Hello,

Can anyone tell me what is the highest voltage that a 220/380V Motor can withstand? I specifically want to know if it could safely work with 440V.

Thank you
Prakash

 

dual ratings on a motor some times means that different connection methods will require different voltages as in star connected 240volt 50hertz and 415 volt 50hz delta connections i.e. (Australian winding spec) both are three phase one source of supply comes from the consumers terminals the other could come from a AC drive etc .But supply authority's will always guaranty supply to + or - 10% of the nominated supply voltage.And if that is not enough to manufacture a motor it would have to with stand up to ten times the nominated supply voltage.But looking back at the supply tolerance of 10% as in Australia the supply voltage could be expected to rise as high as 264volts or fall as low 216volts even though this still considered good it is not desirable. Now to totally lose the plot take a look at surge arresting circuits for Australian devices might work around i.e. go short circuit at 275volts now these are all single phase voltages to earth or neutral . To wind up the question about how much is too much voltage or how much can a motor stand over rating a motor would cost huge amounts for each manufacture and it would cost us as consumers huge sums of money to buy a motor. So i would stick around the surge arresting arresting device per phase to neutral rating. Sorry if this has missed the point or brought to many points in or just out right confused you happy motoring if it starts to smoke guess what something is wrong try again with a different approach.

 

Well, its the current flow through a motor which causes heating. Too much and you overheat the motor and burn out the windings. Raise the voltage and you raise the current in proportion. Motors are typically designed for 10% over the nominal nameplate rating. 440 would be 16% higher than the 380v rating. That's not too bad especially if you made sure that the motor was not fully loaded and was able to maintain its rated speed. Since a motor's ability to limit the current through it depends upon its speed, that becomes critical. But are you really talking about 440v? The nominal U.S. system voltage is 480v. That would be 26% above the motor's rating and that's pretty high.

People often get confused about the voltage ratings. The nominal or system voltage is 480v. The figures you see on motor nameplates such as 460, 440, etc are "utilization" voltages. The manufacturer is expecting that your system has a certain amount of voltage drop and compensates by designing the motor for less than ideal systems. But systems with almost no drop are very common, especially if the voltage is derived from a nearby transformer dedicated to that motor.


Jim Rowell
Rowell Electric

 

NO! that is why it is rated at a 380vac, not 440vac. Of course you can hook it up and burn it up!

 

Prakash

If the motor is not nameplate rated for 440v, do not use it at that voltage. unless you get it in writing from the motor manufacture, it is not wise to operate a motor at a higher voltage than it is rated for. Most motors have been hipot tested by the manufacture to show that the windings will withstand a maximum high voltage (probably 600 to 800 vac for a 480 vac motor), but that does not mean you can operate the motor at that voltage. If is rated for 380vac, that means at that voltage the motor will rotate at some given rpm at a given current, higher votages means higher heating in the windings, higher rpm and eventually the motor will burn up. To answer your question, NO!, it will not operate safely at that voltage. Specify a 480 volt motor and you will be just fine. (8 to 9% lower voltage condition than rated vs a 16 to 17 % over voltage condition!).

Matt Hyatt

 

It's only 15%. My guess is that if not overloaded, it might well run for a considerable period of time, especially if the duty cycle is low.

I have heard of 3 phase motors being single phased for months without any apparent ill effects.

Bob Peterson

 

Just to clarify one thing, the rpm will not go up for an asyncronus motor as it would with a DC-motor. The speed of an asyncronus motor depends mostly on the line frequency and to a lesser degree on load. The speed is somewhat lower than the syncronus speed, and that one is:

rpm_sync=line_frequency*120/motor_poles

most common motors have 2 or 4 poles. 6 poles can be found sometimes and other numbers do exist, but not as often.

If you check your nameplate of any asyncronus motor you will se that the rpm noted always is slightly lower than a speed you get from the above equation with an even number of poles inserted.

