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yuri
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Joined: 13-June 09
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Last Seen: 3rd September 2010 - 04:57 PM
Local Time: Sep 7 2010, 05:49 PM
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2 Sep 2009
Hello.
Today I was trying a small 3ph 380V induction motor (I needed low rpm's) through a GE Vat20 - and it turned out that lacking 1 phase to the VSD the motor run normally. Surprisingly also, current drawn by all the motor's leads (taken by a clamp) when I restore the third phase to the VSD did not differ from what it was when the VSD received only 2 phases. What do you think, is it a (surprising for me) feature of all VSD's - to compensate in such a manner the lacking supply - or only small size drives are able to do so ? (In short - to make 3 ph out of 2ph)
1 Aug 2009
I have (seen) a 3 ph induction 380 V motor running with current difference of about 40 % caused by voltage difference of about 2 % across phases. This because taps on the supply transformer were set wrongly. I doubt the phenomena could be explained but does anyone else has encountered a similar case - insignificant diff in V supply leading to huge diff in A drawn ? The amps (if I remember good) were some 90/120/140 A.
17 Jun 2009
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 ? |
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Lo-Fi Version | Time is now: 7th September 2010 - 04:49 PM |
29 Jun 2009 - 9:23
