BHEL HARIDWAR,CONSTRUCTION OF TURBO GENERATOR AND EXCITATION SYSTEM

A vocational training at
BHARAT HEAVY ELECTRICAL LIMITED,HARIDWAR
IN TURBO GENERATOR
SUBMITTED TO : SUBMITTED BY :
DR. ANNAPURNA BHARGAVA YASH KUMAR NATANI
( PROFESSOR ) B.TECH , FINALYEAR
MR. ASHOK KUMAR SHARMA ELECTRICAL ENGG.
( ASSOCIATE PROFESSOR ) C.R. NO. 13/095

An overview of BHEL Haridwar
 At the foothills of the majestic Himalayas & on the banks of a holy Ganges in
Ranipur near HARIDWAR is located Heavy Electricals Equipment Plant of
Bharat Heavy Electrical Ltd.
 BHEL, wholly owned by the government of India is an integrated engineering
complex consisting of several plants in India, where about 5000 workers are
busy in design&manufacturing of a wide range of heavy electrical
equipment.
 At present 70% of the Country’s electrical energy is generated by the sets
manufacturing by BHEL, Haridwar.

CONTRIBUTION OF BHEL IN DIFFERENT SECTORS
BHEL
TRANSPO
RTATION
TRANS
MISSIO
N
INDUSTRI
ES
RENEWABLE
ENERGY
GENERATI
ON
POWER
SECTOR

PRODUCTS MANUFACTURED IN BHEL,HARIDWAR
TURBO GENRATOR
STEAM AND GAS TURBINE
CONDENSOR
EXCITER
HEAT EXCHANGER

BHEL Haridwar is divided in two sections-
A) CFFP: – Central Foundry Forge Plan
B) HEEP:- Heavy Electrical Equipment Plant
• TURBO GENRATOR AND EXCITER SYSTEMBLOCK1
• POWER EQUIPMENTSBLOCK 2
• STEAM AND GAS TURBINEBLOCK 3
• WINDINGS OF TURBO GENERATOR AND INSULATIONBLOCK 4
• WATER BOX AND STORAGE TANKBLOCK 5
• RINGS , STATOR FRAME ,ROTORBLOCK 6
• STAMPING AND STAMPING DIESBLOCK 7

Why synchronous generator ?
More efficient
Better insulation
Efficient cooling
Lesser rotor weight and inertia
Rigid construction

CLASSIFICATION OF TURBO GENERATOR
The generators may be classified on the basis of cooling system used
in it. Main types are:
1. THRI
2. TARI
3. THDI
4. THDD
5. THDF
6. THFF

T => first alphabet stands for the type of generator – turbo-generator or hydro
generator.
H/A => second alphabet stands for the cooling media used for the cooling of
rotor i.e. hydrogen gas or air.
R/D/F/I => third alphabet stands for the type of cooling of rotor e.g. radial, direct,
forced, indirect, etc.
I/D/F => last alphabet stands for the type of cooling for stator e.g. indirect, direct or
forced cooling.

Components of turbo generator
Stator Frame
Stator Core
Stator Winding
Spring and spring Basket
Magnetic Shunt
Press rings
End Shields
.
• stator
.

• Rotor
Rotor Shaft
Rotor Winding
Rotor Retaining Rings
Compressor Hub
Rotor Fan
Rotor Wedges

• Bearings
• Cooling system
• Excitation system
• Shaft seal

. Stator Frame is made up of structural steel

❷ Stator Core
• The stator core is made of silicon steel with high permeability and low
hysteresis and eddy current losses. The sheets are suspended in the
stator frame from insulated guide bars. Stator laminations are coated
with synthetic varnish; are stacked and held between sturdy steel
clamping plates with non-magnetic pressing fingers which are fastened
or welded to the stator frame.
• In order to minimize eddy current losses of rotating magnetic flux which
interact with the core is built of thin laminations. Each lamination layer is
made of individual segments. Core is mainly used for efficiently carrying
electrical and mechanical flux.
• It is inserted vertically in frame.

Construction of core
• Stampings
Stamping for 500
MW TG

 The stator laminations are assembled as separate cage core without the stator frame.
The segments are staggered from layer to layer so that a core of high mechanical
strength and uniform permeability to magnetic flux is obtained .On the outer
circumference the segments are stacked on insulated rectangular bars which hold
them in position.
 To obtain optimum compression and eliminatelooseness during operation the
laminations are hydraulically compressed and heated during the stacking procedure.
To remove the heat, spaced segments are placed at intervals along the core length
which divide the core into sections to provide wide radial passages for cooling air
to flow.
 Stampings are held in a position by 21 core bars having dovetail section. Insulating
paper pressboards are also put between the layer of stamping to provide additional
insulation and to localize short circuit. Between two packets one layer of ventilating
segments is provided.

