Motor Characteristics

• Power Relationship: Power is calculated as voltage multiplied by current (P = V * I). So, even though a high voltage motor operates at a higher voltage, it will draw less current to produce the same power as a low voltage motor.
• Torque and Current: The torque produced by a motor is directly related to the current flowing through its windings. Since the current required to produce the same power at a higher voltage is lower, the torque characteristics will be similar.

Key points to consider:

• Slight variations may exist: While the overall torque curve will be similar, minor differences could occur due to design variations between the motors, such as differences in winding configurations or cooling mechanisms.
• Efficiency considerations: High voltage motors may have slightly higher efficiency due to lower current losses, but this usually doesn't significantly affect the torque curve.

"Torque and Current: The torque produced by a motor is directly related to the current flowing through its windings. Since the current required to produce the same power at a higher voltage is lower, the torque characteristics will be similar."

That sounds contradictory. I assume the torque vs speed characteristics are similar, definitely same torque at rated load and speed. Wouldn't that imply torque depends on current and volts?

Torque is proportional to current in the same machine. It's actually proportional to current x windings. A high voltage motor will have more windings than an equivalent low voltage motor.

That's no doubt the explanation, but I still think the statement

"The torque produced by a motor is directly related to the current flowing through its windings. Since the current required to produce the same power at a higher voltage is lower, the torque characteristics will be similar."

is wrong, as it implies that at higher voltage/lower current the torque is lower. Especially the 2nd sentence! The 1st part says torque is lower, the 2nd part that it's the same.

It seems that the cart is before the horse...

The torque required at a given RPM is determined by the load. The motor draws enough current to supply that torque. The higher voltage motor has more windings so that less current is necessary to supply the torque.

I don't know what "similar" means in this context...

At rated load (200kW in this case) and full-load speed, the torque must be the same, apart from possible small difference in full-load speed between LV and HV. If the actual load is lower than motor rated power the torque at load is lower, but still the same for both. Though HV has lower current.

My interpretation of "similar" is that the plot of torque vs speed as the motor accelerates is similar for the 2 cases, but they're never going to be exactly the same.

From a mechanical output performance viewpoint, voltage is irrelevant.

There will be difference in inertia, heat generation, mounting dimensions.

In a dual voltage motor the low voltage amperage is twice the high voltage amperes, but the power is the same. The advantage of the higher voltage motor is the smaller wire required to power it. There is a different jumper configuration for high vs low voltage, the jumpers either parallel the windings or put them in series; Same number of windings each way. In large installations this adds up to a lot of$$.As far as power goes, they are the same. There will be a slight increase in PF with the higher voltage motor.

Here is an example showing voltage-amps for each voltage

OP's question was about 2 different motors, not a dual-voltage motor. But in case anybody's interested, some curves below

Image is too blurred to read the text. Can you submit a better image, or provide a link to it?

It's a scan of an ABB catalogue, and inserted image. Don't know if the link below will work.

I copied the data directly into the message and it seemed OK, but then wouldn't transmit. I'll try that again.

I've always had problems adding attachments on CR4, it seems to be much more complicated than on most sites.

"C:\Users\roger\Documents\Calculations\CR4\Motors.JPG"

Trying again

"C:\Users\roger\Documents\Calculations\CR4\Motors.pdf"

Trying as Word

"C:\Users\roger\Documents\Calculations\CR4\Motors.doc"

If you look at this chart, you will see that doubling the voltage halves the current, across all hp and voltages, same as the dual volage motor of my previous posting.

That's what I'd expect.

I don't think my link works, get a 404 message. Tried again pasting in and it failed to transmit. I'll try something else but not too hopeful.

Tried various things with no joy. It's from ABB catalogue Basic Motor Technology, a few years old. I looked on the ABB website but no joy there either.

"C:\Users\roger\Documents\Calculations\CR4\Motors.doc"

This file is only accessible from the computer on which it is stored. If you can open it, you should be able to copy what you want out of it and paste it directly into your CR4 window.

Links only work for files that are out on the internet.

Text below copied before trying to send, and it failed again.

Yes, I found that out about that link.

Copied directly, looks promising but it usually fails to trasmit. I'll try it once more.

This is the message when it fails to transmit.

You have encountered an error on our site. We're sorry for the inconvenience.

A transcript of this error has automatically been sent to our quality control group and the problem will be addressed.

Please hit the "Back" button on your browser and try your request again.

If the problem persists, please try again later.

That's what I was trying to say!

Just wanted to add, in dual voltage motors the phase voltage are the same across the windings, hence making the performance of the motor identical, but differences are on the Line currents.

What do you wish to add? The chart I posted indicates exactly the same thing.

High voltage is preferred in most cases by industry because of the smaller size conductors, and the increased power factor. It adds up significantly when you have 1000's of motors.

Comparing 460 V 230kW motor with 4000 V 300 hp[223.8 kW] fabricated by same ABB [for 4 poles] the efficiency for 4000 V is less [94.5% instead of 95.7%] and also the torque is less 881lb-ft [1194.5 Nm] instead of 1231 Nm.This, in my opinion, it is due the fact the hv rotor inertia is more[103 lb-ft^2 instead of 76 lb-ft^2 at 460 V] and may be because the losses are more.

The only way the torque can be different is if the slip is different.

The torque should be the same or similar if it has the same rating.

It’s more likely that one of those values is a service factor value. The HV design is less likely to have the common 1.15 SF rating.

I agree.

The values are a 15 percent difference.