MANUFACTURING OF TURBO GENERATOR

MANUFACTURING OF TURBO GENERATOR

INDEXIntroduction to turbo generatorStatorRotorExcitation SystemCooling systemGenerator Technical DataTesting Of Turbo GeneratorConclusion

INTRODUCTION TO TURBOGENERATORA turbo generator is a turbine directly connected to electric generator for the generation of electricity. They are mostly used as large capacity generator driven by steam/gas turbine.The turbo generator is invented by Blathy Otto an electrical engineer of Hungary, in 1912.Later it was developed by Michael Faraday a British scientist.

PRINCIPLE OFOPERATION Faradays Law :E.M.F. (Voltage) is induced in a closed path due to change of flux linkages and is proportional to rate of change of flux linkages. The change in flux linkages can be caused by change in flux in a stationary coil or by motion of coil with constant flux or both.

E=Nd/dt

MAIN COMPONENTS USED IN TURBO GENERATORSTATORROTOREXCITATION SYSTEMCOOLING SYSTEMSTATOR The stator consists of followingparts STATOR FRAME STATOR FRAME STATOR WINDING STATOR END COVER BUSHINGS GENERATOR TERMINAL BOX

STATOR FRAMERigid fabricated cylindrical frame and is the heaviest section in thegenerator, withstands weight of core & winding, forces & torques duringoperation.Provisions for H2/CO2 filling

Provision for temperature measurements Provision for H2 coolers

Stator core The stator core is made from the insulated electrical sheet lamination to minimize eddy current losses. It ensure perfect link between the core and rotor. The purpose of stator core is to carry the magnetic flux generated by rotor winding.

STATOR WINDING The stator winding of Turbo Generator is three phase two layer lap winding. Each stator slot accommodates two stator bars. The bar consists of a large number of separately insulated strands which are transposed by 540 degrees.

STATOR END COVER The ends of the stator frame are closed by pressure containing end shields The end covers are made up of non-magnetic material (Aluminium castings). The end shield used at the turbine end and exciter end sideis different in construction for 500MW and 250MW.

BUSHINGS The beginning and ends of the three phase windings are brought out from the stator frame through bushings, which provides for high voltage insulation. The bushings are bolted to the stator frame at the exciter end.

ROTOR It is Rotating part of turbo generator. It has Longitudinal slots for housing field winding. The slot pitch is selected so that two solid poles are obtained with a displacement of 180 degrees.The Rotor consists of the following parts ROTOR SHAFTROTOR WINDINGROTOR RETAINING RINGSFIELD CONNECTION

Rotor shaft It is the rotating part of rotor. It is the axis around which the major rotor rotates. Maintenance of therotorshafts is scheduled on a frequent basis. Bearings and bearing mounts are replaced after a predetermined number of hours of use.

ROTOR WINDINGThe rotor of turbo generator accommodates field winding. The field winding consists of several series connected coils inserted into the longitudinal slots of rotor body.

Rotor retaining rings The conductors are made up of copper with a silver content of approximately of 0.1%, having rectangular cross section and radial discharge. The individual bars are bent to obtain half turns. After insertion into the rotor slots, these turns are brazed to obtain full turns. The series connected turns ofone slot constitute one coil.

To protect end winding of rotor from flying out from the rotor due to centrifugal forces rotor retaining ring is used.

Field connection Retaining rings are made from high tensile non-magnetic alloy steel forgings.The field current is supplied to the rotor winding through radial terminal bolts and two semicircular conductors located in the hollow bores of the exciter and rotor shafts.The field connection provides electrical connection between the rotor winding and exciter

EXCITATION SYSTEMBRUSHLESS EXCITATIONThe main parts ofbrushless excitation system are as follows PILOT EXCITER MAIN EXCITER RECTIFIER WHEEL

Pilot Exciter The three phase pilot exciter has a revolving field with permanent magnet poles. The armature winding is housed on the stator. The three phase a.c. generated by the pilot exciter is rectified and controlled by automatic voltage regulator to provide variable D.C. for exciting the main exciter. The three phase main exciter has stationary field with revolving armature. Thus three phase a.c. power is produced in main exciter which is rectified byrotating rectifier bridge and is fed to the field winding of the rotor (turbo generator) through dc leads.

