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VFD overvoltage fault ?
3

VFD overvoltage fault ?

VFD overvoltage fault ?

(OP)
Hello,
I have (2) vfd's controlling 2 motors(conveyors) with a input voltage of 460 volts in real life I measure 494 volts at the input. The drive manufacturer says  voltage input in good for +10%. 460*1.10=506
But over the past 2 weeks both drive's  have faulted on a overvoltage fault numerous times.The fault has occured when the drive is running at a constant speed. I do not have a line reactors or chokes installed.
Both of the drives, motors are new . In addition to the new conveyor motors at the other end of the plant are 2 new 1000HP 4160 volt compressors DOL starting. We are going to monitor the voltage for spikes etc.. later this week.But while I wait any suggestions?

RE: VFD overvoltage fault ?

2
Possibilities:
  • Regeneration: your conveyors are overhauling slightly at those times and since you are already close to the ragged edge of the voltage tolerance, it doesn't take much to cause a trip. Dynamic Braking resistors could help with that even if you are not planning on using them for braking. They just give any regenerative energy a place to go.
  • In fact if the compressors are coming on and off DOL, they may be causing a voltage sag which causes the VFDs to slow down by lowering the output speed(if programmed that way), then when the line voltage returns it over charges the bus because the load is still regenerating. Seen that a number of times. Again, DB resistors and/or changing the programming of the VFD to react to line dips by coasting, rather than by lowering the output frequency
  • Capacitor interaction. Do your compressors have PFC caps on them? Sometimes a resonance similar to a tank circuit can occur in the interaction of external capacitors and the VFD front-end to cause additional charging of the DC bus. Also make sure they are not using bulk pf correction because if so, when the compressors turn OFF, the pf will go high and that can cause over charging of the DC bus.

RE: VFD overvoltage fault ?

nmark
Nothing much more to add to what jraef has mentioned other than to measure (or monitor via a parameter)the DC link voltage rather than just the AC input.
Your steady state DC link voltage will be 690~710Vdc on this AC line voltage leaving little margin for the other effects as jraef describes.
The +/-10% mentioned by the VFD manufacturer will normally be for short durations rather than continuous duty. Most VFD's have their power devices (rectifiers, transistors) rated for the nominal DC voltage based on the AC supply voltage range specified. Some drives show a voltage range of 380~500Vac and this means the power devices are of a higher rating.
So if your drive has a nominal rating of 460Vac then you really are pushing the boundry by connecting to 494Vac as a nominal as this will not take into consideration any peaks.

RE: VFD overvoltage fault ?

Probably one of ours Patrick!

RE: VFD overvoltage fault ?

You there too? Jeff?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD overvoltage fault ?

Ja.
Since late January

RE: VFD overvoltage fault ?

I was there for ten years. Left in 1975...

My last job (this week-end) was for them. It is a long standing relation.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD overvoltage fault ?

How do you have a "job for them" but not be employed by them?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: VFD overvoltage fault ?

I am their "Mädchen für Alles". Especially for things that others do not want to touch - or have forgotten about...

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD overvoltage fault ?

I didn't want to tempt fate by asking "which VFD?".
and Gunnar, I hope you mean "general dogsbody" rather than the other meaning I've heard in the beer halls of Hamburg... winky smile
 

RE: VFD overvoltage fault ?

The Romans might have called it a "PI IV"

Not that it is from Roman time. But nearly...

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD overvoltage fault ?

(OP)
The drives are running for about 72 hours continuosly and a 2 hour down time roughly but it isn't set in stone and my drive parameters can't be changed on the fly.
I would like to lower transformer tap ahead of vfd's but that involves shutting down half the plant and that is not an option for about 8 weeks, So if anyone is still interested I might have  more info at a later date.

Non Semper Erit Aestas.

RE: VFD overvoltage fault ?

nmark
always interested in feedback.

RE: VFD overvoltage fault ?

nmark,
At the risk of embarrassment, what brand of VFD are they? There are a few out there which are really 415V designs that, unfortunately, some engineer was tasked with upgrading to handle "460V motors in the US", but did so without having investigated the fact that 460V is a utilization voltage, based upon a 480V distribution system. We have that discussion in this forum from time to time; a lot of people not from North America have a difficult time with that concept. I'm curious to know who made that design error.

