Gen Air Tightness

7/31/2019 Gen Air Tightness

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Station: NTPC-Vindhyachal BHEL Ref No.PS-DC-186-500-0018

NTPC Ref no VIN/1/TS/2/007Sheet 1 of 12

Plant area: TURBO GENERATOR

PROCEDURE FOR GENERATOR AIR TIGHTNESS TEST

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LIST OF CONTENTS

PLANT DETAILS

OBJECTIVE

PROPOSAL

SERVICES REQUIRED

SAFETY PERECAUTIONS

EMERGENCY PROCEDURE

STATE OF THE PLANT

METHOD

COMPLETION CRITERIA

APPENDICES


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PLANT DETAILS

500 MW Generator consists of the following components.

a. STATOR

Stator Frame End Shields Stator Core Stator winding Hydrogen coolers

b. ROTOR

Rotor Shaft Rotor windings Rotor Retaining Rings Field Connections

c. BEARINGS

d. SHAFT SEALS

The two pole generator is designed with direct water cooling forthe stator winding, phase connectors and bushings and directHydrogen cooling for rotor winding. Generator losses, such asiron losses, windage losses and stray losses are also dissipatedthrough hydrogen. The generator frame is pressure resistant,gastight and equipped with major components mentioned above.The hydrogen coolers are arranged vertically inside the turbine

end stator end field.

STATUS

Signatures

NTPC BHEL


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The Generator is provided with the following auxiliaries which areessential for generator operation.

They are

Seal oil systems Gas Systems Primary Water System Excitation System

Respective Testing Schedules / O & M manuals are to bereferred for commissioning, operation and maintenance of thesesystems.

Technical Specification of Generator are given below.Generator Type THDF 115/59

Main Exciter Type ELR 70/90 30/6-20

Pilot Exciter Type ELP 50/42-30/16

Generator Apparent Power 588 MVA

Generator Active Power 500 MW

Current 16.166 KA

Voltage 21KV + 1.05KV

Speed 3000 RPM

Frequency 50HZ

Power Factor 0.85 (Lag)

Hydrogen Pressure 3.5 barRated Field Voltage 340 V

Rated Field Current 4040 A

STATUS

Signatures

NTPC BHEL


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OBJECTIVE

The objective of the test is to ensure.

Gas tightness of gas pipe lines in assembled condition includingvalves and instrumentation.

Gas tightness of various joints on generator stator, terminalbushings, primary water system, hydrogen coolers etc.

Effectiveness of the seal oil system at operating pressure.

PROPOSAL

The objective will be achieved through the following proposals.

Testing of pipe between CO2 Bottle Rack and Hydrogen Unit at apressure of 4.8 bar of Nitrogen gas for 2 Hrs.

STATUS

Signatures

NTPC BHEL


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Testing of pipe between Hydrogen Bottle rack and Hydrogen Unitat a pressure of 4.8 bar of Nitrogen gas for 2 Hrs.

Testing of Pipe between Nitrogen Bottle rack and P.W. Tank at apressure of 5.0 bar of Nitrogen gas for 2 Hrs.

Leakage Test of Generator along with Gas System using air at4.0 bar for 72 Hrs

SERVICES REQUIRED

Availability of Instrument air

Availability of Nitrogen gas

Availability of

Test pressure gauge of range 0-6 KSC with least scaledivision of 0.01 KSC

Mercury Manometer with mm scale Generator winding Temp Indicator/Recorder in UCB. Water U Manometer

Availability of man power with required tools

Availability of lighting/communication

Availability of Soap Solution for test.

SAFETY PRECAUTIONS

Debris in the test area cleared.

Approach/Stair Case/Platforms wherever required are madeavailable.

STATUS

Signatures

NTPC BHEL


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Display of board No cutting/welding at all floors made

Portable fire extinguishers are available in the test area.

EMERGENCY PROCEDURES

The test team should be well aware of procedures to be adoptedin case of any abnormality in the activity.

The test team should know well about the procedures to beadopted in case of damage to machinery or injury to personnelconnected to the activity.

STATE OF THE PLANT

Assembly of generator and fixing of end shields and manholecovers completed.

Seal oil system commissioned and put into operation forcontinuous running.

Assembly of gas system piping is completed.

Generator terminal bushings are connected.

H2 gas coolers not be charged with water.

Stator winding filled with primary water and primary water tankkept pressure less. All the valves closed in P.W. System.Connect a U Tube manometer in Waste gas line of P.W. Tankafter valve MKF91 AA 505 and close valve MKF91 AA 506. Open

valve MKF91 AA 513 and AA 505. It is also required to observefor any leakage into primary water system through statorwindings during air leakage test.

STATUS

Signatures

NTPC BHEL


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Instrument air supply connected before valve MKG25 AA 501. Airfor filling should be free from moisture, oil and any mechanicalimpurity.

Precision pressure gauge of class 0.6 for pressure measurementfixed at MKG25 CP001.

A mercury U manometer connected in one line of mechanicalpurity indicator MKG05 CP501 for air pressure measurement andfor observing the leakage rate. Other pipe line blanked andvalves MKG05 AA 501 and AA 502. Kept open.

Soap solution kept ready to check the leakages during test.

All the instruments in gas system are mounted as per scheme.

All the valves provided in H2 Unit are kept open so that all thelines are pressurized during air filling. All valves connected tovents are kept closed.

