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Motor starting

howard d

Cast Iron
Joined
May 6, 2003
Location
Clinton, TN, USA
A dual voltage, 3ph, Y wound motor essentially has 2 sets of windings in parallel for low voltage (240). I thought maybe one set be used to start the motor and then energize the second set when it is up sync speed? I tried to start a 7 1/2 hp motor with 3 ph and it did not seem to work (rotor starts turning, very high current draw, and there is a lot of motor "rattle"). Did not try it on 1ph using start caps (as starting a RPC).

Thought this might be a good way to start large converter motors (40 hp and larger) without the large starting current. Can anyone comment on this?

Howard
 
Generally a motor with all 3 pairs of connections brought out for all 3 windings can be connected either star or delta, this was common at one time in order to use a star/delta starter arrangement for starting large motors, where the 3 windings in star have equivalent to 58% of the line voltage across them.
It seemed more prevalent in Europe to use this method, In My travels I found N.A. favoured the decreased voltage start using auto-transformers.
This is not the same as a dual voltage motor, where you have to take care of exactly how the windings are arranged.
Minder.
 
"Thought this might be a good way to start large converter motors (40 hp and larger) without the large starting current. Can anyone comment on this?"

Y-∆ starting, also called reduced-voltage starting, but which implements reduced starting current, is common for integral HP three-phase motor applications.

For reducing the starting current of an RPC's idler, a pony motor starter may be used, whereby the idler is close to synchronous speed before the it is placed across the line.

Starting current is a maximum from a standing start, where that current may be 6 to 8 times the FLA.

Starting current is a minimum when the idler is at synchronous speed.
 
If you truly have 2 sets of windings, both shown as Wye, then it is a 2 speed 2 winding motor, not really a common everyday thing. Depending on the connected load, starting in low and then shifting to high will not necessarily reduce the starting current much.
 
A dual voltage, 3ph, Y wound motor essentially has 2 sets of windings in parallel for low voltage (240). I thought maybe one set be used to start the motor and then energize the second set when it is up sync speed?

On a typical 9 wire motor when you connect it in parallel for 240v the windings are truly parallel, they energize together (in pairs), nothing different between start and run.

The reason for "2 sets of windings" is just so you also have the option of connecting them in series for 480v (the way it probably came out of the box).

Regards,
John
 








 
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