rotary phase converter, vfd, inverter

[tarzan56007]

I am planning to build a rotary phase converter for my shop probably going to use a 15 or 20 hp baldor motor, most info I have read refers to balancing problems between phases, wondering if a vfd connected between the phase converter and the machinery would do any good with controlling unbalance. Tarzan.

 

[jbartos]

Suggestion: If VFD is contemplated, then why not to use static phase converter? The rotary converter has advantages and disadvantages of rotary machines.
Static converter is does not have the rotating machinery maintenance and operation problems. However, the static converter may produce somewhat worse power conversion quality than the rotary converter.

 

[tarzan56007]

the phase converter is intended to run several smaller motors in the shop and the vfd would be connected to only one of them at this time, mostly for speed control, just wondering if it would also help on the voltage, amperage and phase angle qualities going into that machine. Tarzan.

 

[busbar]

A search for “phase converter” at this site will provide quite a bit of discussion on the subject. A 15-20hp motor on a typical 1ø services is quite large.

 

[aolalde]

A phase rotary converter do not produces a perfect 3 phase balanced voltage, then you will have always unbalace problems on three phase motors connected. The VFD will improve only the balance of the three-phase loads connected to the output.

 

[jbartos]

Comment on the previous posting. It depends on the principle. M-G sets produce the high quality electrical power conversion. They are often used in Nuclear Power Plants.

 

[jbartos]

Suggestion to tarzan56007 (Electrical) May 14, 2004 marked ///\\the phase converter is intended to run several smaller motors in the shop and the vfd would be connected to only one of them at this time, mostly for speed control, just wondering if it would also help on the voltage, amperage and phase angle qualities going into that machine. Tarzan.
///What size of electrical service do you have and at which voltage system? The single phase services tend to be on smaller side. The single phase service may or may not be sufficient to power 15HP to 20HP simultaneously.\\\

 

[tarzan56007]

The service on my shop is 200 amp 230 volt single phase 60 htz and the only reason I am building the rotary phase converter as 15 or 20 hp is because I have a couple of these motors on hand, the most these motors will ever start is 5 hp and the most they will ever run is probably 7 to 9 hp max. thanks Tarzan.

 

[jbartos]

Comment on the previous posting: It is not really the actual motor shaft load what is causing the problem, it is the 15HP to 20HP motor inrush current that is causing the large or excessive load and voltage drop on the service.

 

[aolalde]

JBartos; my guess is that Tarzan is using an “add a phase rotary array” by running an induction motor (15 or 20 HP) no load and with some capacitors. The load is connected to the three motor lines where only two lines have voltage from the single phase electric supply. The connected load adds to only 7 to 9 HP.
The inrush of the 20 HP could be a problem but may be he will use a pulley and a rope to crank the motor.
Certainly an M/G set is the best technical solution but for a small shop it will be a big investment. Starter, Single-phase Motor, coupling, Synchronous generator, voltage regulator and generator output switchgear.
That is why I said that he will have problems with the voltage balance.

 

[jbartos]

Comment on the previous posting: The smaller sized M-G set will be somewhat more expensive, however, it will deliver a better power supply quality that may in turn be beneficial to the sensitive load and machinery special motors.
Alternately, a Diesel Generator may be considered. Many houses buy it nowadays. It appears to be affordable.

 

[JustSomeGuy]

If your only going to be using 1 motor at a time, why not just use a vfd, and skip the rotory converter. Take your largest motor that is going to be ran say 10hp X (1.5) at least = 15hp. Single phase it and derate the vfd to 10hp. But make sure you do not drop a motor across the outputs while the vfd is running.
I have came across many applications like this where there is only 230 single phase available, and need 3 phase for a motor.
Just another cheaper option for you. While single phaseing a vfd you do decrease the life expectancy, do to ripple current on the DC bus, but this is minor at least. Hope this helps you some.

 

[tarzan56007]

I knew that VFDs could be used to provide three phase power to the smaller motors but was unaware that it was fesable for 10 hp motors, that is a good idea, but I guess the main reason for using a rotary converter is money, I will only have around $300 plus a day or two work into my rotary project and am guessing that a 15 hp inverter would be a lot more than that, also it is probable that a couple of motors could be running at the same time, just wondering how does a 15 hp VFD react to running a 3hp motor??

 

[JustSomeGuy]

Well considering your buget it would be a bit more then your planning on spending. I was looking at it from the converter to vfd to motor app.

A 15hp derated to 10hp would be a bit much on a 3hp motor. There are single phase input 3 phase output vfds availble specificly designed for 3hp for around 300 USD. But then if you need more hp then that your stuck again.

With the 15hp you could run multiple motors on that as long as the sum of all currents for each motor does not exceed the 10hp derated rating. Another draw back to that is that if you did use mutliple motors you would have to have them all start and stop at the same time, and running the same frequency. ?? hope this helps clarify. Good luck

 

[jraef]

tarzan56007,
I think you may be missing JustSomeGuys point. If you have some smaller 3 phase motors that need to run from 1 phase service, buy an inexpensive VFD for each motor. Most small VFDs (up to 3HP) are iherently capable of converting your 1 phase to 3 phase. You can easilly find a 3HP 230V VFD for around $300 if you search enough, 2HP should cost around $225, 1HP under $200! If you can only afford 1, put a twist-lock plug on it with matching sets on the motors and move it around for the motor you need to run!

It can also be done at any size like he said, although JSG's formula is a bit off. Over 3HP you really need to double the size of the VFD to allow for the increased 1 phase current on the AC-DC converter section. The current drawn by the 1 phase source will be 1.732 x the 3 phase motor current (plus a little for efficiency losses). At 1.5x it might work if the nameplate FLA happens to fit right, but 2x is a safer bet. The sizing has to do with the capacity of the diodes on the rectifier bridge, AND the necessary capacitors needed to filter the increased ripple from having only 1 phase power.

As to the VFD running a 3 phase motor, that is all they ever do! Think of the output of the VFD as a completely new power source for the motor, created by the VFD specifically for that motor. The input is just the power source for the VFD, and what goes in is mostly irrelevant as far as the motor goes. Some VFDs will even accept DC input power (at the right voltage of course).

BTW as aolalde said, you will end up with unbalanced 3 phase using the motor method, and in the long run that will increase heat in your downstream motors, shortening thier life.

"Venditori de oleum-vipera non vigere excordis populi"

 

[tarzan56007]

This has all been very informative for me and I appreciate everyones opinion, I will build the rotory unit for now because I already have all the parts but in the future I will probably use a vfd for each application, thanks Tarzan.

 

[jbartos]

Comment on the previous posting: The rotary phase converter concept will have some advantages in terms of the power quality of your power supply that might be deteriorated by using VFDs without the proper harmonic compensation on their input side. The above postings did not address the applied VFD input power quality aspects.

 

[WillyT]

What are "M-G sets" Thanks!

 

[jraef]

Motor - Generator

"Venditori de oleum-vipera non vigere excordis populi"

 

[mc5w]

The harmonics from a VFD will destroy the rotor of a rotary phase converter. Most static phase converters such as Ronk's Add A Phase will NOT drive a VFD and are to be used with a motor.

Any phase converter that is used to power a VFD must be made for the purpose.

Mirus International does make a combination static phase converter and universal harmonic filter that will run a 3-phase input VFD off of single phase power. The model series is 1Q3. There might be some other make but Mirus does have some unexpired patents to certain power quality and conversion products.