WTD Test Report

Modern 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.

Wedge Tightness Detector - Set up

Loose wedges lead to vibration and erosion of insulation in generators. These serious problems can cause  electrical failure. The WTD acts as a 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 presented on a computer in the form of numeric values and a color-coded tightness map

The Color-coded map makes it easy to identify suspect area. Details are provided in a numeric tightness report.

WTD Test Report Format

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

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  and listening 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.


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


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.