 Steel spacers are spot welded on stamping (for generators below 500 MW).
These spacers form ventilating ducts where the cold air from gas coolers enter
the core radially inwards there by takingaway the heat generated due to eddy
current losses.
 For 600 MW and above spring like assembly of core stamping is done. Number
of stampings used in one round is 10.5, each stamping is of size 0.5 mm and
core length is 6500 mm. So,136500 stampings are used in a core.

Spring and spring basket
The lower springs prevents a lateral deflection of the core. The flat springs are
resilient to radial movements of the core suspension points and will largely resist
transmission of double frequency vibration to the frame. In the tangential direction
they are, however sufficiently rigid to take up the short circuit torque of the unit. The
entire vibration system is turned so as to avoid resonance with vibrations at system
frequency or twice the system frequency

 The press ring is bolted to the ends of core bars. The pressure of the
pressure ring is transmitted to stator core stamping through press fringes
of non-magnetic steel and duralumin placed adjacent to press ring.
 To avoid heating of press ring due to end leakage flow two rings made
of copper sheet are used as flux shield. The ring screens the flux by
short-circuiting.
 To monitor the formation of hot spots resistance transducer are placed
along the bottom of slots. To ensure that core losses are within limits and
there are no hot spots present in the core. The core loss test is done after
completion of core assembly.

CORE INSERTION PROCEDURE
CORE PRESS RING ELECTRICAL ASSEMBLY
1ST , 2ND & 3RD STAGE HEATING AND PRESSING
STACKING OF STAMPING
CORE PRESS RING INSERTION AND ALIGNMENT
CORE BAR ALIGNMENT AND WELDING
WELDING OF SPRING AND SPRING BASKET
HYDRAULIC AND PNUEMATIC TEST OF STATOR BODY

Magnetic shunt
 The end covers are made up of fabricated steel or aluminum castings. They are
employed with guide vans on inner side for ensuring uniform distribution of air
or gas.
 Cool air flows from sides and hot air flows in centre. Rotor fan sucks the hot air
which then passes through compressor and gets cool and circulates to core.
 They are used to hold the bearings and shaft seal assembly. It is mounted on
both the ends of the stator
 Magnetic shunt is a type of ring which is used to confine the magnetic flux
within the stator. One ring is connected on turbine end and one ring is
connected at exciter end. These rings are made up of steel.
END RINGS

Terminal box and terminal bushing

STATOR WINDING
 The bar consist of solid and hollow strands distributed over the entire bar
cross- section so that good heat dissipation is ensured at the bar ends, all the
solid strand are jointly brazed into a connection sleeve and the hollow strands
into a water box from which the cooling water enters and exits via Teflon
insulating hoses connected to the annular manifolds.
 The water manifolds are insulated from stator frame, permitting the insulation
resistance of water-filled winding to be measured. During operation water
manifolds are grounded.
 There are two types of stator winding
❶ Hollow Winding
❷ Metallic strip wining

WATER SUPPLY IN STATOR WINDING

ROTOR
Rotor rotates in most modern generator at speed of 3000 rotations
per minute. It is also an electromagnet and to give it necessary
magnetic strength, the winding must carry a very high current.
The passage of current through windings generates heat. But the
temperature must not be allowed to become too high, otherwise
difficulties will be experienced with insulation. T
To keep the temperature cross section of the conductors could not
be increased but this would introduce another problems. In order
to make room for large conductor, body and this would cause
mechanical weakness. With good design and great care this
problem can be solved.

 Details of shaft are given here
Length = 9 meter (approx.)
Diameter = 1 meter (approx.)
Material – alloy steel
Number of poles = 2

STEPS INVOLVED IN MACHINING OF ROTOR
STEP 1
• When Shaft Arrives In Shop ,Rough Turning Is Done To Remove
Surface Defects And Impurities.
STEP 2
• Shaft is machined to its final diameter as per the type of tg it
has to be used in.
STEP 3
• Slots are cut on the shaft. There are 28 no. Of slot in a tg rotor.
STEP 4 • Coupling holes on both holes are drilled.
STEP 5
• Final machining of rotor is done after balancing.

POLES ON STATOR FOR COMPRESSOR HUB AND BAFFLE RING

 The conductors are made up of copper with silver content of approx. 0.1%.
As compared to electrolytic copper silver alloyed copper features high
strength properties at high temperature so that coil deformations due to
thermal stresses are eliminated. The conductors are made of hard drawn
silver bearing copper.
 The rectangular cross section copper conductors have ventilating ducts on
the two sides thus providing a channel for hydrogen flow.
 Two individual conductors placed- one over the other are bent to obtain
half turns. Further these half turns are brazed in series to form coil on the
rotor model.

