manfacturing steps for turbo generators

1. BY
K.PRABHU
12BEEE1039

2. STUDY OF TURBO GENEATORS


 AT
 BHEL, HYDERABAD

3. INTRODUCTION ABOUT BHEL
 BHEL, Hyderabad unit manufactures Turbo
Generators of rating up to 200 MW for industrial
applications and for power generation in Steam Power
Plants.
 Turbo Generators manufactured here range from 4
MW to 200 MW

4. RATINGS OF TURBO GENERATOR
 Rated output:200MW
 Rated kva capacity:247KVA
 Rated voltage:15.75kv
 Rated current:9050A
Rated speed:3000rpm
Rated frequency:50hz
efficiency:98.5%

5. INTRODUCTION TO TURBO
GENERATORS
 A turbo generator is a turbine directly connected to an
electric generator for the generation of electric power.
 OPERATING PRINCIPLE:” FARADY’S LAW OF
ELECTRO MAGNETIC INDUCTION
 whenever conductor cuts magnetic flux, dynamically
induced EMF is produced. This EMF causes a current
flow if the circuit is closed
 e = -N d/dt

6. The general components of a turbo
generator are
 Stator- Stator Frame
- Stator Core
- Stator Windings
 Rotor-
 Rotor Shaft
 - Rotor Windings
 Cooling System

7. STATOR FRAME

8. STATOR FRAME
The stator frame is of welded steel single piece
construction.
It supports the laminated core and winding.
Guide bars are welded or bolted inside the stator
frame over which the core is assembled

9. STATOR CORE
 Stator core is made up of silicon steel sheets which are
suspended in the frame from guide bars
 Purpose of stator core:
 1.to support the stator winding
 To carry the magnetic flux generated by rotor winding
 Losses in core:
 1.hysteresis
 2.eddy current
 In order to reduce hysteresis losses steel alloy is used for
the building up of core
 In order to reduce eddy currents thin laminations(0.5mm)
are used.

10. STATOR CORE

11. PREPARATION OF LAMINATIONS
 COLD ROLLED NON GRAINED ORIENTD (CRNGO)
Steel sheets are used
 PRESS TOOLS are used in manfacturing of
laminations
 1.compounding tools
 2.Blanking and slot notching tools
 Compounding tools: in this method stamping with all
the core bolt holes and winding slots in single
operation
 Used for the machines rated above 40 MW

12.  BLANKNG AND NOTCHING OPERATION:
 Core bolt holes are made using blanking tools
 Winding slots are made using notching tools
 Used for smaller rated machines
 500 tons of crank press is used for this purpose
 VARNISHING: After this process laminations should
be varnished for the insulation
 Varnishing thickness should be 12-18mm
 Sheets are dries at a temperature of 260-350 deg
centigrade.

13. STATOR COILS AND WINDING
stator coil is made up of Copper bars or conductors
High voltage insulation(resin poor mica tape) is provided
over the bars
Winding:
The bars are located in slots of rectangular cross section
which are uniformly distributed on the circumference of
the stator core
To minimize the stator losses in the winding, the strands of
the top and bottom bars are separately brazed and
insulated from each other
It is three phase layer lap winding

14. STATOR WINDING

15. RESISTANCE TEMPERATURE
DETECTORS
 The temperature measurements on the generator are
made with RTDs They are placed at various sections of
the core and winding
 The RTD works on the principle of the change in
electrical resistance of a conductor due to temperature
 R=R0(1+Kt)
 R0=resistance refer to room temperature
 K=coefficient of resistance
 T=temperature difference

16. INSULATION OF STATOR
 High voltage insulation(resin poor mica tape) is
provided over the bars
 VACCUM PRESSURE IMPREGNATION SYSTEM(VPI)
 1.stator coils are taped with poor resin mica type before
inserting in the slots of cage stator subsequently
wounded stator is subjected to vpi process in which
first the stator is vacuum dries and then impregnated
in resin bath under the pressure of nitrogen gas

