Motor voltage?

[ronaldrc]

Since the over and under voltage tolerances of most motors are around 10 percent do you think it would be safe to run a 3 phase motor of which the name plate states 440 volts on a 480 volt system, and other that shorting the running life of the motor what other problems might I see?

 

[templdl]

Re: Motor voltage?

My references show that a 10% overvoltage will result in:
Starting torque up 21%
Max. torque up 21%
% slip down about 15-20%
Efficiency, down, at FL down 0-3%, 3/4 load 0-down slightly, 1/2 load 0-down to about 5%
PF Down, FL 5-10%, 3/4 load down 5-15%, 1/2 load down 10-20%
FLA Down slightly up to 5%
Starting current up 10%
FL temp rise up 10%
Max overload capacity up 21%
Mag noise will be up slightly

 

[ronaldrc]

Re: Motor voltage?

Thanks for the reply.


Looks like everything favors running it with the higher voltage of 480 I was sorta worried about it pulling more current and shortenings the life of the motor.

You must have figured that with a computer program to come up with all those specs?

Or a very good motor chart either way thanks.

Thanks again

 

[tom baker]

Re: Motor voltage?

It would be a code violation to operate a 440 v rated motor on a 460 volt system:
110.4 Voltages.
Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

A motor operated at 10% about its rated voltage will draw excessive current, while its a 460 volt system, typical secondary voltage is 480 or higher.

AS the voltage increases, the magnetic field saturates and above 10% overvoltage the current increases.


More information from nema at:
http://www.nema.org/index_nema.cfm/1427/8672E77E-D3BC-494F-A0D0CE6E55B99A74/

Please see additional comments at the end.

[ January 27, 2004, 03:34 PM: Message edited by: tom baker ]

 

[Guest]

Re: Motor voltage?

I was involved in the electric motor business for over 20 years ( motor rewind and sales up to 500 hp) and never had any problem with motors rated 440 volt on 460 or 480 volt networks. The pre nema frames and then nema frames were all rated440 volts. 460 volt was the standard for all motors later on when nema U frames were introduced. The nameplate service facotors on pre nema and nema frames was as high as 1.35. This allowed for much larger voltage and even frequency variations. The amount of core Iron on these older motors was substantially more than is used today. Newer motors use a higher grade of lamination iron and thinner plates allow for better heat dissapation wheras the old units relied on bulk to absorb heat and prevent the windings from overheating. Todays insulation on magenet wire is also far supeior to what was used in the distant past. In my opinion an older motor will operate just fine if operated within the NEMA standard of 10% above or below nameplate voltage. I disagrre that it is a code violation to use this motor on 480 volts. I believe the code contradicts itself on this issue. Nearly all thre phase motors today are nameplated 460 volts so if you interpreted the code to preclude use of these motors on 480 volt networks you would be hard pressed to find anything compatible with the 480 volt rating.I believe the code allows for this when it also mentions that elect4rical equipment be applied and used per manufacturers instructions. Anyway just my opinion as a motor shop guy.

 

[Guest]

Re: Motor voltage?

If you can find a motor rated 480 volts in the grainger catalog( ar anyplace) let me know. Betcha can`t. Joe

 

[ronaldrc]

Re: Motor voltage?

Joe I agree with you I have used 440 and 460 volt motors on 480/277 systems a hundred times through the years I just wanted some other opinions on what people think.

I agree you will not find a 480 volt motor in the Grainers Cat. But a lot of supply houses do carry them.

I also think if a 440 volt motor say a 5 horse is driving a 5 horse load and you apply 480 to it would cause it to pull more amps in turn caus it to over heat and shorten its life. And also the users power bill will be higher.

Thanks for the reply

 

[Guest]

Re: Motor voltage?

Ron I still caNT FIND ANY MAFG IN ANY OF MY CAT INFO BALDOR,LINCOLN GE,WEST.,DOERR RELAINCE etc that offers a motor at 480 volt. If you find one let me know. Actually when the voltage rises nominally say 10% or less above nameplate the current drops.It is only when you reach the "knee " of the saturation curve that cureent starts to rise and it does so dramatically until all the smoke comes out! Theoretically if you can keep the smoke inside the motor it will last forever. Thats what our job was as a rewind shop to put the smole backe inside. Ha ha.All that smoke is what kept us in businees wheas some peop-le hated the smell of a burned up motor I loved it It smelled like money in the bank. Actually voltage imbalance is worse than hi voltag. A 5% voltage unbalance between phase can cause as much as a 20 to 25% increase in amps at rated load. Hope Ive helped in some small way. Joe

 

[ronaldrc]

Re: Motor voltage?

Joe you sound like a pro in the motor field.That point about saturation makes sense.

I don't have any motor cats. But I did use the search engine on the net and it is hard to find a 480 rated motor even there.Most are rated 460 volt.