For a DC-motor it is a completely different matter (but also out of topic)....

/Johan Bengtsson

Do you need education in the area of automation?
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Responding to the original query, yes, a 380V motor can be operated on 440V, but it shouldn't be.

Although frequency, i.e., 50 or 60 Hz, has an impact on the discussion that follows, it is omitted for clarity. Load changes and cooling fan variations are also ignored. Now the reason why it shouldn't be connected to 440V:

A) Commercial motors are designed to operate satisfactorily at a voltage 10% above rating. For the case of the 380V motor, 440V is about 6% above the "acceptable" limit. Not necessarily life threatening.

B) With an increase in voltage, then, for the same load, motor current varies as the inverse of voltage. The motor won't burnup, as someone suggested. In fact "life expectancy" will increase somewhat due to cooler operation. The reason is that a running motor is considered a "constant kVA" apparatus. That is, if voltage varies up or down, then current also varies, but inversely.

C) Contrary to the above, the starting parameters do vary with voltage. In this case the motor is considered a "constant impedance" device. That is, if voltage increases, then, the current will increase a like amount.

D) Why then, shouldn't the motor be operated at 440V? Because, the built-in higher voltage capability covers "anticipated" variations in the distribution system voltage. That is, the 380V motor could operate on a 400V distribution system. However, for the 440V case the usual distribution system voltage is 480V. And, It can be expected to increase 10% to 528V, At this value, in fact, any voltage above say 440V will jeopardize operation.

E) Do not misconstrue the above caveat to mean that higher voltage threatens insulation integrity, hence life expectancy. It does not. Instead, the higher voltage causes the motor's magnetic structure to saturate. This factor will seriously affect operation and hasten failure.

Regards, Phil Corso, PE Boca Raton, FL [[email protected]] ([email protected]) {[email protected]}

 

Just so no one gets confused. This is NOT true. Motor current will go UP when the voltage is increased and DOWN when the voltage is decreased. The motor will run hotter with higher current and cooler with lower current. The only twist to this is will voltage that is TOO low. The motor's torque (strength) is developed from the current. The current is developed from the voltage (more voltage = more curent). The motor's impedance (how hard it is for current to flow through it) is developed by the speed of the motor... more speed = more impedance = less current. If you do not give the motor enough voltage which in turn does not allow enough current to flow which in turn does not offer enough torque then the motor will not have the strength needed to reach full speed. This means it will not develop enough impedance to restrict the current flow and it will remain in a condition with a higher than normal current, run hot and eventually burn out. So in this case (motor startup), low voltage causes a high current to last longer than it should. But it normal run condition, the current is directly proportional to the applied voltage. And you can forget about "magnetic saturation". Please don't post if you are not sure what you are talking about.

Jim Rowell

 

Responding to Jim Roswell's Sat, Dec 27, 2003, 6:53pm, denunciation of my comments on the subject:

Jim, I believe that you are comparing "apples" to "oranges'. That is, you are considering only operation at extreme supply voltages! Paragraphs A and B in my original reply addressed supply voltage variation effects on "normally' operating motors. Reiterating my point, "current is inversely proportional to applied voltage!" Par C addressed variation effects on motor "starting," that is, "current is proportional to applied voltage!"

If you still believe my comments are incorrect, then I suggest you search the web for "Voltage Variation Effects on Induction Motor Parameters." If you are unable to obtain corroboration, I will be happy to fax you references from standards, technical papers, authoritative
texts, and personal case histories. The latter illustrate the catastrophic effects of low supply voltage. Included are very large operating plant installations. One you may consider especially interesting covered a deep-well (10 k-ft ) submersible-pump installation.

BTW, what about "magnetic saturation" bothers you so vehemently?

In keeping with the holiday spirit, I wish all List participants a prosperous, and most of all, a healthful, New Year.

Regards,
Phil Corso, PE
Boca Raton, FL
[[email protected]] ([email protected]) {[email protected]}