Standard motors and open delta

This a proof of concept installation so I am told before they turn loose of the bug dollars.

OK I got a call from a shop that wants to install 2 repaired TECO drives.
The drives are low dollar.
The customer has standard low cost Dayton motors not inverter duty.


They had another firm do the initial startup of these drives and before they even wired the motors up the magic smoke rolled out of these drives. I ASSuME that this is because of the open Delta “Wild Leg”.
I called the VFD supplier and got the response “Those drives will never survive a wild leg installation. Just use them as a single phase installation. The drives are rated for single phase input already. You don't need the third leg.”
I don't know how I feel about this single phase installation. It may be OK I have only used it for training equipment before never production.


They expect to use the VFD to reduce speed on startup only and run at base speed 95% of the time. So what will those standard non inverter duty motors do when we vary their supply frequency?

Running the inverter single phase will work fine if the drive is rated for it.

Do you know what the insulation class of the motor is? The motor will react to a changing frequency just fine. Problems you might encounter would be blowing holes in the motors insulation as well as overheating problems if the motor is fan cooled and run at a lower speed.

Would a soft start not work in this applicaion?

This is a 2 fold proof of concept. The first is to prove we can SAFELY reduced the speed of the machine without a mechanical clutch slipping. The second is multi-part. They want to link multiple machines together. So timimg will be an issue. I have told them that I don't think 2 V/H drives with speeed pots and an operator making adjustments is going to cut it.

Teco, automation direct GS2 series, FUJI ...... etc..... They are all cheap throw away's that work great! but throw in an INPUT line reactor.

In your case with a high leg delta I THINK you would want to run only 2 legs through the line reactor.

single in / 3 out power derates the drive so read charts carefully.

if you want Teco you can't get cheaper than www.factorymation.com

for my $ I lean towards automation direct GS2 series.

You are correct they are all for the most part throw aways. I have seen 3 GS2 arrive DOA. Automation Direct is good about changine them out for you.
I haven't found any low end drive that I realy like yet. The Baldor VS1 SP is about as low end as I like to go.

about 5 years ago the gs2's came out and had firmware problems etc.

no problems since but all the cheap drives have non replaceable fast fuses to protect the igbt's. voltage spikes punch holes in igbt's. I don't often use line reactors on output, even for NON vfd rated motors. but I have solved so many nuisance trips and drive problems with cheap line reactors on input I use 1 at the feed of any panel with VFD's in it now.

Jeff
Not sure about wild leg on open delta - I believe that is for 3 phase delta with one center tapped phase to obtain 120/240 singel phase on a 3 phase 240 secondary. Wild leg 208 V is between center tap and opposite "corner".

What is voltage of motors?

If the motors are used on only 230 or 240 VFD output they should be fine. Most motors are built using insulation intended for 480.

If timing of multiple drives and IDENTICAL position between each set of drive is needed I do not think I would use V/F drives. Not even sure if you could do this with vector unless you had some kind of position sensing ie encoders between drives - then one machine would have a home position and rest would match that position - sounds kinda tricky to me.

As said before make sure drives are either designed for single phase or you derate per factory for single phase.

Re clutch slip What kind of machine is this - constant torque (conveyer) OR?
Is clutch to prevent overtorquing shafting or is it an engage disengage. Depending on machine size think I would take torque reading on machine input shaft - use a torque wrench probably a beam style to get in the ballpark. You will more than likely be taking a breakout torque reading but that is OK gives you a little fudge factor in the calcs.

Dan Bentler

They use 2 transformers at this plant to make 3 phase Look.
Leg to leg 240 so the reduced voltage may help, but the low cost motors may still bit me. In my quote I say "[FONT=Arial, sans-serif]The current motors are not rated for VFD duty. This may cause issues with insulation rating being to low. If this is the case you can expect reduced life out of these motors. Operating these motors at less than base speed will definitely reduce the life span. "[/FONT]
The drives will run on single phase I am including a 30% reduction just to cover the how yea I forgot.
I said position only one of them will need position so I can gear a servo off that podition. The rest just need speed feedback and Vector will be good enough for this job.

