PowerFlex 525 - 4 motors assigned

[dvanovec]

Hi guys, I have a problem with setting up the parameters for PowerFlex 525.
So we have 4x motor connected in parallel to 1 PowerFlex, each motor is rated with as following:

P=0,75 kW
I=1,75A
U=460V
min-1=1725

When setting up the PF parameters, I'm aware of changing the parameter "Motor OL Current" with 1,75A*4, my concerns are now about other parameters such as : Motor NP FLA, Motor NP RPM, Motor NP Power.
I'm really not sure if I should *4 it or set up the values following one motor NP.
Btw. all 4 motors are similiar

Thanks for any help, truly appreciate that!

 

[robertmee]

Hi guys, I have a problem with setting up the parameters for PowerFlex 525.
So we have 4x motor connected in parallel to 1 PowerFlex, each motor is rated with as following:

P=0,75 kW
I=1,75A
U=460V
min-1=1725

When setting up the PF parameters, I'm aware of changing the parameter "Motor OL Current" with 1,75A*4, my concerns are now about other parameters such as : Motor NP FLA, Motor NP RPM, Motor NP Power.
I'm really not sure if I should *4 it or set up the values following one motor NP.
Btw. all 4 motors are similiar

Thanks for any help, truly appreciate that!

You'll need individual motor OL protection for each motor and youll need to set the drive up in V/,,Hz control. Motor RPM won't really matter in v/hz mode, but set it to the motor rpm as they're all the same. Set FLA to sum of 4 motors plus 20%. Set HP to 4x HP. Motor OL Current can be higher than 1.75*4 depending on SF rating of motors.

Rockwell has a good tech paper on this

https://www.rockwellautomation.com/...controlling-multiple-motors-with-one-vfd.html

 

[GaryS]

It’s a bad idea to have multiple motors on a single vfd
The overall performance goes down with each mote you add it’s not possible to setup the vfd properly so that puts you down even more
It’s required to have an OL relay on each motor so the overload in the vfd will be of no value.
When you consider the cost of the separate OL relays and the cost to actually wire them there is no real saving there. I know everybody thinks the motors will all run at the same speed but that not true. Variables in the motor, each normal load and other variables will cause the motor to run at slightly different speed if the motors are sharing a common load then one or more motors could even be breaking causing others to overload

 

[beethoven_ii]

I know everybody thinks the motors will all run at the same speed but that not true.

A company I used to work for have done this for many years and I know it works if you get the motors paired from the manufacturers. They make elevators and de-elevators with side gripping belts on each side and when using paired motors they work great through 1 inverter. If you don't get paired motors or you try to run motors through 2 separate inverters then you are correct that you'll get variations which in my example causes the product to twist inside the elevators/de-elevators. I have seen it myself many times.

 

[robertmee]

It’s a bad idea to have multiple motors on a single vfd
The overall performance goes down with each mote you add it’s not possible to setup the vfd properly so that puts you down even more
It’s required to have an OL relay on each motor so the overload in the vfd will be of no value.
When you consider the cost of the separate OL relays and the cost to actually wire them there is no real saving there. I know everybody thinks the motors will all run at the same speed but that not true. Variables in the motor, each normal load and other variables will cause the motor to run at slightly different speed if the motors are sharing a common load then one or more motors could even be breaking causing others to overload

There are lots of applications where multiple motors on a single VFD make sense and is economical. We use them on vibratory rock feeders where any slight speed variation doesn't matter.

 

[jraef]

Hi guys, I have a problem with setting up the parameters for PowerFlex 525.
So we have 4x motor connected in parallel to 1 PowerFlex, each motor is rated with as following:

P=0,75 kW
I=1,75A
U=460V
min-1=1725

When setting up the PF parameters, I'm aware of changing the parameter "Motor OL Current" with 1,75A*4, my concerns are now about other parameters such as : Motor NP FLA, Motor NP RPM, Motor NP Power.
I'm really not sure if I should *4 it or set up the values following one motor NP.
Btw. all 4 motors are similiar

Thanks for any help, truly appreciate that!

Most of those settings actually don’t matter when doing multiple motor applications, the drive is going to be acting strictly as a variable frequency power source. The motor NP FLA should be set at the VFD Maximum Output Current rating so that it will only trip if all four motor running currents exceed what the drive is rated for. The rest can be ignored / left at factory defaults. They are related mostly to what the display will show if querying on the specifics of one motor, which in this case becomes a moot point.

It IS important here to make sure the VFD is programmed for V/Hz operation, it cannot work in any “Vector” mode. Once you have more than one motor, the VFD has no way to differentiate one from another, it only sees totals.

The NEC absolutely requires that each motor have its own individual OL protection, but a standard OL relay cannot interrupt current, it’s just a control signaling device. So in implementing a standard OL relay, you would wire all of the trip contacts in series to the “Enable” input of the VFD and if one motor overloads, you shut down the VFD and all motors stop. The problem with this use case is that the individual motor circuits are relying on the upstream Short Circuit Protective Device (fuses or breaker) that is feeding the VFD input as the only (legal) protection for, in this case, motors and circuits that are 1/4 the size and the NEC rules on sizing the SCPD often don’t work. Adding fuses on the output side is a really bad idea, so it becomes an issue.

Therefore the ALTERNATIVE to that, and the RECOMMENDED implementation, is to use separate IEC style Motor Protection Circuit Breakers (MPCB) for each motor, such as a Rockwell Bul. 140MT on the output side of the drive. Then because they are on the output of the VFD, there are special versions designed to handle the harmonic rich variable frequency, with in that case a “-D8V” variant. This way any individual motor that overloads will cause that one 140MT to trip, but the others can continue to run. If you WANT to shut down all of the connected motors you can still do that by adding an aux contact to reach MPCB, but it becomes a choice, not a necessity. This is an older document using their predecessor to the 140MT, but the concept is identical.

 

[dvanovec]

You'll need individual motor OL protection for each motor and youll need to set the drive up in V/,,Hz control. Motor RPM won't really matter in v/hz mode, but set it to the motor rpm as they're all the same. Set FLA to sum of 4 motors plus 20%. Set HP to 4x HP. Motor OL Current can be higher than 1.75*4 depending on SF rating of motors.

Rockwell has a good tech paper on this

https://www.rockwellautomation.com/...controlling-multiple-motors-with-one-vfd.html

What about parameters Current Limit1 and Current Limit2? What values should I set up here and also what is the difference between setting those 2 values and Motor OL Current? I thought when theres more Amps than I set up in Motor OL Current, the PF will cut down the output current and goes into some kind of fault ?

 

[robertmee]

What about parameters Current Limit1 and Current Limit2? What values should I set up here and also what is the difference between setting those 2 values and Motor OL Current? I thought when theres more Amps than I set up in Motor OL Current, the PF will cut down the output current and goes into some kind of fault ?

Leave them at default....current limiter is for the drive protection, not the motor. If your drive is sized properly for the load, you shouldn't be near current limit.

 

[dvanovec]

Leave them at default....current limiter is for the drive protection, not the motor. If your drive is sized properly for the load, you shouldn't be near current limit.

Thanks man!
You helped me so much to not only set up the parameters correctly but also to understand the settings, really appreciate that!