Power question 480 60hz to 480 50hz

[ronhturner]

My company is planning on sending a machine to Barbados which is 400 vac 50 hz, along with a 400 vac 50 hz to 480 50 hz transformer to run the machine.
Everything I have read indicates this would be bad on the motors which do not have vfd's. The V/Hz ratio would be off. Is this true and what would potentailly happen?

Thanks,
Ron

 

[Jraef]

Motor's are there to produce torque. The torque that AC induction motors produce is a product of the ratio of voltage and frequency that they were designed for, +-10%. If the ratio is lower, the motor loses torque with that ratio, but the PEAK torque capability ("break-down torque" or BDT) drops at the SQUARE of that difference. If the ratio increases however, the ability for the motor to increase torque becomes limited by what's called "magnetic saturation" of the steel core and the losses increase very rapidly. So what happens is that the excess energy going into the motor becomes heat, not work, and the motor can burn up.

So for your 460V 60Hz designed motors (motors designed to work on 480V systems are designed as 460V to allow for VD), the design V/Hz ratio is 460/60 = 7.67:1. When you hit them with 480V 50 Hz, that supply ratio is 480/50 = 9.6:1, which means it is 25% HIGHER than what the motor is designed for. The torque will be a little higher, but the HEAT in the motors will be a LOT higher and they will likely fail in short order.

They will ALSO turn at 5/6th speed (83% speed or 17% slower, depending on how you look at it). So the motors will do the same work, but take longer to do it, while at the same time be over heating in the longer process. Imminent failure...

Since the motors will be turning at 83% speed no matter what, you are better off just leaving them alone, no transformer. 400V 50Hz is a V/Hz ratio of 8:1, EXACTLY the same as if the supply was 480V 60Hz. In other words the motors will have full torque and designed V/Hz ratio, just running slower.

 

[Besoeker3]

My company is planning on sending a machine to Barbados which is 400 vac 50 hz, along with a 400 vac 50 hz to 480 50 hz transformer to run the machine.
Everything I have read indicates this would be bad on the motors which do not have vfd's. The V/Hz ratio would be off. Is this true and what would potentailly happen?

Thanks,
Ron

Why not run them at 400V 50Hz?
Sure, as Jraef has stated, they will run slower but they would have the right V/f ratio.
Running them at 480V 50Hz is likely to saturate them, make them overheat, and fail. I would strongly advise against doing so.

 

[LMAO]

Motor's are there to produce torque. The torque that AC induction motors produce is a product of the ratio of voltage and frequency that they were designed for, +-10%. If the ratio is lower, the motor loses torque with that ratio, but the PEAK torque capability ("break-down torque" or BDT) drops at the SQUARE of that difference. If the ratio increases however, the ability for the motor to increase torque becomes limited by what's called "magnetic saturation" of the steel core and the losses increase very rapidly. So what happens is that the excess energy going into the motor becomes heat, not work, and the motor can burn up.

So for your 460V 60Hz designed motors (motors designed to work on 480V systems are designed as 460V to allow for VD), the design V/Hz ratio is 460/60 = 7.67:1. When you hit them with 480V 50 Hz, that supply ratio is 480/50 = 9.6:1, which means it is 25% HIGHER than what the motor is designed for. The torque will be a little higher, but the HEAT in the motors will be a LOT higher and they will likely fail in short order.

They will ALSO turn at 5/6th speed (83% speed or 17% slower, depending on how you look at it). So the motors will do the same work, but take longer to do it, while at the same time be over heating in the longer process. Imminent failure...

Since the motors will be turning at 83% speed no matter what, you are better off just leaving them alone, no transformer. 400V 50Hz is a V/Hz ratio of 8:1, EXACTLY the same as if the supply was 480V 60Hz. In other words the motors will have full torque and designed V/Hz ratio, just running slower.

Motor design is not my forte so this is very interesting. So basically just like transformers you can compensate for lower frequency by reducing the voltage by same factor? Makes sense. Induction motor is basically a transformer with moving secondary.

 

[kwired]

If you run them at 400 v 50 Hz, as mentioned they will be 5/6 the speed. If not marginally sized to start with you could change gears, pulleys, etc. to get desired speed on anything not direct driven.

