We need to Rewind an Existing motor rating 400 hp-3.3 kv, 4 pole, having 48 slots, but problem is that they have only used 2 coil in a set with total 12 set in complete winding, with 6 leads coming out. so plz suggest the possibilities which we should look after, along with possible terminology of phase connection.

I think it may be wound concentric style. I've had experience with a 72 slot, 4 pole machine with this same type winding. I have a couple of drawings if that will help.

Send me the nameplate and job sight location and I am sure that we can support.
Respectfully

sir,it is single layer concentric winding.

josh wheat ,plz send those drgs for refrence.
on
bansi.v128@gmail.com

regds

It would be best to convert the concentric winding to lap. Concentric will be more difficult to insulate properly for 3.3kv plus the lap winding should somewhat improve the efficiency. You did not specify but chances are with a 48 slot 4 pole machine would have to be random wound. There will be 12 groups of 2 coils laid in a single layer concentric fashion. The span is 1-10-12. A very easy conversion. Divide the turns in half. The span will be 1-11 therefore the distribution factor will be the same as the concentric winding. There will be 12 groups of 4 coils.Use the same wire size and connection. With the 3.3 kv voltage rating you should use at least inverter duty magnet wire or even better, inverter duty magnet wire with a single layer of Dacron or fiberglass overlay, tape the coils slot to slot, double the phase and ground wall insulation. If you are a member of EASA you should contact their engineers for help.

George:
Excellent answer.
And you are correct: the EASA winding consulting staff is very talented.

Thank you...

Everyone is correct. to have only 24 coils it must be concentric. at 3.3KV I would think it is a form coil in a push through configuration. I am very familiar with this type of winding. The coil is made with one shaped end and one end open. You push the bottom tier of coils through, the small span first, and them form the open end by hand The top tier is then pushed through in the same manner and once again formed by hand. Each turn is insulated as it is made and the joints are staggered along the span so that there is no large build up where the joins are made. It is a lengthy process and this is why you rarely see this type of winding any more.

If it is a push through it will probably be a semi-closed slot and not an open slot. this will make it impossible to convert to a lap winding. If you convert to 48 coils you would need an open slot with a wedge groove. The semi-closed slot does not have a wedge groove and if you opened the slot the amount of iron you would lose would be detrimental.

Because of the medium voltage I would stay away from a random coil like the plague. the turn to turn voltage potential is very high and the introduction of parallel circuits would make matters worse. If I am correct in the configuration of the slot, you have only two choices. Rewind the motor in the concentric configuration or check if a replacement motor is available.

You should check your coil pitch. if the winding is 3300-volts, it will be form coil and 1-9 and 1-11 will not work, you would have an overlap that would require one coil to be a half slot. In a true concentric configuration it would have a coil pitch of 1-10 and 1-12. this would allow for a three tier concentric winding. If my memory serves me correctly each tier of the winding would be a phase.

Quite often they will bring 6 leads out of medium and high voltage windings so that the line coils can be changed periodically. the star point will be made externally. it should be a simple 1-4 connection. the winding is concentric but not consequent so the connection would be start to start and finish to finish.

If it is a push through it can be a bit confusing to look at because the coils are inserted so that they area as close as possible to the same dimensions. The outside tier at the connection end would be the inside tier at the non connection end and vice versa with the middle tier being the same at both sides.