3 phase

There are many books, especially those on ac machinery, that cover that subject in detail.

Bill

-- Ferme le Bush

Here's a website w/ a diagram of the wiring.

hope it helps you out.

Thanks, courtrightk. It's a start. :)

joyful

Bill,

Can you point me to one?

thanks, joyful

Hi,

We have summarized several useful links here including wiring of 3 phase motors:

Regards,

KodKodKod Learning Consulting - Here you get the answers!

Actually *winding* a motor is a bit trickier than *connections* for a motor.

First you have to know the number of slots and the number of poles. Multiply the number of poles by 3 (three phase) and that tells you how many pole-phase groups you need. If you're lucky, that number will divide evenly into the number of slots. But don't be surprised if it doesn't.

Motors will often use several coils in each pole-phase group, and they often be pitched to span exactly the number of slots for one pole (i.e. pole-pitch = 1.0). But it doesn't *always* have to be so. In fact, *generators* will often use shorter pitch between the two sides of coils. This is done to smooth out the generated voltage and reduce some harmonics.

If you're *rewinding* an existing motor, it's best to just carefully note the pitch of the coils (number of slots between the two sides of the coils). Three phase machines usually have all coils the same pitch. Unlike single phase machines where each coil in a group may span a different number of slots.

Small machines are wound with just a single spool of wire to form the coils. But larger machines often will require two or more wires in parallel. For example, one 25hp motor's coils might be wound with two AWG#10 and one AWG#12 enamelled wire (sometimes referred to as "2#10 and 1#12 'in hand'", meaning you have three wires in your 'hand' while winding the coil, although most shops use a coil winding machine and not their 'hand'). Really large machines will use copper bars carefully bent to fit into the slot, turn and return in another slot ('bar wound machines').

Once you've wound enough coils with the right pitch, and insulated the slots, you start installing the coils. Sometimes all the wire ends will be arranged to stick out one end, but sometimes they will alternate sticking out both ends. For the alternating case, you have to be careful which way you install each coil so that the 'ends line up' when it comes time to connect them together.

Some large machines will have multiple coils connected together in parallel within a phase group, but the more common is to connect them in series. Depending on how many connections you want drawn out to the terminations, you may connect all pole-phase groups together in series, or just half of them and bring the connections out to the termination head.

One of the tricky things that a lay-person sometimes has trouble with is the polarity connections between pole-phase groups. An old-fashioned technique is to draw each pole-phase group separately on a piece of paper, 'unwrapping' the stator so the pole-phase groups are stretched out in a straight line. Then, moving in the direction of rotation label them A, C', B, A', C, B' and so on, repeating as necessary. Then underneath each pole-phase group, draw an arrow in alternating directions (e.g. under the A group, draw an arrow pointing right, then under C' an arrow pointing left, then under B one pointing right again, A' pointing left, and so on). These arrows and the sides of the pole-phase group they point to are used to figure out how to interconnect the groups to give you the correct stator connections. Get them wrong and the 'rotating magnetic field' won't rotate. If it starts at all, it will have very poor performance and likely overheat quickly.

Hope this gives you an idea.

daestrom

Daestrom,

thanks for taking the time and replying with all that info. I am in fact in the process of penciling this all out. A seemingly necessary step in my learning. I have a hard time grasping things unless I see them. So far I've got the basic 3600rpm motor diagramed. Once i started scribbling that was simple to figure out. Each phase overlaps the other by 120*. At this point I have 12 leads/ends. Most motors I have seen, if not all in my limited experience, have had 9, including this one. I think this is where your "hooking in series" comes in, but I haven't worked that out yet. This particular motor had 9 with a

1725rpm rating, 36 slots. I need to redraw my diagrams now for that rpm and then take it from there. If I have given you enough details for further comment it will be appreciated. thanks, joyful

1725 RPM would be a four pole stator winding. Times three-phase means 12 pole-phase groups. And that goes into 36 slots evenly, so you have a 'nice' machine.

Three coils per phase group, wired in series. This gives you 12 pairs of wires. When you start at one point and 'unwrap' the stator, you have 12 pole-phase groups laid out like this....

A C' B A' C B' A C' B A' C B'