Hi All,

Wonder if anyone has used such a method call a Eddy Current Starter to start a Wound Rotor Induction Motor and if it was a good or bad experience.

And also does anyone know when did this method come into the market?? I have only just got to hear of it and after briefly looking into it, there don't seems like alot of technology in it.
So it might have been out for decades which isn't popular??

MAGNASTART Brand or similar is what I am refering to and just like to hear some feedback on it.

Thanks
ScIM

Hello SCIM

An eddy current drive will not start a wound rotor motor as it is not a motor starter. You still need to uose a traditional starting means.
The eddy current drive is a "coupling between the motor and the load. The idea is to get the motor to full speed quickly and with low current and torque, and then use the eddie current coupling to ramp the motor up to full speed.
This technique is not new, it has been around for a very long time.
While the motor and the load are at different speeds, there are slip losses. These are dissipated by the eddie current coupling device.
Additionally, even at full speed, there are generally some slip losses which are additional losses that would not be there without the eddie currrent device, so there is a drop in efficiency.

So, you effectively start the motor unloaded and then load it up using the eddie current coupling.

Best regards,
Mark.

Hi Mark,

Thanks on your prompt reply; I was thinking of what you were saying as well when I first heard of it.

It's actually something different as it's not an opposing eddy current driver but it's the eddy current leakage acting as the resistive impedance to the rotor windings and that is changing in accordance to slip. This starter is claiming to be less maintance and other advantages mainly due to less moving parts therefore less to maintain as compared to a usual LRS and a smoother start as compared to a resistive tap.

http://www.irispower.com/motor_other_magnastart.aspx

Above is the website of the eddy current method starting which I am making reference to. There are other companys offering a similar product with the same principle claiming suitability for up to 800kW WRIM.

That's new to me.. but might be something that has been in the market for long? Quite unsure...

And yes, a WRIM will need a motor starter (i.e DOL Starter) for supply to the Stator.
I am actually refering to the Secondary starter. Sorry on the confusion.

Cheers,
SCIM

Hello SCIM

Yes you are correct, the name was too much like another product!!

The slip ring motor requires resistance in the rotor circuit in order to develop torque.
It is certainly possible to creat the effective resistance using core losses and this is apparently what this does.
One of the problems will be that it is not as easy to "engineer" the start curve as it is with resistors.

You still dissipate the same amount of power as you do with resistors, - the slip losses must be the same, but in the same manner as a liquid resitance starter, you reduce the number of contactors.

I have seen schemes where the effective impedance in the rotor is altered by a varying DC bias applied to an exciter coil.

I suppose the big question has to be price??

Best regards,
Mark.