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eltech
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Powerflex 70 with Multiple Motors

08/18/2016 7:04 AM

This is regarding a brand new installation. We are using one 11KW, 220V PF70 on a crane for travel. There are four 2.2KW, 2 pole motors connected to the PF. All has its own overload protection. Two motors are 6m away and the other 2 are 15m away. We have sized a Brake resistor accordingly. We have set 3 speeds 10Hz, 25Hz and 50Hz. We re using V/Hz for control.When running on speed 3, max amps shown on PF is 20A, total FLA of motors are 32A.

The issue that we are having is that we are see hardware over-current fault about 10 times/hr. We cycle power to the PF and start again.

Tech support have not found any solutions as yet. Any help will be good.
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JohnDG
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#1

Re: Powerflex 70 with Multiple Motors

08/18/2016 8:23 AM

"we are see hardware over-current fault" - how do you "see" the fault?

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phoenix911
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#3
In reply to #1

Re: Powerflex 70 with Multiple Motors

08/18/2016 2:34 PM

how do you "see" the fault?

probably a sequence of blinking lights.

If I recall... you should adjust your ramp.

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SolarEagle
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#2

Re: Powerflex 70 with Multiple Motors

08/18/2016 10:27 AM

"continuous drive ampacity should be the total of all motor FLAs plus 10% extra for each additional motor."

http://www.plctalk.net/qanda/showthread.php?t=102376

http://literature.rockwellautomation.com/idc/groups/literature/documents/in/drives-in001_-en-p.pdf

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JRaef
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#4

Re: Powerflex 70 with Multiple Motors

08/18/2016 6:22 PM

HW Over Current Fault is a valid fault display on the PF70 HIM.

What that means is that at some point, something about the load was attempting to draw in excess of 220 to 300% of the drive's rated current. This feature is hardware delineated, meaning it does not wait for any calculations from the drive's microprocessor to act, it is an embedded IC that performs this function as a "last ditch" effort to prevent damage to the drive transistors.

The most common cause on multi-motor applications is cable capacitance charging current. That's the reason why they require that the VFD current rating be the total FLA + 10% in that application.

T2.2kW 220V are likely somewhere around 9.5A each, so the total for 4 would be 38A. If you bought the 11kW HEAVY DUTY version of that drive rated at 54A, it should have been fine. However if someone bought the 11kW NORMAL DUTY rated version of that drive rated at 42A, a load of 38A and multiple motors is right on the ragged edge of acceptable. My guess is that is what's happening here.

Your choices are: buy the 54A rated drive and learn your lesson or buy and install a 54A rated (minimum) load reactor and hope that it slows down the rise time of the capacitive charging current pulses to where they don't cause the drive to trip. If the reactor doesn't work, you will have to buy the bigger drive anyway, and the reactor is another "should be there" option for multiple motors anyway, so leave it there when you do.

If you DID buy the 54A rated drive, then add the load reactor, it will likely take care of it.

If you DID buy the 54A drive and you ALREADY have a load reactor, then your drive is likely defective.

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eltech
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#5
In reply to #4

Re: Powerflex 70 with Multiple Motors

08/18/2016 7:52 PM

Thanks Jraef-Motors rated 8.3A at 220V. 8.3*4+10%=36.5A. It is a normal duty VSD. We may be close to the edge.

Hopefully we will have the reactor in today and hope for the best.

PS.-We don't size Drives, this was recommended for us to use.
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eltech
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#9
In reply to #4

Re: Powerflex 70 with Multiple Motors

08/21/2016 11:25 PM

Reactor is installed-problem has gone away.
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JRaef
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#12
In reply to #9

Re: Powerflex 70 with Multiple Motors

08/22/2016 5:47 PM

"Reactor is installed-problem has gone away."

Thought it would...

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NotUrOrdinaryJoe
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#6

Re: Powerflex 70 with Multiple Motors

08/19/2016 7:34 AM

Did you set up the drive? Do you have the cable and set up software? Many times the parameters of a drive are set to defaults which may not work as well as when the parameters are set up to match your motor.

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rwilliams
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#7
In reply to #6

Re: Powerflex 70 with Multiple Motors

08/19/2016 4:08 PM

At least do the static tune with all the cables connected, it could make the difference.
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JRaef
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#8
In reply to #7

Re: Powerflex 70 with Multiple Motors

08/21/2016 9:08 PM

No, you can't do a static tune on multiple motors and you can't use vector control.

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rwilliams
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#10
In reply to #8

Re: Powerflex 70 with Multiple Motors

08/22/2016 2:06 PM

My mistake, the Static Tune on the P70s builds the motor model for vector control, and doesn't adjust the max allowable di/dt rate to suit the output circuit, as I thought. The values from a static tune are ignored when using V/Hz control, the only way recommended to run multiple motors.
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eltech
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#11
In reply to #10

Re: Powerflex 70 with Multiple Motors

08/22/2016 4:56 PM

I guess all drives works on a similar method, but I did notice the recommendation for multiple motor control for an Altivar 71 is vector control with no tune.
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