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71

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 24, 2022, 03:14:19 am »

Hi LH , I came across this explanation that may help.
As the frequency of the drive is reduced the voltage has to be reduced also.
So in your case your motor is rated at 460 volts at 60 hz.
That is a ratio of 7.666.
if the voltage is reduced to 400 as in your case then the frequency needs to be reduced too. that would mean the drive should be putting out 52 HZ.
The motor would then be running at 120 x 52/2  which equals 3120 RPM.
If possible back the VFD frequency back of to 52 hz and keep the voltage at 400 and see if it runs cooler and has the power and torque needed to run the compressor.
Pete

AC motor characteristics require the applied voltage to be proportionally adjusted by the VFD whenever the frequency is changed. E.g., if a motor is designed to operate at 460 Volts at 60 Hz, the applied voltage must be reduced to 230 Volts when the frequency is reduced to 30 Hz. Thus the ratio of volts per hertz must be regulated to a constant value (460/60 = 7.67 in this case). The most common method used for adjusting the motor voltage is called pulse width modulation (PWM). With PWM voltage control, the inverter switches are used to divide the simulated sine-wave output waveform into a series of narrow voltage pulses and modulate the width of the pulses.

With a standard AC across-the-line motor starter, line voltage and frequency are applied to the motor and the speed is solely dependent on the number of motor stator poles. In comparison, a VFD delivers a varying voltage and frequency to the motor, which determines its speed. The higher the frequency sup plied to the motor, the faster it will run. Power applied to the motor through the VFD can make the motor working speed lower than the nameplate base speed, or increase the speed to synchronous speed and higher. Motor manufacturers list the maximum speed at which their motors can safely be worked.

72

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 24, 2022, 02:01:08 am »

Hi LH, looks right. The nameplate does say 460 volt for delta.
Your connection looks right for Delta.
With Delta connection each phase winding has 460 volts across it.
Talk to the manufacturers and see what they say about trying it in Star.

In a Star connection you would have with the 400 volts your controller can supply a phase voltage of 230 volts.
The current would be down too so you may not get enough power but at least it would not run as hot.
See what they say, as it seems the VFD is not suited to the motor running in Delta.
good luck
Pete

73

Renewable Energy Q&A / Re: Max winding temp

« Last post by lighthunter on April 23, 2022, 08:30:54 pm »

Thanks Pete! Looks like some valuable  info to hang on to.

 This is how i hooked it up.

(1,6)--(2,4)--(3,5) doesnt the nameplate info say the 460V is for delta connection? Or am i reading that wrong?

74

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 23, 2022, 07:39:52 pm »

Hi LH , I have attached some information on terminal markings of motors and connections.
Some of them are  complicated as they are for Dual voltage, or dual speed motors.
It may come in handy though in the future
good luck
pete

75

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 23, 2022, 07:27:01 pm »

Hi LH , from what I have read the bearing sparking is caused by the spikes on the waveform fed from the VFD.
I am guessing that the sharp peaks are inducing a voltage into the rotor shaft and the only place to earth is through the bearings.
The shaft must be operating as one turn of a transformer and as such generating a current flow through the bearings.
I may be wrong but then it makes sense to me.
With a sinewave the drop off of the waveform is much more uniform so an induced voltage would be lower and less damaging to bearings.
It doesn't make much sense to me to have a VFD on a compressor. Maybe they are trying to limit starting current under load by using the VFD on startup but a Star/Delta starter or a compensator ( transformer) starter would be much simpler.
LH on the motor leads, it is very important that they are connected the right way.
If a phase were reversed then problems will happen fast.
Hopefully the leads are marked so that no one can stuff up and get the starts and finishes mixed up.
Usually European motors are marked U, V , W for the start of each winding
and U1, V1, W1 for the ends.
So delta is U and V1 connected together
                 V and W1 connected together
                 W and U1 connected together.

Star would be
Line connected to U, V, W
U1, V1, W1 connected together.

I am not sure what you mean by the terminals when you say two each and not 1 each it sounds like the leads are in parallel. Often if the lead cables are too big one would parallel them up. But then you say that 3 are bound together, that sounds like a Star point.
Can you put a photo of the terminal block and leads up.
Pete

76

Renewable Energy Q&A / Re: Max winding temp

« Last post by lighthunter on April 23, 2022, 05:57:46 pm »

Pete, youve already been way more help than the mfr reps. Seems like youre onto something. Wierd thing is, I never got to remove...disconnect this motor, others did and I was really scratching to understand how to hook it up.  I do know there are 6 leads, always were and 3 terminals, (two each and not 1 each, with 3 bound together.) Since this is VFD the wye/delta start is not needed. Im willing to listen to your experience on this cuz ive tried all i know and it works well, just generates too much heat. Makes total sense downsizing wire if he couldnt get wire in slot.

