Inverters....

[Tiny Spark]

Ok so I had a interesting "conversation" with a contractor today and I have a 2 part question ime hoping you guys can clear up for me.

So the scenario:
3 large cold air handling units each with 2 fans (415v 3 phase) fed through a speed controller, contactor and overloads.
All fans getting extremely hot and burning out.
While testing phase to phase voltages found to be varying some 110v some 300v etc.

Now theres no question in either of our minds that they are burning out because of the fluctuating voltages but we do disagree with reasonings for them.

Now in my mind the inverters will be there to change the frequency of the motors to change the speed and the flow rate of the cold air into the room.

He believes they should never be on a inverter and that its the inverter changing the voltage to change the speed causing the problem.

So 2 questions are:

1) is it possible to change the speed of a 3 phase 415v motor by changing voltage? (because i didnt think it was)

2) should ahu's of this type be fitted with a inverter at all?
(Personally i think its a good thing but the cooling engineer thinks they should be on or off)

Thanks

 

[Tiny Spark]

Thanks darkwood.

In that case when the motors are removed I will recommend they are sent away for analysis and see what Sulzer have to say about them.

Other than that guess we will have to see what happens.

 

[lewlec]

Hi

You say these motors are wired in delta..... Are these motors dual voltage? If so what are they rated? I.e 230/400

 

[Tiny Spark]

Hi

You say these motors are wired in delta..... Are these motors dual voltage? If so what are they rated? I.e 230/400

Hi, yes they are.
Not sure about the other voltage rating but the way they are set up is for 380-440

 

[Darkwood]

Hi

You say these motors are wired in delta..... Are these motors dual voltage? If so what are they rated? I.e 230/400

Facepalm!! Bloody hell i missed that line was an initial question i asked now it would explain a lot if these are duel Voltage motors 230/400 ....-Tiny take a pic or relay the motor plate readings in full if you can if as lewlec spotted you put that they are in delta you could have a set of motors connected in the wrong config unless they are 415/690 motors duel voltage.

 

[Darkwood]

Hi, yes they are.
Not sure about the other voltage rating but the way they are set up is for 380-440

This is not duel voltage this is the tolerance of the windings to function correctly at 50hz if it was duel voltage you may see

200-250 / 380-440 but would more commonly just have a fixed voltage say 230 (delta)/400(star)

 

[lewlec]

From experience, motors as small as 4 kw would be 230delta/400 star. But that's not to say that they are not available in 400delta/ 690star. I would be double checking the motor plate and maybe uploading it on here for us to have a look at.
Regards
Gary

 

[Tiny Spark]

This is not duel voltage this is the tolerance of the windings to function correctly at 50hz if it was duel voltage you may see

200-250 / 380-440 but would more commonly just have a fixed voltage say 230 (delta)/400(star)

No that was the one voltage band, Cant remember the other Voltage band but dont think it was in the 200's.
Ile have a look and take a piki tommorow if I remember.

 

[Darkwood]

No that was the one voltage band, Cant remember the other Voltage band but dont think it was in the 200's.
Ile have a look and take a piki tommorow if I remember.

If these are 230/400 motors then delta connection would explain the burning out of numerous motors as this is for 230 -3ph, star is for 400v as stated on the plate.


If these are 400/690 motors then delta is correct for 400v - if connected wrongly in star it may create torque issues and running issues that can long term damage the motor

as you are getting up to 400v at the motors we are to assume the inverters are 400v -3ph outputs and not 230v -3ph outputs.



If the motor has just one number set i.e. 380-420 then this is a 400v motor and should be connected as the plate shows.

Without trying to teach you to suck eggs i assume you know the different config's of the links over the 6 motor terminals and which give you star and which delta.... you do say this isn't your comfort zone?

 

[Tiny Spark]

Well I will double check tomorrow, I think they are dual voltage but I must say ime feeling pretty mind numbed and tired atm so I may be talking crap LOL

 

[Darkwood]

OK we will leave it here today get a pic of motor plate and terminal arrangements if possible and post cheers DW

 

[Tiny Spark]

Well you were right darkwood this thing is opening up more questions than closing off answers!!

So heres the update:
Went up to check voltage bands of the motors.
Delta: 380-420
Star: 660-720

So anyways curiosity got the better of me and I decided to check the wiring of each motors terminal blocks.

So first units motors were both wired in delta the same as the one motor I had checked before.

2nd unit first in delta (one i checked yesterday) and the second in Star!!
This is obviously a problem!

3rd unit both wired in star.

So now I am left with several questions the top of my list being who and why!!

Moral of the story and personal lesson for me:
Never assume things have been done properly!

 

[Darkwood]

The motors may be wired according to the rating of the windings they have, just because you have various connection set-ups doesn't mean they are wrong, you need to check that the star or delta connection is correct regarding the individual motor , if motors have been changed at different times and/or sourced from diferent companies it may be likely you have a mixed bag of winding ratings.

 

[Tiny Spark]

The motors may be wired according to the rating of the windings they have, just because you have various connection set-ups doesn't mean they are wrong, you need to check that the star or delta connection is correct regarding the individual motor , if motors have been changed at different times and/or sourced from diferent companies it may be likely you have a mixed bag of winding ratings.

Hi Darkwood,
No they are defo wrong according to the motor rating plates.

However I believe the reason they are wrong is because if the above reason.
I had a hunt around and found a old unit with a original motor, These were rated the total opposite of the new ones (The Delta winding was higher than the star).
So my best guess is that whoever changed them just swapped a old one for a new one without checking the rating plate and wired it the same as the original.

 

[Darkwood]

Well if they wired to the wrong voltage on the plate you have your answer and its big questions to the so called Engineer who replaced them and doesn't know the basics of his job!!! If it is as you suggest above you may score yourself some brownie points and a gold star here... a few of us did query t on page one for this very reason and now you understand why

 

[Tiny Spark]

Yep, Like I said lesson learnt there for me.
I never even thought of checking the motors terminal boxes, Its one of those things I just assumed to of been correct but well there we go.
Interestingly there was a older motor which had been replaced at some point which was also wired wrong so god knows how long that had been like that!

Still the whole thing has been of benefit to me as I have learned a little more about inverters and drives so cheers all for your input