Options on a VFD

[Open Neutral]

Have a need for 2HP worth of 480/3ph 60Hz. at a single-phase location. Pondering options.

Obvious one is a VFD set to 60 hz and left there. Then question is; does anyone make a single-phase fed VFD that outputs 480?

Failing that, a single-phase 240 in, 208 3ph out and a 3-ph stepup xfmr, I guess.

Alternate approaches?

 

[Finite10]

Rotary or static phase converter, rotary is said to be better power quality.
LINK
or
LINK
Sounds like you are wanting to start there, but you're asking about a freq drive -so not sure.

 

[hurk27]

there are a few options out there, but to make the best cost effective choice we need to know what the load is?

Here are a few links that might help:

http://www.phaseperfect.com/phasewhitepaper.htm

http://www.phaseconverterinfo.com/phaseconverter_rotary.htm

 

[Open Neutral]

Load is a 2HP water pump.

 

[Jraef]

Couple of issues on VFDs for 1 phase 480V input.

First off, don't put the transformer on the load side, most transformers are not made for that. Do it on the line side. Technically, all VFDs are capable of taking in 1 phase and putting out 3 phase, it's just the nature of the beast. But there are limitations and pitfalls to watch out for when using 480V 1 phase input.

1. Unlike 230V small HP VFDs that often do not need de-rating for 3HP and under, there is no design like that on 480V VFDs, so you must double the VFD size with respect to the motor size in order to compensate for the higher input current and the added DC bus ripple. So for your 2HP 460V motor, assuming the FLA is probably 2.8A or so, you need a 480V VFD capable of 5.6A or more, or about 4HP. Although there are a few VFDs from EU manufacturers like Siemens that are rated at that level, most are going to jump to 5HP.
2. Not all 480V VFDs are capable of 1 phase input simply because whomever designed them did not intend for that use. What happens is that they put in Phase Loss protection, because they KNOW there is no margin for error on the input current and / or they have a separate power supply for the internal electronics that taps off of the AC side (usually only on larger versions though). If the drive has this protection function listed in the specs, look at the parameter list to see if you can defeat it in programming. If not, you cannot use it. Many older Allen Bradley drives are this way for example. If it is there and you can defeat it, no problem. If the specs don't say it has phase loss protection, it should be OK, but it also may be a "gottcha", so if you can, ask your supplier or make sure they accept returns.
3. If your pump is submersible, make sure it is suitable for being run from an inverter. Some mfrs void the warranty if it is, or more specifically, if you don't use THEIR VFD. That's because submersibles don't use industry standard motors, they are essentially custom designed for the pumps they attach to and if older, nobody thought about VFDs in the design. If it's out of warranty anyway, see below.
4. If it's not a submersible, consider putting in a motor lead filter or at least an output reactor unless the motor is "inverter duty", a term that loosely describes design issues that deal with some of the potential problems associated with running from a VFD.

RPCs (Rotary Phase Converters) are not terribly efficient if they have to be running continuously to be ready for a pump call without waiting. Otherwise, you have to accept a delay from when you want the pump to run and when the RPC turns on, gets to speed, and THEN allows you to close the pump starter. It may be only a second or two, but you just need to be aware of that.

Sometimes it's just simpler to use a 230V 1 phase pump .

 

[Besoeker]

Sometimes it's just simpler to use a 230V 1 phase pump .

To me, that seems to be the obvious solution in this case particularly since there is no variable speed requirement.

 

[ptonsparky]

Nothing like spending $1000 for a $500 project

 

[Open Neutral]

The pump is 670 ft down, so pulling it to put in a single-phase unit is non-trivial from a labor standpoint alone.

I had not considered a rotary converter because of efficiency, much less initial cost.

I see 480V 5HP VFDs for far less than the labor, so it's worth investigating. I will confirm the single-phase input aspect with the VFD supplier, and make sure the pump motor will tolerate inverter output.

Hmm, Franklin Electric's AIM manual seems OK with this, with some guidelines.

Filters or Reactors: Required if all three of the following
conditions are met: (1) Voltage is 380 or greater and
(2) Drive uses IGBT or BJT switches (rise-times < 2
μsec) and (3) Cable from drive to motor is more than
50 ft (15.2 m) a low-pass fi lter is preferable. Filters or
reactors should be selected in conjunction with the drive
manufacturer and must be specifi cally designed for
VFD operation

Guess I'll be asking vendors about rise times. I suspect a low pass filter would be pricy.

Also, we have a Siemens EPS20 overload protector that might balk on non-sinewave power.

 

[Besoeker]

The pump is 670 ft down, so pulling it to put in a single-phase unit is non-trivial from a labor standpoint alone.

I had not considered a rotary converter because of efficiency, much less initial cost.

I see 480V 5HP VFDs for far less than the labor, so it's worth investigating. I will confirm the single-phase input aspect with the VFD supplier, and make sure the pump motor will tolerate inverter output.

Hmm, Franklin Electric's AIM manual seems OK with this, with some guidelines.

Filters or Reactors: Required if all three of the following
conditions are met: (1) Voltage is 380 or greater and
(2) Drive uses IGBT or BJT switches (rise-times < 2
μsec) and (3) Cable from drive to motor is more than
50 ft (15.2 m) a low-pass fi lter is preferable. Filters or
reactors should be selected in conjunction with the drive
manufacturer and must be specifi cally designed for
VFD operation

Guess I'll be asking vendors about rise times. I suspect a low pass filter would be pricy.

