VFD Not Ramping to Full Set Speed 1

[Sheperd]

I have a Power Flex 70 VFD which is controlling the speed of a crusher motor. We increase the speed or reduce it depending on the production demand. This speed is manually set in HZ between 30 to 42HZ. After the mechanical feeder was replaced, we started experiencing problems of under speeds and then overload trips. We replaced the mechanical feeder with the one which was running on another section without a VFD, but the problem didn't go away. The VFD will sometimes accelerates to 30HZ whilst the set speed is 40HZ - then decelerates to 10HZ, it will stay there at 10HZ showing current limit alarm and then it will trip with overload.
When you bypass the VFD and run the feeder motor Direct On Line, the motor will run and there will be no trips on the E3 motor protection relay.
We do have an overload relay to protect the motor but most of the time you find it not tripped while the VFD is showing overload trip, that is if the VFD is not bypassed.
We only use the VFD to increase/reduce motor speed when we want to, not to use it as a motor protection unit. We already have a overload relay for that.
We are using Polly V-belts to couple the motor to the mechanical feeder,so most of the time when these trips happens, the V-belts are loosened - then the VFD will ramp up to full set speed. The tension on these V- belts are now loose that even at 42HZ, the feed rate will be still low. So we increased the speed to 47HZ, which is almost the maximum speed of our motor(50HZ). There is too much slip now between the V-belts and the motor pulley, due to this, we are loosing V-belts very often than before. My mechanical team members are not coming to the party in assisting on what is wrong mechanically, the question they are asking me which i can't also provide the answer at the moment is; Is there any means of making sure that the VFD doesn't trip because all we need from it is to ramp up to the set speed leaving the motor protection to the independent electronic overload relay?

 

[waross]

Is the problem VFD on the feeder or on the main crusher motor?
Does the VFD setup match the motor that it is driving?
If the mechanical team members are trying to control speed by intentionally letting the belts slip you may be fortunate that they;
"are not coming to the party".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LittleInch]

It is noticeable here that you're not mentioning anywhere electrical or mechanical power or torque required between motor and crusher.

From the basic info the phrase "After the mechanical feeder was replaced.." would seem to be a good start point.

If it works ok when VFD is bypassed at 50 htz then it would seem that there is now a mis match between motor power and torque and your different mechanical feeder.

torque available at 30 htz will be a lot lower than 50. Is the power required variable by speed to the same extent??



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[itsmoked]

Why Are you not correctly using the VFD's internal protection? Interrupting the VFD's output while it is under a load is asking for VFD damage and may be what started the problem.

Have you gone thru all the VFD parameters and made sure none have changed to something unworkable?

Have you set the display to show delivered torque or current to see what's happening?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

If the drive is going intocurtent limit, it has given you a choice in programming of how it responds to that: trip or reduce speed. You have obviously chosen to have it reduce speed, during which it will override your commanded speed; current limit takes priority. That is the only thing it can do to limit the current by the way, there is no magic sauce involved. When it does that, the current seen by an external OL relay is now artificially no longer tied to the running overload condition so it will not trip. But the drive will still be tracking the actual heat being produced in the motor and may trip regardless of the OL relay, because there are multiple types of OL in a VFD circuit.

So why is your drive having to go into current limit? The usual suspect is simply there is more load on the motor than the drive can make it deliver. That could be mechanical and usually is, but it could also be electrical in that if you have a high resistance phase to phase short in the motor, the drive will go into current limit to prenent that current from tripping, but the current flowing into the fault is not producing torque, so you have a situation where the drive avoids tripping, but essentially allows a fault to continue when it should not. Another drive related possibility is that if you changed the motor in the process, but failed to do the Autotune procedure on it, the drive will not run that motor correctly if using Sensorless Vector Control.

The fact that you seem to indicate that the machine runs fine when not on the VFD might be explained by the fact that the higher current is not so high so as to trip the OL relay quickly, but may have had you let it continue.

Bottom line, you have a lot more investigating to do.




"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[ScottyUK]

The feeder motor is correctly configured for the VFD and has been tuned to it, hasn't it? Obviously check the really basic stuff too, like ensuring the motor windings are in the correct connection - star (wye) or delta - for the available voltage.

 

[Compositepro]

What kind of crusher is it? I have a hard times seeing any benefit to slowing down a crusher. Crushers have very erratic loading with high peak loads. The peaks are handled by the inertia of the crusher not by the motor. A crusher operating at full speed but no feed will have no load and therefore will use relatively little energy. The feed rate controls the average load on the motor.

