DESIGN OF INSULATION SYSTEM BY VACUUM PRESSURE IMPREGNATION PROCESS FOR TURBO GENERATOR

PROJECT GUIDE: K. RAVI KUMAR   PRESENTED BY:

K. R. DHARANI DHARAN

(07N71A0212) CH.V.S.S.PAVAN KUMAR

(07N71A0206)

OBJECTIVE: In large scale industries manufacturing

generators, “QUALITY” plays a vital role. If the quality of the generator manufactured is not maintained properly, then it may lead to heavy losses. The losses may be either in terms of economy or in terms of the power generation.

To manufacture a quality generator, an industry requires sophisticated technology and the proper insulation for the generator, since insulation is the heart of the generator. So, the latest technology for insulation adopted by BHEL (HYD) unit is “VACUUM PRESSURE IMPREGNATION” which is of resin poor thermosetting type.

This type is preferred as it is highly reliable and processes good mechanical, thermal properties and dielectric strength. As the quantity of the resin used is less, the over all cost of insulation is reduced.

INTRODUCTION:Maximum percentage of total power generation is

obtained by conventional power plant. Of these steam, diesel & gas turbine power plant are high speed systems & here always three phase alternator are only used.

In such alternators, insulation plays a vital role of these insulation types, resin poor thermosetting types of (VPI) insulation is preferred as its life period is above 500 years & as its posses good mechanical , thermal properties & dielectric strength as the quantity of resin (the insulating material ) used here is less , so the overall cost of insulation is reduced .

MAIN PARTS IN A SYNCHRONOUS-GENERATOR: STATOR,ROTOR,EXCITATION SYSTEM,COOLING SYSTEM, INSULATION SYSTEM, BEARINGS.

WHAT IS INSULATION?

Insulation is the heart for electrical machines.

Insulation is the property which has enormous resistance to the conductivity .

PROPERTIES: 1. ELECTRICAL PROPERTIES

2. MECHANICAL PROPERTIES 3. THERMAL PROPERTIES4. CHEMICAL PROPERTIES

VACCUM PRESSURE IMPREGNATION:

Dr. MEYER brought the VPI system with the collaboration of WESTING HOUSE In the year 1956.

CHARACTERISTICS:

Low dielectric loss resulting in increased life of insulation and so the machine.

High resistance against the effect of moisture.

Reduction of time cycle of insulation.

Better penetration into minute air gaps in between laminations .

RESIN MANAGEMENT:The resin tank contains the mixture of resin +

Hardener + catalyst for good insulation system.

The chemical name of resin is BISPHENOL-A . it is also called as Diphenol propane.

Hardner is used to solidify the resin. Hardner used in chemical Compositions is ANHYDRIDE is nothing but removal of water molecule (H2o) from a compound.

Catalyst is used to accelerate the rate of chemical reaction among resin and hardener. The Catalyst used in the process is ZINC NAPTHENE.

QUALITY CHECKS ON RESIN MIXTURE IN RESIN POOR PROCESS:

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

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

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

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.

RESIN POOR Vs RESIN RICH:

The insulation tape used in resin poor system has 8% of resin, where as resin rich system has 40% resin.

Here time cycle is reduced compared to resin rich.

Further addition of resin is required from outside

VACCUM PRESSURE IMPREGNATION INSULATION PROCESS:STEPS INVOLVED IN VPI

PROCESS: PREHEATING VACUUM CYCLE DROP TEST HEATING THE RESIN ADMISSION OF RESIN IN TO TANK PRESSURE CYCLE POST CURING COATING THE JOB PERFORMANCE TESTS.

PREHEATING THE JOB:

PREHEATING CHAMBER

The completed stator is placed in impregnation vessel and kept in an oven for a period of 12 hours at a temperature of 60c.

The preheated job next will be placed in the impregnation chamber by a hydraulic mechanism.

Hydraulic lift

VACCUM CYCLE:Vacuum is created so that the dust and the moisture are removed from the job if any. The total stator is subjected for vacuum cycle. After obtaining 0.2 millibar, the total stator is subjected for 9 hours, then vacuum drop test is conducted.

DROP TEST:In this test all the vacuum pumps are stopped and the vacuum drop is checked. Drop should not be greater than 0.06mbar.

PRESSURISATION OF JOB:

RESIN PUMPING BACK TO THE RESIN TANK:

POST CURING:

RESIN HEATING--RESIN INLET:

IMPREGNATION PLANT:Horizontal Chamber dimensions:

Vertical Dimensions:

IMPREGNATION MEDIUM:Epoxy resin : solvent tree class F/Araldite MY-790Hardener : BD 1102Operating Pressure : 6Bars NitrogenTemperature : 90cResin storage capacity : 5x 9000 Liters.Charge Weight : 120T.

Curing Oven:Temperature : 140 to 170cHeating Medium : Circulating hot airMax weight : 120T.

Inner diameter : 4000mmLength : 9000mm

Inner diameter : 1600mmLength : 3080mm

TESTING PERFORMANCE OF RESIN POOR SYSTEM:

BEFORE IMPREGNATION FOLLOWING TESTS ARE CARRIED OUT:

1. BOTTOM LAYER TEST2. TOP LAYER TEST3. INTER CONNECTION CHECKING4. A.C HIGH VOLTAGE TEST5. MECHANICAL RUN TEST

AFTER IMPREGNATION FOLLOWING TESTS ARE CARRIED OUT:

1.TAN TEST.2. HIGH VOLTAGE Tests.

ADVANTAGES OF RESIN POOR INSULATION:It has got better dielectric strength. Heat transfer coefficient is much better.Maintenance free.The cost is less and it is the latest technology.Reduction in time cycle and consumption MW is also less and it gives high quality & good life for insulation.

DISADVANTAGES OF RESIN POOR INSULATION:Dependability for basic insulation materials on foreign countries.If any short circuit is noticed, the repairing process is difficult.

APPLICATIONS:All very high rating generators, with rugged usage, i.e., generally in power plants.(100MW-150MW)

Equipment exposed to frequent surges, like terminal equipments.

Harsh or moist environment.

.

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.

View of a VPI , 125 MW Generator

THANK-YOU