Pilot Exciter Three phase pilot exciter is 16pole revolving field units.

The stator accommodates three phase armature winding and magnetic poles are placed on the rotor. Thus rotating flux is produced which cuts the stationary armature conductors and three phase a.c. is generated.

Main Exciter The three phase main exciter is a 6 pole armature type unit.

The stator frame accommodates the field winding. The field winding is placed on the magnetic poles. The armature consists of stacked lamination and the three phase winding is inserted into the slots of the laminated armature

Rectifier wheel Components in the rectifier wheel are as follows SILICON DIODES ALUMINIUM HEAT SINK FUSES RC CIRCUIT

The main component in the rectifier wheel is silicon diodes which are arranged in rectifier wheel in three phase bridge circuit.The direct current from rectifier wheel is fed to DC leads and then to the field winding of the rotor.

COOLING SYSTEM COOLINGMETHODS FOR TURBOGENERATOR AIR COOLED TURBO GENERATOR In Air Cooled Turbo generator stator winding is indirectly air cooled whereas the rotor winding and stator core is directly air cooled.

HYDROGEN COOLed turbo generator This type of cooling is applicable for rating of 30 MW- 60 MW generators. Inthis type of turbo generator there are vertically side mounted cooler in a separate housing.H2 has a heat transfer coefficient 1.5 times and its thermal conductivity is 7 times that of air.

GENERATOR TECHNICAL DATAPARAMETER UNIT 250 MW 500 MW 660 MW 800 MWMODULE -THRI 108/44THDF 115/59THDF 115/67THDF 125/67RATED VOLTAGE KV 16.5 21 21 27RATED CURRENT Amp. 10291 16166 21334 20129HYDR. PRESS. (g) Bar 4.0 3.5 5.0 5TESTING OF TURBO GENERATOR To estimate the performance ofgenerator, theTURBO GENERATORSare requiredto undergo some tests. SHORT CIRCUIT TEST Reduce the field current to a minimum, using the field rheostat, and then open the field supply circuit breaker. Short the stator terminals of the machine together through three ammeters. The short circuit characteristics is plotted from short circuit results by selecting X-axis as field current and Y-axis as % rated current. From the Short Circuit test, we will get copper losses.

OPEN CIRCUIT TEST Drive the synchronous machine at the synchronous speed using a prime mover when the stator windings are open circuited. Vary the rotor winding current, and measure stator winding terminal voltage. Theopen circuit characteristics is plotted from open circuit resultsby selecting X-axis asfield current and Y-axisas% rated voltage. From the open circuit test, we will get Iron Losses. INTER STRAND TEST This testing is basically done to check any short circuit between ant two consecutive conductors of a bar. For this test all the bare conductors at both the ends are separated from each other so that they do not short circuit.

HIGH VOLTAGE TEST ON ROTOR AND STATOR WINDING (MACHINE AT REST) Similarly all the conductors are checked for any short circuit.The test is conducted on all the phases and rotor winding separately.When High Voltage test is done on one phase winding, all other phase windings, rotor winding, instrumentation cables and stator body is earthed.This test is done to check the insulation of the winding.HELIUM TESTHelium test is done to check leakage within the barand at the brazed portions.In this The helium gas at pressure of 11Kg/Cm^2 is passed through the bar.

CONCLUSIONAs the turbo generators are high voltage machines which are ranging from less than 1500 volts.Hence the machine efficiency is accurate.Turbo generators are also more reliable in nature.As the production of sources are taken from the non-renewable energy sources the cost is economic.