generator commissioning

7/31/2019 Generator Commissioning

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Generator

Commissioning

- SUBODH KUMAR


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GENERAL INSPECTION AND CHECKS

Ensure that erection work of the

Generator and associated equipments are

completed in all respect.

Check that no part of Generator, Exciter,

Bus-duct, CT, PT, Terminal Bushings,

Marshalling Boxes, equipment is damaged.

Ensure safe and satisfactory access to the

equipments.


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Ensure fire protection system is

adequate.

Check that painting work is satisfactory.

Check that Name Plate Details areavailable, labeling and identification is

permanent and satisfactory.

Check that permanent and adequate

lighting arrangements are made.


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Carefully examine the Generator Stator

core, winding, Rotor body, slip-ringsand all other associated equipment forany kind of abnormality, dents, or any

physical damage.

Ensure the quality certificate andfactory inspection and test reports areavailable.


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Ensure that all the RTDs installed are

functioning properly.


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TESTING OF GENERATOR

Laboratory tests and

Field tests to evaluate theinsulation condition of statorwindings of generator.


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Laboratory tests

Laboratory tests have two functions:

The first function is to evaluate thequality of coil manufacturing to ensure

that your machine can achieveexpected service lifetime.

The second function is to examine

any faults and defects of your statorcoils to prevent catastrophic machinefailures.


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Field tests

Field tests provide diagnostic tests andcondition assessment of machine

insulation at your plant to help you todetermine maintenance requirements toreduce maintenance cost.


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Laboratory Diagnostic

Tests of Stator WindingInsulation


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Laboratory tests include:

Voltage Endurance test Thermal Cycling Dissection of Coils

Insulation Failure Analysis Partial Discharge test Dissipation Factor Turn-to-Turn Multi-Factor Stress Forensic Analysis


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voltage endurance test

A voltage endurance test is an acceleratedinsulation-aging test. The test is performedon stator bars or coils at much higher thannormal operation stress levels within a shortperiod of time to simulate insulation agingduring machine operation.

The test can predict the performance of theoverall insulation system and measure the

manufacturing quality. A number of diagnostic tests on stator

insulation can be conducted before and aftera voltage endurance test.


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voltage endurance test Manufacturers of stator insulation could

change its design, type of materials, andthe manufacturing process.

The voltage endurance test can be done atthe prototype and production stage toensure the quality consistency duringmanufacturing. The test gives objectiveassessment of the quality of stator insulation.

If coils fail the test, a remedial action may betaken by the manufacturer to improve thequality of coil manufacturing.


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voltage endurance test

Voltage endurance tests can be applied toboth new coils and spare coils to check

the quality and performance of theinsulation system. Spare coils have beenstored for a long period of time and need

to be tested to check their performance.


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A set-up of the voltageendurance testing


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Insulation failure during a voltageendurance test at 280 hours


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Thermal Cycling Tests and

Multi-Factor Tests Large motors are exposed to

frequent start/stop operations.

Pumped-storage generators andhydro-generators have frequent loadchanges. All of those operations

cause rapid heating and cooling, i.e.thermal cycling effect on statorinsulation.


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Thermal cycling cancause

1. Loss of bond between copper andinsulation;

2. De-lamination and degradation ofground-wall insulation;

3. Insulation failure.


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A set-up of thermal cycling testing onstator windings


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To assess the insulation performanceunder thermal cycling stress as themachine experiences in service, weperform thermal cycling tests on statorbars and coils according to IEEE

Standard 1310 -1996 and IECstandards.

The test insulation system is heatedand cooled at a prescribed rate for a

number of cycles (e.g. 500 cycles). Anumber of diagnostic tests on statorinsulation can be performed during

thermal cycling testing.


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When a generator or motor is

operating, a stator bar or coil is subjectto electrical, mechanical, and thermalstresses simultaneously. Stator winding

have to test under multifactor(electrical, mechanical, and thermalstresses) stress aging simultaneously tosimulate normal service conditions orconditions as required.


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Thermal cycling test result


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Failure Analysis

When your stator coils or bars failed

in service, you want to know whatactually caused insulation failures toprevent future failures. You may need

expert witness to prove the causes ofinsulation failures.


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Failure Analysis

Dissections of a bar or coil can determinethe quality of coil manufacturing and the

causes of insulation failures. The failedcoil or bar will be dissected and examinedunder a computer- controlled microscope.

