QUALITY CHECKS ON RESIN MIXTURE IN RESIN POOR PROCESS:

The resin mixture is a combination of epoxy resin and hardener. The containers of resin and hardener are stored in a cool, dry place. They are closed until processing for protecting against humidity. The impregnating resin mixture in the ratio of 100 parts of epoxy resin is mixed to 100 parts of hardener in a resin tank of the impregnation unit. The epoxy resin and hardener heated in an oven at 125C and sample is taken from every drum to test before release. The resin mixture is sensitive to moisture and therefore it is stored under vacuum below 20C but chilled not below 8C. After thorough mixing, the resin mixture is tested.

TEST ON RESIN MIXTURE:Before beginning impregnation and after stand still period of

more than five days. The resin mixture is tested in the following manner.

1. The resin mixture is tested for viscosity at 60c and limiting value of viscosity is 50m poise above which the resin is rejected.

2. The resin is again tested for the increase in its viscosity at 60 c after 20 hours heating at 100c; the maximum value at this point is 9m poise.

3. The resin is then heated for its saponification number whose specified value is 331.-+3 mg/koh/gram.

4. After this test for the ester number which is the between saponification number and total acid number. Its maximum limiting value is 10. In case it exceeds 10 necessary addition resin or hardener is done. According to saponification number the resin mixture is released after each test for use.

TESTING PERFORMANCE OF RESIN POOR SYSTEM:

BEFORE IMPREGNATION PROCESS:The different test which are carried out laying the bars in the stator

slots. They are:

1) Completion bottom layer high voltage test. 2) Completion top layer high voltage test.3) Winding resistance measurement.

1. BOTTOM LAYER TEST After laying the bottom bars high voltage test is conducted with 1.5

UP for 2minute where Up= 2Un+1, UP- Final test voltage Un-Rated voltage of generator.

2. TOP LAYER TEST:

After laying the top bars high voltage test is conductor with 1.1 Up for 1 minute, where Up=2Un-Final test voltage of generator.

3. INTER CONNECTION CHECKING:

After completion of connection, winding and baking high voltage is conducted with 1.05 Up for 1minute, when one phase is under testing, the other phases are earthen measurement of resistance of individual phases give the checking of interconnection.

4. A.C HIGH VOLTAGE TEST:

After laying top and bottom bars high voltage test with A.C is carried out by connecting all other to ground.

5. MECHANICAL RUN TEST:

Dynamic test carried out to find various losses, they are

1. Mechanical losses2. Iron losses3. Copper losses

AFTER IMPREGNATION:

After impregnation of the stator core by VPI process the following tests are conducted:

1. TAN TEST.2. HIGH VOLTAGE Tests.

TAN TEST:

After impregnation and curing of the winding a dissipation factor Vs voltage measurement as stipulated in the application national and international standard specification is performed for each bar between all-individual phase winding to ground.

Guiding values for the deception factor and its rice with the voltage merely. Given in the KEMA specification the maximum value shell not exceed 0.001 at 20% of rated voltage and rise shell not be greater than 0.006 per 20% of rated voltage up to 60% of rated voltage and 0.08 per 20% of rated voltage up to a rated voltage.

Winding manufacture by the Vacuum Pressure Impregnation Process comply with these limits.

The above test results are specified in the following graphs. First graph shows that voltage Vs Tan curve, it shows different Tan values at different percentage of rated voltage 20%, 40%, 60%, 80%, 100% of rated voltage respectively.

The second graph is a electrical field Vs life of insulation material, it shows that resin poor system of insulation has very long life compared to resin rich system of insulation. At 10 KV the resin poor system insulation as a lifetime of 540 years. Any good machine as life span of 25-30 years by using this insulation we will get a very long life with standard machine.

HIGH VOLTAGE AC TEST:

A C High voltage test is conducted on VPI system after impregnation to verify proper impregnation and dielectric strength of insulation. This test was conducted at 105% of winding test voltage i.e. Up=2Un+1KV Where Up-Winding test voltage Un-rated voltage of machine.

