400VAC Rated Motor to Run on 380VAC System Voltage

Not 100% certain, but I wouldn't imagine there would be any great detriment to operating the motor at a reduced voltage. 380v is presumably referring to RMS voltage, so the peak will be considerably more. The motor is designed to withstand 6-8 times full load current during start up and as such can tolerate some fluctuation in winding current. However It is always adviseable to have a motor fit for purpose. Running a motor at anything other than manufacturers specs will increase the possibility of equipment failure. Approprite thermal protection should mitigate any damage but may cause nuisance tripping. Your best bet is to query the motor manufacturer. Hope this has been of some help.

The answer really depends on the specific application. Short bursts (10 mins once per hour) might be OK, but prolonged operation might not be.

We've seen motor fails where VSD's have run 50Hz motors at 60hz and not compensating maximum voltage appropriately. (Total power to be dissipated in the motor exceeded ability to dissipate heat.)

Contact motor supplier for application data sheets and READ CAREFULLY. Discuss with them for clarification.

Hi, I presume we are talking about an Induction motor. speed of the induction motor N=120f/p. so speed is prop to only frequency.

on the other hand if the FLC is 60A what is the mechanical load on the motor? and the corresponding load current. If you run this motor at 380V supply the voltage is less by only 5% which is not a big problem as your motor is rater for +/- 10%. however for the first try have a 63 Amps circuit breaker and measure the starting and FLC what is the starter arrangement required? is it a direct on line or star delta. The star delta starter, will get rid of 95% of the problems.

Please ensure you keep the voltage within the range of motor else please have a servo stab doing this job. alternatively you can have the input voltage regulated by suitable arrangements at the power Tx like On Load Tap Changer etc.

Hope this is useful.

Regards,

RAJ

As per law when voltage will be reduce the current will be incrice but in your case your rated voltage of motor is 400V +/-10% i.e. 360V to 440V so your motor should be designed for running on the same output on 360V to 440V. So if for some time your voltage level will be go down from 360V it will be little bit over current drawn by the motor, But if the voltage surge will be continues so it will be damage the motor so it is advisable to use a VFD or a Soft Starter to privent the motor from long surge protection and over current drawing and also you cab save energy at the time of less load condition. But when you use VFD it is necessorry to use Line & Load Chowk with VFD.

Dear User,

In my opinion the drop in 5% voltage will not affect the operation of the system, if following points were taken care:

Check the present loading on the motor, which should be equal or less than 80% of FLC

Check if Voltage variation are not more than as mentioned +/- 10%

We have run motors in such condition and we have not faced any problems in the past.

Please go ahead and give your feedback.

I do not think that the kW rating of the motor will reduce in this case.Rather, the current will increase to meet the required kW rating,thereby leading to increased copper loss.

You may think of increasing the supply voltage to 400V by adjusting the transformer tap position, provided other consumers fed from the same bus tolerate the increased voltage (+5%).

This will be advantageous considering reduction in copper loss in other consumers.

I agree with you that the KW Rating at electrical side will not reduce but at the mechenial end i.e. out put of motor will be reduce. Meens RPM & Torque of motor will be reduce. and that is not neccesory that every where tape changing transformer will available so it is bater option that you can use seprate step up transformer for this motor only. If tape changing tranformer is available so you can update it in to auto tape changer so your problem will be solved permanantly.
Is it true or not?

The comments given so far are very good, before any further suggestions, feedback on the motor load is required. Will the motor be 95-100% loaded? If so then you will exceed the nameplate amps if running at 5% voltage drop. You also have to consider the voltage drop of the cable supplying the motor... that too can affect the motor terminal voltage.

Until you give us the motor load, then it is difficult to advise... it's more judgement call.... running your motor above NPA produces more heat, which in turn reduces the life of the motor.

What I will say is this; I regularly "RE-RATE" motors dependent on the load, which wold be less than 100% of max motor power output... anything from 60% to 85% loaded.

I do it because of underload conditions, where I need to keep the running current high.

Yes you lower the voltage, current goes up, HP goes down, that we know. However if you don't require the max motor HP, then you have no problem.

You did state that your motor is ±10%.... really you've answered your own question, if you calculate the FLC at -5% voltage you are within tolerance of the manufactures specs.

Get back to us with the motor load first, and hopefully I can offer more advice.

* Lower voltage does not hurt a motor unless it causes it to stall or otherwise draw current above its rating. You must have enough margin so that the load will start across the line. The starting torque has to exceed the torque required by the load at rest. When line voltage decreases, the torque curve moves down and both starting torque and peak torque are less.

* No matter what, do not exceed rated current for continuous duty. It is current that causes motor heating that has to be dissipated by the windings.

* Determine your lowest anticipated operating voltage AT THE MOTOR TERMINALS (Vrms). Calculate Power = SQRT(3)*pf*FLC*Vrms*. Assume pf = 0.8 to be safe for off rated conditions. Power = 1.73*0.8*60 Amps*Vrms. Is the continuous load less than this? If so, you are OK. If not but it is close, you will have to confer with the motor manufacturer to determine a more accurate power factor to help out and bring you within limits.

* Motors have a service factor, typically 1.15. You can use some of the service factor if you have to, but be sure to pay attention to the bullets below. [i.e. if the continuous load is 105 HP and you have a 100 HP motor with a service factor of 1.15, you will be OK assuming that you pay strict attention to ambient environmental factors, most importantly temperature.]

* Depending on the application, you may have other factors to consider. For example, API requires a safety margin of 1.10 to 1.25, depending on the motor size. [Thus if the load is 50 HP, for example, the minimum motor size is 1.15*50 = 57.5 HP]

* Consider the ambient temperature and other environmental conditions for the application. The motor may have to be further derated.

Just FYI...

"Motors have a service factor, typically 1.15. You can use some of the service factor if you have to, but be sure to pay attention to the bullets below. [i.e. if the continuous load is 105 HP and you have a 100 HP motor with a service factor of 1.15, you will be OK assuming that you pay strict attention to ambient environmental factors, most importantly temperature.]"

If he is talking 380 / 400V, he is talking IEC. IEC motors do NOT have a "Service Factor", that is strictly a NEMA concept. In other words in our terms, all IEC motors are 1.0 SF.

If you run the motor in power supply 3 ph 380 V 50 hz motor rpm will be reduce and you also need to check the specfication of mechanical device/drive. I recomend you to use VFD (Inverter) for solve your problem.

I think you need to read the OP again, the motor he has is 50Hz, the supply is 50Hz... it the operating voltage the issue for the OP.

There is a motor rated at 400VAC +/-10% (360V/440V), 3 Ph, 50 Hz,30kW, FLC=60A. Now I have to run it on the system voltage i.e. 380VAC +/-10%(342V/418V), 3 Ph, 50 Hz.

The RPM of a motor is dependent of the frequency of the supply.. but I guess you knew that already!

As system voltage has reduced, slip between rotor and stator has increased due to

lower values of the linkage of magnetic flux, resulting in Nr = rotor speed decreasing.

May be the effect will be low, but yes it is there.

now that you have made this statement, would you be prepared to calculate the actual slip figure based on the new voltage?

When a motor is given operating specs, do you not think the manufacturer has taken all these parameters into consideration BEFORE they said "±10% NPV"?

What is it turning and what is its torque/speed characteristic?

<...the current may rise above the FLC...>

Not if the motor protection equipment is correctly set, it won't! The current drawn by a motor is proportional to the torque presented to it. Reducing the voltage doesn't alter the load torque, though it might cause it to stall - which is why the motor protection device needs to be correctly set.

The shaft power presented to the motor is the load torque multiplied by the speed of rotation.