Detaermining the Rotation Direction of generators

[petronila]

Dear All,

We are repairing many wind generators some are Induction type and other are Wound Rotor and Synchronous.

Due to are large generarors, sometimes we can´t start up this machines in our shop, but we have to check the rotation direction.

We are interested in to know a good procedure to determine this rotation direction for each geneartor type: Induction, WRIM and Synchronous avoiding the three phase powering.

Thanks in advance


Carlos

 

[electricpete]

Standard phase rotation meter won't work for large machines because it requires rapid acceleration of the machine .

oscilloscope while slowly rotating (consider effect on bearings) should work.
thread237-265331

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[electricpete]

By the way, the voltage comes from residual magnesium of rotor iron. Should work for any of those types if machines

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[electricpete]

Above is very quick and ready if machine is assembled and you can slowly manually rotate it.

If rotor is removed, I'm sure you could do the job with dc supply and compass.

It has also been discussed here that you can put soda can or ball bearings in the stator bore while energized from reduced voltage 3phase.....but I'm not positive that gives a reliable test...maybe rewinders can comment

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[electricpete]

Attached is an updated (more words, more details, hopefully more understandable) version of the attachment describing rotation check while manually rotating.

updated from the version previously posted here:
thread237-219513


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[eeprom]

I have never worked on large wind machines, so this may not be a good suggestion. But is there a way to bump the motor. I know this would be a ton of inrush current. But 1/2 second energized would show the direction.

 

[LiteYear]

electricpete, great write up. While I realise the document's contents aren't original, I think it necessary to highlight the danger of the suggested oscilloscope connection:

Many oscilloscopes and practically all mains powered oscilloscopes will internally connect the -ve terminal of each probe input to chassis earth. One consequence is that all -ve terminals are shorted together. Connecting the -ve terminal of two probes to a different point in the circuit (as shown in the attachment diagrams) will give incorrect results and most likely blow something up.

As the procedure states, the Fluke 199B has independently floating isolated inputs, so the method will work with that device.

Do not assume that any other oscilloscope is similarly isolated! I'd even go as far as to recommend you don't get in the habit of connecting probes in this fashion

 

[electricpete]

While I realise the document's contents aren't original,

You realise wrong. The writeup is completely original. The idea originally was suggested to me from Gunnar. I did the rest. Others may have certainly independently independently developed this practice, but fwiw I haven't heard of that. It was discussed at a roundtable discussion in EPRI Large Electric Motor User's Group, and it was new to everyone else there. It has proved quite useful to our plant.

Many oscilloscopes and practically all mains powered oscilloscopes will internally connect the -ve terminal of each probe input to chassis earth. One consequence is that all -ve terminals are shorted together.

I agree plug-in powered oscilloscopes are more likely to have channels which share a common. Battery powered do not have common channels in my experience. I see you noticed that I identified the specific model in the writeup. It goes without saying that anyone who chooses different model should obviously review suitability for the purpose. (If you have three channels with common reference, you can certainly reference each channel to ground).

Connecting the -ve terminal of two probes to a different point in the circuit (as shown in the attachment diagrams) will give incorrect results and most likely blow something up.

I did not and do not recommend anyone to hook up equipment to short out a voltage. But you will note that we're measuring voltage from residual magnetism of rotor being spun manually. On the machines I have worked with it is around 100 millivolts and winding resistance is around 100 milliohms. So, on the academic question of what happens if you try it, personally I would not predict that would "most likely blow up". But hey, if dramatic is your goal, you've accomplished it.

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[electricpete]

In case it was missed, let me quote directly from the document that I posted:

Equipment: Fluke 199B 2-channel Scopemeter or equivalent isolated-channel instrument. (Almost any modern battery-powered oscilloscope has isolated channels).

I'm not sure how it could have been more plain.



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[electricpete]

Your intention was just to make sure a safety aspect was highlighted.

I gather you felt so strongly about it that you needed to use bold font with exclamation points (the forum equivalent of screaming), and vivid imagery (talking about blowing things up).

If that’s what you felt was needed to get your point across, I’m sure you had the best of intentions. I hope you can also understand why it did not come across well on my end. My apologies if my response seems out of line.

I hope you will continue to contribute on the subject of motors and safety and whatever else you feel is important.


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[MiketheEngineer]

If you are repairing them - THEN you better KNOW what you are doing??!!!

Why do I sense a problem here??

 

[electricpete]

Carlos has been on the forum quite awhile and I don't have any reservations about his knowledge of motor repair .

I'm sure he has some some ideas but looking at all the options. Inm pretty sure he could trace the connection end winding connections. But they are not always accessible and it can be a tedious error_prone task for anyone.

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[electricpete]

regarding inaccessible I should add: tracing t leads from term box to end winding is not always possible.

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[LiteYear]

Sorry to offend you electricpete. The write-up is really valuable. There's nothing wrong with the procedure. My concern was with misapplication of it by someone else, not with your approach. Please don't take it personally.

I've blown plenty of things up (mostly fuses, fortunately) because I hadn't realised something had been shorted through a CRO. If you've helped someone determine rotation direction and I've helped them avoid a potential complication then all is well. If I haven't, then so be it. In any case, I'm sorry to offend and will take it on board that I may have done so with my manner.

 

[petronila]

Hello MikeTheEngineer,

Thanks for taking part of our forum, we are always open to help anyone and we do it with pleasure,also we are able to be helped too.

Like Pete sayds the most of us have experience but sometimes we need a hand in order to choose the right way,thanks Pete for your important and unvaluable support.

Mike, all opinions and criticims are wellcome, however we prefer the ideas that add and constructive criticism. Always you need soemthing, if case of you need, we will be open to gives you our opinions.

Regards

Carlos

 

[MiketheEngineer]

While I do agree - and I am not an ELECTRICAL - your question begged some concern on my part!!

It seemed as basic as asking me to select a simple I-beam - at least to me.

Sorry if I offended.. but we do get crack-pots and students on here all the time!!

 

[petronila]

Hello Mike,

No problem, thanks for the apologize.

Regards,

Carlos