VFD

[jsilva]

I need to feed a new 100HP compressor with built in VFD. The installer wants me to install fast acting fuses to protect the electronics.
The testing paper I received from the manufacture calls for the main power supply to be 460V, and Max fuse of 160A.
The main tag on the compressor in the other hand call for 3ph 380-460V, FLA is 178/147A. The largest motor FLA 164A.
How would I calculate this compressor? Should I provide 160A fast acting fuse since it's being controlled by VFD? or should I calculate 164A* 300% for fast acting fuse?
Any suggestion please!
Thanks,

 

[Jraef]

The VFD installation manual needs to (assuming it is UL listed) give you the maximum fuse size for which that VFD is listed. Smaller than that runs the risk of blowing some very expensive fuses. Often times depending on the VFD design, the input amps of the VFD is actually lower than the output amps (because essentially the VFD corrects the power factor of the motor), so it’s entirely plausible that the maximum fuse size is 160A for a motor with a 147 A FLC, but to be honest, the numbers you posted are a bit confusing. Even if it is supposed to be 147A, a 160A fuse is cutting it a bit close. If the motor is truly 160A FLC, a 160A high speed semiconductor fuse is likely to clear whenever the VFD pulls 150% current, which on a compressor is highly likely.

Either way, don’t go with 300% of the motor FLC unless the VFD install manual says that’s OK, you might end up violating the UL listing of the VFD. In a UL listed VFD (since around 2005), the VFD is required to provide Short Circuit protection for the MOTOR, the SCPD feeding the drive is only there to protect the DRIVE so it is sized for that, per the mfr recommendations.

 

[ptonsparky]

I need to feed a new 100HP compressor with built in VFD. The installer wants me to install fast acting fuses to protect the electronics.
The testing paper I received from the manufacture calls for the main power supply to be 460V, and Max fuse of 160A.
The main tag on the compressor in the other hand call for 3ph 380-460V, FLA is 178/147A. The largest motor FLA 164A.
How would I calculate this compressor? Should I provide 160A fast acting fuse since it's being controlled by VFD? or should I calculate 164A* 300% for fast acting fuse?
Any suggestion please!
Thanks,

IMO, Fast acting fuses won’t protect the electronics. They may limit the burn marks, flying pieces and smoke.

To CYA, I would use the 160 the mfg calls for, whichever that is. Time delay or fast acting.

Sounds like you you have a lot of conflicting information.

 

[Jraef]

IMO, Fast acting fuses won’t protect the electronics. They may limit the burn marks, flying pieces and smoke...

That’s my position too, at least on smaller drives. About the only thing that will make those fuses clear (if sized right) is that one of the rectifier components has ALREADY failed and in that case, there is nothing left to protect with the fuse beyond avoiding a fire, which a less expensive fuse will accomplish. Modern VFDs under about 150HP are now built with devices called IPMs that have all of the rectifier and inverter components in one molded piece so if one component blows, it’s all toast anyway. The only thing the high speed semiconductor fuses do is increase the cost of the failure. But unfortunately the fuse mfrs have successfully convinced most VFD mfrs to list their drives using them, so that’s what you must use.

 

[Besoeker]

That’s my position too, at least on smaller drives. About the only thing that will make those fuses clear (if sized right) is that one of the rectifier components has ALREADY failed and in that case, there is nothing left to protect with the fuse beyond avoiding a fire, which a less expensive fuse will accomplish. Modern VFDs under about 150HP are now built with devices called IPMs that have all of the rectifier and inverter components in one molded piece so if one component blows, it’s all toast anyway. The only thing the high speed semiconductor fuses do is increase the cost of the failure. But unfortunately the fuse mfrs have successfully convinced most VFD mfrs to list their drives using them, so that’s what you must use.

No disagreement with that. We just used standard ABB fuse switches for protection and isolation on standard VFDs. And on the specials we designed and built from coponent level. The IGBT desat protection was orders of magnitude faster than any fuse could offer.

 

[Phil Corso]

Gentlemen...

It would be a disservice to ignore the addition of Surge Arrestors, now called SPD, for Surge Protective Devices! They are a far cry from what we "old", now "Older", engineers called Surge Diverters!

Regards, Phil Corso

 

[kwired]

IMO, Fast acting fuses won’t protect the electronics. They may limit the burn marks, flying pieces and smoke.

To CYA, I would use the 160 the mfg calls for, whichever that is. Time delay or fast acting.

Sounds like you you have a lot of conflicting information.

I agree and CYA is going to only be good as long as warranty is good. 10 hp and smaller drives, maybe you mark up drive a little more just in case and forget the expensive fuses and eat the cost if you must when it does fail. Warranty is likely only a year anyway. Surge protection is going to help you some here.

