The Types of Ceramic Insulators Used in Power Engineering

Insulation, without this, electricity can never be useful. Insulators are the most important part of the electricity. In fact where there is electricity, there are insulators also. Insulators that we are dealing with, here is the ceramic insulators used in transmission and distribution lines. Using bare conductors for carrying electricity is a usual practice. The overhead lines are drawn using transmission poles or transmission towers depending upon the level of voltage transmitted.

Insulators are of different kinds

1) Pin insulators
2) Disc insulators
3) Solid core insulators
4) Hollow insulators
These insulators are used in different lines based on the voltage and the weight of the conductors
Pin Insulators
Pin insulators are used generally upto 33KV lines. In this insulators a porceline insulator with a pin at the bottom is used for drawing lines through the transmission poles. For voltages up to 33KV , generally poles are being use to draw transmission lines. The insulation between the pole and the live conductor is achieved through these pin insulators.
The specification for pin insulators is its rated voltage, and mechanical failing load in KN. This shall be marked on each insulators
Disc Insulators :
This is otherwise called string insulators. As the name indicates, these insulators are used in a string in the transmission lines. Insulators in disc shapes are stringed together, the number of which depending on the voltage that will appear across the string. There is provision in eah disc to string it to the next insulator. These are made of metal and are called socket and pin. Each insulators are marked with the manufacturer's logo, Month and year of manufacture, ountry of manufacture and the maximum failing load in Newton or KN
Solid Core Insulators :
These insulators are used mainly in substations as supports to various electrical equipment. Support insulators are used for mounting the disconnectors (Isolators), Wave traps, Instrument transformers and so on. These insulators are of solid core type. Since the load carried by them are more, and are subjected to several types of stresses from different sides, these insulators are made solid core. Each inslators are marked with the manufacturer's logo, month and year of manufacture and country of manufacture
Hollow Insulators
These insulators, as the name indicates, are hollow. These insulators are used as chambers to accommodate electrical devices. The most common use of these insulators is in circuit breakers. The major part of a circuit breaker is its contacts viz Moving and fixed contacts. During the break of the contacts, that is when a CB trips, tremendous arc is formed and it is important to have this arc quenched effectively and as quickly as possible. There are so many techniques to do this. In all these cases, the arc quenching is carried out inside the hollow chamber. Further, these hollow insulators are used in Transformers and instrument transformers to bring out the terminals , Lightning arresters and so on. Each insulators are marked with the manufacturer's logo, month and year of manufacture and country of manufacture.
The major raw material of a porcelain insulator is clay ie China Clay. This is mixed with Feldspar and Alumna. The latter two components are aded to give the insulators strength. These three components are mixed well and made a homogeneous compound. This is mixed with water and made a paste. This paste is pressed in presses and the water is squeezed out. The resulting semi-solid compound is made into cakes. These cakes are mouled into cylindrical shaped objects, size of which is determined by the size of the insulator. For each types of insulators there are different types of moulds. And for disc insulators and Pin insulators there is a single stage mold where the final shape is produced at singe step.
For Solid core and hollow insulators, these cylindrical shapes are first formed. For solid core, the cylindrical shaped object will be solid core whereas for hollow insulators, it will be hollow ones.
These cylindrical shapes are allowed to dry to a certain extend. After this these shapes are carved in to an insulator using a carving machine. The shape of the insulator depends on the creepage distance to be achieved. According to the requirement of creepage distance, insulators are made. This insulators are then sent for glazing. Insulators are generally provide with certain colours. In India, the general color of an insulator is Brown where as in many other countries, it is Grey. Glazing is done using colored dye, in which the insulators are dipped or the dye is sprayed uniformly on them. After this, markings on the insulators as specified in standards are made.
These insulators are then sent to kilns for firing. This is a process where the insulators are kept in a hot chamber at around 120 degree Celsius and allowed to dry fully. The normal time required to complete the firing is two days, ie 48 Hours. After the firing, the glaze attains its original colour - Brown or Grey. The color or the insulator gives an indication of the level of firing.
Now, it is the turn of metal parts. Metal parts are to be fixed to the insulators so that the insulators can be fitted to another equipment or another similar units. Metal parts are fitted to the insulator using special types of cement. A curing time is given to the final product to have good adhesion of the metal parts to the insulators
The insulator is ready and prepared to take on the stresses and strains of the site and above all take on the ruthlessness of the Potential difference! But, before letting this cute thing to the mercy of the Potential and the mechanical stresses, the ability of the insulator shall be ensured. To ensure this, there are a number of tests stipulated by various IS/IEC standards.