 Rotor winding wedges are metallic bars. These bars are made up of alloy
copper-nickel-silicon. These bars are placed on rotor winding so that due to
centrifugal force rotor windings do not come out. Wedges are made on
these bars.
 Glass fiber is provided between these bars and the winding to prevent the
short circuit.
 The slot wedges extend below the shrink seats of the retaining rings. The rings
act as short-circuit rings to induced currents in the damper windings.

ROTOR TERMINALS
 These terminals are connected to the
excitation system and this side of
rotor is fixed with excitation system.

RETAINING RING AND CENTERING ASSEMBLY

The centrifugal forces of the end windings are contained by piece rotor retaining
rings. Retaining rings are made up of non-magnetic high strength steel in order to
reduce the stray losses. Each retaining ring with its shrink fitted. Insert ring is shrunk
on the rotor is an overhang position. The retaining ring is secured in the axial
position by snap rings. The rotor retaining rings withstand the centrifugal forces due
to end winding. One end of each ring is shrunk fitted on the rotor body while the
other hand overhangs the end winding without contact on the rotor shaft. This
ensures unobstructed shaft deflection at end windings. The shrunk on hub on
the end of the retaining ring serves to reinforce the retaining ring and serves the end
winding in the axial direction. At the same time, a snap ring is provided against axial
displacement of retaining ring. The shrunk slot of current to reduce the stray losses
and have high strength, the rings are made up of non-magnetic cold worked material.

BAFFLE RING
 Baffle ring are
put beneath
fan hub which
makes space
for rotor fan
blades.
 These are
made up of
alloy steel.

FAN HUB
The compressor hub is a type of ring
which is made up of structural steel.
The blades of rotor fan are put on
compressor hub. And the
compressor hub is put on small
poles made on rotor

ROTOR FAN
 The generator cooling gas is circulated
by one axial-flow fan located on the
turbine-end shaft journal. To augment
the cooling of the rotor winding, the
pressure established by the fan works in
conjunction with the gas expelled from
the discharge parts along the rotor.
 The moving blades of the fan are
inserted into T-shaped grooves in the
fan hubs. The fan hubs are shrink-fitted
to the shaft journal spider.
•

BEARINGS
 The rotor shaft is supported in sleeve bearings having forced-oil lubrication. The
bearings are located in the stator end shields. The oil required for bearing lubrication
and cooling is obtained from the turbine oil system and supplied to the lubricating
gap via pipes permanently installed inside the lower half of the stator end shield and
via grooves in the bearing sleeves.
 The lower bearing sleeve rests on the bearing saddle via three brackets with
spherical support sets for self-alignment of the bearing. The bearing saddle is
insulated from the stator end shield and the bearing bracket are insulated from the
bearing sleeve to prevent the flow of shaft currents and to provide for double
insulation of the generator bearing from ground. A radial locator serves to locate the
bearing in the vertical direction and is bolted to the upper half of the stator end
shield. The locator is adjusted to maintain the required clearance between the
bearing sleeve and the insulation of the radial locator.
 All generator bearings are provided with a hydraulic shaft lift oil system to reduce
bearing friction during start up. High pressure oil is forced between the bearing
surface and the shaft journal, lifting the rotor shaft to allow the formation of the
lubricating oil film.
 The bearing temperature is monitored with one double element
thermocouple located approximately in the plane of maximum oil film pressure.

SHAFT SEAL
• With this type of shaft seal, the escape of hydrogen between the
rotating shaft and the housing is prevented by maintaining a
continuous film of oil between the shaft and a non-rooting floating
seal ring. To accomplish this, seal oil from two separate circuits i.e.,
the air side and hydrogen side seal oil circuits, is fed to the seal ring
at a pressure slightly higher than the hydrogen pressure. In
addition, higher pressure air side oil is supplied to the shaft seal for
thrust load compensation of the seal ring.

COOLING
The end windings are enclosed by an annular water manifold to
which all stator bars are connected through hoses. The water
manifolds is mounted on the holding plates of the end winding
support ring and connected to the primary water supply pipe. This
permits the insulation resistance of the water filled stator winding
to be measured.
❶ COOLING OF STATOR
A) Cooling of winding

B) COOLING OF CORE
i) CO2 Supply:- As a precaution against explosive mixtures, air must
never be directly replaced with hydrogen during generator filling nor the
hydrogen replaced directly with air during the emptying procedure. In
both cases, the generation must be scavenged or purged with an insert
gas, carbon dioxide (CO2) being used for this purpose.
ii) Compressed Air Supply:-To remove the CO2 from the generator, a
compressed air supply with compressed air filter is connected to the
general air system of the power plant.
Under all operating conditions, except for CO2 purging, the compressed air
hoses between the filter and the generator pipe system should be
disconnected. This visible break is to ensure that no air can be admitted
into a hydrogen-filled generator

iii) Nitrogen (N2) Supply:-
On a water-cooled turbine generator an additional nitrogen supply is
required for :-
a) Removing the air above the water level in the primary water tank during
initial operation of the primary water system.
b) Removing the oxygen dissolved in the primary water during filling of the
primary water system.
c) Removing the hydrogen gas above the water level in the primary water tank
during shutdown of the primary water system.
d) Removing the hydrogen gas dissolved in the primary water during shutdown
of the primary water system.

