# Problem with Powerflex 70 VFD



## JRaef

acro said:


> ...
> The manual describes the fault - "The drive is not following a commanded acceleration or deceleration because it is attempting to limit bus voltage.
> 
> And the Actions are...
> 1. "Verify input voltage is within drive specified limits" - Every time I have checked it - it is.
> 
> 2. "Verify system ground impedance follows proper grounding techniques" - I have not found any issues with that either, but we do have a grounded leg system here. So one of the phases is tied to ground.
> 
> 
> 3. "Disable bus regulation and/or add dynamic brake resistor and/or extend deceleration time".
> 
> I need to go and check the settings for the Bus regulation and DB resistor, but thought I would check and see if anyone is familiar with this? I did not turn up much on a search here.
> 
> 
> Thanks


#3 should have been listed first, it is the most common cause. But 1 and 2 are the easier ones to check. It's kind of like basic troubleshooting; "Is it plugged in?"

Usually this means your load is over driving your motor at times, like when it is decelerating. Any AC motor can become a generator with two conditions; 1) something is making the motor spin faster than the synchronous speed and 2) the windings are excited so there is a magnetic field. In a VFD, the "synchronous speed" is now a moving target, it's whatever the VFD is telling the motor to spin at. When you have Decel control turned on, that means the VFD is slowly lowering the theoretical synchronous speed of the motor. If the load is high friction and/or low inertia, lowering the speed means you are PREVENTING the motor from decelerating faster than you want. But if the load is high inertia and WANTS to keep spinning at a certain speed, lowering the speed command with the VFD just turns it into a generator. If you do not have Dynamic Braking installed, the energy generated by that motor-turned-generator has nowhere to go but the VFD DC bus and it will trip out to protect itself.

So if that's happening, you either have to turn off the Decel and let it coast, or put in a Dynamic Braking package.

DC bus regulation is a related feature that attempts to regulate the VFD DC bus voltage by automatically altering the output frequency to maintain it. If you have that turned on and don't need it, that will give you nuisance tripping as well. This is controlled in parameters 161 and 162, P5 (Preface page 5) explains it in more detail.

Here is a link to the manual in pdf form, which makes it easier to search than the paper version if that's all you have.


----------



## nolabama

we use a dynamic brake similar to these - if you dont have one they are super easy to put in

http://www.cressall.com/brakingresistors/brakingresistors210.html


----------



## varmit

You say that you have a corner grounded system? If so, YOU MUST REMOVE THE MOV JUMPERS OR THE DRIVE WILL DIE VERY SOON. The drive manual explains this in the early pages of the "wiring the drive "section.

Also, what type of load or equipment is this on? If this is something that has a flywheel effect or is a reciprocating load, and the drive is set to ramp to a stop, the drive will try to override the stop ramp in order to prevent a buss overvoltage fault.

You can:
Set the drive to "coast to stop", if permissible for your application.
or
Add a dynamic breaking resistor.


----------



## nolabama

varmit said:


> You say that you have a corner grounded system? If so, YOU MUST REMOVE THE MOV JUMPERS OR THE DRIVE WILL DIE VERY SOON. The drive manual explains this in the early pages of the "wiring the drive "section.
> 
> Also, what type of load or equipment is this on? If this is something that has a flywheel effect or is a reciprocating load, and the drive is set to ramp to a stop, the drive will try to override the stop ramp in order to prevent a buss overvoltage fault.
> 
> You can:
> Set the drive to "coast to stop", if permissible for your application.
> or
> Add a dynamic breaking resistor.


what are MOV jumpers


----------



## eutecticalloy

JRaef said:


> #3 should have been listed first, it is the most common cause. But 1 and 2 are the easier ones to check. It's kind of like basic troubleshooting; "Is it plugged in?"
> 
> Usually this means your load is over driving your motor at times, like when it is decelerating. Any AC motor can become a generator with two conditions; 1) something is making the motor spin faster than the synchronous speed and 2) the windings are excited so there is a magnetic field. In a VFD, the "synchronous speed" is now a moving target, it's whatever the VFD is telling the motor to spin at. When you have Decel control turned on, that means the VFD is slowly lowering the theoretical synchronous speed of the motor. If the load is high friction and/or low inertia, lowering the speed means you are PREVENTING the motor from decelerating faster than you want. But if the load is high inertia and WANTS to keep spinning at a certain speed, lowering the speed command with the VFD just turns it into a generator. If you do not have Dynamic Braking installed, the energy generated by that motor-turned-generator has nowhere to go but the VFD DC bus and it will trip out to protect itself.
> 
> So if that's happening, you either have to turn off the Decel and let it coast, or put in a Dynamic Braking package.
> 
> DC bus regulation is a related feature that attempts to regulate the VFD DC bus voltage by automatically altering the output frequency to maintain it. If you have that turned on and don't need it, that will give you nuisance tripping as well. This is controlled in parameters 161 and 162, P5 (Preface page 5) explains it in more detail.
> 
> Here is a link to the manual in pdf form, which makes it easier to search than the paper version if that's all you have.