Definitely don't change the volts-frequency ratio.

 

[Tony S]

This may come as a silly suggestion, why not buy the correct motors?

Another point, it is highly unlikely to be a 400V supply. 400V is the fictitious IEC nominal voltage to cover supplies from -6 to +10%, 433V is most likely.

 

[Besoeker3]

This may come as a silly suggestion, why not buy the correct motors?

You'd still end up with 50 Hz speed which may or not OK for the application.

 

[Jraef]

Side note;
Are you absolutely sure that they are going to have 400V 3 phase in Barbados or is someone assuming that? Every international "Mains Voltage" chart I look at says that Barbados uses 200Y115V 3 phase 4 wire 50Hz. So if for some reason someone is going to make their own power for this machine with an on-site generator (not uncommon in Caribbean island nations), maybe they can just generate what your machine needs?

 

[Tony S]

You'd still end up with 50 Hz speed which may or not OK for the application.

As we don’t know what the application is, who knows?

 

[Tony S]

I had a belly full of machines from European countries (mainly Belgian) where we had

I had a belly full of machines from European countries (mainly Belgian) where we had

I had a belly full of machines from European countries (mainly Belgian) where we had to supply 380V to the machines otherwise the warranty would be invalid.

Fortunately I was used to dual voltage plants, first off 550V and 433V followed by 433V and 380V.

 

[olsondavidj]

As others have mentioned, the voltage won't cause you trouble, it's the frequency.

You need to re-evaluate the application and select motors that are appropriate for the new frequency, and honestly it'll probably be easier to source a 50Hz motor that runs at 400V (as opposed to a 50hz rated motor running at 460V), so you could probably eliminate the transformer as well depending on what voltage everything else needs.

Of course you CAN just slap a VFD on all the motors and call it good, but that'll be expensive. And even if you do that, you'd need inverter duty motors anyhow, so in both cases you're buying new motors (plus new expensive VFD cabling and whatnot).

And also if you get a 400V 50Hz motor, you're not sticking an international customer with a US-specific motor. So when the motor inevitably dies they'll be able to more easily source a replacement instead of having to special order one from the US. I mean, an island nation probably won't have one local anyhow, but just like anything else it's easier for the customer to get something made for that market than it is to get something NOT made for the market.



edit: for clarity, when I say "re-evaluate the application" I mean go through the whole drivetrain and load and verify it'll work for whatever motors you can get. As others have mentioned, 50Hz motors won't run the same speed as 60Hz in any case... you will not find an 1800RPM 50Hz motor. So if this is a problem then you'll need to make changes to the load side of the motor(s) to make sure things work properly.

I guess my point was that this probably isn't a simple swap, and it's DEFINITELY not as simple as throwing a transformer on it. You'll likely need to do some work on the engineering side (electrical and mechanical) to make sure it'll all work properly.

So that said, maybe throwing some VFDs in there is actually the cheapest solution, since it would save you from re-engineering the drivetrain. But you won't know until you look in to it.

 

[Besoeker3]

Side note;
Are you absolutely sure that they are going to have 400V 3 phase in Barbados or is someone assuming that? Every international "Mains Voltage" chart I look at says that Barbados uses 200Y115V 3 phase 4 wire 50Hz. So if for some reason someone is going to make their own power for this machine with an on-site generator (not uncommon in Caribbean island nations), maybe they can just generate what your machine needs?

Good points. Maybe the OP could/should clarify that.

 

[kwired]

Good points. Maybe the OP could/should clarify that.

Side note;
Are you absolutely sure that they are going to have 400V 3 phase in Barbados or is someone assuming that? Every international "Mains Voltage" chart I look at says that Barbados uses 200Y115V 3 phase 4 wire 50Hz. So if for some reason someone is going to make their own power for this machine with an on-site generator (not uncommon in Caribbean island nations), maybe they can just generate what your machine needs?

If moving a plant there is probably some chance they can get custom voltage that isn't normally available to most others. They are likely still stuck with 50Hz though.

 

[Open Neutral]

They will ALSO turn at 5/6th speed (83% speed or 17% slower, depending on how you look at it). So the motors will do the same work, but take longer to do it, while at the same time be over heating in the longer process. Imminent failure...

And any cooling fans they drive will also be slower........