lightning arrester: The clouds get charged during thunderstorms and the high potential gradient causes the breakdown of insulation of air producing a lightning stroke.
The clouds get charged during thunderstorms and the high potential gradient causes the breakdown of insulation of air producing a lightning stroke.
The clouds get charged during thunderstorms and the high potential gradient causes the breakdown of insulation of air producing a lightning stroke.
The stroke tries to hit the earth, it is attracted by overhead lines and affects line insulators resulting in flashover or puncture.
The traveling wave reaches to the substation. The insulation of equipment is also stressed.
The device which is used for the protection of the equipment at the substations against traveling waves, such type of device is called lightning arrester or surge diverter.
In other words, lightning arrester diverts the abnormal high voltage to the ground without affecting the continuity of supply.
It is connected between the line and earth, i.e., in parallel with the equipment to be protected at the substation.
Working of Lightning Arrester
When a traveling wave reaches the arrestor, its sparks over at a certain prefixed voltage as shown in the figure below.
The arrestor provides a conducting path to the waves of relatively low impedance between the line and the ground.
The surge impedance of the line restricts the amplitude of the current flowing to ground.
The lightning arrester provides a path of low impedance only when the traveling surge reaches the surge diverter, neither before it nor after it.
The insulation of the equipment can be protected if the shape of the voltage and current at the diverter terminal is similar to the shape shown below.
Location
of Lightning Arrester
The lightning arrester is located close to the equipment that is to be protected. They are usually connected between phase and ground in an AC system and pole and ground in case of the DC system. In an AC system, separate arrester is provided for each phase.
TYPES OF LIGHTNING ARRESTER
Rod Gap
Horn Gap
Explosion Gap or Protective tube
Surge Absorber
Lightning arrester or Surge Diverters
EARTHING:
What is earthing?
The process of earthing is to connect all these parts which could become charged to the general mass of earth, to provide a path for fault currents and to hold the parts as close as possible to earth potential.
In simple theory this will prevent a potential difference between earth and earthed parts, as well as permitting the flow of fault current which will cause the operation of the protective systems
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