Man, I would like to sit down over a cup of joe and ask you a few questions. Everytime I get on here it seems like you only handle the more difficult questions.

In fact I live in San Leandro. We should have a little Bay Area ElectriciansTalk meeting, If only I wasn't so busy at work.


----------



## acro

varmit said:


> You say that you have a corner grounded system? If so, YOU MUST REMOVE THE MOV JUMPERS OR THE DRIVE WILL DIE VERY SOON. The drive manual explains this in the early pages of the "wiring the drive "section.
> 
> Also, what type of load or equipment is this on? If this is something that has a flywheel effect or is a reciprocating load, and the drive is set to ramp to a stop, the drive will try to override the stop ramp in order to prevent a buss overvoltage fault.
> 
> You can:
> Set the drive to "coast to stop", if permissible for your application.
> or
> Add a dynamic breaking resistor.



You guys sound like you are right on.

I did remove the MOV jumpers as the manual suggests. But not right away. The drive was installed by a previous electrician and did run for several months-possibly a year before I got involved and saw that they needed to be removed. The drive has been in service for 5-1/2 years.



JRaef said:


> #
> So if that's happening, you either have to turn off the Decel and let it coast, or put in a Dynamic Braking package.


The load does definitely have a flywheel effect, but it can not run away. It is a vibratory plate feeder for a jaw crusher. So I can see where that would cause the motor to become a generator during portions of the rotation.

I don't think the coasting or flywheeling is a problem, so i will just change some of the settings this morning and not worry about any dynamic braking. However, I do not see a parameter that just simply disables the decel. #142 and 143 allow the time to be set, and I am planning on looking at those two 1st and probably increasing them. 155 & 156 address the stop mode and I am going to make sure they are set to coast.


We'll see how it works out. Headed there now.


Thanks


----------



## acro

Well, I verified the parameters.
161 & 162 where both disabled and like I mentioned before, the only parameters controlling the Decel are 142 & 143.

I don't fully understand the relationship between the two, but they where set to 10 and 0 respectively. I changed the 1st one to 15 with no change in the symptoms. I did not change #143 yet.

And here is a better description of the problem.

I watched the drive for about 5 minutes with a speed of 51.5Hz and it faulted 5 or 6 times. The operator just presses the start button and it takes right off again. During this time, the display alternated between "At Speed" and "Decelerating" at about a 50/50 ratio.

I asked the operator if the change I made effected it, and he said no. I had him speed up to a setting where he said "It will probably run all day and not fault out".

I went back and checked the drive and it was running at 56.2Hz. and it was displaying "At Speed" and I did not see it change in the 5 minutes I watched.


Now, at both settings, the Bus voltage was showing 615 to 625 or so. But when it did fault, it showed in the low 650's right after I cleared it.



I guess I will change 143 Decel Time 2 and see what that does.


Thanks


----------



## JRaef

This is a common problem with Cyclical loads like jaws and shakers such as grizzlies and screens when drives are applied to them. There may be a feature you can use to overcome it, in fact it may actually be turning ON the DC bus regulation, but let me check for you. If not, the usual fix is to add DB to the drive. That would work for sure. 

Just out of curiosity, why is there a VFD on a jaw crusher anyway? Changing speed would not, in my opinion, change the product output. That is totally determined by the gap at the bottom of the jaw. If they are trying to control flow through it, you do that by putting the VFD on the grizzly that's feeding product into it.


----------



## acro

JReaf, this is on the feeder for the crusher not the actual crusher.

There is a type of crusher that can utilize a VFD. We also have a vertical impact crusher that operates such that if you speed it up, the product size decreases.


I messed around with the 2 Decel times and seem to get less faults when I have them set to lower numbers. I have them both set at 5sec now.

