1. Construction of Turbo Generator
Presentation On
Construction of Turbo Generator

2. 1. Overview of bhel

3. Bharat Heavy Electricals Limited(BHEL)
Heavy Electrical Equipment Plant(HEEP)
Block I : Electrical Machine Shop
Block II : Heavy Fabrication Shop
Block III : Turbine Manufacturing Block
Block IV : Coils & Insulation Manufacturing Block
Block V : Condenser Fabrication & Forge Plant
Block VI : Fabrication Shop , Die Shop
Block VII : Carpentry Shop
Block VIII : Heat Exchange Shop
Central Foundry Forge Plant(CFFP)

4. 2. Introduction to turbo generator

5. 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.
Faraday’s Law

6. Generator Modules TARI: Air Cooled Turbo generator
  Stator Winding: Indirectly Air Cooled
 Rotor Winding/ Stator Core: Directly Air Cooled
THRI: Hydrogen Cooled Turbo generator
  Stator Winding: Indirectly Hydrogen Cooled
Rotor Winding/ Stator Core: Directly Hydrogen Cooled
THDF: Hydrogen/Water Cooled Turbo generator
  Stator Winding: Directly Water Cooled
  Rotor Winding/ Stator Core: Directly Hydrogen Cooled

7. Components Stator Rotor Excitation System Bearings Cooling System
Oil Supply System

8. 3. stator

9. Stator Frame

10. 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

11. Stator Core
The stator core is made from the insulated electrical sheet lamination to minimize eddy current losses. Each lamination layer is made of individual sections. The main features of core are: 
To carry electric & magnetic flux generated by rotor winding efficiently. 
To provide mechanical support to the stator winding. 
To ensure perfect link between the core and rotor.
 Therefore the selection of material for building up of core is very important.

12. Stator Core Lamination Preparation Assembly of Core
The process of construction of core includes: 
Lamination Preparation 
Assembly of Core 
Compression of Core

13. Stator Winding
The stator winding of Turbo Generator is three phase two layer lap winding with the pitch of winding so adjusted as to reduce the 5th and 7th harmonics. The number of slots for generation of three phase power must be a multiple of 3 or 6.
Each stator slot accommodates two stator bars.

14. 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.

15. 4. rotor

16. Introduction Rotating part of turbo generator
A high strength alloy steel single forging prepared by vacuum cast steel. 
Longitudinal slots for housing field winding
Damper 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.

17. Introduction
Due to the non -uniform slot distribution is on the circumference, different moments of inertia are obtained in the main axis of rotor. This in turn causes vibration. These vibrations are reduced by transverse slotting of the poles.
The rotor winding is provided with a lateral gap pick up system of cooling in the slot portion, ensuring uniform temperature distribution of the winding.

18. Rotor Winding

19. Rotor Winding
The rotor of turbo generator accommodates field winding. Turbo generator is a two pole machine rotating at a speed of 3000 R.P.M. There are 28 slots cut on two-third of the periphery which support field winding. The field winding consists of several series connected coils inserted into the longitudinal slots of rotor body.
Approximately 60% of the rotor circumference is provided with longitudinally slots which hold the field windings. The slot pitch is selected so that two solid poles are obtained with a displacement of 180 degrees. The coils are wound so that two poles are obtained. The conductors are made up of copper with a silver content of approximately of 0.1%. The solid conductors have a rectangular cross section and are provided with axial slots for radial discharge.

20. ROTOR SLOT WEDGES
The rotor of turbo generator is rotating at a very high speed therefore to protect the winding against the effects from centrifugal forces they are secured firmly by rotor slot wedges.
The slots wedges are made of copper alloy. They are also used damper winding bars.
The wedge and retaining ring act as damper winding in case of asymmetrical and asynchronous operation.
The ring is coated with silver which acts as short circuit rings in damper windings.

21. ROTOR RETAINING RING
To protect end winding of rotor from flying out from the rotor due to centrifugal forces rotor retaining ring is used. Retaining rings are made from high tensile non- magnetic alloy steel forgings in order to reduce stray losses.
These act as short circuit rings to the induced current to the damper system. To ensure low contact resistance retaining rings are coated with nickel, aluminum, silver.
The rotor of turbo generator is rotating at a very high speed therefore to protect the winding against the effects from centrifugal forces they are secured firmly by rotor slot wedges.

22. ROTOR FAN
The cooling air in generator is circulated by axial fans located on the rotor shaft.
In 250 MW rotor two axial flow fans are located on both turbine as well as exciter end side whereas in 500 MW axial fans are located on turbine end side only.

23. Conductor Construction Steps
Insulation check
Conductor cutting
Transposition
Cross over insulation
Stack Pressing
Forming
End Conductor cutting
Pickling Process
Contact sleeve mounting
Coil lug brazing
Testing
Reforming
Insulation
Finishing

24. 5. Excitation system

25. Brushless Excitation
The main parts of brushless excitation system are as follows:
 Pilot exciter
 Main exciter
 Rectifier wheel
 Automatic voltage regulator

26. 6. Cooling system

27. AIR COOLED
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.

28. HYDROGEN COOLED
When the problem of increasing generator rating was talked in it became clear that the air cooled machine did not provide the necessary scope for progress. Not only in circulating the requisite of air through the machine but also because high fan power required to circulate. Evidently to push up generator ratings hydrogen is used as cooling medium.
Advantages of Hydrogen as Cooling Medium:
Increased efficiency: The density of H2 is only 0.07 times the density of air and therefore the power required to circulate H2 is less than that required in air.
Increase in rating: H2 has a heat transfer coefficient 1.5 times and its thermal conductivity is 7 times that of air. Consequently when H2 is used as a coolant, the heat is more rapidly taken up from the machine parts and dissipated.
Elimination of fire hazard: The outbreak of fire inside the machine is impossible as H2 does not support combustion.
Smaller size of coolers: The size of cooler required is smaller in size.
The below given diagram are the cooling of rotor and stator in hydrogen cooling and hydrogen cooled type turbo generator.

29. 7. Testing of turbo generator

30. Types of Tests SHORT CIRCUIT TEST OPEN CIRCUIT TEST INTER STRAND TEST
 HIGH VOLTAGE TEST ON ROTOR AND STATOR WINDING
 HELIUM TEST

31. Thank you