Turbo Generator and Unit Transformer
Turbo generator with auxiliary systems The turbo generator is a three-phase hydrogen-cooled synchronous generator. The stator frame is gas-tight with regard to the outer atmosphere, designed in accordance with standards for machines working in an explosive environment. The stator core consists of insulated magnetic laminations arranged in segments separated by ventilating ducts and tightened elastically inside the stator frame. The stator winding is made as a two-layer bar diamond winding with two parallel branches. The rotor body is one massive piece made of high-alloy nickel-chromium-molybdenum steel. The excitation winding is made of spatially arranged concentric coils connected into a series in such a way as to form a two-pole electric magnet.
The stator core and rotor are directly, and the stator winding indirectly hydrogen-cooled. The generator is also able to work without hydrogen as an air-cooled machine up to a load of 80 MVA.
The generator and auxiliary systems are equipped with process values measuring equipment (temperatures, pressures, etc.) needed for supervision and protection of the generator.
The main rated technical data: power 247 MVA power factor (cos .) 0.85 voltage 13800 V±7.5% current 10334 A reactive power at cos .=0 209.9 MVA speed 3000 rpm degree of efficiency under rated conditions at 100% of rated power 98,65% stator winding insulation class F rotor winding insulation class F hydrogen pressure 0.4 Mpa. Auxiliary systems of gas, sealing oil and cooling water areused for cooling the generator. The role of these systems is to maintain the cooling media within the limits necessary for safe and reliable engine operation. Any appearance of hydrogen in the proximity of the generator is detected by the hydrogen detection system.
The basic rated technical data: excitation current 2720 A excitation voltage 325 V excitation transformer power 2250 kVA excitation transformer ratio 13.8/0.52 kV Excitation system
The rotor winding is fed from the generator terminals through an excitation transformer and a thyristor converter. The thyristor converter is made by a three-phase fully controlled bridge connection. It consists of four forced air-cooled thyristor bridges connected in parallel. The automatic voltage regulator regulates the excitation voltage and thus the generator voltage as well, with the help of thyristor control devices. If an automatic regulator fails the stand-by regulator is automatically switched on. Generator voltage is built up by field flashing from 0.4 kV station emergency supply.
The de-exciting of the generator under normal stop conditions is performed by transition of the thyristor converter to the inverter operation regime. All excitation equipment, except the excitation transformer, is installed in a standard cubicle consisting of 5 compartments placed in a special closed room by the generator.