Valves provided in Generator oil drain lines are opened as

follows: (Liquid detector rack)

MKA 21 AA 501, MKA 22 AA 501, MKA 23 AA 501, MKA 24 AA501, MKA 23 AA 511, MKA 24 AA 511.

Vent valves provided in oil drain lines are closed viz., MKA21 AA502, MKA 22 AA 502, MKA 23 AA 502, MKA 23 AA 512, MKA 24AA 502.

Valves provided in gas impulse line for valve A1, A2 in seal Oilsystem are opened.

STATUS

Signatures

NTPC BHEL


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Values MKG69 AA 504 and MKG69 AA 501 are opened to takedryers in service.

Air leakage test done in stands still condition of generator.

METHOD

Testing of Pipe between CO2 Bottle Rack and H2 Unit

Disconnect pipe lines at isolating flanges Nos. 96 and 97. Keepvalve MKG 59 AA 507 open. Blank one end of this pipe line by atemporary flange. Pressurize the pipe line by N2 gas to a Pr. Of4.8 bar and observe the leakage rate for 2 hrs. There should notbe any pressure drop. (Subject to temperature conditionremaining same).

Connect back the pipe lines on system after successfulcompletion of test.

Testing of Pipe between H2 Bottle Rack and H2 Unit.

Disconnect pipe lines at isolating flange Nos. 94 and 95. Blankone end of this pipe line by a temporary flange. Pressurise thispipe by N2 gas to a pressure of 4.8 bar. Observe the leakage ratefor 2 Hrs. There should not be any pressure drop in pipe line.Check for any leakage during this period by means of soapsolution at all welding joints and rectify any leakage. Connectback the pipe lines in system after successful completion of test.

STATUS

Signatures

NTPC BHEL


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Testing of Pipe Between N2 Bottle Rack and P.W. Tank

Disconnect pipe lines at isolating flange No. 312 and primarywater tank. Blank one end of this pipe line by a temporary flange.Keep valve (MKP91 AA 502 open. Pressurise this pipe by N2 gasto a Pr. Of 5 bar. Observe the leakage rate for 2 Hrs. Thereshould not be any pressure drop in pipe line. Check for anyleakage during this test by means of soap solution at all weld

joints and rectify any leakage. Connect back the pipe lines insystem after successful completion of test.

Leakage Test of Generator along with Gas System using Air.

Air Filling in Generator Casing

Open valve MKG25 AA 501 and fill air in generator and gaspiping upto pressure of 4 Bar. During filling observe theperformance of pressure regulating valve of seal oil system andmaintain the H2 and air side seal oil Pressure as recommended.Close valve MKG25 AA 501 as soon as pressure in the casingreaches 4 bar.

Checks during Air Leakage Test

During the air leakage test, apply Soap Solution at all joints forchecking leakages in following areas:

Joint and bolt heads on Stator body

Weld joints on generator body

Joints of terminal bushings, manhole covers, H2 coolers

etc. Gas piping welding joints and flanged joints.

STATUS

Signatures

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Passing of valves in the system to atmosphere andpassing through valve glands.

Gas drier shell.

Seal oil Tank Flanged joints.

Impulse line connection for pressure regulating valve inseal oil system

Connecting joints of all measuring instruments provided ingas system.

Passing of valves provided in oil/water detector lines.

Sealing joints provided for taking out the stator windingTemp. terminals.

If any leakage is observed the generator should be depressurisedand same should be attended and test should be repeated.

Record half hourly reading on the mercury manometer providedin H2 unit for this test. Record ambient and generator temperatureas measured from RTDs.

STATUS

Signatures

NTPC BHEL


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IV

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Observe for any pressure rise in P.W. tank during test by meansof Water U manometer provided for this purpose. If any increaseis observed, stator winding system should be checked forleakage.

Continue the test till the rate is well within specified limit. If noleakage is observed, pressure drop should be checked for 72 hrs.continuously.

Calculation of Leakage Rate

Loss of air is determined as follows:

V 0.2694x24 VG (P1+Pb1 - P2 +Pb2)

Z 273+T1 273 + T2

Where V = Loss of air in M3 at N.T.P./ 24 Hrs.

0.2694 = 273o K / 1013.25 m bar

Z = Duration of leakage test, Hrs.

VG = Generator volume, m3

P1 = Gauge Pressure within the system at beginning ofleakage test, in m bar.

P2 = Gauge Pressure within the system at the end ofleakage test, in m bar.

STATUS

Signatures

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Pb1 = Barometer reading at beginning of leakage test, in mbar.

Pb2 = Barometer reading at the end of leakage test m bar.

T1 = Temperature of the gaseous atmosphere at beginningof leakage test 0C.

T2 = Temp. of the gaseous atmosphere at end of leakageTest 0C.

COMPLETION CRITERIA

Leakage test should be carried out for 72 hrs at 4 bar andaverage air loss should be calculated. The permissible air loss fora gas tight system is below 2.4m3 at N.T.P. / 24 Hrs.

If air loss is higher, checks should be carried out for detecting theleakage areas.

APPENDICES

The following system drawings to be referred from O & M manual

Gas System

P.W. System

Seal Oil System

Generator Instrumentation Scheme

Waste Fluid System

Waste Gas System

STATUS

Signatures

NTPC BHEL


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PROCEDURE FOR GENERATOR AIRTIGHTNESS TEST

Documents

Gen Air Tightness