 

[jraef]

What kind of crusher is it? I have a hard times seeing any benefit to slowing down a crusher. Crushers have very erratic loading with high peak loads. The peaks are handled by the inertia of the crusher not by the motor. A crusher operating at full speed but no feed will have no load and therefore will use relatively little energy. The feed rate controls the average load on the motor.

Yeah, Bill (Waross) questioned that too; typically the VFD is used on the in-feed conveyor TO the crusher, but the way this was worded, it's hard to tell what he is doing.

That said (and as an aside), Vertical Shaft Impactor (VSI) crushers are sometimes used with VFDs because the velocity of the material being flung against the skirts will change the final product size. VSIs were notorious for always "making sand out of stones" whether you wanted it or not. Slowing them down with VFDs allows users to increase the volume of larger product or adjust to varying hardness of raw materials at mobile sites. But you're absolutely right if it is a hammer mill, jaw crushers, gryratory crusher or horizontal impactor, changing the speed is not a good idea.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Sheperd]

Thank you all for your input to my problem, the VFD is actually on the Feeder, not the crusher(my mistake).

I have attached the parameters from the VFD, the motor parameters are as they are set in the VFD parameters.

I made some modifications temporarily on the Acceleration time from 10s to 20s; On current limit value, i did change it from 44 to 60Amps and then Current limit gain from 250 to 100. I only had one overload trip after changing these settings before they stopped the plant for maintenance until Friday. The mechanical team have a number of issues which were recommended for them to iron out till Friday before start up.
On my side, i just want to make sure i have all the necessary knowledge about this VFD before startup of the plant.

So if there is any more suggestions from anyone, i am all ears. Thank you in advance.

 

[itsmoked]

Good to hear. It would be more useful if you coughed up that xlsx file as a PDF. I and others will not be able to see it otherwise.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Keith. OpenOffice.org opened that file as a Calc file. Try Excel or similar.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

OK, first thing I would do is to change parameter 053 back to a "0" for "Sensrls Vect” (Sensorless Vector Control). For this application, that's what you want. When you do that though, you must then perform an "Autotune" procedure. For right now, you could just do what's called a "Static Tune", meaning you can leave the motor connected to the load and it will NOT turn the motor when it tunes to it. You get better performance if you can uncouple the load and do a "Rotating Tune", but only go to that if you think the Static Tune doesn't cut it for you. Given that it's almost working with your custom V/Hz mode, I think a static tune with SVC will do it for you.

So the Autotune procedure is done in parameter 061, change it to a "1" and when you hit Enter, it will start the autotune procedure, then when 061 reads 0 again, it's done. After you do that, you should set 062 (IR Drop), there is a brief description on what yo set it at for your motor in the manual section for that parameter.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[itsmoked]

That did work Bill. T'was still a PITA but it worked. Thanks.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mikekilroy]

Shepard, Jraef explained why your speed is lower than commanded. You explained that you see overloads. You explained you increase current limit somewhere from 40 to 60 amps and it helped. You said across the line it runs [because that allows extra overloading that the vfd prevents. All 4 of these facts clearly show you are overloading the motor.

So back to the problem. You had a system that used to work, then some mechanical stuff was done and now it it overloaded. See the issue? Either you get the mechanical folks to fix the overload or buy larger motor and vfd.

YOUR job is to learn how to find the output current display on your vfd. Record it. Then compare it to your motor current rating. Simple as that. With these two values, you take them to the mechanical dudes who did the 'change' and show them how much they overloaded the motor and tell them to fix their mistake, or tell you how much more power they now require due to their 'improvements.'

To have us help you specifically, you need to give us the nameplate motor data and the vfd part number and current ratings. with that, we can show you why your motor is no longer capable of running commanded speed, or shuts down vfd on overload.

Like itsmoked, my openoffice refuses to open your file, so I have no clue what parameters you have, changed whatever. If this was a paying job, I would find a way to read your file, but, sorry, it is not. I agree that pdf format is your friend.

http://www.KilroyWasHere<dot>com

 

[waross]

Did the mechanical guys change any pulleys on the drive system?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Sheperd]

After the mechanical problems were sorted mechanically, we never had a single trip from the VFD as was happening before the mechanical problems were fixed. After checking and trying all the ideas i got from all your suggestions, I could confidently challenge the mechanical engineers knowing very well that there were no issues with the VFD. I managed to do this because of all the ideas you guys empowered me with.
Sorry for late feedback, wanted to be 120% sure.
Thanks again

 

[jraef]

Thanks for the feedback on our feedback

But please refrain from thanking us for the feedback on thanking us for the feedback... this could get ridiculous!


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington