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WTD Test ReportModern Electronic Wedge Tightness Detector – (Model WTD 501™)

THE ADVANCED WAY TO TEST WEDGE TIGHTNESS

Stator wedges are traditionally tested for tightness by tapping them with a hammer and listening to the sound produced. This method is slow and prone to

inconsistency. Electronic wedge tightness evaluation is faster, more accurate and provides more consistent results. The WTD Model 501 can be used to test all type of

generators and motor stator wedges, including those with ripple springs.

Loose wedges lead to vibration and erosion of insulation in generators.These serious problems can cause electrical failure. The WTD acts asa sophisticated electronic ear that quickly and reliably provides an electronic map of wedge tightness.

A hand-held probe automatically taps and measures each wedge

approximately 30 times in three seconds. An accelerometer gathers the

data and transmits it to the WTD-501 instrument. Results are presentedon a computer in the form of numeric values and a color-codedtightness map

The Color-coded map makes it easy to identify suspect area. Details are

provided in a numeric tightness report.

A MODERN AND OBJECTIVE TEST OF STATOR CORE WEDGES

Makes sound maintenance decisions based upon Accurate, reliable and consistent results of WTD data

Used for all rotating machinery, including wedging systems with ripple springs

Repeatable, objective, numeric test data removes subjectivity of hand tapping methods

Fast, easy wedge tightness testing

Permanent record of test data

Easy report generation and analyzing

TURBO GENERATOR SLOT WINDING WEDGE TIGHTNESS TEST

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Slot windings of a nuclear power plant turbo generator tested efficiently under maintenance conditions and the details of turbo generator are given as under:

Power Plant Detail:

Plant: Nuclear Power Plant

Machine: Turbo Generator

Model: TGV -250-2PT-3

Rating: 242 MW

Voltage: 16.5 KV

Full load Current: 9992 A

Power Factor: .85

RPM: 3000 rpm

Connection: Star

Cooling: Water Hydrogen

No. of Slot: 30

No. of Wedges / slot: 24

HAMMER TEST REPORT:

The maintenance department of the plant had performed the “Wedge Tightness Test” on turbo generator by traditional method (of tapping the hammer and listening

to the sound produced) many times as it is the most recognized technique in India at present.

But this method being slow, doubtful & unreliable leads to many discrepancies as it is whole sole basis for testing judgment is based on the examiner’s experience and

expertise.

Earlier “Wedge tightness test” was carri ed out traditionally on turbo generator s by the maintenance department of the plant, by tapping the hammer andlistening to its sound as it is amongst the conventional process carried out in the country.

But, the reliability and accuracy level of the method not being up to the mark results for the process are entirely based upon examiner’s experience and

expertise.

In addition, Hummer test report is generated manually which is complicated and difficult to analyze. Many serious problems can arise if Wedge of the turbo

generator is left loose, may lead to vibration and erosion of the stator insulation in turbo generator and may even lead to generator failure.

Thus based on the “hammer report” the maintenance department of the power plant cannot determine whether the wedges of the generator are tight or loose.

WTD TEST RESULTS:

The test conducted by Wedge tightness detector (WTD 501) on all the wedges of Turbo generator, takes approximately an hour to complete and generate the end result.

Wedge tightness detector report is generated with ease and its color code map (different color for different levels of wedge tightness) makes it even easier for analysis.

This following chart illustrates the tightness level of stator winding wedges with the help of numeric data and color code mapping.

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This following chart illustrates the slot tightness and summary (average of all slots) in percent.

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COMPARISON OF WTD 501 TESTS AND HAMMER TEST

WTD 501 TEST HAMMER TEST

Results are much Reliable Results are not Reliable

A sound Maintenance Decision is possible Decision Making is Very difficult

Results are in numeric value Results are not in numeric value

Test takes very Less time Test takes Much time

Easy report generation No such type of report is generated

Result analysis is very easy Analysis is very difficult

Experience and Expertise not required Examiner must required experience and expertise

Conclusion:

Conclusively, loose wedges can cause serious problems in the future and in response need reliable testing of wedge tightness by WTD 501.

Therefore, to conclude we can say that WTD 501 has three different color codes which show different levels of wedge tightness and based on these Accurate, reliable and consistent results of WTD data the maintenance department can makes sound maintenance decisions which is not possible by the traditional methods of testing.

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