7/30/2019 Bharat Heavy Electrical Limited training report
1/72
Page 1 of 72
BHARAT HEAVY ELECTRICALS LIMITEDRAMACHANDRAPURAM
HYDERABAD - 502 032
REPORT ON
Design features of Turbo Generator
A DISSERTATION WORK SUBMITTED TO THE
FACULTY OF ENGINEERING OF
NATIONAL INSTITUTE OF TECHNOLOGY ,RAIPUR
Submitted in partial fulfillment of the requirement for the award of the degree of
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL ENGINEERING.
UNDER THE GUIDANCE OF: PREPARED BY
M.N.V.SURYA PRASAD
(Sr.DGMEME)
BHEL, Hyderabad.
7/30/2019 Bharat Heavy Electrical Limited training report
2/72
Page 2 of 72
CERTIFICATE
This is to certify that the dissertation work entitled Design &
Manufacture of Turbo Generators is a bonafide work carried out by
KATAKAM VENKATA RAMESH, Roll No.10117035 in partial
fulfillment of the requirements for the award of the Degree of
BACHELOR OF TECHNOLOGYIN ELECTRICAL ENGINEERINGfrom
NATIONAL INSTITUTE OF TECHNOLOGY, RAIPURduring the
year 2010-2014.
7/30/2019 Bharat Heavy Electrical Limited training report
3/72
Page 3 of 72
ACKNOWLEDGEMENT
I wish to express my gratitude to my beloved guide M.N.V.SURYA PRASAD(SR.DGM)
BHEL, Hyderabad for her valuable guidance in the successful completion of this dissertation
work. I am very much indebted to him for suggesting this topic and helping me at every stage for
its successful completion.
I express my profound thanks to Sri. NARENDRA D.LONDHE, Assoc. Professor of Electrical
Department, NATIONAL INSTITUTE OF TECHNOLOGY, RAIPUR for their cooperation
throughout this work and efforts for arranging this dissertation work.
Also, I wish to thank all those who have involved directly or indirectly, for the successfulcompletion of my project work.
KATAKAM VENKATA RAMESH
10117035
7/30/2019 Bharat Heavy Electrical Limited training report
4/72
Page 4 of 72
Bharat Heavy Electricals Limited (BHEL)
Bharat Heavy Electricals Limited (BHEL) is an Indian state-owned integratedpower
plant equipment manufacturer and operates as anengineering and
manufacturing company based in New Delhi, India. BHEL was established in 1964, ushering in the indigenous Heavy Electrical
Equipment industry in India. The company has been earning profits
continuously since 1971-72 and paying dividends since 1976-77.
It is one of the only 7 mega Public Sector Undertakings (PSUs) of India clubbed
under the esteemed 'Maharatna' status. On 1 February 2013, theGovernment of
India granted Maharatna status to Bharat Heavy Electricals Limited.
In the early sixties 3 more major plants were set up at Hyderabad, Haridwar and
Tiruchirapalli, which all together form the core of the diversified product range,
systems and services that BHEL offer today.
The company has 14 manufacturing units, 4 power sector regional centers, 8 servicecenters and 18 regional offices besides project sites spread all over India and abroad.
BHEL manufactures over 180 products under 30 major product groups and caters to
core sectors of the Indian economy like Power generation and Transmission,
Industry, Transportation, Telecommunication, Renewable energy etc.
BHEL has acquired ISO 9000 & 14000 certification for its operation and has also
adopted the concepts of Total Quality Management (TQM) and Environmental
Management
BHEL's manufacturing units and other entities have been accredited to QualityManagement Systems (ISO 9001:2008), Environmental Management Systems (ISO
14001:2004) and Occupational Health & Safety Management Systems (OHSAS
18001:2007).
BHEL is exporting power and industry segment products and services for over 40
years. BHELs global references are spread across 75 countries.
The cumulative overseas installed capacity of BHEL manufactured power plants
exceeds 9,000 MW across 21 countries including Malaysia, Oman, Iraq, the UAE,
Bhutan, Egypt and New Zealand. BHEL's physical exports range from turnkey projects
to after sales services.
http://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/New_Delhi,_Indiahttp://en.wikipedia.org/wiki/New_Delhi,_Indiahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/Maharatnahttp://en.wikipedia.org/wiki/Maharatnahttp://en.wikipedia.org/wiki/Maharatnahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/Government_of_Indiahttp://en.wikipedia.org/wiki/New_Delhi,_Indiahttp://en.wikipedia.org/wiki/Engineeringhttp://en.wikipedia.org/wiki/Power_planthttp://en.wikipedia.org/wiki/Power_plant7/30/2019 Bharat Heavy Electrical Limited training report
5/72
Page 5 of 72
BHEL,HYDERABAD, RAMACHANDRA PURAM
It manufactures variety of products such as Turbo
Generators, Steam & Gas Turbines, Switchgear equipment,
Compressors, Heat exchangers, Pumps, Pulverizes, Oilrigs
and so on.
ELECTRICAL MACHINES AT BHEL, RAMACHANDRA PURAM BHEL, Hyderabad unit manufactures Turbo Generators of rating up to 125
MW for industrial applications and for power generation in Steam Power
Plants. The Turbo Generators manufactured here range from 4 MW to 125
MW.
The Turbo Generators are supplied with the turbines and matching excitation
systems and are used mostly in paper, sugar, cement, petrochemical, fertilizer
industries etc., and thermal power stations
BHEL has borrowed technology for manufacturing generators from SKODA
Exports Czechoslovakia in 1960's. Also from M/s. Siemens, Germany and its
sister company KWU (Kraft Werk Union) in Germany.
They borrowed less than 12 modules, from semen's Germany. Till now the
BHEL had developed more than 70 in-house modules.
The turbo generators are based on proven designs and know how backed by
over three decades of experiences gained by BHEL engineers in this field
keeping pace with the latest development in insulation systems to optimize
the design.
BHEL Hyderabad is the only one in Asia that has the latest type of insulation
system called the Vacuum Pressure Impregnation (VPI) system.
7/30/2019 Bharat Heavy Electrical Limited training report
6/72
Page 6 of 72
SPECIAL FEATURES OF THE TURBO GENERATORS DESIGNED BY BHEL:
High output to weight ratio.
Thermo setting class F epoxy insulation, both resin rich and Vacuum Pressure
Impregnation (VPI).
Low loss high-grade silicon steel for laminations.
Optimally designed fans on the rotors.
Better voltage waveform with less harmonic content.
Low wind age loosed and low noise.
Static/blushless excitation.
Split casing design for low manufacturing cycle for VPI design.
Generator Nomenclature:
7/30/2019 Bharat Heavy Electrical Limited training report
7/72
Page 7 of 72
PRODUCT PROFILE OF ELECTRICAL MACHINES
ELECTRICAL MACHINES
7/30/2019 Bharat Heavy Electrical Limited training report
8/72
Page 8 of 72
Introduction to Electrical Machines:
Energy can neither be created nor be destroyed. We can only change its forms, using
appropriate energy- conversion processes.
Machine acts as a generator converts the mechanical energy into electrical energy. The
machine, which acts as a motor, converts electrical energy into mechanical energy. The
basic principle of rotating machine remains the same i.e. Faradays Laws of Electro
Magnetic Induction.
Faradays first law states that whenever conductor cuts magnetic flux, dynamically
induced Emf is produced. This Emf causes a current flow if the circuit is closed.
Faradays second law states that Emf induced in it is proportional to rate of change of
flux. Mathematically,
e = -Nd/dt
e- Induced emf
N- Number of turns of coil
d/dt rate of change of flux
Emf induced will oppose both the flux and the rate of change of flux.
Efficiency of a machine is equal to the ratio f output to input.
= Output / input = Output / output + losses
To increase the efficiency of any machine we must decrease the losses, but losses are
inevitable. There are different types of losses that occur in a generator.They are
broadly divided into two types.
Constant losses Variable losses
a. iron losses. a. copper losses
b. Friction and windage losses
7/30/2019 Bharat Heavy Electrical Limited training report
9/72
Page 9 of 72
Electrical machines are of two types AC machines & DC machines. AC machines are divided
into single-phase AC machines and poly phase AC machines.
1.1. SYNCHRONOUS MACHINES:
Synchronous Generators (or) Alternators are those in which the speed of the rotor and
flux are in synchronism.
1.2. ASYNCHRONOUS MACHINES:
These are the machines in which the flux speed and rotor speed and rotor speed will not
be the same.
Inherently all the machines are AC machines. AC or DC depends upon the flow of current
in the external circuit.
Synchronous generators can be classified into various types based on the medium used
for generation.
1. Turbo-Alternators Steam(or) Gas
2. Hydro generators
3. Engine driven generators
In every machine they are two carrying parts.
1. Flux carrying parts
2. Load carrying parts
In large synchronous machines the stators have the load carrying parts, i.e. armature and
the rotor has the flux carrying parts i.e.; field winding.
Iron losses are also called as magnetic losses and core losses. They are broadly divided
into.
