Power factor correction and intelligent motor control unit

[Ainsley Whyte]

Do you know of one single unit that can offer power factor correction in addition to intelligent motor control for motors above 10hp

 

[petersonra]

Do you know of one single unit that can offer power factor correction in addition to intelligent motor control for motors above 10hp

ALL VFDs have close to a unity input power factor.

Intelligent motor control is a meaningless marketing term. You have to define what you actually need. Very few people need anything more than simple V/Hz control.

 

[Jraef]

ALL VFDs have close to a unity input power factor.

Intelligent motor control is a meaningless marketing term. You have to define what you actually need. Very few people need anything more than simple V/Hz control.

Yeah, you (OP) will need to define what you mean by "intelligent motor control" a little better.

In general though, there are only two ways to correct power factor in a motor circuit; add capacitors, or use a VFD. A VFD is, depending on your definition, "intelligent motor control". So to that end, it fits your request.

Now whether or not it is "intelligent" to spend extra money and constantly waste 3% of your energy on a VFD for a <10HP motor when you don't need to change the speed is a judgement call.

 

[petersonra]

Now whether or not it is "intelligent" to spend extra money and constantly waste 3% of your energy on a VFD for a <10HP motor when you don't need to change the speed is a judgement call.

There are more reasons than speed control to use a VFD on a motor. A few that come to mind.

Control of accel/decel rate to avoid mechanical shock that might damage the machine or product.

Potential elimination of mechanical equipment such as gear boxes, pulleys, belts, and clutches.

Sometimes when a machine is designed, not everything is known about how the machine has to run, so even if it will always run at the same speed, having a VFD allows one to dial the machine in during commissioning without having to change gearboxes or pulleys.

 

[don_resqcapt19]

Yeah, you (OP) will need to define what you mean by "intelligent motor control" a little better.

In general though, there are only two ways to correct power factor in a motor circuit; add capacitors, or use a VFD. A VFD is, depending on your definition, "intelligent motor control". So to that end, it fits your request.

Now whether or not it is "intelligent" to spend extra money and constantly waste 3% of your energy on a VFD for a <10HP motor when you don't need to change the speed is a judgement call.

But the VFD does not provide reactive power to make up for other low power factor loads, correct? It only improves power factor because it changes a poor power factor load to a high power factor load.

 

[kwired]

There are more reasons than speed control to use a VFD on a motor. A few that come to mind.

Control of accel/decel rate to avoid mechanical shock that might damage the machine or product.

Potential elimination of mechanical equipment such as gear boxes, pulleys, belts, and clutches.

Sometimes when a machine is designed, not everything is known about how the machine has to run, so even if it will always run at the same speed, having a VFD allows one to dial the machine in during commissioning without having to change gearboxes or pulleys.

starting and stopping accel/decel can be done with soft starters that go into bypass during run period.

The other things you mentioned are speed control aren't they?

Keep in mind gearboxes, pulleys, belts, clutches also have some energy losses as well.

 

[petersonra]

starting and stopping accel/decel can be done with soft starters that go into bypass during run period.

They are not real good for that purpose though.

The other things you mentioned are speed control aren't they?

You can run the VFD at a fixed speed so it is not about changing speed so much as avoiding mechanical equipment to set the speed.

Keep in mind gearboxes, pulleys, belts, clutches also have some energy losses as well.

True, but VFDs have an energy loss as well.

 

[zbang]

But the VFD does not provide reactive power to make up for other low power factor loads, correct?

AFAIK correct. However if we're talking about a single controller for a single motor, that's not relevant.

 

[don_resqcapt19]

AFAIK correct. However if we're talking about a single controller for a single motor, that's not relevant.

Just double checking as I had a long discussion on another forum with the other party insisting that you can use VFDs as power factor correction for the rest of the plant load.

 

[zbang]

Unless you can adjust a VFD to draw leading VARs, I don't see how it's possible. (There could be some uncommon drive out there that'll do this, but a cap bank will likely be easier and cheaper.)

Maybe someone was thinking of synchronous motors; over-excite one and you get leading VARs, I recall reading that some plants had unloaded sync motors just for PF correction.

 

[don_resqcapt19]

Unless you can adjust a VFD to draw leading VARs, I don't see how it's possible. (There could be some uncommon drive out there that'll do this, but a cap bank will likely be easier and cheaper.)

Maybe someone was thinking of synchronous motors; over-excite one and you get leading VARs, I recall reading that some plants had unloaded sync motors just for PF correction.

That is what I told him but he was insisting that drives and other equipment with front end rectifies provide leading VARs.