APresentation

OnConstruction of Turbo Generator

1. Overviewof

bhel

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)

2. Introductionto

turbo generator

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

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

Components

• Stator

• Rotor

• Excitation System

• Bearings

• Cooling System

• Oil Supply System

3. stator

Stator Frame

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 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.

Stator Core

The process of construction of core includes: 

Lamination Preparation 

Assembly of Core 

Compression of Core

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.

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.

4. rotor

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.

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.

Rotor Winding

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.

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.

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.

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.

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

5. Excitationsystem

Brushless Excitation

The main parts of brushless

excitation system are as

follows:

•  Pilot exciter

•  Main exciter

•  Rectifier wheel

•  Automatic voltage regulator

6. Coolingsystem

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.

HYDROGEN COOLEDWhen 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.

7. Testingof

turbo generator

Types of Tests

• SHORT CIRCUIT TEST

• OPEN CIRCUIT TEST

•  INTER STRAND TEST

•  HIGH VOLTAGE TEST ON ROTOR AND

STATOR WINDING

•  HELIUM TEST

Thank you