Vector Motor true explanation please.

I don't think I've seen anything quite as impressive as a top quality Ward Leonard set-up (as used in many modern elevators).

at work i am a Tech (electrical/Electrionics etc).. we have in use in various forms, speed, torque and position "vector motors". now we have installed, replaced etc these units along with setting up the drives that run them.. etc...

we have a young engineer that thinks they are the best thing since apple pie came along how ever, he can not give any one any explanation the reason why other than being more efficient which is obvious using VFD etc., nor can he explain the operating differences between other motors as far as their inner construction and components of the motor it self.

--- now after long debate and research i have done on the net looking for a concrete detailed break down of a vector motor differences between that of an AC motor i have found that many of the venders out there don't seem to know much more about them either.! so this is what i have come up with from research i have done and my own work experience as far.. the main difference in motor design is that Vector type motors have a larger rotor and can be composed of aluminum or copper laminated instead of the conventional smaller rotors found in AC motors.. this type of rotor gives way to better control over eddy currents to be used for constant torque even at stall speeds. also casings are designed to better dissipate heat. on the control end of it, variable frequency and voltages can be applied via a VFD+V along with the use of a Quad encoder with +/- outputs up to around 1024 PPR for precise movements and direction detection. these motors i have found come in 2,4 or 6 poles maybe more..

the only difference i have found between a vector motor on a VFD and one that is not considered a vector on a VFD is that the vector seems to have better starting torque that i think must be contributed to the rotor size with its type of materials used to gain more stall torque..

am i on the correct track or did i miss something ?

thanks.

-- Real Programmers Do things like this.

we did open some motors that are used on vector drives to analyze the difference, it seems the rotor construction is larger on the average and made up of a combination of materials instead of the generic rotor found in squirrel cage type motors. after some research i concluded with notes found on the web this helped the motor give more torque at lower speeds. in any case, i did connect a couple of these motors directly to a 480 3 phase starter and didn't seem see any thing different about them over the general 3 phase motors we use.

now another question since we are on the subject, those that are using the encoder on the shaft, you said it is used to know the shaft position as well as the RPM and direction of course.. are they by any chance using the Z output on the encoder and if so, does this mean there is some form of index on the shaft the encoder must line up on when mounted?

Thanks..

Jamie wrote: (snip)

I doubt it. The rotor of an induction motor has no position that is different than any other. All that counts is the relative relation between the mechanical position and the position of the magnetic field produced by the circulating current in the rotor bars that slides with respect to the mechanical position.

However, if the motor is specifically intended for use in a servo application, it might have use for a position index mark for absolute position feedback. But that is a servo feature, not a vector control one.

motors designed for use with drives often have heavy insulation on the first few turns, to avoid first-turn failure, which is caused by the very fast rise- and fall-times of the PWM outputs, and is greatly exacerbated by long cables, which in conjunction with s***ty modulation can triple the peak voltage seen at the motor terminals!

the issue you allude to wrt rotors is fairly simple: a vector drive allows you to suck full torque at any speed, including DC. SCIMs are fan-cooled, and the fan is driven by the motor shaft; as such, cooling falls off dramatically as speed is reduced (its IIRC a cube law, and of course 0 speed = 0 cooling). Forced fan cooling is often used, but rotor cooling is still tricky because there is this lovely thermal insulator called an air gap.

Cheers Terry