Drive System Help

We have a new drive system that has 9 rolls that move a sheet product through one part of our process and the material wraps some rolls and lays over others.

The drives are all ABB ACS 800 series 7.5 HP and the data plate on the drive says input 6.9 amps and output is 8.1 amps.

We had an issue where each drive blew its line fuses which are 15 amp class J.

Each drive also has it's own brake resistor that is 44 ohms / 800 watts and 690 volts DC rated and they connect to the BRK + and BRK- terminals.

There is also a UDC+ and a UDC- terminal on each drive which links all 9 drives together by daisy chain.

I understand the process and working of the brake resistor circuit but what are the UDC+ and a UDC- terminal on each drive and why are the all linked togehter like that.

Also is the input fusing being 15 amp class j current limiting seems like it's not the right size for the drive.

It's 12 awg wire so I would think that would be a 20 amp fuse
sized to protect the wire and I would also think it needs to be time delay because the drive should do all the load protection am I correct on this?

The UDC+ and a UDC- terminal on each drive also have a 25 amp semiconductor fuse at each drive which I also don't understand the purpose.

Can anyone please provide me some insight into this system?

Sounds like you have what is referred to as a "common DC bus" setup, where the DC busses of each drive are tied together so that as one is braking, it's braking energy is being used by other motors that are motoring at the same time. It's used as a way of being able to do high duty cycle braking on a machine where everything is tied together mechanically anyway.

Did anything change recently? One catch in this system is that you must be VERY careful about changing out a drive or making changes to the programming of one drive, because they are all working together as parts of a whole unit. If you didn't know why all that wiring and hardware was there, you must not have known that you cannot make changes without fully understanding it.

Don't deviate from the fuse sizing as that is likely the fuse that the drive was listed with. I would contact the machine builder to get them involved. If this happened right out of the gate on a new machine, they may have made a mistake in programming or wiring. All of the drives clearing their fuses sounds suspiciously like a wiring error.

You size your protection to the wire OR the device. It isn't a rule to size it only for the wire.

The DC Buss' connected together allow for the drive system to operate and efficiently share regenerated power for example from a payoff as the motoring power to other sections.

The semiconductor fuses are to protect the DC link of each drive, since if there is a short in the drive, the input fuses could clear, but the buss would still be powered and smoking, taking out all the other drives.

It is typical, even in common buss arangements for each drive to have it's own braking resistor, although they can share one large one with a standalone braking chopper sitting on the buss.

The machine has been runnign for about 2 years no issue. I also see the data plate has the output current listed as higher than the input current but at the same voltage how can that be?

Input is listed as 9.8 amps and output as 11 amps? 480 volts so how can this be?

Also all the motos are 7.5 HP 10.5 amps FLA but for example the # 3 drive is 639 amps drive input and 8.1 amps output but the motor is 10.5 amps FLA.

Why would the use slightly differet size drives when the motors are all the same?

I am familiar with common DC buss as we have an allen bradley system with Power flex 700 drives that are common DC buss but we have a large 3 diode module that takes 3 phases of 480 volts and puts out 690 volts DC to all the drives and we don't have a 480 input directly to the drives like this ABB system does.

Also in our allen bradley common DC buss setup all the brake terminals on each drive terminal togehter and go to one allen bradley chopper module and that has one large brake reistor attached.

Just for my knowledge is one way better than the other?

jraef said:

Sounds like you have what is referred to as a "common DC bus" setup, where the DC busses of each drive are tied together so that as one is braking, it's braking energy is being used by other motors that are motoring at the same time. It's used as a way of being able to do high duty cycle braking on a machine where everything is tied together mechanically anyway.

Did anything change recently? One catch in this system is that you must be VERY careful about changing out a drive or making changes to the programming of one drive, because they are all working together as parts of a whole unit. If you didn't know why all that wiring and hardware was there, you must not have known that you cannot make changes without fully understanding it.

Don't deviate from the fuse sizing as that is likely the fuse that the drive was listed with. I would contact the machine builder to get them involved. If this happened right out of the gate on a new machine, they may have made a mistake in programming or wiring. All of the drives clearing their fuses sounds suspiciously like a wiring error.

Click to expand...

What do you mean by High Duty Cycle braking? Is that very fast braking or braking multiple times per hour? This process one stared runs for days on end without ever stopping.

rdrast said:

It is typical, even in common buss arangements for each drive to have it's own braking resistor, although they can share one large one with a standalone braking chopper sitting on the buss.

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Just for my knowledge which is the better method and why? Anything other than the difference between maintaining one large resistor or multiple small reistors?

rdrast said:

You size your protection to the wire OR the device. It isn't a rule to size it only for the wire.

Click to expand...

How do you choose between sizing the fuse to the wire or the device? By wire it should be a 20 amp fuse but they have a 15 amp fuse so I will assume they sized to the device but what do you use to make that choice when designing a system?

What about standard contactors and overloads? I was taught to size the fuse to the wire so 10 awg wire 30 amp fuse etc. and size/set the overlaod to protect the motor. Is this correct?

