Capacitors

Capacitive loads transduce electrical energy into an electrostatic field that stores energy.

Capacitors are rarely used to perform familiar work operations that resistive and inductive loads do.
(stud welding, heart defibrillators are examples of capacitors at work)

Capacitors are used for a variety of uses in electronics (filtering, timing, coupling) and to correct power factor and assist in motor starting/running in the power electrical field.
 
Power Supply Capacitors Power Factor Correction Capacitors Motor Capacitors

A capacitor stores energy when electrons are separated on 2 plates that have an insulating material between them (dielectric)

If the plates are electrically connected the electrons will discharge from the plate with surplus electrons (-) to the plate with fewer electrons (+)

In a DC circuit a capacitor appears to be an open circuit

Since it can store and release a small amount of electrical charge on either plate in an AC circuit it appears to be a resistor

The symbol for capacitance is C and is measured in F ....  Farads 
(uF , pF)
Capacitors are rate by the amount of Charge (Q) per Voltage applied

As the source frequency increases a capacitor will appear to have less resistance and at very high frequencies appear no to exist (charge is flowing on and off the plates that never fully charge)

Opposition to current flow in an AC circuit with capacitors is called Capacitive Reactance .... Xc

f increases      Xc  decreases    (notice it's opposite in inductors)

f decreases     Xc    increases

 Xc =  

 

phase shifting of current in an inductive AC circuit

note the current leads applied voltage by 90*


the phase shifting caused by capacitors can corrected by adding inductors

 

 

Power Factor

other interesting things happen when capacitors and inductors are combined such as the creation of resonant frequencies

 

When resistance and reactance (XL and Xc)   are added vectors must be used since they are out of phase by 90*
notice: XL and Xc  are 180* out of phase