1. Hysteresis losses
2. Eddy current losses
These losses occur in the stator core.
Copper losses occur in both stator and rotor winding.
The general efficiency of a synchronous generator is 95-98%.
7/30/2019 Bharat Heavy Electrical Limited training report
10/72
Page 10 of 72
1. INTRODUCTION TO TURBOGENERATOR:
A synchronous generator is the core of any generating power plant. A synchronous
generator is a rotating electromagnetic device that converts mechanical energy into
electrical energy by taking the mechanical input from a prime mover (Gas turbine or Steam
turbine) and magnetic energy from excitation.
The different electromagnetic or active parts of a generator are as follows:
1. Stator core
2. Stator coils/ bars
3. Stator winding
4. Output leads, brushings and conductors
5. Rotor excitation leads
6. Rotor coils and rotor winding
7. Exciters
1. Stator core
The stator core serves the two fold function of providing the mechanical support for
the stator coils and carrying effectively the electromagnetic flux generated by the rotor
winding. In order to minimize hysteresis and eddy current losses the entire core is built of
thin laminations. Each lamination layer is made up from a number of individual segments.
2.Stator coils/ bars
The stator coils are the individual entities, which are placed in the slots of the stator
core and finally connected to each other as per a pre-designed scheme to form a three phase
winding. The prime purpose of the stator bars is to carry the load current at minimal
winding losses. These coils are provided with high voltage stresses. Depending upon the size
and rated voltage of the machine different types of stator bars are designed.
3. Stator windingThe stator winding is a short pitch; two-layered type made of individual bars. The
bars are located in slots of rectangular cross section, which are uniformly distributed on the
circumference of the stator core. In order to minimize the losses, the bars are composed of
separately insulated stands transposed by 360 degrees. To minimize the stray losses in the
7/30/2019 Bharat Heavy Electrical Limited training report
11/72
Page 11 of 72
end winding, the standards of the top and bottom bars are separately brazed and insulated
from each other.
4. Output lead brushings and phase connectors
Output leads are taken out from the exciter end of stator from the top and supported
on an insulated glass fabric plate. Six terminals are brought out, three for phase and three
for neutral connections. The phase connectors are connections between the stator winding
phase bars /coils to the output lead bushings.
5. Rotor excitation leads
The excitation leads provide electrical connection between rotor winding and output
from brush less exciter.
6. Rotor Coils and winding:
The construction of the rotor winding consists of placement of pre-formed rotor coils
as per the winding scheme in the slotted rotor body, providing necessary insulation both in
the straight position and overhang, making connections of the excitation leads, wedging of
the straight part and mounting of the retaining rings.
7/30/2019 Bharat Heavy Electrical Limited training report
12/72
Page 12 of 72
2. CONSTRUCTIONAL FEATURES OF TURBOGENERATOR
The turbo generator is designed for continuous operation with voltage variations +/-
5% of the rated voltage and a frequency variation of +/- 1%. In general, the machine is
designed for the altitudes of 1000 meters and above sea level and below an ambient
temperature of 600 maximum, with cooling water temperature of 380 maximum at the inlet.
The generator consists of the following components:
2.1 Stator:
2.2 Rotor
2.3 Bearings
2.4 Ventilation and Protection System
2.5 Cooling System
2.6 Insulation
2.7 Vaccum pressure impregnation system
2.8 Exciter
2.9 Base frame
7/30/2019 Bharat Heavy Electrical Limited training report
13/72
Page 13 of 72
2.1.STATOR
Stator part of the Generator after VPI process
2.1.1.Stator Frame:
The stator frame is of welded construction, supports the core and the windings. In
consists of air duct pipes and radial ribs, which provide rigidly to the frame. Footings are
provided to support the stator on the skid. The stator frame should be rigid due to the
various forces and torque during operation. The welded stator frame consists of the two
end plates, axial and radial ribs. The arrangement and dimensioning of the ribs are
determined by the cooling air passages, the required mechanical strength and stiffness.
The end covers are Aluminum alloy castings. The stator frame is fixed to the skid with the
7/30/2019 Bharat Heavy Electrical Limited training report
14/72
Page 14 of 72
help of hexagonal bolts. The skid is temporarily fixed to the concrete foundation through
bolts.
2.1.2.Stator Core:
The stator core is made up of stacked insulation electrical sheet steel lamination with a low
loss index and suspended in the stator frame from insulated rectangular guide bars. Axial
compression of the stator core is obtained by clamping fingers, pressure plates and non
magnetic clamping bolts, which are regulated from the core. The clamping finger ensures a
uniform clamping pressure, especially within the range of the teeth and provided for
uniform intensive cooling of stator core ends.
2.1.3. Lamination Preparation:
For high rating machines each lamination is built up of six sectors (stampings), each of six
cut according to specifications. Press tools are used in the manufacture of laminations. Press
tools are mainly two types:
1. Compounding Tools
2. Blanking and Slot Notching Tools
Lamination Sheets after preparation process
2.1.3.1. COMPOUNDING OPERATIONS:
In this method, the stampings with all core bolts holes guiding slots and winding slots are
manufactured in a single operation known as COMPOUNDING OPERATION. Press tools used
as known as COMPOUNDING TOOLS. They are used for the machines rated above 40MW.
2.1.3.2. BLANKING AND NOTCHING OPERATION:
7/30/2019 Bharat Heavy Electrical Limited training report
15/72
Page 15 of 72
In case of smaller machines the stampings are manufactured in two operations.
In the first operation the core bolt holes and guiding slots are only made. This operation
is known as BLANKING, and press tools used known as NOTCHING.
In the second operation the winding slots are punched using another tool known as
NOTCHING TOOL and the operation performed by the tool is known as NOTCHING.
The different operation taking places in the manufacture of laminations are:
1. Shearing
2. Notching
3. Deburring
4. Varnishing
2.1.3.3. ASSEMBLY OF CORE:
The stator laminations are assembled as separate cage without stator frame. The entirecore length is made in the form of packets separate by radial ducts to provide ventilatingpassage for the cooling of core. The thickness of lamination is about 0.5mm and thethickness of lamination separating the packets is about1mm. The segments arestaggered from layer to layer so that a core of high mechanical strength and uniformpermeability of magnetic flux is obtained.
To obtain the maximum compression and eliminate under setting during operation, the
laminations are hydraulically compressed and heated during the stacking procedure
when certain heights of stack is reached. The complete stack is kept under pressure
and located in stator frame by means of clamping bolts and pressure plates.
Assembly of Stator core with help of Guide bars.
7/30/2019 Bharat Heavy Electrical Limited training report
16/72
Page 16 of 72
2.1.4. End Covers:
The end covers are the castings of the aluminum alloy and are bolted to the side plates of
the stator frame. The inlet passage is specially designed with built in guide vanes, which
ensure uniform distribution of the air to the fan. Air ceiling is provided around the shaft
and at the parting plane of the top and bottom parts of the end covers so that suction of
oil vapor from the bearings does not take place.
2.1.5.Stator Winding:
The stator winding is a fractional pitch two layer type, it consisting of individual bars. The
bars are located in slots of rectangular cross section which are uniformly distributed on the
circumference of the stator core.
In order to minimize losses, the bars are of separately insulated strands which are
exposed to 360.degrees transposing.
To minimize the stator losses in the winding, the strands of the top and bottom bars are
separately brazed and insulated from each other.
Fig - Wound Stator
2.1.6. Location of Bars:
7/30/2019 Bharat Heavy Electrical Limited training report
17/72
Page 17 of 72
A semi-conducting wrapper of graphite paper in the slot protects the bar. The stator
winding is protected against the effects of current forces in the slot section. To ensure
tight seating of the bar at the slot bottom, a slot bottom-equalizing strip of stress path is
inserted. A top ripple spring is arranged between two compression strips to exert a
continuous pressure on the bars. The bars are shaped so that, cone shaped end windings
are obtained. In order to reduce the stray losses a small cone taper of (13-20deg) is used.
On the wide sides of the bars spacers of insulating material are inserted at regular
intervals.
2.1.7. Enclosure:
The enclosure consists of the inner and outer components. The inner components
comprises of the winding covers, which from an angular enclosure of top and bottom
parts and is designed as required for particular degree of protection, as indicated in the
dimension drawing or in the Technical data. The ventilating circuit is of the double-
ended symmetrical arrangement.
2.1.8. Electrical Connections of Bars and Phase Connection:
Brazing makes electrical connection of Bars: Electrical connection between the top and
bottom bars, one top bar being brazed to the associated bottom bar. The coil connections
are wrapper depends on the machine voltage. After tapping, an insulating varnish is
applied.
2.1.9. Phase Connectors:
The phase connectors consist of flat copper sections, the cross section of which results in
a low specific current loading. The connections to the stator winding are of riveted and
soldered type. The phase connectors are wrapped with resin rich mica type, which
contain synthetic resin having very good penetration properties. The phase connectors
7/30/2019 Bharat Heavy Electrical Limited training report
18/72
Page 18 of 72
are then cured at a certain temperature, with the shrinking tapes contracting so that a
void free insulation is obtained.
