Test result comparisons

[sngpl]

Normally the test results of a piece of equipment are compared with its previous tests and also with test results of similar equipment. Would it make sense to compare it with the same kind of equipment but with different specifications?

For example if we have a 10 MW, 13.8 kV, insulation class F, 0.8 pf etc generator and we carryout a megger tests of the stator winding. We can look at the previous test results, IEEE standards etc for seeing where the stator's insulation resistance is as compared to it self. We can even compare it with EXCATLY similar generators.

1- is it possible to compare it to other generators having different specifications?
2- does there exist a categorization of the generators being employed in the hydro industry?
3- one way could be to categorize generators into micro, mini, small, large hydro generators. Would it make any sense to get test result comparisons on this basis?
4- is there a better way of categorizing for comparisons?

To summarize: how to categorize the generators for comparison of test results?

 

[jplinn]

My experience is that comparisons between different generators is of little value. This may be due to different insulation systems and winding configurations. Comparison of test results for a single generator when normalized for temperature provide better trending. I find that a detailed visual inspection combined with testing provides the best indication of winding aging.

I determine if a windings insulation is satisfactory for continued operation by looking at the following.

1) Physical apperance of the winding and if any visual signs of deterioration are present.

2) The absolute value of the insulation resistance. (Over potential test)

3) In general what is the trend in insulation resistance.

4) Is there a single phase insulation resistance that is significantly different than the other phases.

As you can see these gages tend to limit comparisons between different machines.

The following web page has several very good articles on generator testing.

http://www.irispower.com/techpapers/

This company sells PDA systems, so they tend to make PDA the all encompasing, greatest thing to monitor generator windings. PDA is just another tool to used in conjuction with the testing your are performing now.

JPL

 

[sngpl]

thanks jplinn

But I still am interested in knowing how to divide generators into groups based on for example MW, insulation class, etc.... for comparison of test results with in that group.

I would appreciate any input in this regard.