What is the role of capacitors on motors?

Generally, capacitors are commonly used in motors for starting single-phase motors. This type of capacitor is also called starting capacitor.From the perspective of the circuit principle, it plays the role of phase shifting, because the single-phase motor only has one set of running windings, and the rotor is squirrel-cage. Single-phase electricity cannot produce a rotating magnetic field, and another set of starting windings is needed to cooperate.Because there is only single-phase 220 volt ac, a capacitor is connected in series with the starting winding.The characteristic of the capacitor is that the voltage cannot change suddenly, so the current of the starting coil is 90° ahead of the running coil. This can form two rotating magnetic fields in space, allowing the motor to start normally.

The stator of a single-phase motor has two groups, which are 90 degrees apart in space. They are the starting winding and the running winding. They can obtain currents that are 90 degrees apart.Under the phase shifting effect of the starting capacitor, the single-phase electricity will cause the currents of the starting winding and the running winding to have a phase difference of 90 degrees, generating a rotating magnetic field in the stator space.The rotor will cut the magnetic lines of force to generate current, and then there will be a rotating magnetic field. The stator and rotor magnetic fields interact, and the rotor can rotate continuously.

Some dc motors also have a capacitor connected in parallel to both ends of the armature. This capacitor is mainly used for filtering and anti-interference.Because the dc motor has carbon brushes, a peak voltage will be generated when the carbon brushes and commutator segments are disconnected. Adding a capacitor can release this voltage. Of course, there are also some capacitors connected between the carbon brushes and the ground that can also play a similar role.

One use of capacitors for motors is reactive power compensation. Motors are inductive loads and their power factors are relatively low after use. Power supply rooms need to use capacitors for reactive power compensation.The long-distance reactive power compensation loss is relatively large and the effect is not very good, so sometimes it is necessary to perform on-site starting reactive power compensation directly near the motor. For example, in the star-delta starting circuit below, a capacitor is added to complete this function.

On-site reactive power compensation directly reduces power consumption, obviously improves the power factor, and improves and taps the potential of power grid transmission.