3 phase motor rotation 1

[superbee]

Given an 800hp G.E. Motor directly coupled to a fan why would the manufacturer stipulate the Motor as CW or CCW? I thought that three phase Motors could be reversed by simply switching stator conductors. There is no anti-rotation device.

 

[edison123]

The cooling fans of the motor would be uni-directional.

*Why a man thinks he outrun a chasing dog when it has twice as many legs?*

 

[itsmoked]

Unless on an 800HP motor the fan is made more efficient by using a NON straight finned fan.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[edison123]

Keith

Axial flow fans are also unidirectional.

*Why a man thinks he outrun a chasing dog when it has twice as many legs?*

 

[ScottyUK]

I'm no expert but aren't white metal bearings sensitive to direction of rotation? Probably a rolling element bearing at this size, but an outside possibility.

Also, the motor must rotate in one or other direction given a standard A-B-C phase rotation. Perhaps it is as simple as that.


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Sometimes I only open my mouth to swap feet...

 

[ozmosis]

It could be that the specific application is such that it is critical it only rotates CW or CCW.
We were involved a few years ago in a nuclear power plant and if these fans happened to run in reverse it would have been a case of "last man out turn the lights off..."

 

[Hoxton]

I think that small three phase motors (up to about 200kW) can be rotated in either direction (unless stated on nameplate). I just looked on the ABB website and their small motor rating plates do not give a direction of rotation. I guess that curving the fan blades might give a more efficient fan and thus reduce the motor losses, but then the manufacturer would have to stock both types, or modify them at the distributors.

Larger motors, e.g. the 800hp in the OP can have a unidirectional fan, thus the rating plate will give a direction of rotation. You can swap two phases to reverse the motor, but the cooling airflow will be reduced and the motor rating will be reduced.

These larger motors are usuallly built to order, rather than for stock. If the motor has a single radial fan, you may be able to unbolt it and reverse it, so it works in the other direction. Other designs may not enable you to do this.

Scottyuk, a simple journal bearing will rotate in either direction, but some more complex bearings (eg the offset halves bearings I saw on some turbo exciter bearings), would not. I think some bearings I saw on large vertical motors were unidirectional, because they had scoops to pick up oil to lubricate the bearing.

 

[ScottyUK]

Thanks Hoxton - I knew I had picked that up somewhere. Chances are the bearings on our turbine-generators are in that category. Mind, if we ever get a 365MVA generator to run in reverse we have BIG problems!


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Sometimes I only open my mouth to swap feet...

 

[aolalde]

For 800 HP motor, 95% of probabilities for limited direction of rotation is due to cooling fans being uni-directional type, if the rotation is inverted, the air flow will not follow the designed cooling path, as a result the operating temperature will rise out of the insulation limits.