Utility High Leg, Open Delta Phase Converter, and a Motor That Can't Use Either

[ptonsparky]

The fields in North Georgia are much smaller, usually less than 20 acres. So irrigation would not be practical. Our tractors are seldom more than 40 hp too. We have lots of streams and rivers, but very seldom used as irrigation sources.

I think 3000 acres is around the magic # for profitability. With larger equipment costing close to a million each it takes volume.

 

[fastline]

The customer decided to revert the machine back to 480V input and we will get a 240D-480Y transformer to step up and balance everything.

As a side note, the senior tech who could answer my questions is apparently on vacation and customer did not want to wait till he got back to resolve the issue. This has been a good learning experience for me however so I will not complain too much. The techs are all American that I have been communicating with.

Thanks for the help y'all!

Jonathan

Ha, I deal with systems like this all the time. VERY typical for OEMs to specify "no delta 3P" because they don't want their equipment damaged if connected wrong. However, Having connected $1Ms in equipment, it's highly likely it can get done on 240V-D without a transformer. However, you have to have real electrical skill in evaluating everything in a control for 1P loads, which is likely exactly why the OEM is rejecting that power.

However, if you verify (not likely) they are peeling off 1P from every phase, that could be at issue, BUT my first question should be "does the machine even require a neutral connection"? If not, this is all moot because a motor will care none and all other loads would be either 3P or P-P. What is VERY common is P-P for a control transformer. In short, they are friggin designed to work around delta power!

 

[kwired]

I think 3000 acres is around the magic # for profitability. With larger equipment costing close to a million each it takes volume.

And you can't just get one big machine. Take harvesting equipment for example. If you get a large combine so you can harvest more acres in shorter time, it won't get it done if you don't have larger accessory items to go with it. Larger grain wagons to take it out of the field, larger augers to unload those wagons fast enough to maintain the efficiency you are trying to achieve, larger bins to store the crop in or they will be full so soon you are going to need lots of them plus time to move equipment between them....slow any those items down that combine is sitting their full waiting to be unloaded and isn't harvesting more crop in less time and was wasted money on purchasing the larger unit. Many the larger operators been running at two combines in same field and maybe four tractors and wagons to haul it to the bin. And another guy at the bin site to make sure things are going well there and maybe run errands and such to support the others activities. One machine breaks down, it really slows things down or even halts everything until they get it up and running again. If things going well they might take out a quarter section (~160 acres) or a little more if they don't have to move far to go to the next quarter in an afternoon.

 

[C4ctus99]

If your customer needs to add more equipment down the road you could look at a doing a 480V service and probably use the transformer to supply the old 240V equipment.

Most of their existing equipment is 240V. They would also need a step down transformer to cover all the 120V general purpose circuits also. Maybe a 208/120 service would be worth looking into but for

Ha, I deal with systems like this all the time. VERY typical for OEMs to specify "no delta 3P" because they don't want their equipment damaged if connected wrong. However, Having connected $1Ms in equipment, it's highly likely it can get done on 240V-D without a transformer. However, you have to have real electrical skill in evaluating everything in a control for 1P loads, which is likely exactly why the OEM is rejecting that power.

However, if you verify (not likely) they are peeling off 1P from every phase, that could be at issue, BUT my first question should be "does the machine even require a neutral connection"? If not, this is all moot because a motor will care none and all other loads would be either 3P or P-P. What is VERY common is P-P for a control transformer. In short, they are friggin designed to work around delta power!

I have some of the control diagrams now and with the 240V system it only uses 2 legs and converts to 24V DC. These are the techs saying no 240V high leg system, not any paperwork that they are aware of, just experience is what it sounds like. It is a non-synchronous motor, would that have anything to do with it? I could not find much info during my brief internet search.

As an update, I rewired the saw and installed the transformer yesterday and got the saw up and running today without issue. I will be reaching out to the techs next week when the senior tech comes back to hopefully get more information and some good answers as to their claims and will let yall know what they say to satisfy any remaining curiosity.

-Jonathan

 

[kwired]

Most of their existing equipment is 240V. They would also need a step down transformer to cover all the 120V general purpose circuits also. Maybe a 208/120 service would be worth looking into but for

I have some of the control diagrams now and with the 240V system it only uses 2 legs and converts to 24V DC. These are the techs saying no 240V high leg system, not any paperwork that they are aware of, just experience is what it sounds like. It is a non-synchronous motor, would that have anything to do with it? I could not find much info during my brief internet search.

As an update, I rewired the saw and installed the transformer yesterday and got the saw up and running today without issue. I will be reaching out to the techs next week when the senior tech comes back to hopefully get more information and some good answers as to their claims and will let yall know what they say to satisfy any remaining curiosity.

-Jonathan

High leg 240 volt delta has two legs that are 120 volts to neutral, shouldn't need separate transformer for 120 volt loads.

If you have corner ground delta that would need transformer to get 120 volts and those equipment people maybe wouldn't like the idea of corner ground even if their equipment can handle it (which it likely can).

All general use induction motors are non-synchronous. Synchronous speed motors are motors do run at synchronous speed as in they spin at same speed as the electromagnetic field moves. They have more of a limited use and you don't see them very often. A general use induction motor would have zero torque if it were running at synchronous speed. If running faster then synchronous speed it would have negative torque and essentially is a generator at that point.

