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Old November 14th, 2021, 09:19 PM   #1
DemetrioUrrea
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Powerflex 400 25HP wird amp behavior

Hello I have a powerflex 400 of 25HP for a 60amp 25HP motor, the motor have a belt that move the clarifier of milk. It is a process that requires strength to move.

So I try with the motor without the clarifier the vdf works well with a constant amp of 12 to the max of 50hz that is set up with a ramp of 600 sec.

Then I try with the belt that move the clarifier... The vdf start the ramp with a wird amp behavior like 10 sec 100 amp and then 13 amp for 10 sec.

When it gets to 50hz (the max) it starts the same behavior 13 amp when it reach the max RPM and when it decrease a little bit it gets 100 amp to get to the max RPM again.

In this vdf powerflex 400 I didn't see the % of torque options that the last one Fuji had.

Someone told me that powerflex 400 is not for power processed, they are focus in pumps and blowers more alike, and that I need a vdf vectorial like a powerflex 725.

What do you think...

PD: as the 100 amp is like 10 sec the protections dont show up.
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Old November 14th, 2021, 09:27 PM   #2
DemetrioUrrea
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PD: I made a try with water and hot water, in that point with the max hz (and 6800rpm) when the hot water start to flow the amp gets constant in 75 amp, but the motor dosnt get to the 6800 rpm again it just keep trying in 6700rpm and it mantains the 75amp triggering the motor protection for overload.
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Old November 15th, 2021, 06:24 AM   #3
TWS
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The inertia of the load is too great for the drive.
On a centrifuge application you need to upsize the drive.
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Old November 15th, 2021, 06:53 AM   #4
DemetrioUrrea
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This has something to do with my VFD being a VT or ND and my process being HD o CT ? How do i know when i need a VFD with more HP ?
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Old November 15th, 2021, 07:20 AM   #5
TWS
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Quote" This has something to do with my VFD being a VT or ND and my process being HD o CT " Yes.

From Rockwell literature:

Variable Frequency Drives control AC current frequency, resulting in
the control of acceleration and torque. The major advantages of
starting high inertia loads with a VFD are:
• They provide greater flexibility and performance in torque
control than any form of reduced voltage starting.
• Compared to other reduced voltage starting options, VFDs
precisely control acceleration.
• The line current is less than a solid-state motor starter for
equivalent torque output.
• Derating of VFDs is USUALLY not required.
The major points of consideration when starting high inertia loads
using a VFD are:
• Some drives create harmonics that may exceed harmonic
limitations on the power system.
• VFDs are often more expensive than reduced voltage starting
options.
• VFDs using IGBT technology may generate high frequencies that
may be detrimental to older motors and may require extra
consideration for long motor cables

You should contact a Drives expert to help you with this application.
Attached Files
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Old November 23rd, 2021, 01:51 PM   #6
inick2005i
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I believe if you use an encoder on the motor shaft to report back to an encoder card on the VFD, you can run as slow as you want and accelerate as slow as you want. Running a VFD in open loop mode without an encoder requires that accel times be relatively quick (10 seconds or less) or else the windings just saturate with current with no motor movement.

I have zero experience with such a long accel time (600 sec), but I have heard cases where a 5 second accel time was stalling a motor, but when changed to 1 second it worked fine and never stalled.
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Old November 24th, 2021, 02:33 PM   #7
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Quote:
Originally Posted by inick2005i View Post
Running a VFD in open loop mode without an encoder requires that accel times be relatively quick (10 seconds or less) or else the windings just saturate with current with no motor movement.
That doesn't sound right to me - can you explain your reasoning on this?
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Old November 24th, 2021, 03:16 PM   #8
lfe
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Accelerate a heavy load requires a lot of torque and therefore a lot of current on the motor.

Making the ramp smoother can reduce the current somewhat but also as the start is longer at the end the motor can get quite hot.

A balance should be found between duration and current so the motor and transmission do not suffer excessively.
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Old November 24th, 2021, 04:57 PM   #9
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The PowerFlex 400 is built and sold as an "HVAC" drive for centrifugal machines like pumps and fans, what Rockwell calls "Normal Duty" (because 70% of all VFDs are used on centrifugal machines) and others call "Variable Torque". There is no option for an encoder feedback for this drive, as there is no option for a Heavy Duty (Constant Torque) load profile, it was not made for that.

Someone picked out the wrong drive.
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Old November 24th, 2021, 07:52 PM   #10
inick2005i
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Quote:
Originally Posted by rupej View Post
That doesn't sound right to me - can you explain your reasoning on this?
I know when we have pumps or feeder screws (where I work) running at below say, 7 hertz, the motors may run, but sometimes they will sit there and just humÂ….not spin, and basically only generate heat. Recently on one of our feeders we had to install an encoder on the shaft of the motor and now we can run the screw at almost zero speed without worrying about it stalling. The drive will give more power if it senses the shaft isnÂ’t moving as it should be. The reason we donÂ’t just change the gearbox is because the material setpoints vary so much from product to product, slow line speed to fast. We have a maximum frequency of 90 hertz that we may need occasionally and a minimum of 6-7 hertz that we need occasionally.

Why on earth someone would need to accelerate something over the course of 10 minutes absolutely blows me away. The OP can surely change the way this operation is done so that accel times can be done in a relatively quick manner.
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Old November 24th, 2021, 10:00 PM   #11
DemetrioUrrea
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Hello everyone, that powerflex 400 was not selected by anyone thanksfully, it was the only vfd in stock and we tryed and failed with it. i actually said that it is not te correct vfd and that i need the original, i suspect that the original is a vectorial VFD, it has torque parameters, and it was configured with a ramp of 340 sec...

though it dosnt has a sensor or anything it was configured sensorless.
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Old November 25th, 2021, 11:33 AM   #12
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As mentioned a centrifuge is typically a very high inertia load.
Certainly you will want to oversize the VFD.
And you'll want to operate the VFD in a V/Hz mode.
I've installed various brands of VFDs on centrifuges and found this always to work the best. In Vector modes you'll notice the speed hunting which causes the current oscillations as you described.
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