Motors tags showing 50Hz cycle run in the US

Would machines made overseas with motors tags showing 50Hz cycle run in the US, which is 60Hz cycle?

What will happen?

• The Machine WILL run just fine
• The Machine will NOT run
• The Machine will run for a few months and then will suffer a painful and irreversible death

Thanks for all your answer!

The answer is: "It depends".

What will try to happen is that the motor will try to run 20% faster. Depending on the machine this may mean the same power, 20% more power, or 70% more power. The machine may go into a critical speed and self destruct on vibration, or the unsafe speed may be way over the nominal and it will be OK. The motor may handle the higher voltage, or you could cook some insulation. This may be a belt driven machine and a simple sheave change could solve all.

This is a multivariable problem, and a lot of motor inof and a lot of machine info is needed to give an intelligent answer. Why not contact the machine manufacturer?

Tom made some good points, especially concerning the possible increases in load.

From a pure electrical standpoint a 380/3/50 motor will operate just fine at 460/3/60. The volts to hertz ratio is the same. It will have the same no load and full load currents and produce the same torque/horsepower. It will however (as Tom stated) run faster because of the frequency increase. Thats when the stituation gets more complicated.

I would say that you are more likely to have problems with variable torque loads such as fans and pumps. As Tom says the load could go up proportionally or by a squared factor.

Jim

You could put a freq. drive on it and be ok?

The motor will run faster, and hotter.

Jim Knee, in your middle paragraph you say same torque/hp. Make that just torque. Since the available torque would be constant up to an additional 20% speed, you would have the potential for an additional hp as well (hp=t x rpm/5250).

And therein lies the problem---the motor suddenly thinks it has 20% more hp but soon discovers that it does not have an additional 20% cooling capacity. Overtemp and smoke will be the result.

Now, if the torque is reduced 20% in the overspeed range thus limiting the hp to the nameplate value, the motor would be ok thermally and we would have success. Unfortunately, not many loads decrease torque as speed goes up so other means must be used. Changing pulley/sprocket ratios is probably the most common and certainly the easiest.

Originally posted by Terry Woods:

The motor will run faster, and hotter.

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Originally posted by DickDV:

And therein lies the problem---the motor suddenly thinks it has 20% more hp but soon discovers that it does not have an additional 20% cooling capacity. Overtemp and smoke will be the result.

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Looking at this purely from the motor's perspective, where do we expect the extra motor heating to come from? Granted, you will have some additional magnetic losses as speed increases. But the vast majority of motor losses are proportional to current in the stator. If the motor stays on the volts/hertz line and the shaft load doesn't increase I wouldn't expect motor heating to increase significantly. We aren't operating in the field weakening area at this point.

Think of it this way. If we use shaft horsepower as the primary determinant of motor thermal capacity then a motor should be a constant horsepower device. This means we could run a motor at twice rated torque if we ran at half rated speed. We all know this isn't the case.

The big issue is the shaft load. As most have already said, very few loads that I have encountered decrease in torque as speed increases. Most increase with speed. This means that more torque is required as speed increases, which will cause additional motor heating. Be careful of that.

Keith

50Hz usually isn't the only thing different about those motors. What are the voltage ratings?

I've installed tons of Dutch equipment here in Canada, and the motors typically have both 50Hz and 60Hz specs, with different voltages for each. However, the 60Hz voltages are quite a bit higher than ours, so the motor simply doesn't put out the power it's intended to and the poor buggers run hot. Frequency drives cure most ills, but these have losses as well.

Trouble with Dutch equipment is that when their design says they need a 2.07 kW motor, they somehow manage to put on a motor that's exactly 2.07 kW. So quite often "a bit hotter" means a certain slow death.

In other words, it's like Tom Jenkins, said: "It depends".

Thanks all, this was a hypothetical question with the intention of learning and explaining why a customer of mine would consider buying a machine overseas with motors rated at 50hz,

I guess they all come with VFD mounted. Thanks again!!

DICKDV
I agree with your correction, I think we are all basically saying the same thing.

Jim

The most amazing service I've seen from a group of motors are German built motors running on 480VAC/60Htz. Out of twenty five dual speed motors, We had just one go bad in twelve years. Even more amazing, the blowers they are attached to had zero bearing loss. The fans were built to meet the faster frequency.

Twenty five motors, one lost in twelve years. Yep, they'll run.

Keep in mind we had an excellent maintenance program. Motors were lubed/cleaned on a regular basis. Starters were rebuilt at least once per year.

I wish I had the manufacturer information, but I've moved and forgot who built them. We did keep a spare, because of a three month delivery time.

One can certainly conclude that the motors were considerably oversized for the fans at 50Hz which is typical conservative German practice.

They also were likely NOT the cheapest package to buy initially. (Says something for buying on value rather than price)

Keith, I agree with you on shaft loading being the primary thermal input but heating in the stator goes up as P=E^2/Z.

Since both the voltage and frequency are going up at the same rate, P must be going up at same rate as the frequency. That would be 20%.

Of course, as you point out, this might be 120% of only 3% of the total. If the 3% is much higher, then stator heat input will become more significant.

I haven't a clue what the proportion is between rotor heating at full load and stator heating. Does anybody know?

DickDV said:

One can certainly conclude that the motors were considerably oversized for the fans at 50Hz which is typical conservative German practice.

They also were likely NOT the cheapest package to buy initially. (Says something for buying on value rather than price)

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You are right on these counts. The machine was designed for application in the US, but the normal conservative practices of the Germans were inplace.

Likewise, these were not cheap. The initial cost was very high, but then, on a simular machine, with light duty motors, and less regard for alignment, we went through at least one motor per month. Same maintenance. I did find some high temp motors that were much better.

One other interesting item. The German motors had thermistors built into the frame, and high temp shutdown controls. I had more trouble with the "thermal relays," than I had with the motors.

The American motors ranged in manufacturers, were all 1800 rpm 30 Hp. The German motors were 1800, 28 Hp. This is not a fair comparison, as the fans on each machine were different types. Still they were all loaded to about 85%, and had the same enviornmental conditions.

The fans were built to meet the faster frequency.

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If they knew the fan were going to be run on 60 hz. Don`t you imagine they designed their blowers so the motors to be loaded at the higher speeds. Like DickDv said if not the fans then with pulleys. In some way they change it to a 28 Hp load at 1750 rpm instead of 1450 rpm. We all know you`re not going to take a loaded fan motor and speed it up 20%, leave the same motor and not let the smoke out of it.

The American motors ranged in manufacturers, were all 1800 rpm 30 Hp. The German motors were 1800, 28 Hp. This is not a fair comparison, as the fans on each machine were different types. Still they were all loaded to about 85%, and had the same enviornmental conditions.

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So they actually left their self a little safety factor since it was only loaded 85% at the higher speed. I have a question maybe someone can answer? Years ago before the T frame motors were the U frame motors and I mean true U frame not just the bolt holes in the frame. The U frame 5 hp 1750 rpm motor weighed probably half again as much as a new T frame motor, but they both pulled about the same amount of current. We didn`t take any chances when the U frame 5 hp motor burned up if it was replaced with a T frame motor we went to a 7 1/2 hp. Now I don`t believe the T frame motor though it pulls the same amout of current the U frame motor did has the same power? But I guess on the other hand if the T frame had more turns per phase than the U frame maybe ampere turns would enter into the scenario? So I guess the U frame motor may have had more steel and less copper and still produced the same torque? What do you think do the T frame and U frame motors have the same torque for a given hp & rpm? It looks to me though they both pull the same current the one with the most steel will have more torque? Please shed some light on this.