# Medium voltage VFD



## micromind (Aug 11, 2007)

I've hooked up about a dozen Allen Bradley 4160 VFDs over the years. Never had a problem with them.


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## Helmut (May 7, 2014)

Nothing on Amazon?


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## MDShunk (Jan 7, 2007)

+1 on A-B, for no other reason except that it's probably the most familiar brand to anyone who may work on it later. There are many fine brands out there, but of those who deal with VFD's from many manufacturers, the AB is probably the one they come across the most. If price is a primary concern, however... well..... :sad:

If this site already uses VFD's, there's a pretty decent argument to be made for harmonizing the brand (and, maybe even the model) with what they have deployed already.


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## frenchelectrican (Mar 15, 2007)

I been using AB system too and it work good and I dont heard much bad stuff with AB system and it work good but as MDshunk mention just be aware of price that all. 

The duribity is good on the AB unit.


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## JRaef (Mar 23, 2009)

If the motor is already existing, the A-B PowerFlex 7000 is the best at being totally compatible with older motors that were not designed to be run from inverters, because it is a Current Source Inverter that uses power devices that don’t produce the voltage pulses seen by transistor based drives, and are much much more reliable, having an MTBF of 11+ years. If you go with any other brand, you MUST add a dv/dt filter to the output to protect the motor. The other suppliers will try to convince you that it is unnecessary because it defeats their low price strategy, but the voltage stresses from a transistorized drive, as all Voltage Source inverters are (like the Benshaw) will damage your motor’s winding insulation eventually, usually sooner than later. In addition, many designs have distinct disadvantages when it comes to their failure mode. 

The only other type of drive worth considering (in my opinion) is what’s called a “Cascaded H Bridge” Voltage Source Inverter, what you get with a Siemens Perfect Harmony drive, an A-B PowerFlex 6000, Yaskawa MV1000 or similar product from Schneider (can’t remember their trade name on it, but used to be called a “Harvest” drive in China before they bought it). The reason is that CHB drives are comprised of multiple LOW VOLTAGE cells in series to make the MV, so if something goes wrong, you can bypass a bad cell, remove it, operate the motor at a reduced speed, and work on the cell at your bench. All of the other MV drives on the market are built using MV components that, if they fail, leave you stranded until their factory service person arrives and often have power cells weighing 250-400# that need a special portable lift to remove them for servicing. Those are the cheaper ones and they survive in the market for that reason alone. 

Full disclosure, this is what I do for a living now and I work for A-B now, so my opinions are biased, but I have been in this industry from almost the beginning and have experience with most of the products out there. I used to work for Benshaw but they only got into the MV drive business a couple of years ago, long after I left. I have no direct experience with it because it is too new, but their design strategy is one of the cheap version Voltage Source Inverters. I have yet to see them win a project on the West Coast and I get involved in most of the projects that come along out here. I can probably guess where you are getting your Benshaw price from and although I have to respect their position in the LV drives and motor business, they have zero experience dealing with MV, especially drives. Be careful.


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## micromind (Aug 11, 2007)

I don't think I'd go with low bid on a 4160 VFD. 

Just about any kind of failure would very likely be expensive. Almost certainly more than the difference between low bid and one of the more expensive brands that have been around for a while.


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## glen1971 (Oct 10, 2012)

micromind said:


> I don't think I'd go with low bid on a 4160 VFD.
> 
> Just about any kind of failure would very likely be expensive. Almost certainly more than the difference between low bid and one of the more expensive brands that have been around for a while.


x2.. Not only in repairs, but in lost production time... There is a Powerflex 7000 on a site we've got running a 1,000 hp gas compressor and it is down for the second time in 2 months.. Both times are due to internal failures and are waiting up to 3 weeks to get parts and service tech to install.. The cause (and I had to chuckle) is being chalked up to "flies getting into the drive and shorting out the parts"... Maybe when winter hits, we can run it.. lol..


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## Southeast Power (Jan 18, 2009)

JRaef said:


> If the motor is already existing, the A-B PowerFlex 7000 is the best at being totally compatible with older motors that were not designed to be run from inverters, because it is a Current Source Inverter that uses power devices that don’t produce the voltage pulses seen by transistor based drives, and are much much more reliable, having an MTBF of 11+ years. If you go with any other brand, you MUST add a dv/dt filter to the output to protect the motor. The other suppliers will try to convince you that it is unnecessary because it defeats their low price strategy, but the voltage stresses from a transistorized drive, as all Voltage Source inverters are (like the Benshaw) will damage your motor’s winding insulation eventually, usually sooner than later. In addition, many designs have distinct disadvantages when it comes to their failure mode.
> 
> The only other type of drive worth considering (in my opinion) is what’s called a “Cascaded H Bridge” Voltage Source Inverter, what you get with a Siemens Perfect Harmony drive, an A-B PowerFlex 6000, Yaskawa MV1000 or similar product from Schneider (can’t remember their trade name on it, but used to be called a “Harvest” drive in China before they bought it). The reason is that CHB drives are comprised of multiple LOW VOLTAGE cells in series to make the MV, so if something goes wrong, you can bypass a bad cell, remove it, operate the motor at a reduced speed, and work on the cell at your bench. All of the other MV drives on the market are built using MV components that, if they fail, leave you stranded until their factory service person arrives and often have power cells weighing 250-400# that need a special portable lift to remove them for servicing. Those are the cheaper ones and they survive in the market for that reason alone.
> 
> Full disclosure, this is what I do for a living now and I work for A-B now, so my opinions are biased, but I have been in this industry from almost the beginning and have experience with most of the products out there. I used to work for Benshaw but they only got into the MV drive business a couple of years ago, long after I left. I have no direct experience with it because it is too new, but their design strategy is one of the cheap version Voltage Source Inverters. I have yet to see them win a project on the West Coast and I get involved in most of the projects that come along out here. I can probably guess where you are getting your Benshaw price from and although I have to respect their position in the LV drives and motor business, they have zero experience dealing with MV, especially drives. Be careful.


Someone is going to need to look this up one day.

I would like to nominate this post as a Sticky please.


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