RE: VFD overvoltage fault ?

How do you set the drive speed? I know you say it's constant speed but are you positive? If you're using an analog input for speed then there is always the possibility it's not and you are commanding it to slow down which is causing a regenerating condition that trips it.

The +10% should still be the operating range and the DB resistor operation and trip points should both be above that level. So, the drive should not be tripping if the input voltage reaches 506V. It should have to go another 5% to 10% over 506V to trip.

RE: VFD overvoltage fault ?

LionelHutz
I agree, the drive shouldn't trip within the +10% range of nominal but I was referring to continuous operation in the +10% range. This should be avoided as it will impact on the lifetime of the components within the drive and also limit any tolerance between the nominal DC link voltage and any AC surge or regenerated DC back onto the link.
If the drive nmark has is indicating 460Vac+10% then it is because lower voltage rated components are used compared to drives stating 480Vac or 500Vac +10%.
A typical trip limit of a "400Vac" drive will be 810~820Vdc and this is obviously beyond the +10% voltage range of the 460/480 or 500Vac nominal input.
 

RE: VFD overvoltage fault ?

(OP)
At the risk of offending anyone I won't mention the brand specifically, but the name sounds similar to Yamaha.It does have a "stall" parameter where regardless of accel/decal times it will change speed as slow as necessary to compensate for regeneration.
The drive does not have a dynamic brake resistor.
It is controlled via a analog input but it consist of a HMI with a setpoint screen and the operator has to manually enter a speed as a percentage to increase or decrease and I am positive multiple  overvoltage faults occured without operator changing speed.
The drive does not have a dynamic brake resistor.
From the drive  I am able to get D.C.bus voltage and today it was running pretty close to 700v.
The input was at 500volts ac today.
And the drive is rated at 460v +10%, -15%. The manual says that it faults on a dc bus voltage exceeding 820.So far there has only been a voltage dip in the line momentarily -40 volt but no more faults.

RE: VFD overvoltage fault ?

nmark; you have never cleared up the issue of is there any possibility of the conveyors ever  overrunning?

Is there commanded conveyor speed changes or do they just start up, get to speed, and sit there all day long, faulting occasionally?

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: VFD overvoltage fault ?

(OP)
The operation is they get up to speed and literally sit there all day long unless the product changes. Or they have problems with the product then they need to change speeds but in the past 2 weeks they have been running the same product and have changed speed on average 1-2 times a day. But on Sunday the drives faulted 4 times I wasn't there but have been told product/speed had not been altered . It is possible that on some of the faults speed was changed but it would appear to be in the minority.
New information I have learned today is another drive controlling  a fan (different manufacturer) has smoked.

RE: VFD overvoltage fault ?

(OP)
Forgot to add compressor have not shut off yet tomorrow morning
they will be turned off and on while I  am there.

RE: VFD overvoltage fault ?

Sundays are typically a day for OV trips as generally other loads are off and the voltage tends to creep even higher.
Monitoring the DC bus on the drive display is ok but will not be fast enough to capture transients or spikes on the network. The spikes will not need to be too big wither if the AC is 500V. you will need a scope on the DC link to capture what is happening on the DC link when it trips.
Are the motors driving the gearboxes via belts? sometimes if you get slackness in belts  the slip can cause an OV trip if the DC link is already high.

RE: VFD overvoltage fault ?

Exactly my thoughts, Patrick. Sundays can be a lot higher because other loads are off. Have had cases with bad PF in induction motors due to that. So bad that thermal protection tripped.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: VFD overvoltage fault ?

Sounds much more likely to be power problems than regen.

In view of that, it seems to me that two possibilities exist.  One would be to drop the incoming voltage either by transformer or by adding at least 5% reactance.  The second would be to change the drive to one build to international voltages which typically are 380-10% to 500+10%.  These are much more tolerant of voltage variations than drives built to 460V +/-10% or even 15%

RE: VFD overvoltage fault ?

Huh.
In all the years I have used those "name sounds similar to Yamaha" drives (if I'm interpreting that correctly), for some reason I never noticed that their input voltage specs are 380 - 460V +10%, but I just checked and they are! Wow, the details we can miss sometimes when we are blinded by technology I guess. I cut my drive teeth on that brand 20+ years ago, but have never had that problem. Even as a competitor today I still have respect for their products. Was I just lucky all those years?