I have used VFDs on open deltas before. Is this a problem only with low end drives and what is the problem, other than the smoke escaping?

I have not seen any drives that like the open delta "wild leg". I think PowerFlex drives have a jumper on the board that you cut when installing on Delta.

so , if you just using the drive as a start up with a lower frequency and ofcourse would be a lower voltage and lower torque all on the motor side , and that operation would take from 0 to 20 seconds,then back to normal frequency , that would not affect the motor temperature , should be ok

First off, this is NOT wild leg. This is simply 240V open delta three phase. And, as long as the voltages in the two coils are balanced and the phasing is correct (has to be if on the grid), you will have three phase 240V power.

The problem with any ungrounded source like this is just that! It's ungrounded so the phase-to-ground voltage can be anything including much more that 240VAC if a foreign voltage contacts the network. That's the part that destroys drives.

"Cheap" and "better" drives all have the same issue with respect to unbalanced or floating voltage sources. In order to qualify for the CE label, which is a European standard for radiated electrical noise, the drives have to include a noise suppression network that only operates properly when the incoming power is balanced to ground. If it isn't balanced, the network tries to force it to balance which usually results in the big strong network defeating the little weak network and the result is a damaged drive with a burn hole in the side of the case.

You have to read the Instruction Manual very carefully to find the information but many CE labeled drives now have jumpers or terminals in them that can be disconnected if on a floating or unbalanced source. Opening these disconnects the CE network and the drive will live on the unbalanced power. Unfortunately, you also have to turn off the output short circuit fault and ground fault protection to avoid a lot of nuisance faulting too. This is the case with the ABB ACS150/350/550 drives I work with and most other brands, as well.

I would expect the motor to run just fine on 240V three phase inverter power if it is dual voltage (230/460V) labeled. You cannot expect it to do full torque loading below about 1/3 to 1/4 speed, however. For that you would need a motor with an auxiliary blower or some other way of cooling at slow speed. Above those speeds, you can load to full rated torque and the motor should be ok. It's the 480V and especially 575V applications where PWM power really beats up a motor.

I'm also assuming the motor is not more than about 300 feet from the drive. That's wire feet! Beyond that, even at 230V, you should probably add a reactor to protect the motor.

Good points but.... even a invertor duty motor won't like running at less then 50% all the time. the fan on the motor doesn't turn fast enough to wove enough air over the motor to provide cooling (at least when the motor is in an enclosed space) this lead to nusance trips. We started replacing some dc motors & controllers with vfd & ac motors, then we had to go back and change the sprocket sizes to increase the motor speeds. Apprently these were some rare motors 180vdc high torque, odd shaft size, odd bolt pattern, We eventually switched gears both figurativly and literally the price to replace the dc motor alone was more then a vfd, ac motor, gearbox & sprockets.
as for the wild leg, I only have one x-fmr like that and it's in the shop.
As for the 1ph to 3 ph drives, we use them but. They don't seem to last/hold up near as long as a 3 to 3ph unit.

tracer, the acceptable full load speed range is defined by the motor manufacturer and is presented in their motor data sheets. TEFC motors typically are good for 4/1 turndown from 25hp down. About 3/1 turndown below 150hp, and 2/1 below 300hp.

Due to a lack of reliable definitions for terms like inverter ready, inverter rated, and inverter duty, you cannot depend on them telling you anything about turndown ratios. Some are no different from ordinary TEFC and some are good down to full torque at stall.

But your 2/1 statement across the board is far too conservative.

Of course, you mentioned the problems you had with motors in an enclosed space but that is not due to a lack of turndown capacity but rather an ambient temperature that exceeds the 40 degree C nameplate rating. Even at full speed, there is some ambient temperature where the motor will overheat. And it isn't much higher than 40 degrees C either!