7/30/2019 Bharat Heavy Electrical Limited training report
19/72
Page 19 of 72
2.2. ROTOR:The rotor is forged from a homogeneous steel ingot of specially alloy steel properly
heat treated to meet the required mechanical, metallurgical and magnetic properties. Axial
slots are milled through out the active length of the rotor body to accommodate the
conductors. The slots are dovetailed at the top of housing the wedges.
2.2.1. Rotor Shaft:
Solid rotors are manufactured from forged alloy steel with suitable alloying elements to
achieve very high mechanical and superior magnetic properties. Rectangular or trapezoidal
rotors slots are accurately machined to close tolerances on slot milling machine.
Laminated rotors are made of punched and varnished laminations of high tensile steel are
mounted over machined shaft are firmly clamped by end clamping plates.
2 pole machine rotors are directly cooled for which sub slots are provided for cooling
Generator rotors. 4 pole machine rotors are indirectly cooled for which ventilation ducts
will be provided.
The complete part of the Rotor with winding and Rotor fans.
Rotor Body:
7/30/2019 Bharat Heavy Electrical Limited training report
20/72
Page 20 of 72
This is the RAW Product of the Rotor shaft which used in Generator.
2.2.2. Rotor Winding:
The coils used for the windings are rectangle in cross-section made up of copper with silver
content of approximately 0.1%. This features high conductivity and more of the strength i.e.,
more of the fatigue and creep resistance. Basically they arise due to frequent changes in
temperature. This may lead to deformation of coils. Thus they must be resistant to thermal
stresses.
The rotor winding consists of several coils which are inserted into the longitudinal slots and
series connected such that the coil groups form one pole. Each coil consist of several series
connected turns each, which consists of two half turns, which are connected by the brazing
in the end section. The rectangular cross-section is provided with axial slots for radial
discharges of cooling gases.
2.2.2.1. Placement of Rotor coils in the machine:
Coils are made into two halves.
7/30/2019 Bharat Heavy Electrical Limited training report
21/72
Page 21 of 72
Rotor half coils after annealing process.
The joint of two halves of the rotor coil is called full coil formation.
Fig: The rotor full coil formation after joining the halves coils.
2.2.2.2. Process of Rotor Winding construction:Ventilation Punching:
First the conductors are checked for their quality and ventilation holes are punched and
they are checked for burr. Then edge wise bending is made. The holes are punching for air
gap to enter the air for the cooling of the rotor coils and rotor wedges.
The gap between holes to hole is 10mm or 15mm.
Fig: The copper conductors after the ventilation &champering process.
2.2.2.3. Champering process:
In this process the holes which are punched on the copper conductors are making
smoothing without sharp edges on conductor. Due to punch on conductor the sharp edges
are formed in between the holes. By this the conductor may be cuts and short circuited in the
rotor part and gets damaged. So, Champering process is used.
7/30/2019 Bharat Heavy Electrical Limited training report
22/72
Page 22 of 72
2.2.2.4. Edgewise Bending:
The conductors are bent more than 90o so that it will sustain spring back effect.
Debuggingventilationslotsbytherelevant tools.
2.2.2.5. Annealing &Pressing:
Then the conductors are heated and pressed at the bending so that the cross section of the
conductors will be maintained equal through out. This process is called annealing.
The smoothening at the edges of half copper conductors. By the pressing the coil the
thickness is decreases.
2.2.2.6. 90 Rectification and Marking:
Here the marking the copper conductors making 90 formation at end of the copper
conductor. To form the equal size at the end of the copper coils. At the end of the coils the
two edges is a male and female edge are champered to join the two halves copper conductors
at end.
2.2.2.7. Dovetail Punching & Window dimension:A small portion near the bend is removed so that it does not cause any damage to the
insulation trough while lying in the slots. This process is called relief filing. Then dovetail
punching is made which provides good brazing process when two conductors are joined.
Window dimensions for the conductors are checked. The dimension of the window
decreases from top to bottom conductors.
Bending at the end of the copper coils in the curve shape for the increasing the efficiency.
And also join the both ends of coils.
The copper conductor after the dove tail punching.
2.2.2.8. Reliefing the coils:To remove the roughness on the copper coils become smooth on the surface for the
supporting the windings of the machine.
7/30/2019 Bharat Heavy Electrical Limited training report
23/72
Page 23 of 72
2.2.2.9. Cleaning& Radial Bending:
Then the conductors are cleanedwith thinner (acetone) and then air-dry varnish is applied.
Then keeping the conductors on a dummy rotor makes radial bending. For the conductors
away from the poles prebrazing is done. The cleaning is done copper bearings by the sand
paper, Termer oil. The copper bearings are radially bending for the joint of the other half to
join at the end of another half of the copper bearings.
2.2.2.10. Coil formation:
The edges of coils are joined together at the end of the coils by adding the steel alloy in
between the two edges of copper conductors. By using the Brazing process both are joined
together.
2.2.2.11. Insulation Punching:
By adding the insulation punching in between the copper conductors the silicon sheets are
used in the rotor winding. Then it increases the efficiency and output power of the
machine. This is the protective layer of the winding and coils.
2.2.3. Rotor Retaining Rings:
Just as the rotor wedges secure the rotor coils in the slots along the lift, the overhang
winding is secured by the retaining rings. The retaining ring is non-magnetic alloy steel
forging with very high mechanical properties. This material is stress corrosion resistant.
One end of the retaining ring is shrink fitted on the rotor body and the other end overhangs
the end winding without making contact with the rotor. This arrangement ensures that the
shaft deflection during operation is not obstructed by the retaining ring. The free end of the
retaining ring is reinforced by shrinking a hub an inner diameter of the retaining ring. The
amount of shrink fit is so chosen that the releasing speeds of retaining ring on rotor body
and on hub are beyond the over speed of rotor (i.e. 120% of rated speed).
2.2.4.RotorSlot Wedges:
To protect the winding against the effects of the centrifugal force, the winding is secured
with wedges. The slot wedges are made from an alloy high strength and good electrical
conductivity, and are also used as damper wedged bars. The retaining rings act as short
circuit rings to induced current in the damper windings.
7/30/2019 Bharat Heavy Electrical Limited training report
24/72
Page 24 of 72
2.2.5. Rotor Fans:
The cooling air to the generator is circulated by two axial flow fans located on the shaft at
both ends. Each of fans comprises of a number of individual blades, which are directly
screwed onto the rotor. The number and profile of the blades are so chosen that threaded
root fastening facilitates the change of blade angle depending on operating requirement.
Every fan blade is secured at its root with a threaded pin.The fans circulate required
quantity of cooling air at required head to over come the pressure drop inside the generator.
Fan blades are all minimum alloy die forgings. Threading is mad on the fan blade root such
that they can be fixed into the threaded holes provided on the rotor.
Rotor fans which is used on the rotor part after winding.
2.2.6. Slip Rings:
These are made of forged steel and shrunk on either side of the rotor between the end
cover and the bearing. The mica splitting is used to insulate the slip rings from the rotor
body. The excitation to the rotor winding is taken from these slip rings. The connection
leads are suitably insulated and taken through slots milled on the surface of the rotor.
Wedges are provided to keep the leads in position. A helical groove is machined on the
7/30/2019 Bharat Heavy Electrical Limited training report
25/72
Page 25 of 72
outer surface of the slip rings to have better dissipation of heat, thus minimizing the
brush wear.
2.2.7. Rotor Balancing:
The rotor is balanced with the help of sophisticated balancing machine. The balancing
weights are provided in the hubs under retaining rings and in the fans. The rotor is
dynamically balanced and subjected to an over speed of 20% for 2min.
2.2.8.Field Connections:
The field connections provide the electrical connection between the rotor winding and
the exciter.
2.2.9. Terminal Lugs:
Consists of a copper conductor of rectangular cross-section. One end of the terminal lug is
brazed to the rotor winding, while the other end is screwed to the radial bolt.
2.2.10.Radial Bolt:
The field current lead located in the shaft bore is connected to the terminal lug through a
radial bolt. The radial bolt is made from steel and screwed into the field current lead into
the shaft bore.
7/30/2019 Bharat Heavy Electrical Limited training report
26/72
Page 26 of 72
2.3 BEARINGS
2.3.1. PRINCIPLE OF OPERATION:
In steam turbines, the rotating shaft is supported on two journal bearings, and is axially
located by a thrust bearing. Both these types of bearings in steam turbines work with a
hydrodynamic oil film formed between the two mating surfaces. The hydrodynamic action
can be explained as follows. The rotor pulls the oil into the space between the two mating
surfaces. Because of the viscosity of oil, the layer of oil closest to the shaft drags in the next
layer, which drags in the next layer, and so on. This action forms an oil film between the
rotating shaft and the stationary bearing surface.
