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Types Of Insulators In Overhead Transmission
Transmission line insulators separate, contain, and suspend transmission line conductors. They protect short circuit paths between the earth and the transmission line. There are several types of insulators in overhead transmission lines. The most known are the pin type, suspension type, strain insulator, shackle insulator, and stay insulator.
Types of electrical insulators in transmission lines:
1. Pin-type insulators:
The name “pin” came from its constructional design. Pin-type insulators are used for the transmission of lower voltages. The transmission range of pin type is up to 33 kV (kilovolts). Pin-type insulators are secured with steel or lead bolts onto transmission poles. These are typically used for straight-running transmission lines. There is a groove on the upper end of the insulator for housing the conductor. The conductor passes through this groove and is bound by the annealed wire of the same material as the conductor. We can use this type of insulator beyond 33kv, but that becomes bulky in size & costly.
2. Suspension-type insulators :
Suspension-type insulators are used to transmit above 33kv. Above 33kv using of pin type is uneconomical. In a suspension-type insulator, many insulators are connected in series to form a string, and the conductor is suspended at the bottom end of this string. In contrast, the other end of the string is secured to the cross-arm of the tower. Each insulator of a suspension string is called a disc.
Advantages of Suspension-Type insulators :
(i)Suspension-type insulators are very economical voltages beyond 33 kV.
(ii) Each unit or disc of the suspension-type insulator is designed for low voltage, usually 11 kV. As per the operating voltage requirement, we can add a number of discs in series.
(iii) If any one disc is damaged, the whole string does not become useless because the damaged disc can be replaced by a sound one.
(iv) The suspension arrangement provides greater flexibility to the line. The connection at the cross arm is such that the insulator string is free to swing in any direction and can take up the position where mechanical stresses are minimum.
(v) The suspension-type insulators are generally used with steel towers. As the conductors run below the tower’s earthed cross-arm, this arrangement provides partial protection from lightning.
3. Strain-Type insulators:
Strain-type insulators are horizontally suspended suspension insulators. When there is a dead end or a sharp corner in the transmission line, the line has to sustain a great tensile load of conductor or strain. The discs of strain insulators are used in the vertical plane. When the tension in lines is exceedingly high, two or more strings are used in parallel at long river spans. Voltage rating is almost equal to suspension type.
4. Shackle-Type Insulators:
Shackle-type insulators, similar to strain-type insulators, are used on sharp curves, end poles, and section poles. These insulators are single and round porcelain parts mounted horizontally or vertically. The shackle insulator or spool insulator is usually used in low-voltage distribution systems. They can be directly fixed to the pole with a bolt or cross arm.
5. Stay-insulators :
The insulator used in the stay wire is called the stay insulator and is usually of porcelain and is designed so that in case of breakage of the insulator, the guy-wire will not fall to the ground.
This Is Complete Information On Types of Electrical Insulators, Insulators In Overhead Transmission Lines.
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