Site PF & drives

[Mike01]

when looking at a site evaluating for an existing testing facility [vehicle testing] with multiple test cells utilizing dyno's / drives I discovered that the incoming pf was pretty low [0.8 based on peak utility demand info] this information was provided from the local utility it turns out the equipment is never utilized to its maximum or near maximum capacity and at the low operating end of the drive the pf gets pretty bad and this can be seen in the overall site pf. just curious what causes the bad pf when the drives operate at the lower end of their operating parameters?

 

[GoldDigger]

Are these drives actually commercial VFDs or are they a custom construction by the dyno manufacturer(s)?

 

[mike_kilroy]

when looking at a site evaluating for an existing testing facility [vehicle testing] with multiple test cells utilizing dyno's / drives I discovered that the incoming pf was pretty low [0.8 based on peak utility demand info] this information was provided from the local utility it turns out the equipment is never utilized to its maximum or near maximum capacity and at the low operating end of the drive the pf gets pretty bad and this can be seen in the overall site pf. just curious what causes the bad pf when the drives operate at the lower end of their operating parameters?

Based on most common vfd drives today, the input PF of vfd drives does not change at all due to what the motor is or is not doing; it remains about .98 at all times. So your .80 PF does not make any sense - yet.

There IS the other kind of PF caused by distortion - like diode front end vfds make; is that what they are referring to?

Are your drives AC? DC? SCR? PWM? Line Regen? We cannnot assume what you have (as I did above)...

See? YOU NEED MORE INFO TO ANSWER THIS. WE NEED MORE INFO TO HELP EXPLAIN IT TOO.

I say you should find out from POCO WHICH PF they refer to as .80. Then you have info to begin addressing it.

At that point, you should tell us what drives, sizes, models, etc, so we can give opinions on solutions.

 

[Besoeker]

Based on most common vfd drives today, the input PF of vfd drives does not change at all due to what the motor is or is not doing; it remains about .98 at all times. So your .80 PF does not make any sense - yet.

There IS the other kind of PF caused by distortion - like diode front end vfds make; is that what they are referring to?

Are your drives AC? DC? SCR? PWM? Line Regen? We cannnot assume what you have (as I did above)...

See? YOU NEED MORE INFO TO ANSWER THIS. WE NEED MORE INFO TO HELP EXPLAIN IT TOO.

I say you should find out from POCO WHICH PF they refer to as .80. Then you have info to begin addressing it.

At that point, you should tell us what drives, sizes, models, etc, so we can give opinions on solutions.

I agree. Not enought information.

 

[Mike01]

Unknowns

Unknowns

Guys thanks for the input at this time I do not know the drive manufacturers, these were provided as a package by the equipment manufacturer that varied depending on when / who installed them So I do not know if they are SCR, IGBT, Regenerative, etc. All of them utilize a drive isolation transformer and have different voltage requirements [xfmr. secondaries for the drive xfmr.'s range from 240, 480, 690] kind of a mixed bag. I just recall someone indicating that when equipment operates at the low end that the PF of the units can be pretty bad / low. I was not sure if this is what was driving the low site pf will have to do some additional digging....

 

[GoldDigger]

If the transformers in question are on the input of the drives, then the magnetizing current of the transformer will represent a significant and constant reactive load while the resistive power required by the drive varies with output power.
When the resistive load it at a minimum the PF will be lowest.

 

[Jraef]

If the transformers in question are on the input of the drives, then the magnetizing current of the transformer will represent a significant and constant reactive load while the resistive power required by the drive varies with output power.
When the resistive load it at a minimum the PF will be lowest.

Yes, but that would only represent a small fraction of the load on each drive, they would need to have a LOT of drives to make that show up as poor power factor for the entire site.

My guess is that we should look at the inclusion of the drive isolation transformers as a clue. Modern PWM IGBT drives don't really need them in most cases. So my guess is that these are older thyristor based CSI drives, maybe even eddy current drives! Either of those would definitely cause lower PF as load is dropped.

 

[Sahib]

when looking at a site evaluating for an existing testing facility [vehicle testing] with multiple test cells utilizing dyno's / drives I discovered that the incoming pf was pretty low [0.8 based on peak utility demand info] this information was provided from the local utility it turns out the equipment is never utilized to its maximum or near maximum capacity and at the low operating end of the drive the pf gets pretty bad and this can be seen in the overall site pf. just curious what causes the bad pf when the drives operate at the lower end of their operating parameters?

May be the sensing device has low sensitivity so that for low loads, it fails to compensate for low power factor. So check for it also.

 

[Besoeker]

Yes, but that would only represent a small fraction of the load on each drive, they would need to have a LOT of drives to make that show up as poor power factor for the entire site.

My guess is that we should look at the inclusion of the drive isolation transformers as a clue. Modern PWM IGBT drives don't really need them in most cases. So my guess is that these are older thyristor based CSI drives, maybe even eddy current drives! Either of those would definitely cause lower PF as load is dropped.

Or possibly regenerative DC drives being on dynamomenters. That could account for the low PFC.