Now if the stationary surface is inclined such that the gap between the moving part
and the stationary part gradually reduces along the direction of movement, then the
dragged-in oil gets compressed, and a pressure film is built up. This pressure film takes the
normal load on the moving part. The friction is only because of the shear in the oil, and the
heat generated is also only because of this shear. The heat is carried away by the oil flow. It
may be noted that the pressure built up depends upon the viscosity of the fluid. If, for a given
bearing configuration, a fluid of less viscosity is used, pressure built up will be less, and the
load carrying capacity will be less.
The generator rotor is supported at two-journal bearing. The bearings consist of a
bearing pedestal and bearing shell is split into two halves to facilitate assembly. The bearing
pedestals are iron castings and the bearing shells are the steel castings. The bearing
pedestals are providing with a spherical seating surface and bearing shell rests into with its
7/30/2019 Bharat Heavy Electrical Limited training report
27/72
Page 27 of 72
outer spherical surface. The inner surface of the bearing shell is provided with spherical
grooves and cast with Babbitt metal.
2.3.2. Bearing Oil Supply
The oil required for the bearing lubrication and cooling is obtained from the turbineoil supply system supplied to the lubricating groove in the bottom-bearing sleeve. The upper
bearing sleeve consists of a wide overflow groove through which oil is distributed over the
shaft journal and fed to the lubricating pump.
2.3.3. Bearing Temperatures
One double-element resistance temperature detectors monitor the temperatures of
each bearing. The resistance temperature detector is screwed in the position on side of thelow bearing sleeve from outside with the detector extending to the Babbitt liner.
7/30/2019 Bharat Heavy Electrical Limited training report
28/72
Page 28 of 72
2.4. VENTILATION AND PROTECTION EQUIPMENT:
2.4.1. Ventilation Arrangement:
The turbo generator is cooled by air circulated by means of two axial fans. Air coolers
cool the air after circulation. The air is drawn through suction ducts by axial fans
mounted on either side of the rotor. The warm air flows out through the exhaust at the
bottom of the stator frame.
2.4.2. Space heaters:
These heaters are used to circulate warm air inside the turbo generator and during
outages to prevent condensation of the moisture inside the machine. They are of strip
type and robust design. The heating elements are enclosed in a steel sheet with specific
rating of 15W per sq. inch of the surface. They are so designed that they may be fixed in
the suction ducts of the turbo generator. The heaters are completely covered in order to
prevent the accidental contact with the heat units.
2.4.3. Resistance Temperature Detectors:
The resistance temperature detectors are made up of Platinum resistance elements. The
detectors are placed in a groove cut in a rectangular glass laminate and embedded in
different positions like stator teeth, stator core, and slots. There are 12 active and three
spare elements distributed in different locations in 3 different planes, 5active plus 3
spare elements are placed in stator slots, 4 active are placed in stator core, 3 are placed in
teeth to measure the hot and the cold air temperatures. The resistance thermometers are
fixed in the exhaust hood of the stator frame and the end covers. The leads from these
resistance thermometers are brought out and connected to the terminal board. The leads
coming from the spare elements are brought up to the terminal board and left inside the
machine. These resistance temperature detectors operate on the principle that the
7/30/2019 Bharat Heavy Electrical Limited training report
29/72
Page 29 of 72
resistance of the elements will change depending on the temperature coefficient of the
element. The change in resistance can be accurately measured in a bridge circuit. A graph
is drawn showing the variation of resistance with temperature, which is used to know the
temperature rise under different operating conditions of the turbo generator.
2.4.4. Fire Detectors:
For the protection of turbo generator against any possible fire hazards 12 fire detectors
relays are provided on either side of the stator winding. These relays have a set of
normally open contacts. The set of contacts will close when the temperature surrounding
the first relay exceeds 80deg Celsius. The other relay set of contacts close when the
temperature exceeds 1000. These contacts are wired up to the terminal board provide on
the stator frame for the resistance temperature detectors. Both the sets of contacts are
used for automatic fire alarm shutting down of the turbo generator system and for the
release of CO2 gas from the Carbon dioxide system
2.4.5. Finish Machined Rotor:
The finish-machined rotor will be dynamically balanced at rated speed in a vacuum-
balancing tunnel to an accuracy . The rotor is also subjected to over speed at 120% rated
speed for 2 minutes. Balance condition is also checked over the entire speed range from 0
rpm to 3000 rpm
2.5. Cooling System:
7/30/2019 Bharat Heavy Electrical Limited training report
30/72
Page 30 of 72
2.5.1. Indirect Cooling:Indirectly cooled machines dissipate their losses to a cooling medium, which is entirely
outside the coil insulation. All air-cooled machines, with rare exceptions, are cooled in the
manner, as well as most hydrogen-cooled machines under 100mm VA. Turbo-generators
rated above 100mVA usually employ direct cooling.
2.5.2. Direct Cooling:Direct cooling is the process of dissipating the armature and field coil losses to a cooling
medium within the main conductor insulation wall. Machines cooled in this manner are also
called as super charges or inner cooled by various manufacturers. The cooling medium is
in either direct contact with the conductor copper or is separated only by thin materials
having little thermal resistance. Direct cooling eliminates the temperature differential
resulting from heat flow through the coil insulation, providing greater current-carrying
capability for the same hot-spot temperature rise.
2.5.3. Cooling methods of Turbo Generator:a) Air cooled Turbo Generator (TARI):In Air Cooled Turbo generator stator winding is indirectly air cooled whereas therotorwinding and stator core is directly air cooled. This type of cooling isapplicable for rating of
30 MW- 60 MW generators. In this type of turbo generatorthere are vertically side mountedcooler in a separate housing.
b) Hydrogen cooled Turbo Generator (THRI):When the problem of increasing generator rating was talked in it became clearthat the aircooled machine did not provide the necessary scope for progress. Notonly in circulating therequisite of air through the machine but also because highfan power required to circulate.Evidently to push up generator ratings hydrogenis used as cooling medium.
Advantages of Hydrogen as Cooling Medium:1. Increased efficiency2. Increase in rating
3. Elimination of fire hazard4. Smaller size of coolers
c) Hydrogen/water cooled T.G. (THDF):In large rating machines, hydrogen cooling is not sufficient to remove the entireheatgenerated. For additional cooling, a Primary Water (PW) cooling system withdemineralisedwater flowing through the hollow stator conductors is used. Therotor conductors arehydrogen cooled.
7/30/2019 Bharat Heavy Electrical Limited training report
31/72
Page 31 of 72
2.6. Insulating systems are of two types:
1. Resin rich system of insulation
2. Resin poor system of insulation
2.6.1. Resin rich system:
- Stacking of coils is done. In this case high resin glass cloth is used for preventing
inter half shorts.
- Putty work.
- Nomex is used as transposition pieces. Putty mixture is a composition if mica
powder, china clay and SIB 775 Varnish.
- Straight part baking is done for 1hour at a temperature of 160OC and a pressure
of 150kg/ sq.cm
- Then bending and forming is done.
- Half taping with resin rich tape is done for over hangs and reshaping is done.
- To ensure no short circuits half testing of coils is done.
- Initial taping is done and final tapings is done with resin rich tape to about 13-14
layers.
- Final baling is done for 3hrs at a temperature of 160OC in cone furnace.
- Gauge suiting is done.
High voltage testing is done at four times that of rated voltage and tan testing,
inter strip, inter half testing are done.
Finally glass taping followed by epoxy gel coating is carried out.
Advantages of resin rich system of insulation:
Better quality and reliability is obtained.
7/30/2019 Bharat Heavy Electrical Limited training report
32/72
Page 32 of 72
In case of any fault (phase-ground/ phase- phase short) carrying the repair process is
very easy.
Addition of excess resin will be avoided because of using resin rich mica tape.
2.6.2. Resin poor system:
Resin poor micalastic system is adopted for large range Ac Induction and synchronousmachines. These are designated to meet specific customer requirement hence for uniquein nature to each other. The main insulation consists of resin poor epoxy mica paper tapeall over the oil periphery with varying number of layers on straight and overhangportions.
RESIN POOR RESIN RICH
1. Epoxy resin content is about 8%.2. This method follows Thermo SettingProcess.3. There is a need for addition of resinfrom outside.4. Time required for this cycle is less.5. Repairing is very difficult.6. Overall cost is less compared to resinrich.
1. Epoxy resin content is about 40%.2. This method also follows ThermoSetting Process.3. Further addition of resin is notrequired from outside.4. its a very long process and time
consuming.5. Repairing is easy.6. Overall cost is more.
7/30/2019 Bharat Heavy Electrical Limited training report
33/72
Page 33 of 72
2.7. VACCUM PRESSURE IMPREGNATION:
Preheating of the stator 60C, Duration : 1 Hour
Vacuum Drying at 60C, 0.2 mbar Duration: ~16-18 Hours
Entire stator assemblies are immersed into liquid thermosetting epoxy
resin insulation and vacuum-pressure impregnated.
Resin Temp: 60DEG. C +/- 2DEG. C, Resin Fill ~ 20 min
Resin Level: 100 mm Above job, Settling Time ~ 10 min
Pressurization:
N2 Pressure ~ 4 bar, Raising Time ~ 80 min
Holding Time: 2 Hours.
