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Old January 12th, 2021, 12:00 PM   #1
goghie
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VFD question

Hi,
I found strange situation on site, 4kW motor D400/Y660 volt wired in Y (660V) connected to 400V VFD output. Frequency setpoint was 120Hz. What could be reason for that except error?
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Old January 12th, 2021, 12:40 PM   #2
L D[AR2,P#0.0]
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What if that motor was wired D400 and running at 20Hz?
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Old January 12th, 2021, 01:38 PM   #3
goghie
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Quote:
Originally Posted by L D[AR2,P#0.0] View Post
What if that motor was wired D400 and running at 20Hz?
If you ask me, it would be OK. Motor is slower, but everything is ok and there is enough of ventilation.
I think it is important to mention that it was in closed loop (encoder feedback).
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Old January 12th, 2021, 01:58 PM   #4
L D[AR2,P#0.0]
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Forget my post, I mis-read the content of your original question.
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Old January 12th, 2021, 02:41 PM   #5
jraef
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If you apply 400V to a motor connected for 660V, the motor will develop only 58% of its running torque, and more importantly, only 33% of its PEAK torque capability. Peak torque (Break Down Torque) is what the motor uses to accelerate or re-accelerate after a step-change in load. So what usually happens is that either the motor fails to accelerate in the first place and stalls, or if it does manage to accelerate because the load is very very light, it stalls whenever there is a change in the load.

It CAN however work OK if the load is roughly 1/3 to 1/2 of what the motor is capable of. Why you would have a motor that is 2X to 3X the size it needs to be is another issue though. I have run into this when someone has a motor that was designed for a different task and is being repurposed. It may be far larger than necessary but is already owned as opposed to buying a new correctly sized motor.
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Old January 12th, 2021, 03:05 PM   #6
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Could also sound like a 87Hz setup where the motor was mistakenly connected in Y instead of delta....
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Old January 12th, 2021, 03:16 PM   #7
goghie
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Thanks Jraef.
The VFD came with new motor. Application is Heavy Duty one and it needs Peak Torque. I even suggested to the client to install one size bigger motor. I think it is error, but the guy who installed it before knew how to implement closed loop vector control so I thought maybe there something I overlooked, or maybe he overlooked motor plate.
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Old January 12th, 2021, 03:18 PM   #8
goghie
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Originally Posted by Jobbe9000 View Post
Could also sound like a 87Hz setup where the motor was mistakenly connected in Y instead of delta....
Thought about that one also, but motor is 400/660 not 230/400 and drive output is 3x400V.
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Old January 12th, 2021, 03:26 PM   #9
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Quote:
Originally Posted by goghie View Post
Thought about that one also, but motor is 400/660 not 230/400 and drive output is 3x400V.
Yes, you are right..
But 120Hz just sounds like alot. Especially if the setup is like Jraef says and only provides 58% torque... Raising the frequency above 50Hz (I suspect that you have 50Hz) will lower the torque, and at 120Hz it will be very low.
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Old January 12th, 2021, 04:58 PM   #10
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I might be misreading this, but the motor will develop 4kw when connected to either of those voltages, IF the wiring connections are correctly changed. If I found this situation, I'd ask around as to what the load requirements were, and probably change the motor wiring to match VFD (400V). There might be some reason why the wiring was done this way, however as mentioned above, the effective output of the motor will be greatly reduced.
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Old January 12th, 2021, 07:59 PM   #11
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A few things to think about on this
The voltages don’t sound right 400V Delta / 600V Star
The windings are usually all the same voltage meaning 400V Delta / 800V Star
The Star / Delta is usually a start up configuration to limit the starting inrush
Delta is a single winding phase to phase voltage is 400v
Star is 2 winding in series to a center point each winding is still 400v
2 400v windings in series “ Star” would be a phase to phase line voltage of 800v
You say it as a 50hz system what is the number of poles on the motor or the base speed of the motor.
A 2 pole motor at 50 hz would have a base speed of 3000 rpm
If as you say the vfd set point is 120Hz then a 2 pole motor would run at 7200 rpm. That’s way over the what would be a normal running speed and could be in a dangerous condition. Anything over 5000 rpm should be considered carefully
Most consider 3000 to 3500 rpm the max for a motor
I have done jobs where we ran a motor over 7000 rpm but I had the motor rebuilt with precession bearings and had it balanced to the expected max speed never had a problem with them but as I said before I took the time to have the motor redone to meet my needs.
Remember with an ac motor running below base speed it’s running in constant torque and variable HP and above base speed it’s running at constant hp and variable torque. With a set point of 120hz it sounds like the equipment was originally from North America with a max output freq of 120hz
400v on the vfd would mean it’s a 400v class 400v to 480v input
You can select the operating the output voltage Volts / Hertz 400v motor would be 8v per hertz that would also be the same volts / Hertz as 480v 60hz motor
What you show is possible but proceed with caution
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Old January 13th, 2021, 01:26 AM   #12
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Quote:
Originally Posted by GaryS View Post
A few things to think about on this
...
Star is 2 winding in series to a center point each winding is still 400v
2 400v windings in series “ Star” would be a phase to phase line voltage of 800v
...
Not in Europe

In the US there are usually motors on which the windings can be connected in pairs in parallel or in series and the voltages at which they can operate have a factor of 2 between them.

However in Europe I have never seen that type of connection and only star/delta connection with a factor of 1.73 is usually supported.

400V/690V voltages are the most common for motors in Europe, normally connected in delta, as the voltage currently used in most industrial installations is triphase 400V 50Hz
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Last edited by lfe; January 13th, 2021 at 01:32 AM.
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Old January 13th, 2021, 02:06 PM   #13
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Quote:
Originally Posted by GaryS View Post
A few things to think about on this
The voltages donít sound right 400V Delta / 600V Star
...
It would be 400 Delta, 690 Star. 400 x 1.732 = 692...

The other older voltage rating was 380/660V, but that has been superseded. People still get confused...
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Old January 13th, 2021, 02:49 PM   #14
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Quote:
Originally Posted by jraef View Post
It would be 400 Delta, 690 Star. 400 x 1.732 = 692...

The other older voltage rating was 380/660V, but that has been superseded. People still get confused...
You are absolutely right.
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Old January 13th, 2021, 08:12 PM   #15
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New motors usually are supplied with the links set for the highest voltage . Maybe the field guy just wired the phases the same as the old motor but didn't check the links . Duh .
Paul
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