Capacitor

Capacitor is a type of passive element which stores the energy in the form of Electric charge. Inside the capacitor, It contains two conductors with having some distance in between them & a dielectric material is filled in between that distance. The dielectric material can be air, ceramic, paper or glass.

Dielectric is a type of insulator which get polarized when electric field get applied across it.

Capacitors are characterized with its capacitance Which is having a units farad (F). Capacitor is a type storage element which stores Electric charge (Q) Such That, Q=C*V or C=Q/V (Where C is Capacitance & V is Voltage)

[An image of 2.5µF capacitor & 40+4 µF capacitor shown below, Both having a rated voltage of 440VAC.

440VAC Capacitors- 40+4 µF (Left) & 2.5µF (Right)

CAPACITOR'S BEHAVIOUR

(STATEMENT)Capacitor Accept AC While reject DC

BEHAVIOUR ON DC SUPPLY

Voltage level is constant in DC supply. At starting, when DC supply get connected to the capacitor; Current flows & capacitor starts charging itself until its voltage get equal to the supply voltage.

When capacitor's voltage get equal to the supply voltage than no current flows towards the capacitor. At this condition, Capacitor get fully charged & behave like an open circuit element. When power supply break off across the capacitor, Capacitor's charge get available across the circuit until capacitor discharges itself completely.

BEHAVIOUR ON AC SUPPLY

AC sinusoidal supply continuously changes its position with respect to the time. In ideal case, When sinusoidal voltage at its peak level; current do not flow as capacitor is fully charged at this stage & thus Current stays at zero.

Alternately, When supply voltage at its lowest point; at zero; Capacitor discharges its capacity. Current waveform stays at peak when voltage waveform is zero.

The charging & discharging of capacitor remains continuous in AC supply. Which makes current leads the voltage by 90°

Voltage & Current waveform of Capacitor on AC supply

CAPACITOR'S APPLICATIONS

Power Factor Correction

Power Factor is very important which explains how efficiently our system is consuming Electrical power. 0.8 Power factor which means that 80% power is consumed as a useful power & rest of the power is loss which is 20%. But as a consumer we have to pay for full 100% electricity consumption which includes payment for the losses also. That's why balanced & stable power factor is very important.

Maximum industrial load is inductive which makes the power factor lagging. Since Capacitors are contrary to inductor which produces counter effect opposite to inductor makes the power factor leading. To counter this lagging power factor due to the inductive load, Capacitor banks are installed in distribution system.

Inductive & capacitive loads should be balanced to get near around the unity power factor. For this, Automatic power factor controller works in distribution system which connects & disconnects the capacitors according to the running load.

Unity power factor balanced between lagging & leading power factor

Capacitor banks connected in Automatic power factor control panel

Starting Auxiliary for 1 Single Phase Motors

1Single phase motors are not self starting As it has only a single phase which is revolving all around. All the Magnetic poles in the winding changes simultaneously at a same time which does not produces a revolving magnetic field rather than a pulsating magnetic field.

For a revolving magnetic field, Another auxiliary winding(Starting winding) is connected across the main winding through the capacitor. Capacitor across the starting winding creates another phase in the circuit. Now, Both the windings together produces revolving magnetic field which make it possible for single phase motor to get a self start.

Filer Circuit

Resistance(R) is the opposition to the flow of electrical current in DC supply. While in AC, there is Impedance(Z) which is the combination of both the resistance(R) & reactance(X). Reactance is further categorized as capacitive reactance(Xc) & inductive reactance(XL).

Capacitive element or capacitor produces capacitive reactance in the circuit while Inductive element or inductor produces inductive reactance in the circuit.

Capacitive reactance(Xc) is equal to 1/2πfc. Where f is frequency of the supply & c is the capacitance. Which means larger the frequency lower the reactance. In short, we can say capacitor accept higher frequency & rejects lower frequency. That's why we are saying Capacitor accept AC & rejects DC.

This capacitor's property is used in filter circuit in along with other elements to filter out the particular frequency or range of the frequencies from the circuit.

GIF-Capacitor filters the AC components from the circuit

Capacitors behind Sensors

Capacitor is a element with two conductors & a dielectric material in between, Both the conductors are identical to each other & having uniform distance in between.

Capacitance value changes when distance between the conductors changes.
Capacitance value changes when effective area of the conductors changes.
Capacitance value changes when any type of the changes occurs in its dielectric material.

Any change in two conductors & dielectric material produces changes in the capacitance value & this change in capacitance is used in sensing. Generally a microcontroller is attached with capacitor which observe the changes; Any change in the capacitance value; microcontroller produces an output accordingly.

Capacitive sensing, Capacitive Pressure sensor, Capacitive proximity sensors are some of the examples of capacitive sensors.

CONCLUSION

Capacitor is passive element which stores the Energy in the form of Electric charge.
It contains two conductors with having some distance in between them & a dielectric material is filled in between the distance.
Dielectric is a type of insulator which get polarized when electric field get applied across it.
The dielectric material can be air, ceramic, paper or glass.
Capacitors are characterized with its capacitance Which is having a units farad (F).
Capacitor stores Electric charge(Q) Such That, Q=C*V or C=Q/V [C=Capacitance & V=Voltage]
Capacitor accept AC/ frequency signals & rejects DC/non frequency signals.
Capacitive reactance is inversely proportional to 2πfc [f=Frequency & C=Capacitance]
Applications of capacitors- Capacitor banks for power factor correction, Filter Circuit, As a starting auxiliary for single phase motor, Capacitor sensors.