Resin is withdrawn back
2.7.1. Characteristics of VPI insulation system:
1) Higher mechanical bond
2) Void free resin with high mica content ensures better heat transfer.
3) High dielectric strength, low dissipation factor, hence longer electrical life.
4) Higher thermal stability, ensures class-F under running conditions.
5) Less maintenance
6) Cost effective
7) Low inflammability, hence limited damage during abnormal operations.
8) High resistance to oil, acid, alkali and moisture.
9) Manufacturing cycle is less
10)Frame size is small, machine cheaper.
11)Elastic response to thermo-mechanical stress, machine suitable peak load
operation.
12)Tan Delta temperature tie up is small,Voltage grading at ends will be effective.
2.7.2. VPI SYSTEM OF INSULATION:
For vacuum pressure impregnation (VPI)of cage core stators up to 120 MW capacity which,
is the largest of its kind is India. This system conforms to the latest insulation system
adopted by KWU-SIEMENS technology. The stator coils are taped the porous resin poor mica
tapes before inserting them in the slots in cage core. Subsequently, the wound stator is
7/30/2019 Bharat Heavy Electrical Limited training report
34/72
Page 34 of 72
subjected to a special VPI process in which first the stator is vacuum dried and the
impregnated in a resin bath under pressure of nitrogen gas. Then the stator is cured in an
oven.
The main characteristic if this system of insulation is also follows:
1. Better heat transfer resulting from resin penetration into minute air gaps in between
laminations and bar insulations.
2. Low dielectric loss resulting in increased life of the machine.
3. High resistance against the effect of moisture.
4. Reduction of time cycle of manufacture.
2.7.3. Advantages of VPI:
Longer electrical life.
Higher thermal conductivity
Lesser thickness of insulation higher voltage stress.
Small dissipation factor tip-up (void free insulation).
Better elastic response to thermo mechanical stresses
Insensitivity to high temperature and temperature changes(suitable for gas
turbine application).
Low inflammability
Higher resistance to effect moisture
Higher chemical resistance to corrosive gaseslubes oils,acids&alkalis.
Lesser manufacturing cycle of machine.
Higher p/w ratio,lower cost of machines
7/30/2019 Bharat Heavy Electrical Limited training report
35/72
Page 35 of 72
Wound Stator at VPI Plant
Impregnation Plant
7/30/2019 Bharat Heavy Electrical Limited training report
36/72
Page 36 of 72
2.8. Excitation system:
2.8.1. Brushless Excitation system:The main parts of the brushless excitation system are:a) Pilot Exciterb) Main Exciter
c) Rectifier Wheelsd) Automatic voltage regulator
a) Pilot Exciter:Three phase pilot exciter is 16 pole revolving field units. The stator accommodatesthree
phase armature winding and magnetic poles are placed on the rotor. Thusrotating flux is
produced which cuts the stationary armature conductors and threephase a.c. is generated.
7/30/2019 Bharat Heavy Electrical Limited training report
37/72
Page 37 of 72
PMG Rotor and Fan
b)Main Exciter:
The three phase main exciter is a 6 pole armature type unit. The stator frameaccommodates
the field winding. The field winding is placed on the magneticpoles. The armature consists of
stacked lamination and the three phase winding isinserted into the slots of the laminated
armature.
c) Rectifier wheel:
7/30/2019 Bharat Heavy Electrical Limited training report
38/72
Page 38 of 72
Components in the rectifier wheel are as follows1. Silicon diodes2. Aluminium heat sink3. Fuses4. RC circuit
The main component in the rectifier wheel is silicon diodes which are arranged inrectifier
wheel in three phase bridge circuit. The direct current from rectifierwheel is fed to DC leads
and then to the field winding of the rotor.
Rectifier wheel
d) Automatic voltage regulator:
The main features of AVR are:
It has an automatic circuit to control outputs of auto channel and manual channel and
reduces disturbances at the generator terminals during transfer from auto regulation to
manual regulation.
It is also having limiters for the stator current for the optimum utilization of lagging and
leading reactive capabilities of turbo generator.
There will be automatic transfer from auto regulation to manual regulation in case do
measuring PT fuse failure or some internal faults in the auto channel.
The generator voltage in both channels that is in the auto channel and the manual channelcan be controlled automatically.
2.8.2. Advantages of Brushless Excitation:
Eliminates slip rings and brushes
7/30/2019 Bharat Heavy Electrical Limited training report
39/72
Page 39 of 72
Eliminates all problems associated with transfer of current via sliding contacts
Eliminates the hazard of changing brushes on load
Brush losses are eliminated
Minimum operating and maintenance cost
High response excitation with fast acting AVR
Rotor Earth Fault Measurement through provision of Instrument Slip Rings
Brush less Exciters Nomenclature:
E A R 50 / 15 - 30 / 8 - 3
Exciter
Air-cooled
Rotating Rectifier Diode Wheel
Diameter
Length
rpm
No. of poles
Number of diodes in a bridge arm
2.8.3. PERMANENT MAGNET GENERATOR (PMG):
This is a very small 3 phase synchronous generator , in which armature windings are located
in the stator and the rotor is provided with permanent magnet poles .Since permanent
magnet poles are provided , no field winding(or excitation) is required. With the help of
PMG, the generator can build up voltage in the absence of any DC excitation.
7/30/2019 Bharat Heavy Electrical Limited training report
40/72
Page 40 of 72
The 3 phase AC produced in the PMG stator is rectified and fed to the main exciter field
through an AVR.
The PMG is also a high frequency generator, generally at 150 Hz or 300Hz.
Fig :Permanent Magnetic Regulator
7/30/2019 Bharat Heavy Electrical Limited training report
41/72
Page 41 of 72
3. TESTING OF TURBOGENERATOR
Testing is an activity, which basically evaluates a component, and or a product (built
up of component assemblies) as to whether it has the technical capability that has been built
into it by way of design, materials, and technological processes employed while
manufacturing and workmanship.
As such, testing activities can broadly be classified in to a number of categories as follows:
- Type tests.
- Routine tests.
- Process tests.
a) Advantages of testing:
Provides quality assurance.
Meets the requirements of legal & contract requirements.
Ensures process capability & develops checklist.
Have an approved procedure.
Check the equipment before use.
Calibrate the test equipment & instruments.
Ensure interlocks of the equipment
b) Performance tests on turbo generator:
With the increasing trend on standardization every country has its National
Standards covering a wide range of subjects, In India; the Indian Standards are valid and
applicable. The machines produced at Hyderabad fully conform to Indian and also
International Standards and many machines are being exported to various countries. The
performance tests on turbo generators include the following
Measurement of Insulation resistance.
Measurement of ohmic resistance of windings in cold state.
Applied H.V. tests.
Measurement of vibrations and mechanical losses.
Measurement of no load characteristics.
Measurement of short circuit characteristics.
Determination of excitation on load and checks of voltage rise (regulation).
Measurement of leakage and potier reactance.
7/30/2019 Bharat Heavy Electrical Limited training report
42/72
Page 42 of 72
Measurement of losses and determination of efficiency.
Heat run tests.
Retardation test.
c) Test Procedure:
During manufacturing of Turbo-generators the following stage tests are to be carried out on
individual components to ensure quality of the product and to reduce last minute delay
during acceptances tests. The standards for these tests will differ from plant to plant.
1. Stator
Checking up of Resistance temperature detectors while core building.
Ring flux test.
Tan delta measurement on stator winding after impregnation.
H.V. test on coils during manufacturers and assembly.
Capacitance measurement.
2. Rotor
H.V. test on excitation connecting leads.
H.V. & inter- turn insulation tests on field coils during the winding process.
Impedance measurement field coils.
3. Over-speed test.
Over-speed test involves mechanical running of the rotor at the prescribed % over-speed for the stipulated period of time. It is later subjected to a very close mechanical
inspection to investigating into the effects of over speed if any.
The rotor isbalancedto the required levels as per standards. This brings us to measurement
of characteristics and losses of the generator.
Measurement or determination of efficiency of the machine is an important step.
For determination of efficiency, losses measurement on the drive system is to be done and
derive machine losses by subtracting drive motor losses.
4. Determination of efficiency
Having measured the losses, the efficiency can be estimated from the formula.
Efficiency =(inputlosses / input = output / (Output + losses)
Tolerance on guaranteed efficiency is 0.1 (1-efficiency) when measured by summation of
losses method.
7/30/2019 Bharat Heavy Electrical Limited training report
43/72
Page 43 of 72
5. Measurement for leakage &potier reactance
Leakage reactance is measured on the stator alone when winding is completed. The
procedure involves supplying the winding from a 3-phase variable voltage source and
measuring currents voltage and power at the stator terminals. Depending on the source
capacity upto 0.25In may be passed. Potier reactance as per accepted standard practices is
taken as 0.6 to 0.65 of total leakage reactance. It can alternatively be calculated from the
zero power factor test measurements.
