Electric Motors

Question 1

Electric motor

Answer 1

Electric energy converted to mecanic energy (rotary motion)

Answer 2

~Starting current
~rotor seizure
~rotor runaway

~series wound&raquo_space;high starting torque
~Shunt parallel wound» good speed control (cannot start under load)
~compound wound»series/parallel

Question 3

Rotor seizer

Answer 3

~can occure due to mechanical failure of a motor bearing or the load motor is attached
~this will lead to the motors control circuit attempting to ocntrol the rpm
~this can lead to overheated windings ,burning out of the fuse or breaker doesnt trip first

Question 4

Rotor runaway

Answer 4

~under no load condition motors will suffer rotor runaway
~this is a condition where the rotor rpm exceeds a safe maximum
~this is usually a mechanical device which prevents damage ,but if not contained the rotor will disintegrate causing a catastrophic motor failure
~in addition to a mechanical protection ,the field coil is compound wound providing a self regulating function to the motor

Question 5

Torque is determined by

Answer 5

~supplied current
~field strength
~Lorentz law

In a motor ,speed is proportional to voltage and inversley proportional to load.

Question 6

Ac motor works in

Answer 6

Syncronous&raquo_space;rotates a t the same rpm as input frequency

Asyncrhronous» out of phase with input frequency

Question 7

Ac motors

Answer 7

The rotor is the magnet and the armature in the stator coils

Question 8

Induction motor (squirrel cage)

Answer 8

~Used for fuel booster pumps to prevent arcing and explosion
~no electrical supply to the rotor
~stator creates a rotating to the rotor
~the bars in the rotor are drawn to the rotating field and create rotation