Like I said before, I am not real sure of the relationships of these values. I assumed that larger numbers would be better as it would allow more time for the motor speed to reach the desired speed. But, I had both of the parameters set to 20 sec and got more frequent faults than I did at 5 sec. Changing the 143 to an actual value and not 0.0 did seem to help for sure, but it is still faulting very often.


There are many parameters in the manual that are not present when I scroll through the menus on my drive.


----------



## JRaef

The general consensus here is to turn the DC bus regulation ON, not Off as it is now. That's what that function is for. As it sees the DC bus start to climb because of regen from that counterweight in the shaker, it artificially raises the output frequency so that the relative synchronous speed is at or ever so slightly higher than the over driven speed and the motor no longer regenerates. The downside is if your incoming line voltage fluctuates too, that can cause nuisance tripping. I say try it and see if that fixes it.

By the way if this all sounds unfamiliar to other VFD users, it's a fairly uncommon feature. I've only seen it in the PF70 and up A-B drives and Toshiba G3 and up. I think the Siemens MM440 had it but that German translated manual was so complicated I could never find it.

And yes, I'm aware that VSI crushers use VFDs to change product output. In a prior life I did a lot of VFD work in the mining and aggregate industry and actually helped a couple of the VSI OEMs develop and test the concept. It's become a pretty common option now but it took a leap in high HP VFD technology and affordability to make it practical and that didn't happen until only 5 or 6 years ago. Since then I see a number of them are now applying drives to cone crushers too, it changes the contact time and can optimize throughput. But that's why I was questioning putting a VFD on a jaw crusher, no point.


----------



## varmit

You can not disable the ramp time parameter. The drive follows this slope when changing speed, in addition to it's use in the "ramp to stop". In the "coast to stop" mode, the decel ramp is irrelevant when stopping.

Your best bet, to eliminate the trips, would be to add dynamic braking. On most any cyclic load, a breaking resistor will be required, as about half of the machine rotation, the load is causing regeneration back to the drive. You will PROBABLY need a dynamic breaking resistor of about 50% of the wattage of the motor. As your experiments show, often there is a "sweet spot" where the machine will run trouble free, but it never seems to be a speed that the machine is ever ran.

Ramp 1 / Ramp 2 settings allow you to set up two different ramp profiles, in the drive, and to select between these two profiles with a programmed digital input. This can be useful if the machine runs two very different products.

Y'all are very lucky that he drive has lasted this long with the MOV jumpers installed. I have seen Pflex 4 and Pflex 40s fail on initial power up due to someone leaving the jumpers in. However, I have seen Pflex 70s run for years with them in, on either corner grounded or ungrounded power systems.


----------



## acro

Good info.

So even though I don't care if the speed is not truly steady, the drive does. And there is no way to get the drive to allow the motor to momentarily operate at a faster speed?



I basically have to install some braking resistors to "force" the motor to operate at a more steady RPM? That stinks. So i am looking at 30kw+ for the resistor.

It just seems so excessive.

I have some old grounding restors - wonder if that would work? They look very similar, but the similarity probably ends there. The one I have is a 165ohm 25amp 4160v

But I really would like to find a way around it.


----------



## nolabama

They are super easy to install, zero maintanence. You will be happy you did.


----------



## acro

Yea, but $$$ that was not planned for.


----------



## acro

nolabama said:


> You will be happy you did.



Why happy? Other than to get the drive to stop faulting? Are there other benefits?

Process wise, the speed variation(if you can call it that) does not cause a problem.


But I guess if it comes down to the fact that the resistor has to be there to protect the drive, I can live with that. As long as I can guarantee that it will cure the Decel Inhibit fault.



My motor is 40hp - which converts to just under 30kw. Could I use 2.3ohm 43kw or a 5.4ohm 51.9kw resistor interchangeably?

Or does the DBR have to be more closely matched to the load.



Also on my mind is that the environment for the resistor is extremely dusty.


Meanwhile, I am going to change the Bus Regulation to "Adjust Freq" and see how that does.


----------



## acro

Well, I should have checked on the drive before my last post. Changing the decel time to 5 from the original value of 10 seems to have eliminated the problem - at least for the last day and a half we where running.


I did go ahead and change the bus regulation perJReaf's groups recommendation, as I can understand the benefit of letting the drive try and compensate for the variations.

I am just surprised the decel parameter works backwards from what I was thinking.


----------