6. Line-to-Line sustained short circuit test
The negative phase sequence reactance is can be determined from the line-to-line
sustained short circuit test.
Negative phase sequence reactance (X2) = P / 3. (Ik2)2
Where P = Power measured and Ik2 is negative phase sequence current measured during
line-to-line sustained short circuit test.
7. Line to line and to neutral sustained short circuit test
From this test zero phase sequence reactance can be determined.
Zero phase sequence reactance (Xo) = Vo / Io.
Where Vo = Voltage from measured in open phase voltage and Io is current measured in line
to neutral during line to line sustained short circuit test.
8. Retardation test for determination of Moment of Inertia
The machine speed and time are noted during free coasting down of the machine.
Moment of inertia = (4 x 365000 x P x T)/ N2 Kg-m2
Where: P = Power input in kW to keep machine at rated speed. N = Rated Speed in rpm.
T Time in seconds from curve. (Tangent drawn at rated rpm)
3.1. OBJECTIVES OF TESTING:
Testing is the most important process to be conducted on a machine after it is designed. The
testing of machine is necessary primarily to establish that the machine performance
complies with the customer specifications. Tests ensure that the piece of equipment
concerned is suitable for and capable for performing duty for which it is intended.
7/30/2019 Bharat Heavy Electrical Limited training report
44/72
Page 44 of 72
Testing is done under condition simulating closely as possible to those, which will
apply when the set is finally installed with a view to demonstrate to purchasers
representative its satisfactory operation. Test provides the experimental data like
efficiency, losses, characteristics, temperature limits, etc. for the use of design office, both as
confirmation of design forecast and also as basic information for the production of future
designs.
a) Introduction
With ever increasing rating of the modern turbo generators and reliability of service
expected, testing at manufacturers works has become of paramount importance. The
machine performance is evaluated from the results of the equivalent tests.
b) Advantages of testing
- Provides data for optimization of design
- Provides quality assurance
- Meets the requirement of legal and contract requirements.
- Reduction in rework cost.
- Ensures process capability and develops checklist.
- Increases confidence levels in manufacture.
- Establishes control over raw materials.
- Helps in building of safety and general operation and manual.
3.2. TYPES OF TESTS
Tests on turbo generators are classified under the following headings, which is also
the order in which these are performed during the course of manufacture.
Tests on the materials and components during the manufacture so as to control the
quality of the materials in process also known as Process tests.
Performance tests on the machine to prove the performance of the generator in
accordance with the required standard.
3.3. TESTS DURING MANUFACTURE/ PROCESS TESTS:
Tests on rotor winding
Tests on stator coils.
7/30/2019 Bharat Heavy Electrical Limited training report
45/72
Page 45 of 72
Balancing and over speeding of rotor.
3.3.1. Rotor winding
The rotor coils and their insulation are subjected to a high stress when in normal
operation. Thus a thorough inspection of these is necessary before putting them in the rotor
slots as otherwise any replacement of the faulty insulation or cell would necessitate
removing the coil binding rings and the wedges, which is a cumber job. A series of graded
voltage tests are conducted on the rotor cell and coils dusting assembly and also when
finished to test its electrical strength against likely creep age to ground or inter turn
breakdown.
3.3.2. Tests on the Rotor Coils
1. Between turns:
The rotor coils turns are made up of a number of turns which are formed in halves and
then assembled with their inter turn insulation and boned with an adhesive in the steam
heat press. Although the normal working voltage per turn is very small, a turn to test of 240
volts is done to exercise quality control.
2. Top turn trough:
The insulation the top and bottom of the rotor slot provides adequate and safe creep
age distance between copper and rotor steel, in case of slotted copper 500 volts for one
minute to test the top trough.
3. Collecting leads:
A high voltage equivalent to the shipping test plus 1500v is applied to the collector
leads when fitted in bore with studs of seals fitted but before connecting to the windings.
3.3.3. Tests on stator coils
As per the standards the stator winding has to be subjected to a shipping pressure test of
(2 x line voltage +1kv). This power frequency voltage applied for one minute.
In order that machine when found with stands this final voltage test and any faulty coil is
eliminated during various stages of coil manufacture and winding. Because of the
continued application of HV tests overstress the winding insulation, the voltage is
reduced in various stages.
1. Tests between parallel strips
7/30/2019 Bharat Heavy Electrical Limited training report
46/72
Page 46 of 72
This is a test of strip insulation provided for eddy emf, on low voltage at the order of 350V
for 3 seconds is applied.
2. Coils in manufacturing and Winding Sections:
When the coils are first tested, a voltage of 8kV in excess of shipping pressure test is applied,
and this voltage tests are repeated.
3. Tests on Thermocouples:
1000V Megger test is applied to the thermocouples.
3.4 BALANCING AND OVER SPEEDING OF ROTORS
1. Balancing:
One of the most important preliminaries to testing is that of balancing the rotors.
Before over speeding, the rotor is dynamically balanced, in cold as well as hot conditions. A
set of run up and run down is taken sure those critical speeds are well away from the
running speed.
2. Over Speeding:
In order to check the soundness of all parts and fitting on rotor assembly, the rotor is
run at an over speed of 14% for five minutes or 30% for one minute.
3.5. PERFORMANCE TESTS/ TESTS ON COMPLETED MACHINE:
The machine is assembled and erected at the heavy rotating plant test bay for test.
a. Dry out insulation resistance of rotor & stator windings
Before starting with running tests, the stator windings are dried out by circulating
current in the winding from an external dc source Input of power is so controlled as to limit
the temperature of the end windings to a maximum of 800C by thermometer.
Progress of dry out is observed by one minute insulation resistance reading with
1000v Megger. With the application of heat, the insulation resistance will initially drop and
then will rise again over a period of time and finally becomes approximately constant
temperature. Ration of ten-minute reading, i.e. polarization index, when more than 2 gives
an indication of good dry out. Insulation resistance readings of rotor winding to ground are
taken.
7/30/2019 Bharat Heavy Electrical Limited training report
47/72
Page 47 of 72
b. Resistance of machine windings
Measurement of cold winding resistance, both for stator and rotor must be very
accurate since it forms the basis of calculating rise in temperature of rotor winding under
cold and hot conditions by resistance method.
All precautions are taken to ascertain correct temperature of the winding white
measuring cold resistance. Since the winding resistance of turbo generator is quite low: a
modified form of wheat stone bridge i.e. Kelvins double bridge does away with the necessity
of accounting for the resistance of loads. Resistance between phases for stator and between
slip rings for is recorded along with the cold winding temperature at the time of
measurement.
c. Phase sequence test:
The phase sequence test is to check the agreement of the terminal markings that
have been specified using the Phase Sequence Indicator.
3.5.1 Performance tests
The performance tests on the turbo generator are classified as:
- Type tests
- Routine tests
- Heat run tests
3.5.2. Type tests
These are specially requested tests form the customer. They are not performed on all
machines i.e., they are specific to machine. They include
Mechanical measurement of leakage reactance of stator winding
Measurement of residual voltage of stator winding at rated speed
Line to line sustain short test and determination of negative sequence reactance [X2]
Line-to-line and neutral sustain short circuit test and determination of negative
sequence reactance [XO]
Retardation test for determination of GD2
3.5.3. Measurement of leakage reactance of stator winding
7/30/2019 Bharat Heavy Electrical Limited training report
48/72
Page 48 of 72
This test is done on the stator winding with out rotor, generally before assembly on
test bed for running test.
Purpose
To determine total leakage reactance
To determine potier reactance
To determine armature leakage reactance
3.5.4. Before running the machines ensure:
Lubricating oil is flowing through bearings and the gear box.
All the instruments are working
Roll the machine and check all the parameters. Slowly raise the speed to one-sixth
rated speed. Observe slow roll vibrations, temperature and oil flows. Raise the speed
to one-third rpm slowly and record the vibrations, temperature and oil flows.
The vibrations are measured at rated speed on both the bearing housings (pedestals)
in horizontal, vertical and axial directions with the help of vibration meters, which
are internally connected to the monitor and the vibrations, are noted in the form of
graphs.
The temperature of stator is monitored by monitoring resistance temperature
detectors embedded in core, tooth and winding. Now raise the speed to two third the
rpm by observing all the parameters, critical speed and record them. The machine is
rolled and run at rated speed after ensuring the bearing oil and left at rated for
stabilization of bearing temperatures.
7/30/2019 Bharat Heavy Electrical Limited training report
49/72
Page 49 of 72
INSULATION
History of Insulation
Since the beginning of civilization, humans have recognized the need for insulation. Man
clothed himself with wool and skins from animals. He built homes of wood, stone, earth, and
other materials for protection from the cold winter and the heat of summer.
Ancient Greeks and Romans discovered asbestos and found many uses because of its
resistance to heat and fire. The Romans used cork for insulation. One use was in shoes, to
keep their feet warm. As industrialization expanded, cork was used as insulation for ice
houses. Blocks of ice were cut from frozen lakes in winter and stored in cork-lined ice
houses for use in summer. When mechanical refrigeration came into use, cork was used to
insulate pipes and equipment.
