Monthly Archives: fevereiro 2018

Three-phase motor

An electric machine has as main function to transform electrical energy into mechanical energy. This machine is mainly composed of the stator and the rotor, the first being the static part and the second the moving part. Also called an electric motor, this machine operates according to the principles of electromagnetism, that is, through an electromagnetic field created by the voltage applied to the windings of the stator, causing motion by magnetism in the rotor.

It is necessary to understand the various tests and calculations made to better know the operation and characteristics of this electric machine and with this we intend to study first the operation of a three phase induction motor.  reelcraft S601021-30 This type of electric motor is a two-speed squirrel cage rotor motor. The speed of the motor will depend on the connection of the motor. The operating principle for the change of speeds in the motor under study is the switching of one pair of poles (2p = 2) to 2 (2p = 4), thus obtaining synchronism speeds of 3000rpm and 1500rpm respectively. Starting from the approximate equivalent circuit of the asynchronous three-phase machine, we will calculate the values ​​of the circuit for the motor under study by means of tests in vacuum, locked rotor and in load.

Cage type induction motors

When the electric motor is energized it acts as a transformer with the secondary being shorted and therefore will require a line much larger than the rated current, which can reach seven times the nominal current. The companies that supply electric power require that there is a limitation of the starting current of the motors according to the conditions of your system, ie the available installed power (generated or purchased) and the dimensioning of the conductors.

This requirement is made so as not to impair the quality of the power supplied, because at the time of departure of a large motor there will be a voltage drop in the feeders and other consumers will receive the power under a lower voltage. A concessionaire in a small city will require a decrease in starting current in small engines while concessionaires in large cities will be able to accept the direct departure of much larger engines.

As the rotating field “drags” the rotor increasing its speed, the current decreases until reaching the nominal current when the rotation reaches its nominal value. If the engine is idle, it will quickly get its rated speed and the current will decrease accordingly.