 

[fastline]

Most of their existing equipment is 240V. They would also need a step down transformer to cover all the 120V general purpose circuits also. Maybe a 208/120 service would be worth looking into but for

I have some of the control diagrams now and with the 240V system it only uses 2 legs and converts to 24V DC. These are the techs saying no 240V high leg system, not any paperwork that they are aware of, just experience is what it sounds like. It is a non-synchronous motor, would that have anything to do with it? I could not find much info during my brief internet search.

As an update, I rewired the saw and installed the transformer yesterday and got the saw up and running today without issue. I will be reaching out to the techs next week when the senior tech comes back to hopefully get more information and some good answers as to their claims and will let yall know what they say to satisfy any remaining curiosity.

-Jonathan

You mean "asynchronous", which is very standard. IMO, this sounds like the typical case of people not having both competence and authority. However, you didn't really answer my question as to a neutral. If no neutral connection, ANY chatter about wye or delta is totally MOOT. Why? Leg-leg voltage is all you care about, and as mentioned, it is standard industrial practice to bring in 3P only (no neutral) into a machine, then convert to different voltages internally as needed. Why? One is removing the need for a neutral, the other is this exact delta issue.

I swear people lose their mind with the term "high leg delta". It only damages stuff if you don't know what your doing. We wired a full machine shop off delta. Countless VFDs, controls, and motors.

 

[C4ctus99]

High leg 240 volt delta has two legs that are 120 volts to neutral, shouldn't need separate transformer for 120 volt loads.

Correct, I was thinking from the perspective of a 480V service and read too quickly and missed the part about the step down. Currently they only have a single 3 pole machine that needs 480 as opposed to the other 25 circuits in the building so probably would not make too much sense for their situation.

All general use induction motors are non-synchronous. Synchronous speed motors are motors do run at synchronous speed as in they spin at same speed as the electromagnetic field moves. They have more of a limited use and you don't see them very often. A general use induction motor would have zero torque if it were running at synchronous speed. If running faster then synchronous speed it would have negative torque and essentially is a generator at that point.

Makes sense. I did not have the time to dig deep enough to see that general use induction motors are the non-synchronous. Thanks for the info!

You mean "asynchronous", which is very standard. IMO, this sounds like the typical case of people not having both competence and authority.

Non-synchronous is the label given in the drawings. It may very well be the case, but I will be the one liable if I do not listen to them.

you didn't really answer my question as to a neutral. If no neutral connection, ANY chatter about wye or delta is totally MOOT.

There is no neutral connection. In the 240V configuration two legs are used for the power supply feeding the 24VDC controls. I recall having read in multiple different places throughout the years that having a higher voltage to ground on one leg can help some motors with efficiency; is that something I misread or is it true in some motors? I ask as I have never understood why that would be the case because, like you said, phase to phase should be all that matters. Also, hopefully I will be able to find out if the technicians just don't know what they are talking about next week

 

[ActionDave]

I recall having read in multiple different places throughout the years that having a higher voltage to ground on one leg can help some motors with efficiency; is that something I misread or is it true in some motors?

Motors don't care about voltage to ground. Within a certain range, plus or minus ten percent of nominal voltage, all motors are happier with higher voltage because the running amps will go down. Most motors that run on 240V are engineered to run on 208V but are better off with 240V again, because the running amps are lower.

 

[kwired]

I recall having read in multiple different places throughout the years that having a higher voltage to ground on one leg can help some motors with efficiency;

Doesn't matter. Three phase motor operates line to line to line. With corner grounded delta supply one of them would be at ground potential, still is 240 between each of the three conductors and motor only cares about that aspect. A motor will draw approximately 10% less current on 240 than on 208, at least when operating at rated output. KVA remains pretty much the same though. Minor differences that would be considered negligible can occur.

 

[JESILVAM]

Good Evening, been running into an increasingly problematic situation with a customer.

Service from Utility is 120V/240V 3P with B phase in panel reading 210V phase to ground. They recently got a new upcut saw and after consulting with the manufacturer I was informed that I cannot use a service with a high leg for that motor. The customer did not want to pay the extra money for a new service (would have saved a lot of headache) and in my ignorant state I decided to try using a rotary phase converter to take the two good legs and generate a third phase. Today I learned that the converter is wired open delta and the manufactured phase is 240V to ground. I am now looking at potentially getting an isolation transformer to rectify the high leg issue at point of use.

With all that being said, motor wiring and transformers are not my strong suit (through an unfortunate blunder of the staff I did not get to take that course during my time in the apprenticeship) and some help and direction would be appreciated.

My question is, would there be a way to rewire the idler (motor) portion of the phase converter to eliminate the high leg issue? This would save me a hassle and some cash trying to return the converter. Also, I have a very basic understanding of the different types of transformers and there functions but if there are any threads y'all could point me to explaining some of the difference between open delta, closed delta, grounded, unground, wye, and open wye I would be much obliged.

Thanks,
Jonathan W

Let see your case: If the new upcut saw is 3 phase, 120/208V, you must NOT connect it to a 120/240V 3 phase delta system because it will burn. You can buy a dry type transformer that converts 240V input to 120/208V output with a capacity 20-25% higher than your load and that´s all. For example: If the load is 5KVA, buy a 7.5KVA transformer or higher... you must know the peak starting current of the load to size the transformer.

 

[zbang]

because it will burn.

Highly unlikely (please read the entire thread).