Ross, your right also, i'm guessing where this came from, chicago pneumatic, 400v might have been the likely voltage fed to vfd so wouldnt have been any more available. I did talk with rep of mfr. Of drive, danfoss, and he said it was capable of outputting 480 no problem but then encountered the locked software.  Soon i should know if they will send a guy out to change it. If not, im tempted to reload danfoss software, my hesitancy on that involves liabilities of a blown compressor. Even though i know zero chance of a voltage change causing that its just the idea of a modification. Changing a volt setting in my opinion is not changing functional design. Reloading software deleting I/O and rewiring/configuring the pressure control loop is changing design. At the time of failure a new motor did not exist even though this unit is little more than 10 yrs old. Now i really wish id have insisted on a "new motor". Yet this issue existed when it was delivered new. What Pete describes with need for insulated bearings etc fits this description exactly. Any thoughts if bearing arcing is a function of heat or not related? Ive heard of this before, even seen it but ive never understood it. Is it always a VFD that causes it? Or is it motor design? Maybe we could remove the vfd, put wye/delta contactors for startup and run it direct. Ha, here i go again wanting to change design. I better stop thinking about this 

Thanks a million guys! Your input is appreciated!

77

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 23, 2022, 05:45:53 pm »

HI Ross, I was mainly thinking of the current the motor is drawing. For it to be running so hot and to have burnt out twice already something is definitely wrong. In Star the motor would only be drawing 1.73 times less current. Whether it would have the power needed for the compressor is something that would only be found out on experimentation.

You may be right the controller may be the wrong one for that motor.
I guess the manufacturer needs to come and look.
Pete

78

Renewable Energy Q&A / Re: Max winding temp

« Last post by rossw on April 23, 2022, 05:23:39 am »

Star connected, that would explain the max 400 volts on the VFD. Long shot but worth a check.

For a given motor, I'd expect that a delta-connected motor would run on a lower voltage than the same motor star-connected.
But they're not so close as 400/480V.
I think a 480V 3phase supply would only see 277V across each coil in a star connected motor.

Isn't 400V common in Europe? Is it possible the motor and VFD were not a "pair"?

79

Renewable Energy Q&A / Re: Max winding temp

« Last post by Pete on April 22, 2022, 02:14:26 am »

Hi LH.
Siemens motors eh, the bane of my motor rewinding days. Most other motors have plenty of spare room in the slots where the windings go. So some more room for cooling, not Siemens, they fill the slots totally.
They also seem to have small frames for the HP ratings they squeeze in.VFDs create. There is mention of sparking and heating in the motor bearings and the need for insulated bearings in some cases. Sounds like it may relate to your compressor.
Also compressors being required to start under load can be a problem, if the drive is set at too low a speed or voltage the motor will not have the torque to overcome the load and will run hot.
I wonder, I helped a fellow sparky once who was having trouble with a motor on a VFD that was drawing way over the rated current. It was only a small motor but it was connected wrongly. The motor was only 1kw from memory and it was delta connected. When the drive was turned on it ran very hot, the current was way up and the VFD just shut down.
I suggested that we change the terminal connections to Star and that solved the problem.
Seems that someone changed the motor or changed the connections and it all went pear shaped from there.
Check the nameplate on the motor to make sure it is not supposed to be Star connected, that would explain the max 400 volts on the VFD. Long shot but worth a check.
Pete
Have a look at this article, it is short but mentions some of the problems
https://new.abb.com/drives/segments/motors-and-drives-in-potentially-explosive-atmospheres/effects-of-variable-speed-drives-to-motors

80

Renewable Energy Q&A / Re: Max winding temp

« Last post by lighthunter on April 21, 2022, 07:12:39 am »

Hi Pete
Ive not made much progress as yet but am hopeful the mfr. of compressor will come through soon. I emailed them about coming onsite to make the voltage change hoping they will go for that rather than giving out access to their software.

What revolutions is it running at when on 400 volts?"
At 400V 60Hz is the output frequency, as for the RPM , i dont know yet. I will try with a tach to get that number. Hopefully i can estimate load or how underpowered it is by the slip.

"may be worth adding an external fan to increase cooling"

I wish i could... fact is i dont think i could improve on it. It uses the entire enclosure for the aftercooler radiator airflow which is ducted from outside and has a centrifugal fan of something like 10HP. There is so much air flowing around that motor its crazy, i dont think i could improve on that. It literally takes effort to shut a cabinet door while on there is so much air pressure from fan.

"Siemens" you nailed it, thats the brand of this motor.

I will get an rpm measurement at various frequencies including A and V.

Thank You so much for your thoughts! I hate to give up on it seems so close. My hope is that if voltage were bumped from 400 to 480 the motor would not run high temp.