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Motor Current Varying Without Load |
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 Nov 20 2009, 05:35 AM
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#1
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Senior Member  Group: Full Member Posts: 277 Joined: 21-October 06 Member No.: 2,159  |
Dear Friends;
I have been facing a problem with a 10KW, 22A, 66HZ, 380V VFD compatible motor. The motor rotates a shaft having slitting knifes. First time it happened that motor current increased up to 34A. During checking I found that at 0-20HZ, its current was near about 34A (without load) and as speed increased current decreased at 13A. There was no any jamming in rotor moment found. We re-winded the motor, replaced the bearings, connected the motor at direct line, checked it current without load and found the same behavior as written above. Any bode have any idea? For me, this is a rotor problem but it looked like ok. -------------------- "Don't assume any thing, always check/ask and clear yourself".
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Nov 20 2009, 05:45 PM
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#2
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Member Group: Full Member Posts: 78 Joined: 13-June 09 Member No.: 5,502 |
Hello.
I support your suspicion of the rotor. It happens - laminations insulation (there should be some although all looks so monolithic) degrades, some bars get distorted, rotor may be slightly shifthed along the axe, and the motor would draw more current and heat up. With current differences 34 and 13 - it must be very hot. The rewinders, at a good repairing shop should have the appliance that measures rotor losses - so it was some time ago, am not sure what they use now. It's like a half-transformer, into which you put the rotor (thus forming its "second winding"). You may want to bring the rotor to them. Best regards. |
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Nov 20 2009, 06:52 PM
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#3
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Posting Freak Group: Moderator Posts: 2,336 Joined: 24-April 02 From: Christchurch, New Zealand Member No.: 1 |
Hello AB2005
It sounds to me as though the V/Hz ratio is wrong at the low speeds. Typically this is due to a voltage or torque boost setting, or a 60Hz motor programmed in as a 50 Hz motor. You say that the motor is a 66Hz motor. I am not sure if this is a typo or actually a 66Hz motor. In this case, the motor data must be programmed in as a 66Hz motor. If you set it as a 60Hz motor, you will overflux the motor and the current will be too high. At higher speeds, the VFD may be voltage limiting and this will reduce the flux. Best regards, Mark. -------------------- Mark Empson administrator
Skype Contact = markempson | phone +64 274 363 067 LMPForum | LMP Tech Warehouse | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | LMP Software | Mark Empson Website |
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Nov 24 2009, 06:10 AM
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#4
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Senior Member Group: Full Member Posts: 277 Joined: 21-October 06 Member No.: 2,159 |
Yes, problem has been found in rotor which winding has shorted.
Thanks to friends for replying. -------------------- "Don't assume any thing, always check/ask and clear yourself".
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