Heat @ 0 hz.

[ptonsparky]

I'd put a reactor on the load side of the drive, especially with 480 volt system.

Also did you mention what frequency the motor typically runs at (other then the one minute no speed period occasionally)? I though you did but am not finding it. More important is does it run for long periods at low speeds, you can get away with more on fans and pumps as they are variable torque, but constant torque loads don't like the reduced cooling effects from the slower fan speed when the torque level is still high. I had to put a VFD rated motor with external cooling fan on a high pressure pump because we only were running that thing at about 30 Hz a lot of the time. Rewound a 50 Hp motor on that one 3 or 4 times, each time about a year had passed, before switching to the new motor - haven't had a failure yet and it has been there maybe close to 10 years now. Never have had a load side reactor on that one either - though the distance was probably in the 50 foot range. Think I would put one on it if I were doing it today though.

43 hz with ON time of about 8-15 minutes, OFF time of 6-12 minutes. Eight to ten cycles of ON/OFF. End of day, motor runs @ 58 hz for about 50 minutes.

 

[Jraef]

Again, what is the purpose of the 0Hz speed command? If it is just being used as a "wait state", then make sure you don't have the DC Injection Braking turned on. Typically the DCIB would be turned off when no needed to stop a load, so if it's true that your load does not really need braking, do leave that on by default. Thye usual setting is for DCIB to be triggered by a commanded speed below some level, like 10%, but it will assume that you would turn it off, not try to hold at zero Hz. So what will happen is that it will continuously inject DC current until you tell it not to. If you don't need it at all, any DCIB time is a complete waste.

Also, some low end drives don't allow you to turn the DCIB off at all, expecting, again, that you would remove the run command rather than gove it a zero speed command. What drive it is?

 

[mike_kilroy]

Also, some low end drives don't allow you to turn the DCIB off at all, expecting, again, that you would remove the run command rather than gove it a zero speed command. What drive it is?

I have to agree; too much missing information.

What is the drive? model?
Is it sensorless mode? have encoder feedback? v/hz mode?
What is happening during this 0hz command time? Overhung load?

I am ASSUMING it is
1) vector mode with encoder feedback if you dial up 0hz with enable/run command and have motor nameplate rated current
2) so an outside force trying to make it run more than 0rpm, thus the 2.x amp rated current

Again, since you run at fan cooling speed and also off both for effectively infinite time compared to this 1 minute, I do not see how it would be possible at only nameplate rated current to burn out any part of a motor in 1 minute. Yes, of course the 20 minute guestimate thermal time constant is with fan running, so without it this might drop to what? 10 minutes? Your 2hp motor has MASS. Its windings are on the outside so there is cooling to the air. I don't buy you burned up a motor doing this already - it sounded like the motor that may have burned up under your warranty was run across the line the way you wrote that post: if so, I am totally with Jraef that across the line stalled might take only 20 seconds to burn a winding; but that is not so with a vfd in series.... something else is wrong if a motor already burned up with this setup?

 

[mike_kilroy]

Why I asked, IDK.

It was faulting on overcurrent even with no load on the motor. Less than a year old so I get to eat it regardless. Connections were good in the peckerhead. Bearings good. Guessing a winding to winding fault because it did not take long to let the smoke out once I took the drive out of the equation.

I don't know what IDK means, but are you saying you had one pc of a 2hp TENV motor burn up on this VFD in less than 1 year doing the cycle you described?

 

[kwired]

Again, what is the purpose of the 0Hz speed command? If it is just being used as a "wait state", then make sure you don't have the DC Injection Braking turned on. Typically the DCIB would be turned off when no needed to stop a load, so if it's true that your load does not really need braking, do leave that on by default. Thye usual setting is for DCIB to be triggered by a commanded speed below some level, like 10%, but it will assume that you would turn it off, not try to hold at zero Hz. So what will happen is that it will continuously inject DC current until you tell it not to. If you don't need it at all, any DCIB time is a complete waste.