The root causes of insulation failures areinvestigated


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Failure Analysis

The following chemical tests on theinsulation system can be also conductedfor insulation failure analysis:

Resin content analysis;

Thermo-gravimetric analysis;

Thermo-mechanical analysis;

Fourier transform infraredspectroscopy


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Insulation failure of a 13.8 kV, 44 MWhydro-generator

ac v y cause e a ove nsu a on


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ac v y cause e a ove nsu a onfailure by dissection and microscopic

examination

P i l Di h


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Partial DischargeMeasurements

Partial discharge (PD), corona inceptionmeasurements provide a non-intrusive indication ofthe void content and other problems, which may bepresent in a stator bar or a coil.

Partial discharge measurements can identify

insulation defects which could be caused byimproper impregnation, inadequate resin, voids,or poor consolidation of the insulation.

These measurements are normally undertaken at the

rated phase-to-ground voltage. PD specialists canassess insulation condition based on PD test data.


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Generator insulation damage due topartial discharge activity


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FIELD TEST


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TEST PROCEDURE

1. Generator is disconnected from the

bus duct.2. Ground all the RTD wires coming

from the Generator.

3. Carry out the IR test on the Each

Phase to Ground separately.(note

Insulation Tester used and Ambient temp. in deg C.):


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This test is performed injecting a stabilized high DCvoltage and measuring the current after 15seconds to calculate Insulation Resistance (IR).

We can perform this test between phases orbetween the 3 phases and the ground. IR highlydepends on temperature and must be corrected. Italso depends on the winding class and on thecuring state of the machine.

IR should be above a minimum value related withthe rated voltage of the generator.

The Polarization Index (PI) is the ratio between IRafter 10 and after 1. As a ratio, it is almost no

temperature dependant. The results indicateinsulation contamination, moisture, cracks orfissures in the insulation.

Standards indicate that this test should be carried

out before more aggressive tests like Hipot orSur e tests.


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D.C. winding resistance:

Carry out the D.C. winding resistance

test of the Stator Winding (each

phase separately)


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Winding Resistance (DC) [m]- The

test injects a current and measures theterminal voltage in eachphase. The resultis the pure resistance of each phase andmust be temperature corrected.

The resistance per phase should be verysimilar between them.

It gives an indication of the integrity ofthe windings and the connections,indicating shorted turns, looseconnections, wrong connections and open

circuits.


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FEILD TEST INCLUDE:

Visual Inspection test Digital ELCID

PD Data Interpretation and Analysis

Corona Probe TEST Dissipation Factor (tan delta test)

AC and DC Hi-pot test

Wedge Tightness test Core repair, if loose

Insulation Condition Assessment


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EL CID Test

Electromagnetic Core ImperfectionDetection (EL CID) is used to checkthe integrity of inter-laminar insulation

for stator cores of generators.A fault current occurring within the

laminated stator core results in a hot

spot and can cause a catastrophicfailure of a generator and motor inservice.


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An EL CID test can

detect faults and defects in the statorcore;

check effectiveness of core repairs;test the stator core before and after astator rewind to check any damagescaused by rewind;

check the quality of a new statorcore;trend the stator core condition.


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EL CID testing on 80 MW hydro-generator


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EL CID testing on a Turbo-generator


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ADVANTAGE OF ELCID TEST

In comparison with a traditional loop (ringflux) test, an EL CID test offers the followingbenefits:

Uses a portable excitation transformer

instead of a large excitation transformer in aloop test to considerably reduce testcost;Saves 30% of test time and labor cost of a

loop test.

Conducts low power testing (EL CID usesonly 4% of the rated magnetic flux) to

avoid further damage to fault areas;


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Does not have safety concerns to

test personnel;Records test data by a computer

for trending of test results.

Provides an easy and in-expensivetest method to check the quality

of a core repair or a re-wedgingoperation.


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EL CID testing requires goodknowledge of the EL CIDinstrument and stator cores togive a reliable test result.

O li / ff li PD t t d PD


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On-line/off-line PD tests and PDdata analysis;

Partial discharge (PD) testing is a recognizedtool to diagnose stator insulationdeterioration and the other related problems.

The tests can be performed under the on-line condition (when a machine is running) orthe off-line condition (when a machine isstand still).

On-line PD testing can give early warning ofpotential machine failures and providemachine condition information for predictive

maintenance.


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WHAT IS PARTIAL DISCHARGE

PD is a localized electrical discharge( spark) in an electrical system thatdoes not completely bridge the

electrode.

Partial discharge (PD) corresponds

to ionization of gas around or withinsolid insulation.


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This phenomena only occurs at

higher AC voltage (specially > 3KV).

Higher the voltage, the more

destructive the activity. PD is a leading indicator of insulation

breakdown.

OFF LINE PD MEASUREMENT


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OFF-LINE PD MEASUREMENT


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OFF LINE PD TESTINGLIMITATION

Testing does not observe loadchanges

Testing does not occur atoperating voltage.

