using 380volts rated motor on 415volts system

[eengineer01]

Can a 380(+/-10%)volts, 50(+/-1%)Hz rated motor be connected to a 415(+/-6%)volts, 50(+/-3%)Hz system, without any modification or use of any transformer?
please explain with reasons.
regards,

 

[nbucska]

The specs seems to be unrealistic-- is this a school
homework ?

At max. load and voltage may run hot -- with reduced reliability.


<nbucska@pcperipherals.com>

 

[jbartos]

Suggestion: It depends how the motor is engineered and designed. It might, if designed for it.

 

[amptramp]

Supposedly, NEMA design motors are capable of operating within a +/- 10% tolerance on voltage and +/- 5% on frequency (IEC motors have similiar specs).

380 + 38 = 418

If it is a NEMA design motor, it should operate ok. (The system frequency spec might be a problem if the motor spec is correct - depends on your application.)

However, I agree with nbucska. Operating on the edge will cause the motor, when operating at full load, to run hot, have a reduced lifespan, and operate inefficiently.

It would be wise to oversize the motor (derate).

http://www.marathonelectric.com/motors/manuals/SB537.pdf

 

[jOmega]

Engineer01:

Correct me if I am wrong, but it seems you have described an IEC type motor (not a NEMA motor). Ergo, tolerances stated for NEMA motors may or may not apply to your IEC motor.

Expanding upon Joseph Bartos' statement, consider:[ul][li]at 380/50 ... the motor is designed for 7.6 v/Hz[/li] [li]at 415/50 you would be supplying this motor with 8.3V/Hz[/li][/ul] In this case, you would be over-exciting the motor, moving the iron closer towards saturation. You can expect the magnetizing current to increase, the Power Factor to decrease, core losses to increase, and the efficiency to decrease as well.

It is not unlikely that the motor will run hotter even when lightly loaded which will reduce the expected life of the motor.

Now then, all this being said.... consider that the definitive answers for your particular motor cannot come from a Forum such as this. Because we don't own the design of your motor, we are not capable of assessing the impact that over-exciting this motor will have upon it. There are too many unknown factors that the Forum members are not privy to.

For example, none of us know how much thermal margin your particular motor has. None of us know how much the iron can be pushed before the motor is in trouble.

You should be asking the ... Motor Manufacturer.
After all, who better knows the design factors of your motor and what it is capable of tolerating and not tolerating.

I sense in your post that running this motor on the higher voltage is necessary and that you are attempting to assess the risks.

While a transformer certainly is an answer....it need not be rated at the full kVA of the motor. You could use a Buck-Boost transformer, connected in Buck mode, to knock down the 35 volts difference between 415 & 380.
(kVA calculation based upon 35 volts and load FLA)

You could also use a VFD (inverter) which would also give you the frequency stability. This is a more expensive approach but also has some pluses and minuses. On the Plus side, it affords variable speed control and can be set to limit at 380/50 for a 415/50 input. On the Minus... your motor may not be suitable for inverter power or it may not be suitable for much of a speed turndown (below 50 Hz) for thermal reasons..

Again, I would recommend you discuss this with the motor manufacturer.

 

[jbartos]

Suggestion: I do not recommend a 380V motor designed to NEMA standards MG-1 with +/-10% voltage tolerance to be connected to 415 (+/-6%) volts, since:
1. 380V + 0.1x380V = 480V, which is permissible continuous motor terminal voltage maximum.
Now, the 415V power supply maximum can be:
2. 415V + 0.06x415V = 439.9V
Clearly, (439.9V/380V) x 100% = 115.76%, which is too excessive for the motor complying with NEMA standard MG-1. A special, custom-made motor would have to be applied.