Also, some low end drives don't allow you to turn the DCIB off at all, expecting, again, that you would remove the run command rather than gove it a zero speed command. What drive it is?

I could see a voltage or current proportional control (0-10v or 4-20mA) as the frequency reference possibly calling for speed reference of zero based on whatever condition is being monitored to select needed motor speed, yet is still in run mode, so drive is still receiving a run command. But I thought it very well may be a case of braking current being injected - which may be needed on a load that has gravitational or other forces trying to move the load when we need to hold it in position. I don't think OP has such a situation though and needs to make sure breaking options are turned off or at least set to minimal settings if they can't be turned off.

 

[kwired]

I don't know what IDK means, but are you saying you had one pc of a 2hp TENV motor burn up on this VFD in less than 1 year doing the cycle you described?

You answered it- the IDK question

 

[mike_kilroy]

For reference, I tried to find how fast a TEFC motor will heat up or cool off if fan is not rotating. The best I found is that time constant goes to 2x nominal. So take your 20 minute thermal time constant motor; it would heat up in 10 minutes to 63% of max temp from ambient.

We have no clue what the real cycle is; there is off time, there is run time at 43hz (effectively same as at rated speed for cooling), there is 58hz run (again same as full cooling). We have no clue what the actual current is during these other cycles. Might be the issue is the motor is overloaded during THEM, not the 0hz mode? No idea. Too much missing data. If the 60 sec rated current 0 speed is directly after your 12min off time, then the actual temp we start at is lower. Too much missing info.

In any case, if I had to continue making guesses, it would be my professional guess that you have a 99.2% probability of NOT harming this motor during this 60 sec 0 speed full current rated load portion of the cycle. But to put my 100% guarantee blessing on it, I would need to know the missing data.

ref: https://www.gedigitalenergy.com/multilin/family/motors/Motor_Thermal_Model.pdf

 

[Jraef]

I don't know what IDK means, ...

LOL, IDK means I Don't Know...

 

[Electric-Light]

What happens in "AB" is minimal if you're using a VFD. This is what happens when you plug a stand still motor into full line voltage at 60 Hz.

Once you're at cruising speed, load determines the load.
Torque is load.

The acceleration time from 0 to set speed depends on how your VFD is programmed.
If it's set for current limit only, it will accelerate as fast as possible given the load.

If it's set for constant acceleration, it will trim the motor current down to accelerate no faster than set rate. If it's too heavily loaded to accelerate at the set rate, then it will trim acceleration so it stays within limit.

When a train comes to a stop, it uses regenerative braking and switch over to mechanical brakes to "hold" the car. It applies torque to unload the brakes and let go the brakes so it starts creeping forward instead of rolling down or jerking forward. You'll need quite a bit of current if you were to hold a fully loaded car still up a hill. If it's holding from rolling forward, the torque is in reverse direction. So, 0 Hz could be the transition phase.

If it was on a flat ground, the torque needed to "hold" is minimal, but if it's using DC current to lock it in place, it would be quite high.

 

[ptonsparky]

Drive is an AB PwrFlex 4

Command to 0 hz was a quick way to remove load from another motor that we monitor current on. Current level at the Monitored Motor started a shutdown sequence. Yes, power monitoring is without a doubt the better method.

My thought at the time was that 0 hz command to a motor that cannot turn either direction due to the load friction would result in no or very little current to the motor.
Wrong again. I should have looked.

Minor detail that struck me up side the head this morning. Operating characteristics of the MM load changed a couple times in the last week or so. We had been looking for current below 4.35 amps to start the shut down (after the 0 hz command). The current did not go that low so the command to 0 hz was maintained for an extended time. I do not know how long or how many times that happened but the operator noticed and manually stopped the process. Yes, they checked for bearing problems etc. It is now back at the 4.35 amps again.

In short, the normal minute or so at 0 hz could very well have been 30 minutes or longer, once a day, before the motor decided to fault at 4 AM.

The load was not locked up when the motor was faulting on OL. It could be spun with the finger tips. Wonders of gear reduction.

