The DC motor for earthing switch is mainly used to fix the positive and negative poles of the power supply to the commutator of the rotor directly through the insulating seat on the back cover of the motor, and the commutator is connected to the coil on the rotor, 3 The alternating polarity of the coils alternates with the two magnets fixed on the outer casing to rotate. Since the phase changer is fixed to the rotor and the brush is fixed to the outer casing (stator), the friction between the brush and the phase changer is generated when the motor rotates to generate a large amount of resistance and heat. Therefore, the efficiency of the brush motor is very low. But it also has the advantage of being simple to manufacture and low in cost.
The performance of the DC motor for grounding switch is closely related to its excitation mode. Generally, there are four types of DC motor excitation methods: DC excitation motor, DC shunt motor, DC series excitation motor and DC compound excitation motor. Master the characteristics of each of the four ways
1. DC-excited motor: The excitation winding has no electrical connection with the armature, and the excitation circuit is supplied by another DC power supply. Therefore, the excitation current is not affected by the armature terminal voltage or the armature current.
2. DC shunt motor: The circuit is connected in parallel, shunted, and the voltage across the shunt winding is the voltage across the armature, but the field winding is wound with a thin wire, which has a large number of turns, so it has a large resistance, so that its excitation current Smaller.
3. DC series-excited motor: current series, partial pressure, excitation winding is connected in series with the armature, so the magnetic field in this motor changes significantly with the change of armature current. In order to prevent large losses and voltage drops in the field winding, the smaller the resistance of the field winding is, the better, so the DC series motor is usually wound with a thicker wire, and its number of turns is small.
4. DC compound motor: The magnetic flux of the motor is generated by the excitation current in the two windings.