The temperature of the elementary conductors of the stator winding of a 225 MW turbogenerator has been measured using miniature fiber-optic sensors, built in to the winding during manufacture. This is the first time that practical bench tests have been made in Russian electrical machine construction practice. The results of the experiment are used as the initial data for determining important parameters of the construction of turbogenerators with air cooling, namely, the thermal conductivity of the body insulation in the slot, and the heat-transfer coefficient in the front parts of the stator winding.Keywords: turbogenerator, stator winding, fiber-optic temperature sensors, thermal conductivity of the housing insulation.As the construction of large turbogenerators has developed, the need to measure local temperatures of the elementary conductors of the stator winding on actual machines has increased. The value of such information in designing new machines is the fact that, in addition to direct information on the actual temperature at which the body insulation operates, the designer obtains more refined fundamental thermal parameters, namely, the specific losses in the winding and the thermal resistances. A priori estimates of these parameters at the design stage contain well-known uncertainties, due, in particular, to production-technological factors. Thus, the specific losses in the winding are not indifferent to local contacts between individual conductors, while the thermal resistance between a copper winding and the wall of the slot depends on the presence of air microcavities between the outer surface of the insulation and the tooth of the stator.Since, when operating a turbogenerator, the stator winding is subjected to a high electrical potential, when measuring the temperature galvanic coupling between the copper winding and the recording apparatus must be eliminated. This can be achieved using a fiber-optic thermometer [1 -3]. Specific difficulties arise in making such measurements, due to the need to guarantee the safety of personnel and of the machine being tested. In particular, the problem of the practical arrangement of the sensors and of the measuring channel in the stator winding necessitates considerable miniaturization of these components of the measuring system. The mechanical stability of these components must be guaranteed and the requirements of reproducibility of the calibration characteristics of the sensors during the whole production cycle and during the tests of the machine must be satisfied.Direct measurement of the temperature of the copper of the stator winding using fiber-optic sensors are at the initial stage of development at the present time. The first attempt to use such sensors when testing a 250 MV · A turbogenerator was reported a few years ago by the Japanese Hitachi Company [4].In this paper we present the results of the first successful attempt, made in Russia, to use fiber-optic sensors to measure the temperature of the elementary conductors of the stator winding in bench...