ADVANTAGES OF RESIN POOR SYSTEM OF INSULATION

(1) It has got better dielectric strength

(2)Heat transfer coefficient is much better

(3)Maintenance free

(4) It gives better capacitance resulting in losses due to which the

insulation life will be more

(5)The cost is less and it is the latest technology

(6)Reduction in time cycle and consumption MW is also less and it

gives high quality

DISADVANTAGE OF RESIN POOR SYSTEM:

(1)Dependability for basic insulation materials on foreign countries

(2) If any short circuit is noticed, the repairing process is difficult

ADVANTAGES OF RESIN RICH SYSTEM OF INSULATION:

1. Better quality and reliability is obtained.

2. In case of any fault (Phase to ground (or) phase to phase short)Carrying the repair process is very easy.

3. Addition of excess resin will be avoided because of using resinRich mica tape.

DISADVANTAGES OF RESIN RICH SYSTEM OF INSULATION:

1 It is a very long procedure.

2 Due to fully manual oriented process, the cost is more.

3 It is possible to process stator bars only.

COMPARISN BETWEEN RESIN POOR AND RESIN RICH SYSTEM

RESIN POOR SYSTEM

1. The insulation tape used in this

system has 8% of resin.

2. These method follows thermo-

settling process.

3. There is a need for addition of

resin outside.

4. Reduction in time cycle for this

process.

5. No tests are carried out while at

processing stage.

6. Processing of bars along with

stator processing of exciter coils

along with exciter are possible in

RESIN RICH SYSTEM

1.The insulating tape material used

in this system has 40% resin.

2.It as in resin poor.

3.Further addition of resin is not

required from out side

4 It is very long process and time

consuming.

5.Tests are being carried out while at

processing stage.

6.Processing of stator bars only

possible in resin rich system.

resin poor.

7. The cost of repairs is more.

8 The over all cost is less

compared to resin rich system.

7. Repairing work is easy.

8. The total cost in this process is

more.

APPLICATIONS:

1) All critical machines

2) Equipment exposed to frequent surges

3) Harsh or moist environment

4) Motors that run at service factor

VPI PROCESS CONTROL:

Throughout the VPI process computer to endorse homogeneous resin fill

continuously monitors each stator.

1) Ensure uninterrupted power supply

2) Adhere to the process strictly.

3) Assessments of critical failure in the system that can occur during

process and it emergency preparations.

ASSEMBLY OF STATOR AND ROTOR:

Stator and rotor after their manufactured and tested they are

brought for assembly. Rotor is inserted into the stator using a crane and the

following are checked

Bearing shell Id measurements

Bearing shell blue matching

Top and bottom blue matching of bearings

Journal diameter

Bearing shell & bedding top & bottom

Stator alignment trough centering

Air gap

TESTING OF TURBO GENERATORS:

OBJECTIVE OF TERSTING:

Testing is the most important process to be conducted on a machine after

it is designed. The testing of machine is necessary to establish that the

machine performance complies with the customer specification. Tests

ensure that the piece of equipment concerned is suitable for and capable for

performing duty for which it is intended.

Testing is done under conditions simulating as

closely as possible to those which will apply when the set is finally installed

with a view to demonstrate to purchaser’s representative its satisfactory

operation test provides the experimental data like efficiency, losses,

characteristics, temperature, limits etc for the use of design office, both as

conformation of design forecast and also as basic information for the

production of future designs.

INTRODUCTION:

With ever increasing rating of the modern turbo generator and

reliability of service expected, testing manufacture’s works has become of

paramount importance. The machine performance is evaluated from the

results of the equivalent tests.

ADVANTAGE OF TESTING:1. Provide data for optimization of design2. Provide quality assurance 3. Meets the requirement of legal and contract requirement4. Reduction in rework cost5. Ensure process capability and develops checklist6. Increase confidence level in manufacture7. Establish control over raw materials.

PERFORMANCE TESTS:

The performance tests on the turbo generator are classified as:

1. Type tests2. Routine tests3. Heat run tests

In our project we are doing only with Routine Tests.

ROUTINE TESTS:

These tests are carried out on each generator to ascertain that it is

electrically and mechanical sound. These tests are carried out on different

machines & are classified as:

1. STATIC TEST:

Measurement of Insulation Resistance of stator & Rotor winding

before &after High Voltage test (M/c at test)

High voltage test on stator & rotor winding (M/c at rest)

Measurement of polarization index of stator windings.

