STUDY OF DESIGN

&

MANUFACTURING OF ALTERNATOR

NAME:-DIBYARAJ KRISHNA BEHERA GUIDED BY:-

ROLL NO:- 111EE0197 UPENDRA DEEP

INTRODUCTION• Electricity play a pivotal role in nation building and economic

development.

• Development of heavy and large scale industries as well as medium scale industries, agriculture transportation, etc., totally depends on electrical power resources of energy .

• World wide energy consumption is 167,496 TWh

• Need to increase in power generation,to provide a decent standard of living for people of india.

• Need to utilize available resource in efficient manner.

Energy intensity of different economies:-The graph shows the ratio between energy usage and GDP for selected countries. GDP is based on 2004 purchasing power parity and 2000 dollars adjusted for inflation

TURBO GENERATOR

TURBO GENERATOR

R Y B N

CT PT

AC O/P

DC I/P

6 poles

AC O/P

Substation

Diodes, Fuses,

Heat exchangers

Thyristor, Converters

AC O/P

150Hz

ROTOR ARMATURE

Exciter Yoke 150Hz

6 poles

o/p leads on statorPrime Mover (turbine)

Gas steam

STATOR RRW

PMG

FUNCTION OF TURBO GENERATOR•The generator rotor is driven by a prime mover and on driver side gas/steam/hydro/diesel depending on the equipment to which it is meant for.

•The non-drive side of the rotor is equipped with a rotating exciter armature which produces AC voltage. This is rectified to DC by using a DC commutator/Rotating diode wheel depending upon the type of exciter.

•The rear end of above exciter armature is mounted with a permanent magnet generator rotor.

•As above rotating system is put into operation. The permanent magnet stator produces AC voltage which is rectified by thyristor circuit to DC.

• The AVR field is controlled by taking feedback from main generator terminal voltage, to control external field variations required.

• The rectified DC supply out of exciter is supplied to turbo generator rotor winding either through brushed or central lead which will be directly connected to turbo generator rotor winding. This depends on the type of exciter viz., DC commutator machine or a brush less exciter.

• The main AC voltage of generator is finally available at turbo generator stator.

PRINCIPLE OF GENERATOR• An electrical machine is an electromechanical device, which either converts

mechanical energy into electrical energy or vice-versa.

• The machine that converts mechanical energy into electrical energy is called is a generator.

• The basic principle of operation of all an alternator is – FARADAY’S LAW OF ELECTRO MAGNETIC INDUCTION.

• It state that “ whenever there is relative motion between a conductor and magnet an EMF is induced” ,which is directly proportional to the rate of change of flux and the number of turns.

E = -NdФ/dt

• Thus to produce relative motion either the armature has to rotate or the magnet. In a D.C Generator the armature is the rotating part and in A.C Generator (Alternator) armature is the stator.

STATOR

• STATOR :- Stator is of welded steel single piece construction with radial and axial ribs having adequate strength and rigidity to minimize core vibration and suitably designed to ensure efficient cooling.

• STATOR FRAME:-Stator frame is made of two end clamping plates with axial ribs, welded round the periphery after core assembly.

• Guide bars are welded inside the stator frame over which the core is assembled.

• For GTG, stator frame is made for the open air cooling .These are suitable for outdoor installation for large capacity generator.

STATOR CORE• Stator core is made of silicon steel sheets with

high permeability and low hysteresis and eddy current losses.

• Stator laminations are coated with synthetic varnish and are stacked and held between sturdy steel clamping plates with non-magnetic pressing fingers which are fastened/welded to stator frame.

Steel - 95.8%

Silicon - 4.0%

Impurities – 0.2%

• Silicon steel sheets used are of COLD ROLLED NON- GRAIN ORIENTED (CRNGO) as it provides the distribution of flux throughout the laminated sheet.

• The segments are punched in one operation from electrical sheet steel lamination having a high silicon content and are carefully deburred .

• Eddy current loss depend on the thickness of the laminations

• .Hence to reduce the eddy current loss core is made up of thin laminations which are insulated from each other.

• The thickness of the laminations is around 0.5mm

• Hydraulic compression

• Deburring

STATOR CORE ASSEMBLY• The core building or assembling method depends on the insulation

system used:-

1) For resin rich insulation system the laminations are stacked in the frame itself.

2)For resin poor insulation system (VPI) cage core of open core design is employed.

• The stator core laminations are assembled as separate cage core without stator frame. The entire core length is made in the form of packets separated by radial ducts to provide ventilating passages for the uniform cooling of the core.

• The thickness of laminations separating the packets is about 1mm.

• The lamination separating each packets has strips of non-magnetic material that are welded to provide radial ducts.

STATOR WINDING

• The stator winding of all synchronous generator is star connected with neutral earthed.

• This arrangement has the advantage that the winding has to be insulated to earth for the phase voltage and not the line voltage.

• Star connection also has the advantage that it eliminates all triple frequency harmonics from the line voltage.

STATOR COILS

• The stator coils are the individual entities which are placed in the slots of the stator core & finally connected to each other as per the predesigned scheme.

• The stator coils are provided with high voltage insulation to isolate the coils from the stator core by with standing voltage stresses.

• There are three types of coils manufactured in BHEL,Hyderabad

1) Diamond pulled multi turn coils

2) Multi turn bars

3) Roebel bars

ROTOR

The rotor used in turbo generator is of cylindrical type and the windings used are distributed winding.

The rotor consists of the following:

• Rotor shaft

• Rotor winding

• Rotor wedges

• Damper winding

• Retaining ring

• Slip ring

• Rotor fans

 

INSULATION SYSTEM

• In electrical machines insulation is most important requirement to sustain high voltages and basically insulation is the heart for electrical machines.