AC Drive Input current VS output current is not a simple thing. You are converting the AC to DC, charging a bunch of capacitors, and then inverting that back into a variable frequency (at the very least). It isn't a direct relationship.

Common braking unit vs individual ones:
Individual braking units work no matter what for their connected motor, and in common buss situations can all switch on at the same time, spreading the load out.
Individual braking units are built in to virtually every AC drive out there, why spend extra money on another external one?.


You don't size the primary fusing for a transformer by the wire size feeding it, do you?

You size it for the rating of the transformer plus an allowable overage. At least most engineers do.

You don't fuse motor starters for the capacity of the wire, you fuse them for the size of the motor (or do you use #28 wire because it is a motor requiring one amp)?

First a 15 amp line fuse and a 25 amp buss looks about right.
Each line only carries 1/3 of the total current while the DC Buss carries 100% of the regen current. They require semiconductor fuses because they need to clear any fault current as quick as possible usually about 1/4 of cycle or 4 ms. the line fuses on a vfd are only there to isolate the vfd from the line in case of a fault. as for why the line fuse blew I would check to be sure the vfd setting are correct motor full load current drive rated current. if the line fuse is replaced and holds then I has to be a setting if the vfd was shorted the fuses would blow on power up.

As for the common bus I would have to question there setup. normally in a common bus set up the brake transistor in each vfd is disabled and a single brake module or modules sized to handle the full capacity of all vfd braking at 100% at the same time. Using separate braking modules on the vfd's could cause a failure of all the vfd's at the same time. the reason for this is that it is impossible to get ant 2 braking modules to turn on or off at the exact same voltage level. if one turned on early the rest would never turn on at all but all the buss current (total regen power ) will be passed through the one brake module. The only saving grace in the system described is the 25amp buss fuses they would blow and isolate the vfd and its brake module so the load on that vfd's brake module would be just that one motor.
I would guess that some of the buss fuses are already blown and you don't know it. the only way to check them is remove them. I have seen this happen many times.

Even when you use multiple buss brake modules on a common buss they are always connect 1 master and the additional units are slave from the mater. when the master turns on to dump the power all the slaves turn on, the same goes for when the master turns off all the slaves turn off.
I refer to Yaskawa drive manuals and their support team.

by the way on the system described it is real close to seeing a benefit from a line regeneration system. It may be worth the time to talk to drive manufacture. Most times the brake even point is around 100hp total load

Originally posted by Tim Ganz:

What do you mean by High Duty Cycle braking? Is that very fast braking or braking multiple times per hour? This process one stared runs for days on end without ever stopping.

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You are taking the term "braking" too literally in this case. What is really meant is generating operation, or the torque direction being opposite the rotational direction. For example, if one motor is trying to hold back the pull of another that would be "braking" operation. Take a look at the graph here:
http://what-when-how.com/induction-motor/operating-quadrants-induction-motor/
Operation in quadrants 2 and 4 are braking.

High duty cycle braking just means you are braking alot. Are you attempting to stretch this material some as it passes through the rollers? Are the downstream rollers running faster than the upstream rollers? If so the upstream rollers will be causing their motors to generate power back to the drives continuously. I suspect that is why the drive busses are tied together. The upstream drives are creating energy that must be managed. You can either:
Burn it up in resistors
Put it back on the AC line
Share it with another drive that can use it.
The designer chose option 3.

Originally posted by GaryS:

As for the common bus I would have to question there setup. normally in a common bus set up the brake transistor in each vfd is disabled and a single brake module or modules sized to handle the full capacity of all vfd braking at 100% at the same time.

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I disagree with this. I see it about even in the systems I work with. It really depends on energy flow. If it is a "fully contained" system (all the generated energy is used by other members of the system) and the total inertia is relatively low compared to the size of the drives and motors, individual resistors are a good fit. While GaryS is correct that you can't count on all the drives initiating regen at the same time in most "fully contained" systems the bleeder resistors are used very seldom; typically only for e-stop. In addition, as one resistor starts to be taxed the general buss level will continue to rise, causing other resistors to come into play. The one thing I would say is that if you have a mixed bag of drive horsepowers and there are a few that are significantly smaller than the others, don't use the resistors on the small ones.

Originally posted by GaryS:

by the way on the system described it is real close to seeing a benefit from a line regeneration system. It may be worth the time to talk to drive manufacture. Most times the brake even point is around 100hp total load

Click to expand...

This is too simplistic a rule of thumb. A 15HP centrifuge would be a much better candidate for a line regenerative system than a 600 total horsepower slitter/winder with a drive unwind. It all comes down to excess energy management. If you very consistently have a total surplus of energy then line regeneration makes sense. If you only very occasionally have excess energy then not so much. The one exception MAY be that a line regenerative supply can provide a near unity power factor. If your utility power factor penalty is exceptionally high you might want to look into a line regenerative supply for those reasons.

Keith

kamenges said:

... If it is a "fully contained" system (all the generated energy is used by other members of the system) and the total inertia is relatively low compared to the size of the drives and motors, individual resistors are a good fit. While GaryS is correct that you can't count on all the drives initiating regen at the same time in most "fully contained" systems the bleeder resistors are used very seldom; typically only for e-stop. In addition, as one resistor starts to be taxed the general buss level will continue to rise, causing other resistors to come into play. ...