RE: VFD overvoltage fault ?

I agree with the others. Sunday will have the lowest demand on the power system in your area so the voltage will be the highest. So, it looks like a source problem.

I would still have a DB resistor in this application. It should not have to be very large because you should just need it to dump some energy when any temporary over-voltages appear on the buss.

You have never answered if the conveyor can drive the motor? The drive may have that decel feature but it likely will not allow the motor to run over 60hz. So, if the conveyor drives the motor over 60hz the drive will hold the frequency there and trip.

Another thing, saying your operators are not changing the frequency doesn't mean there isn't a problem with the analog circuit changing itself.

RE: VFD overvoltage fault ?

With regard to Lionel's post, it is also possible when running in vector mode to have the speed loop tuning so overtuned that the oscillations cause regen.

Seems unlikely here but, absent anything more obvious, it wouldn't hurt to check.  Of course, if running open loop scalar V/Hz, that wouldn't be a possible cause.

RE: VFD overvoltage fault ?

Quote (LionelHutz):

The drive may have that decel feature but it likely will not allow the motor to run over 60hz. So, if the conveyor drives the motor over 60hz the drive will hold the frequency there and trip.
In the "sounds like Yamaha" drives, the stall prevention feature is active all the time, not just when accelerating. It will drive the output reference frequency down, overriding any commanded speed, in order to reduce current (which is how it detects a potential stall). That's why I postulated that the compressors starting DOL on the system may have dropped the voltage, which would make the conveyor motor current rise for a given speed command. But if the stall protection kicks in and lowers the speed command, and then the mass on the conveyor wants to keep moving, you can end up in regen without having to go above 60Hz. All it needs is for the motor to be overhauled beyond whatever the output frequency is at any given moment.

I had that problem on roll handling conveyors at a paper mill. They used vacuum grapplers to handle the rolls, which took 2 x 400HP vacuum pumps. When they cycled on and off while the paper rolls were moving, the conveyor drives would trip on OV. We just disabled the stall prevention, I don't really like that feature much anyway. It's one of those things that tends to create more problems than it solves.

RE: VFD overvoltage fault ?

(OP)
I have a power analyzer on the line side of the drive.I haven't downloaded yet to get all the gory details but when 600HP 4160v compressor turns on a -40volt line dip occurs the same occurs with a 1000hp turning on so far no tripping on a OV fault.
The line feeding the drive is seeing peeks of 690v to 710v. But at sometime in the wee hours last night 1 drive faulted twice on OL.After investigating wiring methods which are not up to par looking at installing load reactors between drive and motor.Will  try and go about upgrading wiring also( having   motor wires installed in own conduit instead of PVC conduit with multiple motors).Half the length is in pvc the other half is metallic wireway with everything but the kitchen sink in it.Motor wire lengths are less than 150 feet from drives.

RE: VFD overvoltage fault ?

(OP)
The wiring from the analog ouput at the plc is shielded cable in its own conduit (18 gauge) less than 50 foot away from drive. The HMI communicates with the plc via ethernet.

RE: VFD overvoltage fault ?

Jeff I'm not getting how stall prevention is 'realized' by an internally generated 'slow down'?  Would you want to increase the drive 'signal' to prevent stalling?

I guess we can stop asking nmark about overriding. He ain't gonna tell us....

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: VFD overvoltage fault ?

(OP)
Sorry Itsmoked I googled overriding conveyor and I still don't understand the term. Would someone care to enlighten me please?

RE: VFD overvoltage fault ?

I think they mean what I know as overhauling, but in any case the question is "Can the load on the conveyor drive the system?"  Traction elevators are a very common example of an overhauling system when going up with the counterweight heavier than the cabin or going down with the cabin heavier than the counterweight.

RE: VFD overvoltage fault ?

(OP)
Thank You David.No the load is not overriding/overhauling conveyor.

RE: VFD overvoltage fault ?

Booyah! 2thumbsup

That's good, and removes a likely cause of your over-voltage errors.

Thanks nmark.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: VFD overvoltage fault ?