Joe from now on I'm not going to buy nothing but totally enclosed motors

[ January 26, 2004, 10:35 PM: Message edited by: ronaldrc ]

 

[hillbilly]

Re: Motor voltage?

Ronald, if you apply 480 volts to a 440 rated motor that is delivering constant hp the nameplate amperage will be less, not more.
steve

 

[iwire]

Re: Motor voltage?

Tom's reference to 110.4 seems to make the practice of using 440 or 460 motors on 480 a code violation even though we all seem to agree it is common practice.

110.4 Voltages.
Throughout this Code, the voltage considered shall be that at which the circuit operates. The voltage rating of electrical equipment shall not be less than the nominal voltage of a circuit to which it is connected.

If we look at Table 430.150 part of the text before the table says:

The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440 to 480, and 550 to 600 volts.

For 440 to 480 we use the 460 column.

So does this text override 110.4?

 

[ronaldrc]

Re: Motor voltage?

I think we need to consider the definition of Nominal.

It is a loose term use to specify a particular operating voltage out of many and which may vary in that particular range.

The code specifies that you use the nominal voltage to do your calculations with not that the voltage has to be that very voltage, if it did we would be hurting in this area its never 208 0r 240. Its usually over the nominal.

Just my two cents.

 

[tom baker]

Re: Motor voltage?

Ok I may be wrong on allowing a 440 volt motor on a 480 volt system.
But, its clearly a violation to use a 200 volt (for 208) rated motor on a 240 volt system with utilization voltage for the motor of 230 v.

Motors are rated with a utilization voltage that is lower than the sytem voltage, 200 for 208, 230 for 240, to allow for voltage drop from the source.

What about 440? Hmmm, not sure, its a secondary voltage that went away a long time ago. 110 and 220 still exist at the big box stores, like this:
Homeowner: I need to install a 220 v plug for my welder.
Big box sales person: Sure you'll find the 220V plugs on aisle 6 right next to the 110 v outlets.

What I would be concerned with is the motor current does increase if the applied voltage is more than 10% above the motor rating. So a 440 V motor may ok in one location, but not another.

 

[caosesvida]

Re: Motor voltage?

again, what a interesting thread here, I learned a lot, thanks to all who contibute.

 

[ronaldrc]

Re: Motor voltage?

Yes its a great tool to our trade.I know I learn something about every time I open this forum up.

Tom I don't know where or which motors have an increase of current draw when you run it at a higher voltage most don't but some do.

From my experience I have found that motors which create their own load such as a fan motors do.

Many a times I have went on trouble shooting calls and had to up the heaters in the starter because of this.Usually when I measure the voltage it is on the high side.

To many people in this field are taught that if you increase the voltage on a motor it will automatically decrease the current draw or reduce the amperes and this is not always true.

Ronald

 

[hillbilly]

Re: Motor voltage?

Ronaldc, in my last response I stated that if the motor was delivering CONSTANT HP and you increased the voltage, the current would go down. In certain situations, it is possible that the motor would draw more current with a given increase in voltage. Constant HP is delivered when the motor supplies constant torque at a constant RPM. A good example is a motor that powers a conveyor system that runs at the same speed all the time and carries the same load. The power output is always the same and any increase in motor voltage (pressure) will require less current (flow) to maintain the same amount of work. Many loads are not constant and are inverse as far as torque is concerned. A example is a centrifugal pump (or fan) motor as compared to a motor powering a flywheel for a stamp machine. Centrifugal pumps require low starting torque (hence less motor current) during start and gradually increase in load as the pump develops head pressure and starts moving fluid. After the pump develops it's running head pressure, the motor torque will remain constant as long as the head pressure on the pump remains the same. If the head pressure increases, the flow (and the required current) will go down. Reduce the head pressure and the opposite is true. The flwheel is the opposite and requires high starting torque (more current) to get it moving (inertia) and the required accelleration torque gradually decreases as the flywheel comes up to full speed and develops equilibrium with the load. At that point it remains constant. The motor powering the pump will draw less current at higher voltage (during start and run) with acceleration (basically)remaining the same. The flywheel motor will draw higher momentary current with a higher voltage due to the higher inrush and locked rotor current developed during starting as it tries to accelerate faster. I didn't get this from a text book. This is what I experienced in my 25 years designing, installing and serviceing industrial machinery. It may lack some refinement, and I look forward to discussing it more on this forum.
We're all here to learn.
steve

 

[ronaldrc]

Re: Motor voltage?

Hillbilly my experience is also practical and not from the book. I think you and I see motor ampere from the same viewpoint.

I also like Joes story about keeping the smoke in the motor.I think he had a good point about the laminations being saturated.Once all the magnetic fields have been create in the armature and field that can be place there and can be no stronger the voltage has no choice but to increase the amperage.But there are other factor that play apart in increasing current with increasing voltage.But I still believe after hearing Joes story about the smoke we should all buy totally enclosed motors from now own.