Equipment will not be at ratedtemperature.


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ONLINE PD MEASUREMENT

The HV couplers are connected to themachine terminals to detect partial

discharges from the stator winding. A computer-controlled instrument

measures PD signals detected by the HV

couplers. PD specialist then analyzes thetest data to provide an insulationdiagnostics report .


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RFCT

l


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Coupling Capacitor


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The nature, type, region, and severityof PD activity can be identified asfollows through data analysis:

Slot discharge

De-laminations

Internal partial discharge fromvoids

Grading paint discharge

Loose windings End winding discharge

PD Corona


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PD - Corona


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PD t ki


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PD - tracking


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PD- slot Discharge


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EFECT OF PD

Rise to ozone

Nascent oxygen (strong oxidizingagent)

Power loss

Intense heat in the dischargechannel


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PD ANALYSIS

Magnitude

Number density

Polarity

Phase angle of occurrence

Quadratic rate


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WEDGE TIGHTNESS TEST

This test is done to check the tightness ofslot wedges of stator winding.

Looseness of wedge due to - shrinkage of slot packing material.

High mechanical stress

vibration


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Corona probe measurements

Corona probe testing can pinpoint partialdischarge location in each slot.

It supplements online/off-line partialdischarge tests by precisely locating partialdischarge to a particular coil or a spot.

The corona probe can also be used as a

testing tool to measure levels of PD activity.Corona probe testing can be performed eitherwith the rotor in or out of the machine.


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it is normally a requirement that the rotorsare removed from the stators so that the

electromagnetic probe can be inserted intothe stator frame. The stator winding isenergized at various voltages up to phase

voltage. The probe is moved along eachindividual slot and the levels of dischargecurrent are recorded from the peak milli

ammeter.


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Corona probe testing to pinpoint theexact location of partial discharge activity


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HI POT (DC Leakage currentmeasurement)

This test applies to the insulation a voltage for 1minute above nominal values. Maintenance testvoltage is less than the factory test voltage. Theresult is generally pass or fail. This test willinsure that the machine will supportextraordinary service conditions but because of

its aggressiveness, its usually not carried out asa predictive maintenance tool.

O ( k


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HI POT (DC Leakage currentmeasurement)

Vdc= 1.6 x (AC test voltage)

or 1.5 Vph

(d f )


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Dissipation factor (Tan-Delta) is one of the mostpowerful off-line nondestructive diagnostic toolto monitor the condition of solid insulation ofvarious high voltage equipment.

By measuring the electrical properties such as

capacitance and Tan-Delta regularly onperiodical basis, it is possible to ensure theoperational unexpected breakdown.

TAN DELTA (dissipation factor)TEST


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WHAT IS TAN DELTA

It represents Di- electric losses concept ofthe insulating material.

HV

LV

INSULATIONELECTRODES


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Perfect Insulation between the two

electrodes will act as a perfectcapacitor.

V

I

Cp


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Tan = Ir/Ic= loss angle

= phase angle

Max allowable

Tan = 0.03For new machine Ir

Ic

V

I

T d lt t d


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Tan delta measurement procedure

Suitable KVA rating transformer

Equipment should be disconnected

Kit to be grounded and test voltage israised in steps up to rated phase voltage.


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Measurement Analysis:

Change in above quantities with machineage.

Statically variation of the quantities of thesimilar machine.

CORE LOOSENESS & REPAIR


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CORE LOOSENESS & REPAIR


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TESTING ON ROTOR


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RSO TEST

AIR PURGE TEST

INSULATION RESISTANCE TEST

WINDING RESISTANCE IMPEDENCE TEST

CC BOLT AIR TIGHTNESS TEST

DPT & UT OF RETAINING RING

RSO TEST


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RSO TEST

RSO test is performed to detect faults inrotor winding.

Electrical faults in the rotor fall into twomain categories:

Fault from the winding to the rotor body (Earth fault)

Fault between parts of the windings ( Inter

turn winding faults)


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RSO TEST (SIMULATE EARTH FAULT ) ON


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RSO TEST (SIMULATE EARTH FAULT ) ON

GENERATOR ROTOR UNIT 9

RSO TEST(SIMULATE INTERTURN FAULT ) IN


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RSO TEST(SIMULATE INTERTURN FAULT ) INGENERATOR ROTOR UNIT 9

ROTOR AIR PURGE TEST


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DPT/UT of retaining ring

These test are performed tocheck the internal cracks of the

retaining ring.

CC Bolt Air Tightness test


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CC Bolt Air Tightness test


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THANK YOU

generator commissioning

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