ANALYSIS OF THE EFFICIENCY OF AIR-COOLED TURBOGENERATORS

The article provides an overview of current air-cooling schemes for modern high-load high-capacity turbogenerators with full air cooling. It outlines the main limitations that restrict the use of various cooling options, as well as potential areas for improvement and ways to enhance the efficiency of air-cooling systems. Two main cooling schemes applicable to high-capacity turbogenerators are compared: multi-chamber forward-flow cooling scheme and independent cooling circuits for the rotor and stator. Special attention is paid to the power consumption in these circuits for cooling the active parts of the generator. Ventilation losses are determined by the cooling air flow rate and the specific pressure required to move a single volume of air along the cooling circuit. Improving the efficiency of the cooling system is possible by minimizing the two specified parameters. It is advisable to consider the cooling circuits of the rotor and stator separately. The paper shows that for both cooling circuits, an exhaust circuit with independent cooling circuits of the rotor and stator provides higher efficiency, i.e., lower power consumption for ventilation. In the rotor cooling circuit, this is achieved through the use of a fixed guiding device, which reduces the specific pressure applied to the air in the rotor’s pressure elements. This reduces the ventilation heating of the air in the rotor and the cooling air flow rate. With the correct choice of the initial twist value in front of the rotor in a fixed guide device, the influence of the first indicated effect dominates over the second. In the stator cooling circuit, where the limiting hot element is the tooth zone and core winding, the flow separation scheme is more efficient due to the exclusion of exhaust hot air from the gap between the rotor and the stator from further participation in cooling the active parts of the stator. In a multi-chamber forward-flow cooling path, air from the gap is discharged through the cooling channels of the exhaust hot compartments of the stator core, which requires an increased flow rate in the stator cooling circuit to dilute the hot flow of the rotor circuit. This leads to higher power consumption in this cooling scheme and forces the designer to complicate the scheme by introducing additional air coolers and increasing the dimensions of the active parts to reduce specific electrical loads and heat generation.