Normal running amps for the 2 hp motor on the VFD is about 1.7.


A 0 HZ command at the end of the day is still used, but that initiates the shutdown process instead of waiting for the MM to go undercurrent.

 

[Electric-Light]

Drive is an AB PwrFlex 4

Command to 0 hz was a quick way to remove load from another motor that we monitor current on. Current level at the Monitored Motor started a shutdown sequence. Yes, power monitoring is without a doubt the better method.

Are you saying there are multiple motors driving the same machine?
So, which motors are doing which?
Separate drives?


What I am visualizing is that you have driven rear wheels connected to one motor, and driven front wheels off of another motor. You're wanting to drive it with just the front motor and have the rear motor just roll along. What it seems to me is that by putting rear's drive to 0 Hz, you're causing brake to get applied to rear wheels in an effort to bring the system down to a stop while the other motor works hard to drive the front wheels to pull through it.

 

[mike_kilroy]

....In short, the normal minute or so at 0 hz could very well have been 30 minutes or longer, once a day, before the motor decided to fault at 4 AM.

So I stand by my suggestion that 2.x amps (motor rating) applied for 60 sec during the cycle previously listed would not harm that motor.

Now that the parameters of the cycle have radically changed, all bets are off.

Hopefully you did not sign off on this scenario: if you did, then you indeed should be on the hook to buy them replacement motors; and continue to buy more until this scenario is corrected.

 

[ptonsparky]

So I stand by my suggestion that 2.x amps (motor rating) applied for 60 sec during the cycle previously listed would not harm that motor.

Now that the parameters of the cycle have radically changed, all bets are off. Once I felt being "hit upside the head" I agree.

Hopefully you did not sign off...no signing off on this, no one else was involved on this scenario: if you did, then you indeed should be on the hook to buy them replacement motors and labor; and continue to buy more until this scenario is corrected as of two days ago.

I can not remember when I did not pay up for my screw ups. Pain is lessened if done promptly and I can understand why.

Are you saying there are multiple motors driving the same machine?
So, which motors are doing which?
Separate drives?


What I am visualizing is that you have driven rear wheels connected to one motor, and driven front wheels off of another motor. You're wanting to drive it with just the front motor and have the rear motor just roll along. What it seems to me is that by putting rear's drive to 0 Hz, you're causing brake to get applied to rear wheels in an effort to bring the system down to a stop while the other motor works hard to drive the front wheels to pull through it.

Picture a series of conveyors, one feeding product on to another, each with a separate motor and respective VFD or Starter. In Hand operation nothing is linked. In Auto, everything from Start to Stop sequence is monitored. Speed, Amps, Temperature, time of day, tons per hour.

 

[mike_kilroy]

GOOD man ptonsparky!!

Just a thought: any chance you can put this offending vfd into v/hz mode instead of vector? Seems to me then it could be commanded to 0hz any time you need to, and the output current will be 0amps, so problem solved? Assuming a little less speed control is acceptable.... but if it is simply following speed of previous conveyor at say 10% faster or slower or something, it may work well? Sometimes KISS is better?

Good luck!

 

[Jraef]

GOOD man ptonsparky!!

Just a thought: any chance you can put this offending vfd into v/hz mode instead of vector? Seems to me then it could be commanded to 0hz any time you need to, and the output current will be 0amps, so problem solved? Assuming a little less speed control is acceptable.... but if it is simply following speed of previous conveyor at say 10% faster or slower or something, it may work well? Sometimes KISS is better?

Good luck!

The PF4 is not a vector drive, V/Hz only. That's why I was questioning the DC Injection Braking setup, the drive should NOT be putting out any current at zero Hz unless it was braking, and it will only brake if told to. Stop telling it to brake the load, no current.

Look at the setting of P037. If it is set to 2 or 6, that's your problem. If it were set to 3 or 7, the DCIB would automatically turn off when it gets to zero Hz. I would just disable it, set P037 to a 1 or 5.