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Discussion Starter · #1 ·
Hi, I am new to this forum and non english speaker (please pardon my broken english)

I recently installed a sumitomo VFD to a 3 phase motor 7.5 kW (delta connection). When i run the VFD, the motor hums and didn't rotate at first, then i opened the fan cover and give the intial push to the fan when running the VFD. i am puzzled till now, why is it happening ? and now when i run the VFD, sometimes it needed a push sometimes not. then sometimes the rotation of the motor is CW and sometimes is CCW. Please could somebody tell me what is happening and what went wrong ?
 

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Sounds like a bad VFD or one of your phases is not connected. It is also possible that the motor has a burned out phase.

That's my guesses. Hopefully someone with more VFD experience comments soon.

And you english is better than some of the english speakers on here!
 

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AK_sparky said:
Sounds like a bad VFD or one of your phases is not connected. It is also possible that the motor has a burned out phase. That's my guesses. Hopefully someone with more VFD experience comments soon. And you english is better than some of the english speakers on here!
take a analog meter and check voltage at the u terminals when drive is running, then check the voltage at the motor terminals, double check motor terminations, if you still haven't found the issue, get a megger and hit the conductors from u terminals to motor then the motor windings themselves.

Op it sounds like a single phased motor, especially where it started after you nudged the fan by hand
 

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Sounds like a bad VFD or one of your phases is not connected. It is also possible that the motor has a burned out phase.

That's my guesses. Hopefully someone with more VFD experience comments soon.

And you english is better than some of the english speakers on here!
I agree, classic symptom of a single phasing motor. The output of a VFD can be difficult to check without the right meter. If you have a spare motor of any size close to this one or smaller, hook it up temporarily to this drive. If the same thing happens, the problem is in the drive. If not, the problem was in the motor or the connections. Then re-connect the real motor again and if the problem went away, you had a bad connection, if not, you have a bad motor.
 

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What is described is exactly how a 3 phase motor will act if supplied by 2 phases.

I'm not familiar with Sumitomo VFDs, but the majority of the VFDs I've seen will trip if the motor is single-phased.

First, check current on all 3 output phases, most likely one of them will read zero or close to it.

Next, disconnect all 3 phases at the output of the VFD and check resistance. All 3 should read very close to the same. If not, check at the motor.

If these check out good, then with the wires disconnected at the output of the VFD, megger both the motor and the wire from the VFD to the motor.

Your English is very good, I know it's not easy to learn, but you've succeeded. Well done!
 

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Discussion Starter · #7 ·
Thanks for all of your advise
i will try to measure the VFD output and motor terminal plus winding continuity plus resistance.
i have tried to connect the VFD to a smaller motor (1.5 kw, 380 V, Start connection) and it runs without nudging the motor at all, but i think i need to re-test again.
Anyway the VFD and the motor is brand new, is it possible factory defect, or i screwed up anything ? Either the case i will update again when i tested the motor and VFD.
 

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My money is on a bad connection then, sounds like the VFD is fine.

Micromind, actually there are many drives that do not know if the motor is single phasing. Vector drives will know, because they are looking at a motor model all of the time, but on some, when you place it in V/Hz mode, the motor model is ignored. In that case, many drives will not even know that the motor is not connected at all! I have had several field calls on drives "not making the motor spin even though the display says 60Hz", which turned out to be open disconnects at the motor, or they used fused disconnects at the motor and one fuse was bad.
 
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Discussion Starter · #10 ·
Speaking of displayed frequency on VFD, the frequency fluctuating 7-9 Hz when the motor stalled and need a nudge. Is it normal ? Normally VFD would accelerate and running normally right ? Thanks.

If i were to test the motor by supplying 380V with star connection for a short period (like stardelta starter), will the motor burnt out or broken ?
 

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Speaking of displayed frequency on VFD, the frequency fluctuating 7-9 Hz when the motor stalled and need a nudge. Is it normal ? Normally VFD would accelerate and running normally right ? Thanks.

If i were to test the motor by supplying 380V with star connection for a short period (like stardelta starter), will the motor burnt out or broken ?
vfd stops at 7-9hz because current become too high and this prevents overload fault on the vfd.
check motor windings resistance
 
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