• . Insulation is the property which has enormous resistance to the conduction band are very large i.e. Fermi energy level is very high in insulating materials.

• The property of good insulating material is non-conductive electricity .

• A good insulating material needs the following properties.

• The basic function of the insulation is to provide isolation to the live wire from live wire of earth.

• It should be a good conductor of heat and bad conductor of electricity.

• It should withstand the designed mechanical stress.

• It should have good chemical and thermal resistivity and environmental resistivity.

• BHEL,is practicing only thermosettling practice of insulation

• .The thermosetting process of insulation are basically of two types.

• Resin Rich System of insulation.

• Resin poor System of Insulation

•Resin present in the insulation consists of the following material in percentage.

MICA paper tape - 40-45% Glass paper tape - 20% Epoxy resin - 40%• MATERIAL FOR RESIN RICH BARS• Prepag• Nomex• Epoxy resin rich mica tape• Glass tape• PTPE tape• MATERIAL FOR RESIN POOR HALF BARS• Epoxy glass cloth• Nomex glass fleece• Fine mica polyester glass cloth• Nomex• Form micanite• Fine mica tape

•  

An ideal insulating materials should have

• High dielectric strength, sustained at elevated temperatures.

• High resistivity or specific resistance

• Low dielectric hysteretic

• Good thermal conductivity

• High degree of thermal stability i.e. it should not deteriorate at high temperatures.

•   CLASSIFICATION

  CLASS TEMPERATURE

Y 90C A 105C

E 120C

B 130C

F 155C

H 180C

C above 180 C

• We use class F insulation for star winding.

• Varnish is used as insulating material for laminations

VACUUM PRESSURE IMPREGNATION

• BHEL Hyderabad has installed the VPI system foe cage stators up to 12MW capacity wise high being the largest in India. This system conforms the latest insulation system adopted by KWU-SEIMENS TECHNOLOGY.

• The stators coils are taped with resin poor mica tapes before inserting in to the stator slots and then subjected to the VPI process, where it is vacuum dried first and then impregnated in a resin bath under the pressure of nitrogen gas.

• Then the stator is cured in the oven.

• The main characteristics of this insulating system are:-

1) Better heat transfer resulting from penetration into the minute air gaps in between laminations and bar insulation.

2) Low dielectric losses resulting in increased life of insulation and so of the machine.

3) High resistance against the moisture

4) Reduction of the time cycle of insulation

EXCITER

• Excitation systems have a powerful impact on generator dynamic performance and availability, it ensures quality of generator voltage and reactive power, i.e. quality of delivered energy to consumers.

• Main functions of excitation system are to provide variable DC current with short time overload capability, controlling terminal voltage with suitable accuracy, ensure stable operation.

TYPES OF EXCITER:-

• Static: These require direct high DC supply. This supply is taken by the input leads to the carbon brushes via the slip rings to the rotor windings hence magnetizing them.

•  Brushless: These have no slip rings or carbon brushes.

 

• Types of brushless exciters are:

1) Separately excited or non-overhang exciter- Used more often as it comes as a separate unit and is easy for maintenance and is coupled to rotor shaft.

2) Self excited overhang or Overhang exciter: Here the exciter is attached to the rotor shaft (over it). In case there is an excitation failure, the entire rotor shaft must be removed from the generator body unlike separately excited type where only that unit can be replaced. It takes less space hence only one bearing is present

• The brushless exciter consists of:-

1) Rectifier Wheel,

2)three phase main exciter,

3)three phase pilot exciter

4)metering

5) supervisory equipment.

• It is an AC exciter with rotating armature and stationary field. The armature is connected to rotating rectifier bridges for rectifying AC voltage induced in the armature to DC voltage.

• the Rotating Rectifier Wheel (RRW) consists of fuses, diodes and heat exchangers

TEST ON GENERATOR1) DC High voltage tests

2) Inter turn insulation test by comparison of RLC waveform. 

3) Inter strip insulation test on Stator half coils. 

4) 50 Hz AC high voltage test. 

5) Capacitance and tan delta measurement on stator bars and stator winding.

 6) DLA measurement on stator winding. 

7) Partial Discharge measurement on stator winding.

8) HV test (before impregnation)

9)HV test (after impregnation)

 

• Tan Delta Test: In Electrical AC System, the Dissipation Factor Tan δ or Power Factor Cos ø is considered as the indication of quality of insulation.

• Insulation Resistance test: A highly regulated, stabilized DC voltage is applied across the insulation, measuring the amount of leakage current flowing through it and then calculating (using Ohm's Law) a resistance measurement. The resistance measurement is in mega ohms. This test is done to evaluate insulation integrity.

• Core Flux test: The purpose of a core flux test is to test the integrity of the insulation between the lamination plates in the core of a stator. Core flux test is done after core assembly. Windings are inserted after this test.

• ELECTRICAL TESTS

• SCC test: Current is measured using two current transformers: one between R and Y phases and another between Y and B phases. Important test: SCC: 15KVA, 110V

• Speed is decreased from 3000rpm to zero in steps and impedance is hence calculated.

• OCC Test: Voltage is measured using two potential transformers: one between R and Y and another between Y and B phases.

 

CONCLUSION• As demand of power is increasing everyday so manufacturing of large scale

Generator is highly national importance. BHEL is playing a very vital to meet this demand and for economy of ours nation. BHEL has acquired the latest technology in the insulation system, the VACUUM IMPREGNATION SYSTEM of insulation, which has various advantage like cost reduction with improved quality.

THANK YOU