2. RUNNING TEST:

Measurement of Mechanical losses, short circuit characteristic and losses

Measurement of Mechanical losses, Open circuit characteristic and losses

Measurement of rotor impendence (rotor inside stator)

STATIC TESTS Measurement of insulation resistance of stator & rotor winding before and

after High voltage test:

Equipment:

(a) Megger (1000/2500v)

(b) Ear thing Rod earthing wire/ c able

* IR of the stator and the rotor winding are measured separately before and

after HV test using Megger of 2500V for stator & 1000V stator windings.

The values are taken at 15 sec and at 60 sec.

* Absorption coefficient of insulation is found out as

Absorption coefficient= 1Rat60

1 Rat15

This value should be> or= 2

If IR values are quite high, the absorption coefficient is not considered

because of early saturation (often observed in low voltage winding like rotor

etc). With dry winding its value will be some where in the vicinity of 2 or

even more. With damp winding it winding it will decrease to one.

Absorption coefficient of 1.8 & 1.7 may be satisfactory, while a value below

1.5 indicates a damp machine.

* Minimum IR value

The minimum value of insulation resistance (Rm) at 60min is

recommended as:

Rm =( Kv+1) ohms.

Where KV is voltage in kilovolts to be applied for tests.

In practice a fairly high value is obtained.

The winding is discharged to earthy after each measurement

2 . Measurement of polarization index of stator winding :

The polarization index of stator winding, all the three phases together,

is measured using 2500v megger after HV test. The IR values are noted at 1

min and 10min from starting of measurement.

The PI is evaluated as follows

Polarization index (P.I) = I.R. Value at 10min/I.R. value at 1 min

The minimum allowable PI value is 2.0

3. High Voltage test:

Equipment

*50 Hz A.C High voltage transformers and its induction regulator/input

autotransformer.

* Potential transformer (35 or100KV/100V)

* Voltmeter

*Binding wire

* Earthing Rod and Earthing wire/cable

When H.V test is done on one-phase winding, all other phase

windings, rotor winding, instrumentation cables and stator body are earthed.

The high voltage is applied to winding by increasing gradually to required

value and maintance for 1 minute & reduced gradually to minutes. The

transformer is switched off & winding discharged to earth by shorting the

terminal to earth using earthing rod connected to earth wire/cable.

The test is conducted on all the phases & rotor winding separately.

HV Test Levels:

Stator winding: (2Ut+1) KV =23 for 11 KV machine

Rotor winding: (10 Up) volts (with min of 1500v & max of 3500v),

Where, Ut= Rated of machine under test Up= Excitation voltage.

RUNNING TEST:

1. Measure of mechanical losses, short circuit characteristic and losses:

* The machine is prepared for short circuit characteristic using current

transformer and shorting links

* The machine is run at rated speed and drive motor input voltage

and current are noted and machine is excited

* Gradually in steps, at 20%, 40%, 80%, 90%&100% In. (In: rated

current of machine)

* At each step the following parameters are noted

a) Stator current (Ia&Ib)

b) Rotor current (If) corresponding to stator voltage.

c) Drive motor voltage (vd) and current (Id) corresponding stator

voltage

* The excitations is reduced and cut off, the speed is reduced and the

machine is cooled at lower speed. The machine is stopped when it is

sufficiently cooled down (stator core temperatures to be less than 60 c)

From the above data, characteristic curves are plotted as

follows:

a) %In v/s If

b) %In v/n machine losses in kw

2.Measurement of mechanical losses, open circuit characteristic and losses:

* The machine is run at rated speed and drive motor input voltage and

current are noted and machine is excited gradually in steps, at 20%

En (En: rated voltage of machine)

* At each steps the following parameters are noted

a) Stator voltages (Vab, Vbc & Vca)

b) Rotor current (if) corresponding to stator voltage

c) Drive motor voltage (Vd) and current (Id) corresponding stator

voltage.