B) COOLING OF ROTOR
The hydrogen cooler is a shell and tube type heat exchanger which
cools the hydrogen gas in the generator. The heat removed from
the hydrogen is dissipated through the cooling water.
The cooling water flows through the tubes while the hydrogen is
passed around the finned tubes.
The cooler consists of individual sections for vertical mountings.
This arrangement permits the coolers to be mounted without an
increase in the overall generator axial length or cross-sectional area
of the stator frame.

ADVANTAGES OF HYDROGEN OVER AIR :-
 Density of hydrogen = density of air
 Low noise produced and low windage losses
 Specific of hydrogen = 14.5 × specific heat of air
 Life of rotor is increased
 Fire hazard

INSULATION
High-voltage insulation is provided according to the proven Micalastic
system.
With this insulation system, several half – over lapped continuous layer
of mica tape are applied to the bars. The mica tape is built up from large
area mica splitting which are sandwiched between two polyester backed
fabric layers with epoxy as an adhesive.
The number of layers, i.e., the thickness of the insulation depends on
the machine voltage. The bars are dried under vacuum and impregnated
with epoxy resin which has very good penetration properties due to its
low viscosity .After impregnation under vacuum, he bars are subjected to
pressure ,with nitrogen being used as pressurizing medium (VPI process).

Class Y upto 90 degree celsius
Class A upto 105 degree celcsius
Class E upto 120 degree celsius
Class B upto 130 degree celsius
Class F upto 155 degree celsius
Class H upto 180 degree celsius
Class C > 180 degree celsius
Types of insulation

EXCITATION SYSTEM
The basic use of given exciter system is to produce necessary DC for
turbo generator system.
The Exciter consist of -:
1.Rectifier wheels
2.Three phase main Exciter
3.pilot Exciter
4.Cooler

 The three phase pilot exciter has a revolving field with permanent-magnet poles.
The three-phase ac generated by the permanent-magnet pilot exciter is
rectified and controlled by the TVR to provide a variable dc current for exciting
the main exciter. The three phase ac induced in the rotor of the main exciter is
rectified by the rotating rectifier bridge and fed to the field winding of the
generator rotor through the dc leads in the rotor shaft
 A common shaft carrier the rectifier wheels, the rotor of the main exciter and the
permanent-magnet rotor of the pilot exciter. The shaft is rigidly coupled to the
generator rotor. The exciter shaft is supported on a bearing between the main and
pilot exciters. The generator and exciter rotors are thus supported on total of three
bearings.

 The three-phase pilot exciter is a 16 pole revolving-field unit. The frame
accommodates the laminated core with the three-phase winding. The rotor
consist of a hub with mounted poles. Each pole consist of 10 separate
permanent magnets which are housed in a non-magnetic metallic enclosure.
The magnets are braced between the hub and the external pole shoe with
bolts. The rotor hub is shrunk onto the free shaft end.
PILOT EXCITER
ROTOR OF PMMG

COOLING OF EXCITER
 The exciter is air cooled. The cooling air is
circulated in a closed circuit and recooled in
two cooler sections arranged alongside the
exciter.
 The complete exciter is housed in an enclosure
through which the cooling air circulates.The
rectifier wheels, housed in their own enclosure,
draw the cool air inat both ends and expel the
warmed air to the compartment beneath the base
plate.

RECTIFIER WHEEL
 The main components of the rectifier wheels are the silicon diodes which are
arranged in the rectifier wheels in a three phase bridge circuit. The contact pressure
for the silicon wafer is produced by a plate spring assembly. The arrangement of
the diode is such that this contact pressure is increased by the centrifugal force
during rotation.
 Additional components are contained in the rectifier wheels. Two diodes each are
mounted in each aluminum alloy heat sink and thus connected in parallel.
Associated with each heat sink is a fuse which serves to switch off the two diodes
if one diode falls (Loss of reverse blocking capacity).
 For suppression of the mo mentary voltage peaks arising from commutation, each
wheel is provided with six RC networks consisting of one capacitor and one
damping resistor each, which are combined in a single resin-encapsulated unit.

TESTS PERFORMED ON TURBO GENERATOR
 Mechanical heat run
 Short circuit test
 Open circuit test
 Temperature rise
 Bearing vibration and Hydrogen leakage
 Dielectric test
 Discharge test

BHEL HARIDWAR,CONSTRUCTION OF TURBO GENERATOR AND EXCITATION SYSTEM

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