Mineral fiber - another important insulating material - was first used by the natives of the
Hawaiian Islands to blanket their huts. The fibers came from volcanic deposits where
escaping steam had broken the molten lava into fluffy fibers.
Man-Made mineral fibers were developed in the early industrialization period. Steam was
injected into molten slag, a waste product from iron furnaces. It has been widely used for
both building and industrial insulation. As more and more uses were found for it, mineral
fibers were modified and molded into different shapes such as pipe covering.
A pipe covering made from corrugated layers of asbestos paper was developed for hot
applications. This type of insulation obtained its efficiency from air pockets in the
corrugation. The development of the more efficient fiberglass made this material obsolete.
Another obsolete material widely used for many years was 85 percent magnesia. This
material was similar to the calcium silicate used today but it contained asbestos fibers as a
binder. This material was used extensively until the mid-fifties when calcium silicate made it
obsolete.
7/30/2019 Bharat Heavy Electrical Limited training report
50/72
Page 50 of 72
Materials made from layers of high-fiber-content felt or paper, with layers of asphalt
saturated felt formerly were used on moderate-to-cold temperature applications.
Today materials manufactured from fiberglass, ceramic, mineral wool, calcium silicate,
foamed plastic, glass, and other substances are used in many shapes and forms. The most
widely used material is fiberglass which is available in loose fill, blanket, board, and molded
pipe shapes.
Insulation uses range from conventional building and pipe insulation to insulation for
equipment and systems operating at extremely low or high temperatures. Insulation is a
vital part of industry. It is used in many ways and forms to improve our environment. Its
importance will continue to increase as technology advances and energy resources and
conservation are high priority.
Electrical Insulation
An electrical insulation system (EIS) is defined as an insulating structure containing one or
more electrical insulating materials (EIM) together with associated conducting parts
employed in an electrotechnical device. This is a rather simple definition for what can be a
very complex combination of materials. An EIS is composed of two sets of components
major ground insulation components and minor components.
Major ground insulation components are EIM. That is, these materials are the electrically
stressed components used to separate conducting parts at different electrical potentials.
Typical examples of major components include magnet wires, varnishes, and flexible sheet
materials used for core insulation, as high-low barrier insulation, or slot liners in motors.
Minor components are those materials used in combination with the major ground
insulation for mechanical, heat transfer, decoration, or other non-electrically stressed
applications. Typical examples of minor components include pressure-sensitive tapes,
sleeving and tubing, lead wires, phase insulation, and potting compounds.INSULATING
MATERIALS
Insulating materials
This report lists a number of commonly used insulating materials found in electronic and
electric equipment. Although this listing is somewhat long, it is not comprehensive- the
7/30/2019 Bharat Heavy Electrical Limited training report
51/72
Page 51 of 72
choices available canbe overwhelming. Fortunately many superb and inexpensive materials
are available and the finalchoice may be somewhat arbitrary and the designer is advised to
obtain samples of several candidates before making a final decision. Trade names do not
represent a particular brand preference but areincluded for cla:rity.
Table for classes of insulation:
Insulation
class
Maximum Permissible
operating Temperature (C)
Y 90
A 105
E 120
B 130
F 155
H 180
C Over 180
The following are brief explanations of those insulation techniques.
i) Class-Y insulation: Withstands atemperature of up to 90C; typically made of cotton, silk,
or paper
ii) Class-A insulation: Withstands a temperature of up to 105C; reinforced
Class-Y materials with impregnated varnish or insulation oil
iii) Class-E insulation: Withstands a temperature of up to 120C
iv) Class-B insulation: Withstands a temperature of up to 130C. This has a form that
inorganic material is hardened with adhesives. This is the first insulator using this structure.
v) Class-F insulation: Withstands a temperature of up to 155C; for example, made of Class-B
materials that are upgraded with adhesives, silicone, and alkyd-resin varnish ofhigherthermal endurance
vi) Class H insulation: Withstands atemperature of up to 180C; for example, made of
inorganic material glued with silicone resin or adhesives of equivalent performance
vii) Class-C insulation: Withstands a temperature of up to 180C or higher; made of 100%
inorganic material
7/30/2019 Bharat Heavy Electrical Limited training report
52/72
Page 52 of 72
As explained above, electrical insulation is classified with its maximum allowable
temperature. By adopting an insulation technique of higher thermal endurance, electric
instruments can be downsized.
INSULATING MATERIALS
A.B.S.: Acrylonitrile, butadiene, and styrene combine to form this common plastic often
usedto make housings or other mechanical parts.ACETATE: Acetates have good electrical
insulating properties and is the material used to make movie and microfilm.
ACRYLIC: Lucite and Plexiglass are trade names for acrylic which has widespread use
wheretoughness and transparency are required. Solvent cement is quite effective for
welding pieces together.
BERYLLIUM OXIDE: A hard white ceramic-like material used as an electrical insulatorwhere
high thermal conductivity is required. Beryllium oxide is highly toxic in powder form
andshould never be filed or sanded and consequently has fallen out of common use. Power
semiconductorheat sinks can still be found with beryllium oxide spacers for electrical
insulation.
CERAMIC: Ceramics are used to fabricate insulators, components, and circuit boards.
Thegood electrical insulating properties are complemented by the high thermal
conductivity.
DELRIN: This Dupontacetal resin is made from polymerized formaldehyde and finds
usessimilar to nylon. The material is rigid and has excellent mechanical and electrical
properties making itsuse common in appliances and electronics.
EPOXY/FIBERGLASS: This laminate is quite common due to its superior strength
andexcellent electrical properties even in humid environment. Most modern circuit boards
are made from a
grade of epoxy/fiberglass. (Grades include G10/FR4 and G11/FR5 extended temperature
grade.)
GLASS: Glass insulation comes in a wide variety of forms including solid glass, fiber
tapes,fiberglass sheets and mats, woven tubing and cloth, and various composites. High
temperatureoperation is a key feature.
KAPTON: Polyimide film has exceptionally good heat resistance and superb mechanical
andelectrical properties. Kapton tapes are fairly expensive but often indispensable.
KYNAR: As is Teflon, Kynar is a floropolymer with excellent chemical and
abrasionresistance. It is readily machined and welded.
7/30/2019 Bharat Heavy Electrical Limited training report
53/72
Page 53 of 72
LEXAN and MERLON: These polycarbonates have excellent electrical insulating
properties.Optical grades are available and the material is so tough that it meets U.L.
requirements for burglaryresistance. Non-transparent grades are machined to make strong
insulators, rollers, and othermechanical parts.
MELAMINE: Melamine laminated with woven glass makes a very hard laminate with good
dimensional stability and arc resistance. (Grades G5 is the mechanical grade and G9 is the
electrical
grade.)
MICA: Mica sheets or "stove mica" is used for electrical insulation where high
temperaturesare encountered. Thermal conductivity is high so mica insulators are useful for
heatsinking transistorsor other components with electrically conductive cases. Puncture
resistance is good but the edges of themica should be flush against a flat surface to prevent
flaking. Mica finds uses in composite tapes andsheets which are useful to 600 degrees
centigrade with excellent corona resistance. Sheets and rods ofmica bonded with glass can
tolerate extreme temperatures, radiation, high voltage, and moisture. Thisrather expensive
laminate may be machined and it will not burn or outgas.
NEOPRENE: Neoprene rubber is the material used for most wet suits. This black rubber
iscommonly used for gaskets, shock absorbers, grommets, and foams.NOMEX: Nomex is a
Dupont aromatic polyamide with an operating temperature range over220 degrees
centigrade and with superb high voltage breakdown. It is an excellent choice
forstandardization since it outperforms many other materials.
NYLON: Nylon has good resistance to abrasion, chemicals, and high voltages and is oftenused
to fashion electro-mechanical components. Nylon is extruded and cast and is filled with a
varietyof other materials to improve weathering, impact resistance, coefficient of friction,
and stiffness.
P.E.T.: Polyethylene terephthalate is a highly dimensionally stable thermoplastic with
goodimmunity to moisture. This excellent insulator has a low coefficient of friction and is
excellent forguides and other moving parts.
P.E.T.G.: A clear, tough copolyester commonly used for durable "bubble-packs" or
foodcontainers.
PHENOLICS: Phenolic laminated sheets are usually brown or black and have
excellentmechanical properties. Phenolics are commonly used in the manufacture of
switches and similarcomponents because it is easily machined and provides excellent
7/30/2019 Bharat Heavy Electrical Limited training report
54/72
Page 54 of 72
insulation. Phenolic laminates arewidely used for terminal boards, connectors, boxes, and
components. (Grades x, xx, xxx arepaper/phenolic and grades c, ce, l, le are cotton/phenolic
which is not the best choice for insulation.
Grade N-1 is nylon/phenolic and has good electrical properties even in high humidity but
exhibitssome cold flow.)
