Types of Capacitors; Paper Capacitor; Mica Capacitor; Ceramic Capacitor; Electrolyte Capacitor; Oil Capacitor

Types of Capacitors:-

Capacitors are classified according to type of material used as its dielectric, such as paper, oil, mica, or electrolyte.

(A)    PAPER CAPACITORThat kind of capacitor is made of flat thin strips of metal foil conductors that are separated by waxed paper.

   àRange is 300 picofarads -4 microfarads.

èVoltage =600 volts.

In these capacitors, Capacitors are sealed with wax to prevent the harmful effects of moisture and to prevent corrosion and leakage.

There are so many outer covering used in paper capacitors out of these simplest being a tubular cardboard covering. Some types of paper capacitors are encased in very hard plastic. These types are very rugged and can be used over a much wider temperature range than can the tubular cardboard type.

(B)    MICA CAPACITOR

These type of capacitors are made of metal foil plates that are separated by sheets of mica. Mica is used as Dielectric medium.  The whole assembly is encased in molded plastic.

There are following advantages of Molded plastic coverings:-

1. Corrosion and damage to the plates and dielectric are prevented.

2. Molded plastic case makes the capacitor mechanically stronger.

Mica is an excellent dielectric and can withstand a higher voltage than can a paper dielectric of the same thickness.

Ranges is from 50 picofarads to 0.02 microfarad.

(C)CERAMIC CAPACITOR

This type of capacitor is named as Ceramic capacitor because it contains a ceramic dielectric.

There are two types of Ceramic capacitors:-

1.Hallow Ceramic Cylinder

In this capacitor is named as Hallow ceramic cylinder capacitor as both the form on which to construct the capacitor and as the dielectric material. The plates consist of thin films of metal deposited on the ceramic cylinder.

2.Disk Shaped Ceramic Capacitor

A second type of ceramic capacitor is manufactured in the shape of a disk. After leads are attached to each side of the capacitor, the capacitor is completely covered with an insulating moisture-proof coating.

Range1 picofarad - 0.01 microfarad

voltages Range is as high as 30,000 volts.

(D)    ELECTROLYTIC CAPACITOR

These types of capacitors are used where a large amount of capacitance is required. In these type of capacitors electrolyte is used as dielectric medium. Electrolyte used in these capacitors may be in form of liquid. Liquid type electrolytic capacitors are no longer used as care is needed to prevent spilling of electrolyte.

A dry electrolytic capacitor consists essentially of two metal plates separated by the electrolyte.

In these capacitors capacitor is housed in a cylindrical aluminum container which acts as the negative terminal of the capacitor. The positive terminal is a lug on the bottom end of the container.

Multi-section electrolytic capacitor is illustrated in figure. In figure above there are four capacitors enclosed in one capacitor. Four lugs shown above acts as positive. Each capacitor is identified by an embossed mark adjacent to the lugs, as shown in figure above.

Note the identifying marks used are the

(a)    Half moon

(b)    The triangle

(c)    The square

(d)    No embossed mark.

By looking at the bottom of the container and the identifying sheet pasted to the side of the container, you can easily identify the value of each section.

Internal construction of an electrolytic capacitor similar to paper capacitor. The positive plate consists of aluminum foil covered with an extremely thin film of oxide. This thin oxide film acts as the dielectric of the capacitor. Next to and in contact with the oxide is a strip of paper or gauze which has been impregnated with a paste-like electrolyte. The electrolyte acts as the negative plate of the capacitor. A second strip of aluminum foil is then placed against the electrolyte to provide electrical contact to the negative electrode. When the three layers are in place they are rolled up into a cylinder as shown in figure above.

An electrolytic capacitor has main disadvantages as:-

Electrolytic type capacitor has Low leakage resistance as it is polarized. This means there are chances that positive plate be accidentally connected to the negative terminal of the source as the thin oxide film dielectric will dissolve and the capacitor will become a conductor.

As electrolytic capacitors are polarity sensitive there use is restricted to a dc circuit only or to a ac circuit where a small ac voltage is superimposed on a dc voltage.

Special electrolytic capacitors are available for certain ac applications, such as a motor starting capacitor.

Range of Dry type capacitors is 4 microfarads - several thousand microfarads.

Working voltage of approximately 500 volts.

(E)    OIL CAPACITORS

That type of capacitor is often used in high-power electronic equipment.  Oil filled capacitor is similar to Paper capacitor only difference is that paper capacitor is immersed in oil. Since oil impregnated paper has a high dielectric constant, it can be used in the production of capacitors having a high capacitance value. Such a capacitor is referred to as a SELF-HEALING capacitor.

For Knowing about fixed and variable capacitors visit here:-
http://electrialstandards.blogspot.com/2015/05/fixed-and-variable-capacitors-fixed.html

To know how capacitor stores charge visit link below:-
http://electrialstandards.blogspot.in/2015/05/what-is-capacitor-how-capacitor-stores.html

To know about  capacitor series and Parallel operations visit link:-
http://electrialstandards.blogspot.com/2015/05/capacitor-in-series-and-parallel.html