Powerflex 525 - Overvoltage

[Jackllx]

Hi All,

I'm quite familiar with the powerflex 525 and very familiar with VFDs in general, I've got a problem where on a conveyor where a product transfers from one conveyor (one VFD) to another conveyor (another VFD) the drive which is receiving the load will get an overvoltage fault.

I've checked that the speeds are the same, disabled the bus reg and checked for slip but everything seems to be OK.

The fault occurs when both drives are at full speed when the product is transferring from one to the other, which to me would indicate that the previous drive is pushing the downstream drive...but this isn't the case

Does anyone have any ideas?

Thanks,

 

[drbitboy]

I am not sure of the exact jargon, but how is each VFD controlled? Are they using torque control, speed control, something else, and what other parameters are involved?

 

[Jackllx]

I am not sure of the exact jargon, but how is each VFD controlled? Are they using torque control, speed control, something else, and what other parameters are involved?

Initially they were in vector control but I've changed it to bog standard frequency

 

[GaryS]

From your discription it tells me thwt the receiving conveyor is running a little slower then the sending conveyor and when the product is passed from the faster conveyor to the slower conveyor the receiving conveyor has to brake the produce and slow it down. The braking engery is causing the bus voltage to increase and overvoltage the vfd
the soluton is to set the conveyor speeds the same or install a braking resister on the receiving conveyor vfd.

 

[rupej]

From your discription it tells me thwt the receiving conveyor is running a little slower then the sending conveyor and when the product is passed from the faster conveyor to the slower conveyor the receiving conveyor has to brake the produce and slow it down. The braking engery is causing the bus voltage to increase and overvoltage the vfd
the soluton is to set the conveyor speeds the same or install a braking resister on the receiving conveyor vfd.

+1, or try setting the downstream conveyor a touch faster than the upstream.

 

[Jackllx]

+1, or try setting the downstream conveyor a touch faster than the upstream.

From your discription it tells me thwt the receiving conveyor is running a little slower then the sending conveyor and when the product is passed from the faster conveyor to the slower conveyor the receiving conveyor has to brake the produce and slow it down. The braking engery is causing the bus voltage to increase and overvoltage the vfd
the soluton is to set the conveyor speeds the same or install a braking resister on the receiving conveyor vfd.

Thanks for the replies, yeah I thought as much the same but the frequency of the drives are definitely the same.

Perhaps they are geared slightly differently....I will run the receiving conveyor faster or maybe get a tachometer on the rollers

 

[dmroeder]

Thanks for the replies, yeah I thought as much the same but the frequency of the drives are definitely the same.

Perhaps they are geared slightly differently....I will run the receiving conveyor faster or maybe get a tachometer on the rollers

The frequency being the same doesn't mean that the conveyors are running the same speed. A quick and dirty test would be to place to objects a known distance apart on the upstream conveyor (say, 2 boxes an inch apart), then run the object to the downstream conveyor. If they run into each other, then obviously the downstream conveyor is running slower.

 

[Jackllx]

The frequency being the same doesn't mean that the conveyors are running the same speed. A quick and dirty test would be to place to objects a known distance apart on the upstream conveyor (say, 2 boxes an inch apart), then run the object to the downstream conveyor. If they run into each other, then obviously the downstream conveyor is running slower.

Thanks for the reply, yes of course, however they are geared the same and they're identical conveyors.

Even whilst running downstream faster than upstream this overvoltage trip happens.

All the obvious stuff I have already tried before posting to the forum, just a really strange problem.

Might swap two drives over and see if its a problem with the drive, but it only happens with really heavy pallets which suggests that it's not the drive itself and it's a parameter.

I will put a log on the DC bus voltage....see if I spot anything there.

 

[dmroeder]

Curious, what HP motor and what size driver are we talking about here?

 

[Jackllx]

Curious, what HP motor and what size driver are we talking about here?

They're both 0.5hp, single phase

 

[GaryS]

A few things to consider here
Just because the set point on both vfd’s are the same dos not mean then the output frequency is exactly the same. There are many reasons for this one of them is the internal clock that runs everything on the vfd may have a slightly different speed this will effect the output frequency.
Then you have motor slip all motor have slip and here again it depends on many factors
The manufacture the load on the motor, the higher the load the larger the slip.
Then you have the mechanical load issues the small difference in the drive system can make the conveyors run at different speed, belt tension on the conveyor can make the conveyors run at different speeds there are others as well
To avoid the problem you are having is to setup your line so the receiving conveyor is always a little faster than the sending conveyor

Just adjust the speeds accordingly and I am sure that your problem be disappear

 

[Jackllx]

I've got both conveyors going into overvoltage fault when they're at speed conveying a heavy load will installing a break resistor on both of them sort the issue out? On a powerflex 525, or do they only dissapate the extra DC Bus voltage when they're breaking?

 

[kekrahulik]

I beleive the bus will dissipate to the brake when it gets too high.

Before you go there, check you DC bus voltage level when you aren't running product. Whats your incoming voltage to the drive (measured with a meter). If your incoming voltage is too high, your bus will be too high, and you could be living on the edge of overvoltage.

 

[Jim3846]

you can try 1 of 2 things.
extend the accel and decel out in time where ramping up or down does not cause overvoltage.

Or

Add a braking resister to both vfds and change a few parameters for braking in the drive.

or if you think your having heavy loads change out the vfd to a 1 HP and change the overload settings to the motor. That way you have extra amps for the vfd to handle the load.

When I get a heavy load the VFD usually goes into current limiting which is when the vfd ramps up in freq, the VFD will stop at a slower freq or current limiting.

Is the drive current limiting ?