HV insulators

 As it is known, all HV insulators (insulators of TL) are exposed to active influence of the atmospheric precipitation which is especially dangerous under the high pollution of the environment especially of air. Therefore to increase the flashover voltage (the electric flashover on a surface) the shape of external surface in such insulators is design in such form that to extend  the creepage distance.

 

HV insulators for overhead transmission lines are usually as follows: cap and pin, pin and longrod. These insulators are designed in a way so that in dry condition the puncture voltage exceeds the flashover voltage approximately in 1.6 times that provides the absence of puncture at overvoltages.

 

Suspension string insulator has the porcelain or glass disk (plate) with a spherical head.  Internal and external surfaces of the head are made in form that in case of  tension of the conductors provide only compression load for the material (it is known that strength  of porcelain and glass at compression is considerably higher than at tension). That is the way to provide the high mechanical strength of glass string cap & pin insulators. They are capable to withstand the tension load of the conductors in TL in thousand kilos. To increase the reliability of the insulation and increase the flashover voltages the glass string cap & pin insulators are connected in strings.

 

Longrod insulators for transmission lines (HV insulators) are manufactured from high-strength porcelain and from composite materials. The mechanical strength of porcelain pin insulators is less than the cap and pin insulators have as the porcelain in pin insulators works on a tension and sometimes bending,  and as to cap and pin insulators – on compression inside of cast iron cap of the insulator.

 

Pin insulators are used on transmission lines and are mounted on a supporting structure by means of the metal pin or a hook. Because of the high bending effort applied to these insulators they are used for the voltage not higher 35 kV.