DRK INSTITUTE OF SCIENCE AND TECHNOLOGY STUDY OF AIR COOLED TURBO GENERATOR Internal Guide : Batch No : 4 Mrs.Punyavathi Madam Presented By: 1.B.Supraja -10N71A0203 2.V.Saicharan -10N71A0223 3.N.Veera Tejeswar -11N75A0201

INTRODUCTION A turbo generator is the combination of a turbine directly connected to an electric generator for the generation of electric power.

CONTENTS Construction of turbo generator Insulation system Vacuum pressure impregnation system 3. Tests on turbo generator 4. Conclusion

T-G MAIN PARTS STATOR ROTOR EXCITER COOLING SYSTEMS BEARINGS

STATOR Stator Frame Stator core Stator winding Stator end covers Phase connectors

STATOR FRAME > It is of welded steel single piece construction > It supports laminated core and windings > It consists of guide bars and footings

STATOR CORE > It is made of silicon steel lamination > The stator laminations are assembled as separate cage core without the stator frame Purpose: 1.To support the stator winding 2.To carry the electromagnetic flux generated by rotor winding. > Cold rolled non-grain oriented (CRANGO) silicon steel sheets used.

STATOR WINDINGS > Stator Winding is the one which induces e.m.f and supplies the load. Stator winding is placed in the slots of stator core. > Generally two layer lap winding chorded to about 5/6 pitch which practically eliminates 5th and 7th harmonics. > Copper material is used to make coils.

STATOR END COVERS & PHASE CONNECTORS > These end covers are attached to end flanges of stator frame and also rest on the foundation plate. > End covers are made up of non-magnetic material {Al-casting} to reduce stray load and eddy current losses. > Phase connectors consist of flat copper sections, which results in low specific current loading.

ROTOR Rotor is the rotating part of alternator. It is used to support field winding placed in slots on the rotor Two types of rotors 2-pole rotor 4-pole rotor

PARTS OF ROTOR

ROTOR SHAFT Rotor shaft is a single piece solid forged from a vacuum degassed steel ingot. slots for insertion of field winding are milled into rotor body. The rotor teeth at the ends of rotor body are provided with axial and radial holes for cooling purpose.

ROTOR WINDINGS The rotor winding consists of copper strips (5.3mm) connected in series by brazing they and placed in rotor slots. The slot wedges are made up of high electrical conductivity material and act as damper windings.

ROTOR WEDGES These are used to protect the winding against the effects of centrifugal forces, the winding is secured in the slots with wedges. There are also used as damper winding bars. RETAINING RINGS made up of non-magnetic high strength steel in order to reduce stray losses. ROTOR FANS: the two axial flow fans located on the rotor shaft one at each end made up of aluminium.

EXCITATION SYSTEM The basic use of given exciter system is to produce necessary DC for turbo generator.

BRUSHLESS EXCITATION

COOLING SYSTEM Cooling is one of the basic requirement of any generator. Various methods of cooling 1. Air Cooling-60MW Hydrogen cooling-100MW Water cooling-500MW H2 & water cooling-1000MW

BEARINGS The generator rotor is supported in two sleeve bearings. To eliminate shaft current the exciter and bearing is insulated from foundation plate and oil piping. The temperature of each bearing is maintained with two RTD’s embedded in the lower bearing.

INSULATION SYSTEM In electrical machines insulation is the most important requirement to sustain high voltages and basically insulation is the heart for electrical machines. The property of good insulating material is non-conductive to electricity and conductor for heat. An insulator should satisfy the following properties Electrical properties Mechanical properties Thermal properties Chemical properties

CLASSIFICATION ACCORDING TO TEMPERATURE Permissible temperature Materials Y 90 Degrees Cotton, Silk, Paper. A 105 Degrees Varnished Paper E 120 Degrees Synthetic Material of cellulose base B 130 Degrees Mica, Asbestos F 155 Degrees Material Of Class-B with Binding Material of Higher Thermal Stability. H 180 Degrees Glass Fiber and Asbestos Material and Built up mica with silicon Resin. C Above 180 Degrees Mica, Porcelain, Quartz, Glass with silicon Resins of higher thermal stability.

VACUUM PRESSURE IMPREGNATION SYSTEM In order to minimise the overall cost of the machine & to reduce the time cycle of the insulation system VPI system is used. Process of VPI General Preheating Impregnation Post curing Electrical

TESTING OF TURBO GENERATOR A T-G has to be tested for proper fabrication and trouble free operation. From the tests one can determine the external characteristics needed for application of these machines. Also, one can find the efficiency, rating and temperature rise of the machine. Some of the tests are discussed in sequence now.

ROUTINE TESTS ON TURBO GENERATOR 1) Mechanical run test and vibration measurement. 2) Short circuit characteristic and losses measurement. 3) Open circuit characteristic and losses measurement 4) Phase sequence check. 5) Shaft voltage measurement 6) Impedance measurement at standstill, at 1/3,2/3 and 3/3 of rated speeds. 7) Insulation Resistance measurement on stator and Rotor winding. 8) PI value measurement. 9) High Voltage Test on stator and rotor winding. 10) RTDs Checks. 11) DC Resistance measurement on stator and rotor winding.

ROUTINE TESTS ON BRUSHLESS EXCITER: Mechanical run and measurement of vibration at rated speed Open circuit characteristics Load magnetization characteristics Measurement of IR value and high voltage Measurement of D.C.resistance of armature windings, main pole winding and quadratue axis coils.

CONCLUSION