in the winding are important parameters in the design and operation of a transformer. There is a standard method for estimating the value of this hot spot but there is very little information on the position at which it occurs. Also, devices have been developed which when inserted in a winding will measure the local temperature. These instruments could be used to measure the hot-spot temperature of a winding in a transformer on load. However, it would obviously be advantageous if the position of the hot spot could be estimated so that the device could be installed in the optimum position. The work reported here attempts two things: first, to improve on the standard method for estimating the winding temperature distribution and hot-spot temperature and secondly to estimate the position of the hot spot. The computer program developed to do this can be used to estimate the flows, fluid temperatures and boundary temperatures for any network of flow paths. However, only its application to a transformer is considered here. The method used to obtain the required predictions is described, and estimates are presented of the winding temperature distribution for a particular design of transformer operating with a steady load.