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Why should add capacitor of the electric machinery
The function of capacitor in electric appliance:
1. Capacitors are mainly used in AC circuit and pulse circuit, the capacitors generally play partition DC role in the DC circuit.
2. Capacitance is neither produced nor consumed energy, is the energy storage element. 
3. Capacitors in power system is an important device to improve the power factor; and is obtain the function of main components of oscillation, filtering, phase shift, bypass, coupling in the electronic circuit.
4. Because the load used in industry is mainly the inductive load of the motor, so the capacitive load should be used to balance the power grid.
5. On the ground wire, why have to some go through the capacitor and then grounded? Answer: in the DC circuit is anti-interference, the interference pulse through the capacitive grounding (in this role is to separate the direct circuit in the potential relationship); AC circuit also have this way through the capacitance to the ground, general the capacity is small, also have the function of anti-interference and potential isolation .
6. What is the compensate power factor of the capacitance? Answer: because set voltage first need to have a charging process in the capacitor, with the charging process, it will gradually increase of the capacitance voltage, it will be the first have current, after the establishment of the voltage process, usually we call the current lead voltage of 90 degrees (in capacitive current loop without resistance and inductance components, called pure capacitance circuit). Electric motor, transformer and other coil inductance circuit,
Because the current through the inductor cannot be mutated, it is the opposite of the capacitor, need to establish the voltage at both ends of the coil, after have the current (when inductance current loop without resistance and capacitance, called pure inductance circuit), the current hysteresis voltage of the pure inductance circuit is 90 degrees. Because the power is the voltage times the current, when the voltage and current are not simultaneously generated (such as: when the voltage of the capacitor is maximum, the electric current is full, the current is 0; the inductance is first with the voltage, the inductor current is also 0), in this way, the product (power) is also 0! This is the reactive power. Then, the relationship between the voltage and current of the capacitor just relationship and the voltage and current of the inductance instead, capacitance inductance compensation of reactive power, which is the principle of reactive power compensation. How it is connected to the required motor on the line it not charged? The reactive power compensation is parallel to the motor, if used in the starting of the motor is connected in the starting winding.
General single-phase AC motor starting capacitor cannot choose too large, too large to make the starting torque angle deviation from the maximum, and the secondary winding current consumption increases. Too small will start not to move the motor, to cause the motor to burn out in a long time!
Because of single-phase motor phase angle is 180 degrees, only can product a left and right swing around the equilibrium magnetic field. To produce a single phase motor rotation will need to add a secondary winding, the 220V voltage of the same power supply is connected to the auxiliary winding and the main winding simultaneously, since power is the same power, the motor cannot generate a rotating magnetic field, or balancing oscillating magnetic field, the motor is still unable to rotate, at this time it is required through the auxiliary winding series capacitor phase shift to produce a rotating magnetic field, the phase angle of 90 degrees. For less than 1000W single-phase motor without requiring large starting torque, you can press the calculation: Motor power per 100W required working capacity of 1-4UF, starting capacity is 4-10 times the working capacity of the capacitor. If the capacitor is required to start up to 10 or more of the capacitance of the capacitor, the voltage of the capacitor is not less than 400V.

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