Well a traction elevator is one example of an overhauling load, but that is an intentional one. What I was referring to is an unintentional overhaul.

What I mean by that is, your conveyor is undoubtedly moving a load (otherwise, why have it?). That load represents a mass and we all know that a mass in motion wants to stay in motion. So your VFD is running the conveyor at say, 40Hz which represents 80FPM just to keep it simple. Suddenly the voltage drops and the stall prevention feature changes the VFD output speed reference to 25Hz, without a change in your external speed command reference. The mass on the conveyor is still moving at 80FPM and even though the speed is decaying, will take a certain amount of time to slow down to where the VFD speed is telling it to be. During that time, the mass on the conveyor is "pulling" the conveyor belt along with it as the speed decays, spinning the motor at a speed greater than the frequency output of the VFD. So it becomes an external driving force on the motor shaft spinning the motor at super-synchronous speed. All the while, the VFD output is keeping the windings excited. AC motor + excitation current + external driving force at super-synchronous speed = AC induction generator!

I still think you should try just disabling that stall prevention feature. That's why I don't like it. As itsmoked's question points out, it seems almost counterintuitive to do it this way. But that feature is intended to be used primarily when power constrains dictate that you CANNOT increase current as the motor begins to slip more, so it pulls back the speed command in an attempt to decrease the load on the motor. That works on some types of loads, but NOT inertia loads like a conveyor can be.

OK, I'm done. I wanted to be clear about what I have experienced but I could very well be all wet here anyway, so no more soap box. I promise... soapbox

RE: VFD overvoltage fault ?

No soap box about it!

So anti-stall should really be called the reduce-speed-to-match available-voltage feature.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: VFD overvoltage fault ?

We seem to have gone from voltage related trips to current related trips(over-load). I'm trying to think if stall could create an over-voltage situation and I would probably say not (but I don't have the experience of the yamaha-thingymagig) so I'm thinking the OL and OV are now quite different problems.
 

RE: VFD overvoltage fault ?

Hey Jeff, I wasn't really referring to the stall prevention at all. Most drives can be set to different types of acceleration and deceleration control to protect the motor and/or drive. Another example is the deceleration control where the drive quits decelerating if the deceleration is going to cause an overvoltage trip. A third example would be torque control which controls the ramp time based on the a motor output torque limit.

What I was referring to is that if you set the maximum frequency to 60hz then this is usually a hard fixed limit. If the motor is forced into generating past 60hz the drive needs to have the capability of getting rid of the regen energy or it will trip. The drive will not allow the frequency above 60hz to protect itself from the trip.

Now, in this case, the conveyors are not supposed to be able to drive the motors so it likely does not apply. But, it can apply in some applications (pump jack).

So, it would seem we have a case of too much supply voltage.

nmark - The reactor needs to be between the source and the VFD. I still don't like this solution because the reactor has little voltage drop at low load or when the VFD is off so you'll likely still get trips at those times. The solution is that you need to lower your plant voltage. If the voltage is rising on Sundays you need to see if the utility will do something about it.

Now, having said that, I have seen a VFD trip on overvoltage due to a crappy job on the VFD to motor wiring. I believe there was ringing on the buss that was affecting the buss voltage sensing circuit. When it did happen the drive was tripping constantly though which doesn't seem to be what's happening in your case. I really think it was just luck the drive did not fail in that case I saw.
 

RE: VFD overvoltage fault ?

Out of curiosity, what is the parameter for "Input Voltage Setting" set to?  Is it the default 460V, or have you changed it to match your nominal input voltage of 496V?

This parameter is the reference for the drive protective features such as overvoltage, brake resistor turn-on, stall prevention etc..

(This is right out of the manual for one of the drive series of a company that has the same first and last letters mentioned above)

RE: VFD overvoltage fault ?

(OP)
Thanks to all who have responded.
Currently the  stall parameter is disabled and the input voltage parameter is set to 500volts.
So far only 1 fault on overload 3rd shift on Wednesday and no faults over the weekend.

RE: VFD overvoltage fault ?

nMARK, You are not alone. I am currently getting the same issue with ours. Make sure the DB resistors have a good hookup and the braking module works. We did what you did until we could figure it out.

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