Excessive current at motor startup 2

[sry110]

Hopefully this will be a simple one for you electrical guys:
I have a 4-pole 3.0kW motor, 380V/3-ph/50Hz, whose data sheet shows D (delta) connection and starting current of 40 Amps. The Customer reports that when they started the motor, it pulled 70 Amps which consequently caused the motor trip out on over-current.

I noticed that 70 divided by 40 is 1.75, which looks close to 1.732 (square root of 3). Then I looked at the catalog for the motor and found that the rated current for this motor in 400V Delta connection is a factor of approx. 1.73 higher than the same motor in 690V Wye connection. Also, 690 divided by 400 is 1.73.

I'm not drawing any conclusions, just providing some observations. Can anyone explain what could be causing our motor to draw approx. 1.75x its rated starting current at start-up?

 

[advidana]

Why can't use the larger motor and see if that works. Sometime the practical solutions are the best.

 

[ScottyUK]

Expensive though! New motor, almost certainly a new or modified starter, possibly a larger cable...

 

[3DDave]

ScottyUK - good list.

On the mechanical side, what about new mounting, reduced clearances with other equipment, greater unexpected weight, more unused torque just looking to break something.

The only mechanical suggestion I'd have to to uncouple the motor and see if the problem persists. If it goes OL by itself, it's not the load. One can also verify the breakaway torque for the rest of the machine.

The thing that stands out is the motor starter is selected by the customer. Seems like a good way to have a problem.

 

[waross]

Is the trip instant? It may almost seem as if switching the motor on switches the over current device off. I happens so fast that the motor may only twitch or not move at all. That is a magnetizing transient issue. The issue is with the over current device.
If the motor turns for a few seconds or longer before an over load trip, that is a motor, connection, voltage, over load setting or load issue.
Again, how is the start current measured.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MatthewDB]

Is this a 6 wire motor? If one phase is reversed, the motor will produce greatly reduced torque and draw very high current.