ElCid vs Loop Test On Generators?

This guy?

Yes. Everything the loop test would tell you that the other one doesn't.

Your two tests "Elcid" and "loop" do not ring any bell's in the old memory - except the Spanish hero (El Cid - movie, Charlton Heston?).

From what you write

1. "Elcid" is a low voltage & current test, cold static Machine??
2. while "loop" may be where you run the generator into a full voltage load (Grid?) at zero power factor lagging.

The second test can push stator and rotor currents to maximum rated values at rated voltage/speed and reveal excessive temperature rise or mechanical contact at full expansion, if run a long enough time. Obviously this is a more thorough test but takes more tester time, testgear and electricity.

Test 1 is a cheaper option, but is only meaningfull if you know for certain the relation of the measurement to full voltage/current tests, that is you have tested a number of similar machines at full/voltage current as well as "elcid" and can have a view based on experience.

Essentially, test 1 can tell you the iron is OK and you have about the right number of winding turns, it does not show much about rotor state (unless you can do an open & shorted rotor test and turn the rotor slowly through 360 degrees) - it would not tell if the wire was too thin or the cooling fan mounted the wrong way round! Test 2 is obviously more comprehensive.

Thanks JohnDG for the paper references - they explain the tests pretty well.

I have done loop tests on generator stators after repairs & rewedging, and it is great for spotting defects in the insulation and wedging. You can look for the defects (evident as hot spot in real time with an infrared imager. However, as the OP stated, the test is laborious to set up since you need to induce a significant loop current through the test setup. We used a 2400V contactor and HV cables fed from an aux supply to run several hundred amps through the loop. It took a day to set up, a few hours to do the test, and then the rest of the day to tear down.

I haven't used the EL-CID test method, but from what I can gather, it can only give you part of what the loop test can. It can be set up more easily and quickly, but you trade that off for less information.

In my book, if you want the better test, do the loop, but if you don't have the time and resources, do the EL-CID. I would also recommend a Doble insulation power factor test on the stator insulation, with RIV (radio interference voltage) measurements. It can point to issues with the overall stator insulation such as moisture problems, end turn issues, and general insulation deterioration.

With my experience, I would say that ELCID detects even smallest shorts which in fact may not be a hot spot if checked with loop test. Here exception would be core end packets which are stepped. normal moving prob would not cover these packets and held held probe would be used individually on each tooth of each packet. Here the accuracy may not be that good. Except for this limitation, if the results are acceptable (within acceptance norm) then loop test would not be necessary. However, if ELCID shows peaks beyond limit, then loop test is a must to see how it behaves from thermal consideration and acceptance norms for loop test would prevail.