AC Motor Operation in High Electro-Magnetic Fields

Since the magnetic fields outside of a gap change by the inverse square of the distance, you will probably not change the motor dynamics itself by much. This does assume that the motor itself will not be going into the gap of the high magnetic field. However, frequently designers will forget this inverse square relationship and forget that magnetic materials placed into these fields will enter quite easily, but the forces required to extract will require considerably more than anticipated.

This has happened more than once with beam steering magnets with adjustable gaps of permanent magnets. "Close the gap just a little more. Darn that didn't adjust the beam right. Close it just a little bit more. (Repeat as desired.) This is not getting us anywhere, open the gap back up. What do you mean it won't move." Sometimes a scientist won't believe it's a bad idea until they break something.

Hi Redfred...

Thanks for your input, it was much appreciated & has brought some light onto the situation for me.

From what I can understand from the feed back is this...

The AC motor operation is not adversly affected in this type of application.

So, what my main concern would be now though is, "How to we control the unit as in forward/reverse motions & with the up/down operations. I feel that simple relays & switch gear might be comprimised by the Magnetism". your thoughts on this area?

Thank you again

LOWIQJO..

Same rules apply about field strength with relay and control circuit locations as with AC motors. But you are quite correct that relays will be more sensitive to the effects of these fields. So placing the relays in a suitable NEMA class steel box instead of a plastic box should shield the relays for the most part. It would also be a good idea that all cabling outside of the shielding box be twisted pair cables with the signal and return twisted together.

Morning Redfred,

Thanks again for the feedback. You have given us some things to run with.

We are still endeavouring to get the Tesla spec's on the magnetic field strength in the area concerned. Once I have these I will post them for some further comments & let everyone know the outcome of the machine trials.

cheers again..

LOWIQJO

One thing I forgot to mention though. If you must place the motor inside the field itself you will not get the expected forces produced. For the rotor or stator magnetically permeable material will prematurely saturate. Careful analysis and/or wide torque reserves will be required to determine if feasible. Likely it will be easier to not permit the motors themselves to sit in these fields.

I don't think there is much effect on the motor. In my plant, I have two equipments that installed just beside the Electric DC Arc Furnace slagging door. The 1st equipment is for the supply of oxygen to our furnace and the other equipment is for sample and temperature measurement. Both equipment are driven by electrical motor.

The magnetic field is really strong and it can really damage the "Peace maker" if someone having it, and goes near the furnace. Even normal gear hand watch will get magnetized.

Both electrical motor does not have any problem so far. It been operating for a few years now.

G'day Simon... Thank you for your imput Simon.

Will keep you posted with what the outcome is if/when we do go down that track. We are still waiting on magnetic strength data to see what we are actually up against...

Cheers & thanks again

LowIQJo.. :)

Normaliy shoud not have any effect.However if u want to be safe you can enclose the motor in a enclosure of non magnetic material .but ensure ventillation is available could be a forced ventillation which will blow the air over the motor continuously.

Depending on the strength of environmental magnetic field it is going to effect motor performance, unless motor is shielded with some nonmagnetic cover.

Environmental magnetic field will offer a bias to the internal magnetic path,and it will enter in more magnetic saturation.however this all will depend on how strong is outer field.

Ha, ha, it is exactly what I wanted to say:. GA

Yes you correct indeed, Thank you very much,

That makes perfect sense from a mechanics point of view

Not only from a mechanics point of view, but also from an electronics design engineer's point of view and all serious motor manufacturers.

The phenomenon is caused by eddy currents being induced into the motor core either from external magnetic field or from magnetic surges induced by the windings due to the use of a VFD (VFD duty motors are designed to withstand this).

The resulting voltages into the rotor core try to arc to the motor shell thru the bearings, so in order to avoid them, you need to: Either conect the rotor shaft to the shell with a brush, thus eliminating the arcing path (think of a gas truck dragging a ground strap) or use ceramic housed bearings.

Yahlasit