المحركات الكهربائية - الطاقة الكهربائية .. الفيزياء

Electric motors - Electrical energy .. Physics

Electric motors

Electric motors convert electrical energy directly into mechanical energy used in homes on the one hand, such as shavers whose power does not exceed a fraction of a kilowatt, and industrial motors on the other hand whose power reaches several thousand kilowatts. They all work according to a method opposite to the method of operation of the generator: when the current passes through a suspended conductor and is left to itself within a magnetic field, it creates a force perpendicular to both the directions of the current and the field together. We see in the drawing all these directions and they are determined in the generator by the thumb, index and middle fingers of the right hand (Fleming's rule for the right hand) and in the motor by the thumb, index and middle fingers of the left hand (Fleming's rule for the left hand).

Some motors are designed to operate on continuous power, others on alternating power, and there are types that operate on both power supplies, and for this reason they are called combined motors. DC motors are the most commonly used motors in areas where speed change is of great importance, such as car and electric train motors. They consist of a fixed electromagnet (the stator provides the motor with its magnetic field), and a number of coils surrounding the production member in it (the rotor), which is fed with current by a commutator that transfers current from one coil to another as long as it continues to rotate. The most important AC motors are of two types: the synchronous motor (its speed is controlled by the frequency of the alternating power supply), and the induction motor. In the first type, the poles of the magnet in the stator alternate according to the direction of the current, creating a rotating magnetic field that generates a force that causes the rotating member to rotate. This type of motor is characterized by not being self-starting, and the reason for this is the speed of rotation of the field in the stator, and thus its inability to overcome the inertia of the member The rotor prevents it from moving, so a DC-powered starter must be used. Since the speed of movement is controlled by the supply frequency, which is difficult to change, the use of this type of motor has been limited to areas where the load is heavy and requires a constant rotational speed, as in pump and compressor motors.

(Fleming's left-hand rule tells us the direction of the movement of the conductor in a magnetic field, while Fleming's right-hand rule gives us the direction of the induced current in a moving conductor inside a magnetic field).

(Left-hand rule - for motors)

(Right-hand rule - generators)

(Electrical connections for DC motors, in which a control resistor is used to change the speed of the motor).