The excitation is reduced and cut off , the speed is reduced and the machine

is cooled at lower speed. The temperature are checked from machine is

stopped when it is sufficiently cooled down (stator core temperature to be

less than 60c)

* From the above data, characteristic curves are plotted as follows:

a) % En V/S If

b) % En v/s machine in Kw.

3. Measurement of rotor impedance (Rotor inside stator)

* Equipment:

a) 50HZ (power frequency) a.c.source

b) Ac/Dc power analyzer

c) Current transformer (50A/5A or 100A)

d) Connecting leads

A variable 50Hz A.C. voltage of 1 is applied across the slip rings

/input leads and readings of voltage and current are noted down

from 50V to 200V in steps of 50V

This test is done at 1/3, 2/3 and at rated speed

Evaluation of Impendence:

Z= V/I ohms

Where Z = impendence in ohms

V=voltage

I = Current

Impendence measurement:

1. At rated rpm (Rotor inside stator)

2. At standstill (Rotor inside stator)

3. At standstill (Rotor outside stator)

TAN TEST:

Equipment: Schering Bridge

This test is conducted to check the presence of impurities in the

insulation & tan value for each phase & also for combined phases is noted

down.

Tan value should be generally less than or equal to 2%.

TESTING RESULTS:

Vph (0.2Un ) Rated KV= 10.5KV , 3000RPM.

Uph Tan

2.1 0.815

4.2 0.832

6.3 0.869

8.4 0.903

10.5 0.938

Wph Tan

2.1 0.806

4.2 0.820

6.3 0.857

8.4 0.899

10.5 0.941

Vph Tan

2.1 0.811

4.2 0.830

6.3 0.868

8.4 0.905

Uph Vph Wph Tan

2.1 1.18

4.2 1.209

6.3 1.230

8.4 1.254

10.5 1.268

Rating: 31.25, 250 MW, 11KV, 1640A, 0.8pf, 3000rpm.

SCC:

Ia Ib %In If Vd Id Dm

O/P

0 0 0 0.01 559.0 404.58 226.16

337.2 337.6 20.57 94.7 515.95 443.1 228.60

664.8 666.2 40.5 187.1 516.04 481.4 248.44

1005.8 1006.1 61.34 281.51 516.52 533.6 275.6

1324.9 1326.5 80.84 369.16 516.54 651.25 336.35

1495.2 1496.9 91.2 415.2 516.18 690.3 356.32

OCC:

Vab Vbc Vca %En If Vd Id Dm

O/P

35.3 35.3 35.3 35.32 0.01 512.4 419.85 215.16

2281.2 2282.5 2281.8 20.74 40.44 512.93 423.15 216.62

4447.42 4441.4 4448.2 40.44 77.05 512.4 442.45 226.71

6662.0 6665.0 6663.0 66.58 116.65 512.3 466.43 288.95

8845.0 8849.0 8846.0 80.4 160.3 512.19 501.08 256.64

10015.0 10019.0 10017.0 91.06 186.56 512.25 517.25 264.93

Resistance Measurement:

Instrument: Micro ohm meter

Resistance at 25c (m) Resistance at 20c (m)

Rotor 264 258.92

R75 = (( 235+75)/(235+20)) x R20= (310/255) x (0.2587)=0.3147

Rotor current = 562 A

Efficiency = (output)/(output+losses)

Losses = 99.532 + 9.9532 + 39.39 + 385.15 + 286. 38 = 820.40

Efficiency= (25000/25000 + 820 .40 ) = 96.82%

CONCLUSION:

Considering the manifold advantages of VPI System of insulation the

leading manufacturers of World are going to adopt this system for generators

up to 400 MW with hydrogen gas cooling. It has better thermal, electrical,

mechanical and chemical properties and its life time is about 54o years.

In view of the above, in the coming decades the Indian grids will use more

of such generators. In the scenario of World market which demands

generators with less cost at the best possible time with better reliability VPI

system of insulation will provide most viable solution.

B I B I L O G R A P H Y:

1. Electrical Machines: R.K.Batta Charya

2. Electrical Design, Operation and Maintenance Manuals:

BHELHyderabad

3. Engineering Chemistry: Daniel Yesudian

4. Electrical insulating Materials: R.K.Rajput

5. Electrical Machines: M.G.Say