An Experimental Determination of the Heat-Transfer Coefficients in the Channels of a Turbogenerator Stator with air and Hydrogen Cooling

Abstract

The heat transfer coefficients in the ventilation channels of a turbogenerator stator of new construction, containing slot-shaped axial channels in the teeth, are investigated. Experiments are carried out on a full-scale physical model with air cooling and on a turbogenerator with hydrogen cooling. In the latter case, active heat-transfer sensors, simulating the slot-shaped channels, are built in to the circulation circuit of the cooling gas of a commercial turbogenerator with hydrogen cooling when it was undergoing bench testing. The results of the experiments can be used when designing high-power turbogenerators with total gas cooling.The use of straight-through axial channels of slot-shaped form in the teeth of a stator ( Fig. 1) has led to an increase in the use of active materials and, in the final analysis, has enabled the unit power of turbogenerators with indirect gas cooling of the stator winding to be increased [1,2]. The presence of such channels in the ventilation system radically reduces the thermal resistance between the winding and the cooling gas by virtually eliminating the resistance across the active steel packet of the stator.Since the effect achieved is higher the more intense the forced convection in the slot-shaped channels, the use of such channels in newly constructed turbogenerators with hydrogen cooling is of even greater practical interest than in the present structures that use air cooling [3].Determination of the heat transfer coefficients on a full-scale model of the stator air-cooling system. In thermal technology practice, an investigation of heat transfer in channels of irregular shape is, as a rule, carried out on laboratory samples, which closely reproduce the geometry of natural objects. Such a full-scale experiment was used to investigate a new construction of a 225 MW turbogenerator with slot-shaped channels in the stator teeth with air cooling.To determine the thermal characteristics of this cooling system in the experimental equipment we simulated the ventilation conditions in a group of radial channels with a bypass through axial channels in the teeth. The sources of heat in the radial channels were plane two-section electric heaters made of constantan using direct current. The heat sources in the axial channels were electric coils, built into the walls of the axial channels. The working surfaces of these and other channels were fitted with an appropriate number of thermocouples. The temperature of the cooling air was measured at the input and output of the radial channels. The local heattransfer coefficients were determined in the axial slot-shaped channels at different distances from the input to the channels. In this case the air temperature in the corresponding section was taken on the assumption that it has a linear distribution along the channel.An important result of this investigation was establishing the fact that there is a considerable intensification of convective heat exchange in the radial channels which supply the axial channels in the teeth with air. To co...