Dahlander Wind Or Something Else?

[Eurybates]

Hi all. Hoping that somebody has had this issue and could maybe shed some light.

 

I recently detailed a motor unaware that it was a 2 speed. It appeared to be a two pole two parallel path connection with six leads out. I had a look at the supplied 3 position barrel switch to discover it was not a reversing switch but a pole changer.

 

The motor is 36 slot with six groups consisting of six coils each with a pitch of 1 – 10 constant (or) 1-5-7-9-11-13 concentric / 0.5mm copper wire and 48 turns (one in hand).

I should have noticed it was under pitch while winding. What is worse, I then decided to double cross sectional area halve the turns and turn it into a series connection.. which would have worked had it been a parallel to begin with!.

 

I thought at first that it must be a two star type connection which I have done many of before, however each lead has two circuits and there was no internal star or any other internal connection All 12 conductors are accounted for. Normally the 2 wye are supplied by the consequent connection on each phase and the other open ends are the second star point made externally by links (or a switch) for the 2 pole and then the external star is supply for the 4 pole with the consequent connections left open.

 

After some research I came across the dahlander parallel wye or series delta. But here is my issue

I can not draw it out with the magnetic north and south poles to make sense on paper as a line type diagram. Normally my rule is if I can draw it then it will work. Would anybody be able to help me with this? Just with the North in and South out diagram when series delta or parallel wye. It would be a load off my mind and much appreciated.

[Eurybates]

OK. Figured it out. Was not drawing it correctly and now it's embarrassingly obvious. If anybody stumbles onto this post and wants the complete details for constant torque dahlander (including easy to understand magnetic pole diagram) just reply to this post and I can email.

 

Cheers

[edingwall]

 

Hi Eurybates, 

Dahlander three phase motors use pole control to operate on two speeds, at a ratio of 2:1.

By the switching sequence of 3 contactors, motor can operate as either a low speed delta wound motor , where the number of magnetic poles within the stator is doubled and the motor speed is reduced to one-half, or a high-speed double star motor where the number of magnetic poles within the stator is halved and the motor speed is doubled.

I was looking at the Dahlander motor and I can't get my head around how the motor pole configuration changes when connected in double star. Would it simply be that when in delta, the phase windings are connected in series therefore all the poles are available, and when connected in double star, the phase windings are connected in parallel and therefore the number of poles available are halved?

 

Thanks, 

Ewan 

[marke]

Hello Ewan

Yes, in essence, there are coils in series which you can feed on end, or short the ends and feed the center.

The trick is how the coils are physically arranged around the stator, so it is a special coil arrangement.

A similar technique is used for alternative ratios such as 4 pole / 6 pole  or 6 pole / 8 pole using what is described as pole amplitude modulation (PAM).

NB Be careful using VFDs and soft starters on pole amplitude modulation motors!

Best regards,

Mark.

[edingwall]

Hi marke,

Thanks so much for the fast reply!

 

So, just for clarification, for the winding configuration in double star when the centre taps are connected, this causes the two phase windings, or two poles, to connect in parallel and essentially become 1 winding, or one pole, which doubles the motor speed.

And the reverse process occurs when connected in delta?

Thanks again,

Ewan 

[marke]

Yes, there are some variations of this theme, but that is essentially correct.

[edingwall]

Thanks for the reply Marke, its very much appreciated!