A
Presentation On
Summer Training At
Bharat Heavy Electricals Limited, Haridwar
CONSTRUCTION OF
TURBO GENERATOR
INTRODUCTION A 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.
PRINCIPLE OF OPERATION
In case of turbo generator, Rotor winding is supplied with DC current (through slip rings or brushless exciter) which produces constant magnetic field.
3 phase stator winding is laid in stator core.
When generator rotor is rotated (by a turbine) magnetic flux produced by rotor winding also rotates.
Voltage is induced in stator winding according to Faraday’s law.
3 phase stator winding also produces magnetic flux revolving at synchronous speed ((=120*f/p ). Rotor also rotates at synchronous speed. Both the magnetic fields are locked and rotate together.
GENERATOR MODULES
COMPONENTS USED IN TURBO GENERATOR
1. STATOR Stator frame
Stator core
Stator winding
End cover
Bushings
Generator terminal box
Stator frame Rigid fabricated cylindrical frame and is the heaviest
section in the generator Withstands weight of core & winding, forces & torques
during operation Provisions for H2/CO2 filling Provision for temperature measurements Foot plates for supporting on foundation Provision for H2 coolers
STATOR FRAME
STATOR CORE
PURPOSE:- Support the
stator winding
To carry the magnetic flux generated by rotor winding.
The stator core is made from the insulated electrical sheet lamination to minimize eddy current losses. Each lamination layer is made of individual sections.
Stator Winding The stator winding consist of two
layers made of individual bars. To minimize losses, bars are composed of separately insulated strands which are transposed by 360° .
To minimize stray losses in end winding, strands of top and bottom bars are separately brazed.
Bushings
A Generator bushing can be the weak link in the electricity supply chain. It is generally anticipated to be maintenance free but several clues prior to failure must be watched.
The bushings are bolted to the stator frame at the exciter end.
ROTOR
Rotating part of turbo generatorA high strength alloy steel single forging prepared by
vacuum cast steel. Longitudinal slots for housing field windingDamper winding is provided which safeguards the
asymmetrical and asynchronous operative conditions.Rotor of cylindrical type used in turbo generator.Supported on two journal bearings.Provision of axial fan for forced ventilation.
MAIN PARTS OF ROTOR
Rotor Body
Damper Bar
Silver Plated Rotor End Wedge
Rotor Winding
Retaining Ring
Silver Plated Shrink Seat
Transverse Slots
Rotor Wedge
ROTOR WINDING
Rotor coils are made of silver-bearing strap copper for greater creep resistance.
The coil is accurately formed to precisely fit in the rotor slot with minimum distortion.
Ventilating slots are punched in the straight portion of the coils to allow for radial discharge of cooling air
Rotor Slots
Slots for field winding are step milled over the entire length of the rotor body.
Step milling minimizes stress level at the root of the teeth.
Grooves for slot wedges are accurately machined into the slot walls.
Retaining Rings
Retaining rings support the rotor coil end turns against the centrifugal forces encountered during high-speed operation.
They are made from forgings that meet rigid specifications and are resistant to stress corrosion cracking.
Circular steel plates are shrunk into the outer end of the retaining ring to add section and to reduce distortion.
Rotor Fans
Steel axial flow fans are fabricated, tested and balanced. The fans are keyed and shrunk on the rotor body outboard of the retainer rings.
Conductor Construction Steps
1. Insulation check
2. Conductor cutting
3. Transposition
4. Cross over insulation
5. Stack Pressing
6. Forming
7. End Conductor cutting
8. Pickling Process
9. Contact sleeve mounting
10. Coil lug brazing
11. Testing
12. Reforming
13. Insulation
14. Finishing
Brushless ExcitationThe main parts of brushless excitation system are as follows:
Pilot exciter
Main exciter
Rectifier wheel
Automatic voltage
regulator
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.
This type of cooling is applicable for rating of 30 MW- 60 MW generators.
In this type of turbo generator there are vertically sides mounted cooler in a separate housing.
TESTING OF TURBO GENERATOR
SHORT CIRCUIT TEST
OPEN CIRCUIT TEST
INTER STRAND TEST
HIGH VOLTAGE TEST ON ROTOR AND STATOR WINDING
HELIUM TEST