17.  Process:
 1.stator is initially heated minimum for one hour to
remove moisture
 Heated stator shall be inserted in heated impregnating
vessel. stator shall be dried under vaccum (should not
exceed 50hrs.
 Stator is to be flooded with impregnation resin
mixture so that highest point of winding lies at least
100mm below resin level pressure is applied so that
resin penetrates in the tape to fill all the gaps

18. Vacuum Pressure Impregnation
Plant

19. ROTOR
 Solid rotors are manufactured from forged alloy steel
with suitable alloying elements to achieve very high
mechanical and superior magnetic properties
 Rotor consists of electrically active portion and two
shaft ends
 60% of rotor body circumference has longitudinal slots
which hold the field winding
 Rotor Winding: The field winding consists of several
series connected coils inserted into the longitudinal
slots of the rotor body. The coils are wound so those
two poles(one north pole and south pole) are obtained

20.  COILS MATERIAL: made up of copper with silver content
of approximately 0.1% .
 Silver alloyed copper have a high strength properties at
high temperature so that coil deformation due to thermal
stresses are eliminated.
 INSULATION: The coils are insulated from the rotor body
with L-shaped strips of glass fibre
 ROTOR SLOT WEDGES:To protect the winding against the
effects of centrifugal forces, the winding is secured in the
slots with wedges. The slot wedges are made of copper alloy
featuring high strength and good electrical conductivity.

21. ROTOR

22. VENTILATION AND COOLING
 Losses in the generator raise the temperature of the
generator .due to temperature the insulation will be
effected .
 Various methods of cooling:
 1.air cooling
 2.hydrogen cooling
 3.hydrogen and water cooling
 Closed circuit hydrogen cooling mounted axially on
stator frame

23.  For the rotor two axial fans are located at each shaft
end.
 Draws the cool air from the atmosphere
 Flowpath1:to the rotor winding
 Flow path 2:to the stator winding

24. TESTING
 MECHANICAL RUN AND MEASUREMENT OF
VIBRATIONS AT RATED SPEED: machine should be run at
rated speed and the vibrations are measured in all
directions.
 Vibrations should be less than 5 microns and noise level
should be in b/w 75-90db
 SHORT CIRCUIT TEST: in this machine should run at
rated speed. output terminals of stator are short circuited
and excitation gradually increases up to the rated current
in the winding. winding temperature should be less than
60deg centigrade. we will get copper loss

25.  Open circuit test: machine should be run at rated speed
and excitation increases gradually up to the rated voltage
 From this test:
 1.core loss can be calculated
 Shaft voltage :when the rotor shaft rotates inside the stator
there will be induced emf in rotor in addition to this
voltage will go to the bearings at the shafts of rotor . Shaft
voltage measures with high impedance voltmetres.
 This increase the heating in rotor .to avoid this bearings
placed on insulation HGL

26.  FLUX TEST ON STATOR CORE: before winding in the
slots flux is generated in the core by passing current .if
there any break of inter laminations or shorts between
laminations eddy current flows which raises the
temperature called hotspots . This test is used to
detect the hot spot.
 INTER TURN INSULATION TEST: insulation between
the windings of rotor is tested by applying current at a
frequency of 500HZ . Insulation should be withstand
to this test

27.  HIGH VOLTAGE TEST ON STATOR AND ROTOR
WINDINGS: high voltage is applied to windings by
increasing gradually to required value and mainted for
1 minute and reduces gradually
High voltage test levels:
Stator winding-(2*ratedvoltage+1)kv
Rotor winding-(10*excitation voltage)v

28.  1.INSULATION RESISTANCE MEASUREMENT TEST:
Resistance is measured by placing two copper plates
above and below the laminations .maximum
acceptable value should be 1Mohm per kv of rated
voltage. This test ensures the quality of varnish on
laminations

29.  TESTING OF STATOR BARS: after laying of top and
bottom bars their balancing is done and then they are
tested for voltage of 2(rated voltage)+3kv
 In front of customer test it is carried out 2(rated
voltage)+1KV

30. ADVANTAGES AND DISADVANTAGES
 The life span of machine is long
 Cost is low compared to the other generators
 In US 90% electrical generation done by turbo
generators.
 Disadvantages:
 Repairing and maintaining cost is high