Click to expand...

This is how I see it too.

In fact, the problem here might (in a far fetched way) be related to the "E-Stop" function. If this is a distributed system, INTENDED to just share the energy between loads during normal operation, you do indeed run the risk of how it might react to an E-Stop situation if not careful. If the E-Stop commands all of the VFDs to go into immediate Braking, and there is no motoring load to absorb the regen energy, the scenario can indeed cause the first one to come on to become overloaded. But as said, the rest will follow quickly and share the burden; UNLESS, the spike in regen energy is so fast that the first one on causes the VFD associated with it to turn off the DC chopper to protect it, shifting the burden to the 2nd one on, which does the same thing, etc. etc. etc until they ALL turn the brake choppers off. If then the VFDs are all set up to change to DC Injection Braking if the chopper is off, that could cause their fuses to blow if set too high. Just speculating here though, it's kind of far fetched.

Another scenario is that the drives are PROGRAMMED on purpose to ignore the Dynamic Braking function because of the potential risks inherent in a distributed load sharing situation, and respond to an E-Stop command by going into DCIB instead, which again could potentially cause the fuses to blow if there is too much inertia remaining in the system.

Bottom line is that we can speculate on this all day long, but none of us knows what your system is intended to do or how the drives are programmed. So again, a call to the people who designed and built it is in order. Increasing the fuse size might move the next failure into the VFDs themselves, they are much more expensive than fuses.

Side note: drive Input Amp rating is at the corrected power factor of the load, drive Output Amp rating is INCLUSIVE of the power factor of the load, so looks higher because the transistors must pass both the active and reactive current of the motor.

Common buss is not as simple as you would think yes it all about energy but first you need to control it, on a lightly loaded system the system shown would probably work ok but ok is never good enough effectively you have 9 separate switches with resister load on each all coming on and off at different voltage levels with there energy source coming from the same source (the DC Buss)You can never get them to turn on or off at the exact same voltage never going to happen. as I said before when the first module turns on the buss voltage will start to drop (energy duped as heat in the resistor) with the buss voltage dropping the other modules will never reach their turn on level so the first module will have to handle all the excess energy by its self. it may be able to do that if the regen load is light enough but its a gamble. if it fails it could take out any or all the remaining drives the buss fuses my or may not isolate the fault in time nobody can say for sure. this is same reason that you can not use multiple small contactors in parallel the first one to close will take all the load on startup and the last one to open will take all the arc one of them will be destroyed very quickly. I have seen people try this and I have never seen it work

most drives built today are designed with 10-20% internal braking what that is 10 % braking 100% of the time or 100% braking 10% of the time. On a common buss system yoy can count on just where the energy is coming from or the level of energy. on a winder unwinder system if you hit the stop button and try to regen all motors to a stop
the actual braking load could exceed 500% of the capacity then with only module turning on to dump all energy (remember only the brake module with the lowest sense threshold will turn on all the rest will stay off until the buss fuses open and isolate the drive) also keep in mind that no manufacture will give you a guarantee that any protection device will protect your drive.
as for if all works as planed then you will not have any problems but why put fuses in first place after all they are only needed if things go bad.

it's poor engineering to design any drive system to not be able to handle 100%
on this system as described I really don't see where a common buss system is of any real benefit there may be some but with the separate brake modules I see more problems than benefit.

it keeps coming back that every drive shares the load equally that is not what happens

all the drive manufactures recommend a single brake module on a common buss its the only way to keep things under control.
the machine builder like to use the multiple brake module on the separate drives because is cheaper and as long as nothing go wrong while is under their warranty they getaway with it. later when things go bad this the owners problem.


As for the line regeneration most manufactures will agree that about 100hp is the point to start looking at line regeneration it's not a fixes value some systems can benefit below that other it may need to be a much higher value. is just a point to start the conversation as to weather is would be a benefit or not.

common buss = common brake nodule any other way is looking for trouble

I don't think I did a good job explaining the system. Each drive has it's own external brake resistor not the internal that comes with the drive.

Also the load are large water filled steel rolls and the motor drives a gearbox that is 20:1 so there is almost zero inertia. When you hit stop the rolls only continue a couple inches and these rolls run very slow.

As I said we have other common buss systems and I have a basic understanding of them and I see no value in this one being a common buss system.

Well we have the full story now. The plant had a power blip last night so the system was stopped almost like an estop but worse.

It also appears that the reason the fuses blew is because the drives were damaged. They put new fuses in all 9 drives and 2 of 3 fuses blew again in each drive. Why 2 of 3 and not all 3?

Does anyone know where I can get a troubleshooting manual for ABB ACS 800 U1 drives? I don't know what to check to determine if they are fully toast.

I found these with Google.

https://library.e.abb.com/public/0cb03a89ae71bba5c1257b97004fdb01/EN_ ACS800_01_HW_K_A4.pdf

http://www.abb.com/AbbLibrary/Downl...iew=Result&DocumentKind=Manual&SortBy=DocKind

Stu....