Overhead power lines

Two mechanisms exist for electric power transmission-underground cable transmission and overhead line transmission. Underground cable transmission is not commonly used because it is very expensive and it is very difficult there to provide proper insulation. The main components of overhead lines are conductors, line supports, insulators, cross arms, phase plates, danger plates, lightning arresters and anticlimbing wires. Conductor material should have high electrical conductivity, high tensile strength, highly economical and low specific gravity. Some commonly used conductor materials are copper, aluminium, steel cored aluminium (aluminium conductor steel reinforced), galvanized steel and cadmium copper. Line supports should have high mechanical strength, less weight, cheap, longer life span and accessibility. Commonly used line supports are wooden poles, steel poles, RCC poles and steel towers. Insulators are used to insulate line conductors from line supports. Commonly used insulators are pin type insulators, suspension type insulators, strain insulators and shackle insulators. These insulators should have high mechanical strength, high electrical resistance, high relative permittivity, non-porous and high ratio of puncture strength to flashover.

Gas welding

Welding is an important industrial tool to join cuts. Gas welding is an important welding process which is actually a fusion welding process. Here heat is developed by the combustion of oxygen or air with a fuel like acetylene, hydrogen butane etc. The commonly used combination is oxygen-acetylene which can reach up to 3000 degree Celsius temperature and is most preferred for welding metals and metal alloys. Oxygen is filled in a steel cylinder at a pressure of 150 kg per square cm. Colour code used for oxygen cylinder is black. Acetylene is also filled in a cylinder at a pressure of 16 kg per square cm. Here acetylene is dissolved in a cylinder containing porous silicate filler. For directing the flow, a welding torch is used. This torch also helps to mix up the gases and control the volume of the gases. Here flame is produced by ignition technique. Pressure regulators are also required here to regulate the cylinder gas pressure. Green colour hose is used for oxygen gas and red colour hose for acetylene. For the protection of eyes from heat, ultraviolet rays and infrared rays, goggles are used while gloves are used to protect hands from heat and the metal splashes. To clean the surfaces of joints before and after welding, a wire brush is used.