Selecting correct copper wire size for motor windings 4

[wmusleh]

I have just gotten into motor re-winding. In some cases, I get motors that have the original windings removed which I usually rely on when rewinding . Could I use your expertise in finding resources (formulas, online calculatrs etc) to help find the correct wire sizes to use when rewinding for 3phase and single phase motors?

Thanks all for your help

 

[Motorwinder]

Figuring total circular mils of your wire (in hand) divide your number of circuits and your amps.

Example: 10 amp motor figuring a 1 wye connection, you want about 3000 circular mils total for 300 circular mils per amp.

For delta motors take your amps times .56. 10amp motor would be 5.6 amps. The same 3000 cm would be 535 CMA.

You also want as much as you can fill the slot. I try to keep it above 300 CMA for open drips, and 350 to 400 for TEFCs.

 

[edison123]

Once you have figured out the number of turns in a slot, the copper size will work out itself since the slot cross-section is finite.

Muthu

http://www.edison.co.in

 

[rhatcher]

Motorwinder and edison123 have good (lps) answers to this question.

Motorwinder's solution will allow you to determine the exact wire size that is required based on amperage. Calculate the winding amps as determined by the connection and use 300-400 CMA depending on the frame type. In many cases, there will be extra space left in the slot after allowing for the amount of wire required. Use spacers or fillers in the slot so that the slot is filled and the wedges are tight before varnishing. This should result in a normal insulation service life.

edison123's solution is to determine the # of turns according to the connection and then to pick a wire size that results in the slot being completely filled. This usually results in having a greater wire size than is required.

The advantage to greater wire size is that the motor will run cooler than normal and will probably have a greater insulation service life. This may also allow running the motor at a slight service factor overload (1.10-1.15) without reducing the service life (overheating). The disadvantage is that copper is very expensive and you will spend more money for wire than necessary.

We usually use Motorwinders method (300-400 cma) to select wire size and only use edison123's method (complete slot fill) for motors that operate in high temperature environments or motors that run continuously at heavy load.

 

[edison123]

Nice comparison hatcher. You nailed my philosophy but then I have wonderful clients.

Muthu

http://www.edison.co.in

 

[wolf39]

I fully back edison123's approach. In most cases it makes sense to fill the slots with copper and not to use space fillers (how much do space fillers cost?). This is especially true for large motors with continuous operation.

Copper nowadays costs US$ 10 per kilogram but one has to compare the copper expenses with the savings in power consumption accumulating over the lifespan of the motor in question. Every single kilowatt at 10 cents per kWh over one year of continuous operation (8760 hours) does result in a saving of 876 dollars per annum.

Wolf

http://www.hydropower-consult.com