Also, we have a Siemens EPS20 overload protector that might balk on non-sinewave power.

Fair points.
I was called in by our local water company to investigate failures on submersible pump motors - they were each failing about once a month. They were 60 kW (about 80 hp) and driven m
by variable frequency inverters from one of the main manufacturers.
I found rise times like this:

The major time intervals are 2us, minor 0.4us.
I commented thus:
"Rate of change of voltage (dv/dt)
Rate of change of voltage was very fast. In all cases it was either outside the limits of the IEC TS60034-17 technical specification, or marginal. For the rise times measured the maximum dv/dt should not be greater than approximately 1600V/us. The average dv/dt measured at the pump house was 2500V/us."

Output chokes (reactors) solved the problem.

The input to your proposed 480V inverter will have a three-phase rectifier with six diodes. With your single-phase supply, only four of the diodes will carry the current. This has two main effects for ratings. Obviously the diodes will be more heavily loaded. Perhaps less obvious, is that the DC link capacitor will have much more ripple current and the peak currents in the diodes will be much higher. On larger inverters it is quite common to have a DC reactor between the input rectifier and the DC link capacitor which reduces the ripple current. I don't have a lot of experience with small inverters but I'm pretty sure that many or even most don't have a DC reactor. That could be an issue to consider.

On the transformer, I'm with Jraef. Put it on the input side.

 

[weressl]

Sometimes it's just simpler to use a 230V 1 phase pump .

Gets my vote too. Not only simpler but overall cheaper.

 

[Besoeker]

Gets my vote too. Not only simpler but overall cheaper.

But the better part of 700 feet down a well just might have some bearing on costs.

 

[Jraef]

The pump is 670 ft down, so pulling it to put in a single-phase unit is non-trivial from a labor standpoint alone.

I know what you mean. I once had to have a submersible pulled from a 500' well because the current was way too high and flow was way too low, which everyone assumed was my VFD. I took the chance on offering to pay for the extraction. Rig rental and riggers for one day exceeded the cost of the pump. Turned out to be a coupling set screw that was over tightened though, so I was vindicated.

Also, we have a Siemens EPS20 overload protector that might balk on non-sinewave power.

You will no longer need the OL relay if you have a VFD. The motor protection in a VFD is better than even that OLR, especially in that it relates itself to motor speed.

 

[weressl]

But the better part of 700 feet down a well just might have some bearing on costs.

Nothing like giving a set of data with a KEY item missing, then supplying it with a sneer and laughing how stupid the answer based on the original set sounds. What a way to gather support on your NEXT question.:roll:

 

[Besoeker]

Nothing like giving a set of data with a KEY item missing, then supplying it with a sneer and laughing how stupid the answer based on the original set sounds. What a way to gather support on your NEXT question.:roll:

In fairness, old fellow, the original point was about providing three-phase at a location where only single phase was available. That it is a pump 700 feet down a well came to light when the application was later questioned.
The OP wanted a solution. Some us, myself included, chose to suggest an alternative solution without knowing all the circumstances.
We'd have done better in simply answering the question asked.

 

[Open Neutral]

I appreciate all the input. I surely did not intend to sneer at anyone. In retrospect I could have provided been more verbosity on my original scenario description.

My response to the initial "pull the pump" suggestions was just to explain why I had not already leapt at the seemingly most straightforward solution. It may come to pass that such is the answer, once we cost things out.

If there is a fixed freq converter whose price beats the VFD approach, I'm all ears....

We are in this pickle because the quotes to get PG&E to supply 3-phase at this residence are so large as to cause us to fallback and punt. [$60K for 208 200A; and only $40K for 240/120-400A.]

But the well had to pass the county checkoff before they would accept submission on the building permit.... and then we found......

Thanks for the reassurance on the protection; I was pretty sure that was the case but wanted confirmation. I know I'll have to make the pump start/stop actually work the VFD control input but that's looking trivial.

 

[Open Neutral]

On the transformer, I'm with Jraef. Put it on the input side.

I was originally thinking an output side transformer might act as a low-pass filer, and help round off the sharp transitions.

 

[Besoeker]

If there is a fixed freq converter whose price beats the VFD approach, I'm all ears....

If you make it fixed frequency (and voltage), it would have to be rated for direct on line starting of the motor which could be six times the motor full load current.

Some UPS inverters have a "walk in" feature that limits inrush current but I'm not sure just how well that would work on a motor.

 

[iwire]

We'd have done better in simply answering the question asked.

You guys are engineers, you can never just answer the question asked. :grin:

 

[weressl]

You guys are engineers, you can never just answer the question asked. :grin:

So you're willing to admit that you can't see how complex the question is when ALL the possible data is supplied?

 

[Jraef]

I was originally thinking an output side transformer might act as a low-pass filer, and help round off the sharp transitions.

Sort of, but most COTS transformers are not built for this and you are asking for failure. A Load Reactor is better for that purpose, but I'm not sure if that Franklin spec is going to accept a simple Load Reactor (assuming here that you have a Franklin pump and need to make sure you follow their recommendations). You can contact a distributor for TCI (Trans Coil Inc) or MTE for load filters; regardless of where you buy them most of the ones on the market are actually made by one of those two companies.