Q:why ac superconducting motors are common and not dc?

It's about the superconducting DC homopolar motor. Always a solution I guess.

Q:I'm looking for a right angled dual shaft AC motor around 3hp, preferably geared. Any idea where I could find one?

If you want the motor directly mounted to the gear box, you want a C flange style gearbox and a C flange style matching motor.

Q:Is it possible to increase an HP of motor by doing some changes in winding ?

Not practically. The horsepower rating has to do with the mechanical torque that the motor can deliver to its shaft. Typically, the limitation is the temperature rise in the windings. To increase the horsepower output, you would need to change the windings in a way that would allow more current to flow without causing the motor temperature to exceed the maximum temperature of the insulation of the windings. That means rewinding the motor using insulation material that has higher temperature withstand capabilities. Physically, this may result in different physical dimensions and may not be possible. In any case, economic practicality is also probably an issue - it may cost more to have a specialty shop rewind the motor that it would cost to buy a replacement..

Q:If it won't work, why won't it?..Have you tried it before?

Yes, if it was a universal motor. Your question made me read through this:

Q:i mean in the sense of working ,construction wise ..........

dc motors are generally permanent magnet type and rotate at high speeds 4000 to 6000 rpm. In many cases, for automatic control, such high speeds are not required. So there will be a gear train to reduce the speed. This gear train might introduce avoidable errors such as due to backlash. In short a dc servomotor is a geared dc motor. there are however torque motors which have very low inertia. These are also dc motors with special construction. Low inertia is essential for servo applications. In ac motors, stepper motor is popular. A variation of this is the ac servomotor, which has fairly low speed. Otherwise, speed is in the range of 1500rpm to 3000 rpm. Changing the speed of an ac motor is no joke. One has to provide adequate voltage, but lower the frequency! You cannot control speed well by reducing the voltage as torque decreases substantially.

Q:have new blower motor, new resistor, fuses and relay are good, I get no voltage on high setting, but I get voltage on all other settings.(testing with Multimeter at motor connector) Cannot figure out what to do, I will try to test the control switch, but not sure proper way to test it. Any ideas as to what i should check next. not sure how to test the wires leading out of the control switch.

go to junk yard and replace the switch its no good

Q:can avr improve power from dc to ac inverter?

If, I understand your question properly? The most that the AVR chip will do for you? Is smooth out the wave signal of the AC power. As, AC over your home power lines comes in as a sine wave. Most common inverters are not capable of producing true sine wave. Most, at best produce a modified sine. Which means an inverter is just fine for small appliances. Like a coffee pot, small refrigerator, etc. But, create static and white noise for laptop, TV's radios, etc. These require a pure sine wave AC signal. So, yes, it will improve the purity of the power. But, nothing to boost/amplify power.

Q:how are the torques in ac motors controlled, is the relationship between torque and armature current still applies?? T= k(flux) Ia .... ? does this formula still applies in ac motors or only to dc?? please explain

The torque equation applies for DC motors and synchronous AC motors, but no induction motors.

Q:I'm interested in learning what happens to a three phase motor if one phase loses power 1) while running, 2) prior to start?I've I've got a three phase motor with only two phases still good, can I manually rotate it to give it a quot;kick startquot; so it will continue to run in two phases?

In case it's a Delta wound Motor the current going through each phase will exceed the designed current.It willcontinue to run for some time as the rotating magnetic field will still be produced and then one phase will blow and the motor will stop.This will be true for case 1 and 2 both. In case it is a Star wound motor the rotating magnetic field will no longer be produced and the motor will not run.True for 1 and 2 both. You can't give it a kick start to run.Thats true only for single phase motors which either need a manual starting torque or a capacitor toprovide it.

Q:Its a squirrel cage motor from a microwave fan. It has five wires; white, yellow, orange, red, and blue. Inside, it has 16 electromagnets on the stator. How is this motor used?

This may be a multi speed (3) motor and they are using one speed of it. The mfg uses one motor in many different appliances. Does this uW have an exhaust fan which runs on differet speeds? The colors mean nothing in general. I assume that Yel Org are common and Red, Yel, Blu are (3) speeds. Powering it up one way is CW and the other way is CCW. Examining the cage will tell you which way to turn it.