Single-phase series excitation (series excitation) motor use is quite common, such as hand drill, Angle grinder and other kinds of hand-held electric tools and small appliances are mostly used in single-phase series excitation (series excitation) motor, the most obvious feature of this motor is a carbon brush.
Single-phase series excitation (series excitation) motor mechanism single-phase series excitation (series excitation) motor structure and DC series motor structure is basically the same. The stator is composed of a core and an excitation winding, and the rotor is composed of a core, an armature winding, a commutator and a rotating shaft. The excitation winding and armature winding are wound winding, the two through the carbon brush and commutator to form a series loop, which is also the origin of series excitation. The stator winding, the excitation winding, usually has only one pair of magnetic poles. The coils of the rotor winding, also known as the armature winding, are not closed and only form a closed loop when the carbon brushes are in contact.
The characteristics of single-phase series excitation (series excitation) motor: series excitation motor has the advantages of starting without capacitor, fast speed, start torque and so on, but also has big noise, carbon brush easy to wear, strong electromagnetic interference and other shortcomings.
Why can the speed of the series motor be very high?
The speed of the series motor is relatively high, which can reach thousands of thousands of revolutions, or even higher. For example, the motor speed of the hand drill is more than 6000 RPM.
Why does the series motor have the characteristics of large starting torque?
In the case of motor determination, the torque of series motor is mainly related to magnetic flux and armature current. The group will induce the back electromotive force when cutting the flux line. The higher the speed, the greater the back electromotive force and the greater the restriction on winding current.
For the series motor, the position of the stator magnetic field is fixed, at the moment of power, the rotor and stator are relatively static, there is no cutting flux line, so there is no back electromotive force. The current is large, the flux and armature current are also large, and the resulting electromagnetic torque is also large. As the speed increases, the back electromotive force increases, the current decreases, and the torque also decreases.
This is a characteristic of the series motor, the slower the speed, the greater the torque, we usually use hand-held power tools should have such a feeling.