Main rectifier is what you are protecting with those expensive fuses, load end is protected by the software. But if front end has already failed, so what, less spectacular failure mode still leaves it not working. When those small drives have a failed front end you end up replacing the entire drive anyway.

 

[Besoeker]

Gentlemen...

It would be a disservice to ignore the addition of Surge Arrestors, now called SPD, for Surge Protective Devices! They are a far cry from what we "old", now "Older", engineers called Surge Diverters!

Regards, Phil Corso

Not sure about the relevance to the OP's point.

 

[Phil Corso]

Besoeker...

Was not Surge Protection mentioned!

Phil

 

[Russs57]

I don’t have a lot of experience with drives. All of the ones in this size range that I have dealt with had their own fuses.

I would be reluctant to put fuses ahead of the drive that were very sensitive. IMHO you could end up single phasing the drive and putting extra stress on the other diodes. In short doing more harm than good. I would add a phase monitor if I did what you are proposing.

Perhaps newer drives won’t run on two phases but older ones would.

I wonder how many replace capacitors on a regular basis? Loved the older drives that had discrete parts made to be replaced in the field.

 

[Besoeker]

Besoeker...

Was not Surge Protection mentioned!

Phil

Not by the OP unless I missed it.

 

[Jraef]

I don’t have a lot of experience with drives. All of the ones in this size range that I have dealt with had their own fuses.

I would be reluctant to put fuses ahead of the drive that were very sensitive. IMHO you could end up single phasing the drive and putting extra stress on the other diodes. In short doing more harm than good. I would add a phase monitor if I did what you are proposing.

Perhaps newer drives won’t run on two phases but older ones would.

I wonder how many replace capacitors on a regular basis? Loved the older drives that had discrete parts made to be replaced in the field.

Most modern drives now monitor the DC bus ripple as a way of mitigating an input phase loss. Under light loads, the extra ripple can be handled by the bus caps so as long as the bus ripple getting to the transistors is low enough, there is no reason to shut down the drive. That way you can use the VFD as a phase converter by simply over sizing it, or on loads like centrifugal pumps you can mitigate the phase loss by overriding the speed command to lower as necessary to shed load, but keep operating. The ones that don't allow this yet will for the most part add Input Phase Loss protection. There may still be a few older designs out there that do neither, but they are falling by the wayside as the market demands more flexibility from the drives.

 

[kwired]

I don’t have a lot of experience with drives. All of the ones in this size range that I have dealt with had their own fuses.

I would be reluctant to put fuses ahead of the drive that were very sensitive. IMHO you could end up single phasing the drive and putting extra stress on the other diodes. In short doing more harm than good. I would add a phase monitor if I did what you are proposing.

Perhaps newer drives won’t run on two phases but older ones would.

I wonder how many replace capacitors on a regular basis? Loved the older drives that had discrete parts made to be replaced in the field.

I believe such fuses often are well above the drive rating as far as the overload trip point, they are specified because of how they respond to short circuit/ground fault level of current. As earlier mentioned it mostly leads to less spectacular failure mode, but when that rectifier at the front end of the drive has failed it is still bad whether it blew it to smithereens or not. If it is on a small drive, it cost about as much or even more to repair it than to to replace the whole drive, so it makes one question the real value of those expensive fuses on a lot of applications.

 

[GoldDigger]

So this really does approach the situation of the old joke about semiconductors being devices that fail rapidly and spectacularly to prevent damage to expensive fuses?

 

[kwired]

So this really does approach the situation of the old joke about semiconductors being devices that fail rapidly and spectacularly to prevent damage to expensive fuses?

On small drives yes. On large drives it validates the warranty if the repair is going to cost more than the fuses.

 

[Phil Corso]

Besoeker... Was not Surge Protection mentioned! Phil

Beseoker... Perhaps I should have said, "Why weren't Surge Protection Devices, suggested, by VFD experts ! Phil

 

[Besoeker]

Beseoker... Perhaps I should have said, "Why weren't Surge Protection Devices, suggested, by VFD experts ! Phil

Well, we never used them nor felt the need to use them.

 

[kwired]

Well, we never used them nor felt the need to use them.

Do you commonly have surge protection elsewhere on premises that you feel is sufficient enough to also provide reasonable protection to your drives?

 

[Besoeker]

Do you commonly have surge protection elsewhere on premises that you feel is sufficient enough to also provide reasonable protection to your drives?

The drive input semiconductor devices usually have snubbers.
A little tale. One of our customers, a pump manufacturer, supplied pumps to Hong Kong. His customer supplied the VFDs. I won't say who the manufacturer was but a well known brand. The diodes on the input bridge kept failing. I was called in to investigate. I had prior information on the drives. No snubbers. I went equipped to remedy that.
It was a fix.

Oh well, it got me ten days in Hong Kong.