POLYESTER (MYLAR): A strong material often used in film sheets and tapes for graphic
artsand electronics. Those shiny balloons and "space blankets" are usually made from
metalized Mylar.
Mylar is also used as a dielectric in capacitors.
POLYOLEFINS: Polyethylene is the white Teflon-like material used for food cutting board.
Different densities are available with the ultra-high molecular weight grade at the top
offeringtoughness outlasting steel in some applications. Polypropylene is another widely
used polyolefin.
POLYSTYRENE: A clear insulator with superb dielectric properties. Polystyrene
capacitorsexhibit little dielectric adsorption and virtually no leakage. Liquid polystyrene or
Q-dope is a low-losscoil dope used to secure windings and other components in RF circuits.
POLYURETHANE: Polyurethane is another common polymer which features abrasion
andtear resistance along with a host of desirable characteristics. Degrading little over time
or temperature,polyurethane is popular in both commercial and consumer applications.
PVC: Polyvinylcloride or PVC is perhaps the most common insulating material. Most wiringis
insulated with PVC including house wiring. Irradiated PVC has superior strength and
resistance toheat. PVC tapes and tubing are also quite common.
Electrical and electronic housings are commonly molded from PVC.
SILICONE/FIBERGLASS: Glass cloth impregnated with a silicone resin binder makes
anexcellent laminate with good dielectric loss when dry. (Grades include G7.)
SILICONE RUBBER: A variety of silicone foam rubbers are available for insulating
andcushioning electronic assemblies. Silicone rubbers exhibit a wish list of characteristics
includingsuperb chemical resistance, high temperature performance, good thermal and
electrical resistance, longterm resiliency, and easy fabrication. Liquid silicone rubbers are
available in electrical grades forconformal coating, potting, and gluing. Silicone rubbers
found in the hardware store should be avoided.
in electronic assemblies because they produce acetic acid. Silicone rubbers filled with
aluminum oxideare available for applications requiring thermal conductivity.
7/30/2019 Bharat Heavy Electrical Limited training report
55/72
Page 55 of 72
TFE (TEFLON): Teflon is an excellent high temperature insulation with superb
electricalproperties. Teflon tubing and wire insulation comes in a variety of colors and
typically feels slippery.
The insulation is impervious to the heat and chemicals normally encountered in
electronicsmanufacturing but the material will "cold flow" so Teflon insulation is avoided
where sharp corners or
points are encountered. Laminated TFE circuit boards take advantage of Teflon's excellent
microwavecharacteristics.
Teflon emits a dangerous gas when exposed to extreme heat. White Teflon terminals are
commonlyused where extremely good insulation is required. The slick surface repels water
so the insulationproperties are fantastic even in high humidity. High quality I.C. sockets are
made from Teflon toreduce leakage currents. Teflon and Teflon composite tapes with
adhesive are available. FEP is a lower
temperatureTeflon.THERMOPLASTICS: Other thermoplastics include Polysulfone,
Polyetherimide, Polyamideimide, and polyphenylene with trade names like Noryl, Ultem,
Udel, Vespel, and Torlon. Thesematerials are grouped here for completeness and are not
particularly similar. For example Vespel is SPpolyimide with amazing properties but
commanding an equally amazing price- a 10 inch sheet couldcost thousands of dollars,
whereas Polysulfone (Udel) is a rather good engineering material with a costfor the same 10
inch sheet near thirty dollars.
ELECTRICAL INSULATING PAPERS
A variety of insulating papers are available specifically designed for insulating electrical
circuits.
Rag and craft paper often called Transformer Paper is often used to separate windings
intransformers or in applications where no sharp edges might poke through the relatively
weak paper.
Grey and tan are common colors.
Fishpaper is a curious name referring to a grey cotton rag paper usually vulcanized and
oftenlaminated with Mylar. The Mylar may have paper on one or both sides and many
thickness grades areavailable. Tear and puncture resistance are excellent and the thinner
grades are easily cut with scissors.
Other "sandwich materials" are available including 100% polyester laminates and are
usually a distinctcolor. The paper/Mylar laminates resist soldering heat better since the
7/30/2019 Bharat Heavy Electrical Limited training report
56/72
Page 56 of 72
paper doesn't melt and theDacron/Mylar laminates resist moisture best. Laminates with
thicker polyester centers are fashionedinto insulating plates in many electro-mechanical
devices. A typical application may be observedinside most older electrical timers where a
printed and folded piece of laminated paper keeps the user'sfingers away from the high
voltage when adjusting the position of the on and off trippers. Papers madewith
temperature resistant nylon and/or glass weaves have excellent electrical properties and
goodtemperature resistance.
Thin sheets of epoxy-fiberglass usually green in color are commonly used for insulating
PCB's andelectronic assemblies with potentially sharp projections. Puncture resistance is
superb even for sheet thin enough to be quite flexible.
A simple clear polyester sheet is sometimes used for insulation but is offers far less puncture
andtemperature resistance than the laminates. The ordinary appearance may prove to be a
liability also:one computer maker uses such a sheet to insulate the motherboard from the
chassis and many noviceshave left this critical insulator out when reassembling their
computer with disastrous results. Die-cutlaminates look important and are easily printed.
TAPES
Tapes are made from many of the above materials. Vinyl tapes are commonly used for wire
insulationand are available in all the colors necessary for color coding. Mylar tapes are
common in electronics:
film capacitors often have a final wrap of yellow Mylar tape. Acetate tapes are used where
goodconformability is desired as when covering coils as is white cotton cloth tape. Glass
cloth electricaltape with thermosetting adhesive (adhesive that permanently sets with
temperature) is used to secureand protect heater windings or insulate components exposed
to heat. Kapton, Teflon, and otherinsulators from the above list are used to make high
performance specialty tapes for harsh temperatureor chemical environment.
FOAMS
Foams are available for both thermal insulation and mechanical / acoustical insulation.
Choosing afoam for vibration damping can prove difficult. Many foams become stiff at cold
temperatures and will"take a set" at elevated temperatures. Some foams may have excellent
temperature characteristics butexhibit too much "spring" giving the assembly an
unacceptable resonance. Evaluate several materialsbefore choosing- foams are made from
many of the insulating materials mentioned above. Some of themore common foams are
listed below.
7/30/2019 Bharat Heavy Electrical Limited training report
57/72
Page 57 of 72
NEOPRENE: Neoprene foam (black) is often used for shock absorbing and vibrationdamping.
POLYSTYRENE: Styrofoam is the white foam used in inexpensive ice chests and
packingpeanuts. It is an excellent insulator but cannot tolerate elevated temperatures.
POLYURETHANE: Urethane foams are available in both rigid and flexible forms.
Theinsulating properties are excellent and elevated temperature tolerance is good.
Machined pieces of rigidpolyurethane are often used as thermal insulators in electronic
equipment. The soft foams are good for
vibration and sound attenuation and are available with a wide variety of properties.
SILICONE: Silicone foams provide excellent vibration damping characteristics and
excellenthigh temperature performance and chemical resistance.
VINYL: Vinyl foam has very little "spring" and is useful for vibration damping.
LAMINATES: Various foams are often laminated with a heavy center layer to create a sound
and vibration barrier. Lead has been used as the massive layer but the obvious concerns
have led todifferent materials such as metal oxide filled plastics.
The complete list of foam rubbers, plastics, and other foam materials could fill a bookshelf so
thispartial list should not confine the imagination. The yellow pages of any large city will
yield the namesof plastic companies which usually carry the solid insulating materials
mentioned. Gasket supplierswill have a surprising assortment of sheets and foams including
specialty electronic materials. Themanufacturers can often supply the name of distributors
but if they don't it doesn't mean that localsuppliers aren't there. Check thoroughly before
buying some huge minimum quantity from the factoryalmost all of the materials mentioned
are available from distributors in small quantities. Industry directories will supply the name
of material suppliers if the local distributors cannot. Used bookstoresoften have old copies
of "E.E.M.", "Goldbook" or "Thomas Register" which can give you a list ofmanufacturers. Ask
for the name of the local factory representative since he will probably know thenames of
local suppliers in his territory since he probably visits them on sales calls.
VPI insulation system
INTRODUCTION:
BHEL, Hyderabad manufactures 2 pole and 4 pole turbo-generators in the range of 1.5 MW to
200 MW with voltage levels varying from 440 volts to 13.8 KV. It meets the demand from
7/30/2019 Bharat Heavy Electrical Limited training report
58/72
Page 58 of 72
state electricity boards, process industries like sugar, paper and pulp, cement, petro-
chemicals, oil, steel, aluminum etc. The first ever generator manufactured was of 11 KV, 60
MW capacity in the year 1966 and the stator bar with epoxy resin rich insulation system was
ejected out of the mould. After two decades of rich experience in this resin rich insulation
system, for a better and more reliable insulation system of stator windings, Total Vacuum
Pressure Impregnation (VPI) Insulation System with epoxy resins had been introduced in
the year 1984 for the generators at BHEL, Hyderabad.
The total VPI insulation system presents the following advantages:
Void free insulation
B
Top Related