Strain Insulators; Stay Insulator; Shackle insulators

Strain Insulator

Strain insulators working principle is same as that of suspension insulators and they have only difference is that when insulator used in vertical position then it is known as suspension insulator and when used in horizontal position then it is known as strain insulator. 

When there is a dead end or there is a sharp corner in transmission line, the line has to sustain a great tensile load of conductor or strain. A strain insulator must have considerable mechanical strength as well as the necessary electrical insulating properties.

Rated System Voltage	Number of disc insulator used in strain type tension insulator string	Number of disc insulator used in suspension insulator string
33KV	3	3
66KV	5	4
132KV	9	8
220KV	15	14

Stay Insulator

 For low voltage lines, the stays are to be insulated from ground at a height. The insulator used in the stay wire is called as the stay insulator and is usually of porcelain and is so designed that in case of breakage of the insulator the guy-wire will not fall to the ground. Stay insulators give protection in the event of accidentally broken live wire that can accidentally energizing a stay wire and remaining in contact with line which does not trip. In such cases , the bottom portion of the stay would have no voltage due to insulation, stay insulator will normally installed in the middle of stay wire.

Shackle Insulator or Spool Insulator

The shackle insulator or spool insulator is usually used in low voltage distribution network. It can be used both in horizontal and vertical position. The use of such insulator has decreased recently after increasing the using of underground cable for distribution purpose. The tapered hole of the spool insulator distributes the load more evenly and minimizes the possibility of breakage when heavily loaded. The conductor in the groove of shackle insulator is fixed with the help of soft binding wire.