liveforphysics said:
The motor is a current driven device, no amount of voltage creates any magnetic field to generate torque.
My old swedish university book sugests that the torque is proportional to voltage squared. Here is my translation of it (holding it in my hands):
M=(3*U^2*s)/(Omega_s*R), where:
M represents torque in Nm
U represents voltage in V
s represents difference between magnetic field speed and the actual rotor speed. This is for three phase asynchronous motor, set this value to 1 for three phase PM synchronous motor.
Omega_s represents 4*Pi*f/number_of_poles. f is the controller frequency in Hz.
R=resistance in Ohms
3 phase asynchronous motors do create torque by using the voltage, 400 three phase AC for example. They use more current at start, and less when not needed. This without any controller involved. It's starting current can be very high, several hundred amperes, fast fuses usually do not like this. Close to top speed they use almost nothing. When connected to 1,5V AC they produce less staring current and typically do not move at all. Their torque is zero because of the low votlage, current is not limited in any (other) way. On the other side very low current at high voltage can move things around.
In reality both current and voltage are needed together if we want to move things around, and in Europe they teach us that up to 999 Volts there are no downsides besides the life threat
. Passing 1000V, nasty things start to happen, sparks between the wires that are too close and so on. Typically 10A to 20A is the range we should keep out current at, if we want highest practical efficiency - this according to my university books. This because the wires thicker than 2.5mm^2 are very difficuilt to work with, safety switches are larger, and so on.