Universal Induction Motors 380-420/460 50hz/60hz

[yuri]

Hello.

One question bothers me to which I cannot find right explanation.

A 50Hz one pair pole induction motor rotates 3000 rpm minus "slip", or "lag", or "friction" (difference between rotating field in the stator and the actual rotations per minute).

A 60 Hz one pair pole motor rotates 3600 rpm minus the slip.

 

But we have also induction motors able to work both 380 - 420V 50HZ and 460V 60Hz, that is, universal ones.

However, how their universality is realized?

 

Variant 1: at 380V 50Hz the motor is slowest and lest powerful. At 460V 60Hz the same motor is quickest and most powerful.

Thus, the slip is maximal at 380V 50Hz - let's say 8 % (2760 rpm), and minimal at 460V 60Hz - let's say only 2% (3528 rpm).

 

Variant 2: the trick lies in the construction, in the stator and rotor's iron. At the greater frequency the motor construction exerts greater impedance. The resultant currant at 460V 60Hz does not differ substantionally from that at 400V 50Hz. Neither the rpms non consequently the work. By that, the slip is minimal at 400V 50Hz - let's say 3% (2910 rpm), and maximal at 460V 60Hz - let's say 19,1% (the same 2910 rpm)

 

Could someone tell me how indeed behaves the universal induction motor ?

[marke]

Hello yuri

 

Welcome to the forum

 

I believe that you are looking at a universal motor, not a universal induction motor.

A universal motor operates differently from an induction motor as the motor has a stator and an armature where the coil on the armature is driven by the supply voltage. It is not a short circuited winding.

The universal motor has brushes and a commutator to apply voltage to the armature and it will operate on AC and even on DC within certain voltage ranges.

 

The universal motor is not a synchronous or pseudo synchronous motor, unlike the induction motor.

I am not aware of any "induction motor" that is not affected by applied frequency.

 

Best regards,

Mark.

[yuri]

Thanks for so unexpectedly prompt reply, the problem concerns refrigeration compressors.

Manufacturers of a Maneurop, for instance, state (on the compressor's tag) that it can be run either at 380-420V 50Hz or at 460V 60Hz. But by that, there stays 19 A FLA - only once. Does it mean that at 400V 50Hz and at 460V 60Hz it will draw one and the same (maximal) currant at the one and the same (maximal) load?

And as I understand it, this compressor's motor is supposed to work with greater loads when connected to 460V 60Hz. Yes, the V/Hz ratio being the same, the powers are different - as and because the speeds are different.

Do I think correctly? Thank you again.

 

 

[yuri]

(Unused yet to the posting mode here,) thanks for the so prompt reply.

The problem concerns the refrigeration compressors. A "Maneurop"'s manufacturers, for instance, state on its tag that it can run either at 380-420V 50Hz or 460V 60Hz. By that, there stays only once 19A FLA at the tag. As I understand it now, the ratio V/F being the same, the compressor's motor is still capable of handling greater loads at 460V 60Hz than at 400V 50hz as its speed (torqe) is greater.

Am I thinking correctly?

[yuri]

(Seem to be unable to post any more), still, thanks for the prompt reply, but now I see:

a compressor's motor capable to run either 380-420V 50Hz or 460V 60Hz is capable to deliver different works, handle different loads, depending on voltage and frequency, the ratio V/F being the same, speeds being different (slips, probably, the same for both frequencies - at the same torque).

 

 

[yuri]

So my first post was nonsense. A "universal" (still I prefer to abide to that term) 3 ph compressor able to run 380V 50Hz or 460V 60Hz in the latter case is simply more powerfull. Correct?

 

One has really get used to the mode of posting and server work here. All my posts which I hold for lost popped suddenly up.

[marke]

Hello yuri

 

Your posts were slow showing due to anti spam measures on the forum. They did come through!!

 

It is normal for the rated FLA to remain the same at 50Hz and 60Hz where the V/Hz is constant. This gives a higher power rating at 60Hz than at 50Hz.

 

In the case of a compressor, I would expect that the load on the motor will increase with the increased speed and so will be higher at 60Hz than at 50Hz. It is possible that the load increase will be linear with speed and so the actual load current will remain the same.

Centrifugal loads such as pumps and fans will have a non linear increase and the load at 60Hz will be much higher than the load at 50Hz.

 

Have agood day,

Best regards,

Mark.

[yuri]

Hello Mark

 

Thanks for your reply but still there remain some foggyness about that motors. And I was wrong in my last post(s) - it has turned out that the power stated on the tags is equal for the both applications ! But how on earth kWs of an engine may be the same for it working on 400/50 and on 460/60 ? Will not it rotate qwicker on 460/60 and thus move more substance and thus produce more work? and from that does not follow it should have more power ?.....but no, the tags state: power the same ?!

[marke]

Hello Yuri

 

If it is a true universal motor, then it is not synchronous. The speed will not change with frequency.

The behaviour is much more like a DC motor, even when it operates on AC.

 

Best regards,

Mark.

[themotorman]

Hello Yuri

 

If it is a true universal motor, then it is not synchronous. The speed will not change with frequency.

The behaviour is much more like a DC motor, even when it operates on AC.

 

Best regards,

Mark.

 

My first post, thanks for making this forum.

Please make sure we are either talking induction motors, that can have a wound rotor with brushes, but usually have a squirrel cage construction or a "universal " motor that is usually a DC brushed motor where the armature windings and the field winding are connected in series so that as the AC changes polarity once every cycle the motor keeps going in the same direction. Universal motors used o be very commonplace , used in many household appliances and not used for large motors over 1 HP due to the poor efficiency .

I am sure that you can find the voltage, frequency and speed relationships for induction motors if you do a isearch. If you are interested in this topic look up variable speed induction motor drives too.

[yuri]

Hello Mark.

Then let me drop that term "universal". I am only concerned with AC synchronous (induction) motors suitable for both 400V 50Hz and 460V 60Hz. How their power me be equal - as manufacturers state on the nameplates (that meaning able to produce equal work at both applications). But at 460 V 60Hz such one will produce more work as its speed will be higher ! ?

Best regards, thanks for your replies.

[marke]

Hello Yuri

 

If the induction motor is operated with the same flux levels on 50Hz and 60Hz (this requires that the V/Hz ratio is equal) then the motor is capable of producing the same shaft torque. Power is torque times speed, so the motor is capable of producing more power at 60Hz than at 50 Hz.

If the V/Hz ratio is reduced, then the torque capacity will also be reduced and so the power may also be reduced.

 

If you look at the ratings on a hermetic compressor assembly, the power rated is commonly not the power rating of the motor, it is the refrigeration power of the compressor. This may not change with speed depending on a number of factors.

 

Best regards,

Mark.

[yuri]

Hello Mark.

Now as I looked at some tables on performance and compared it is all clear. Of course, current remains the same if we go up in V's and Hz's but retain at the the same time the same V/F ratio. Speed will increase, and el power and refrig capacity will increase - it is impossible for the latter not to change.

What confused me earlier, was one and the the same stated el power on a plate - just opposite 400V/50Hz 460/60Hz. They had probably done just a mistake.

The best regards.