What is a Surge Arrester?
Surge arrester is a voltage limiting device installed inside the installation equipment panel to protect the insulation, equipment and machines not only from lightning, but also from transient voltage produced by switching, sparks, load shading and other electrical faults such as ground faults etc.
Surge arresters are used to limit the current and voltage surges to protect the low and high voltage appliances as well as communication lines. The most common surge arrester is a non-linear metal oxide resistors type in a porcelain or silicone rubber housing, and are fitted in parallel with the intended circuit to protect from surges and connected to the earth grid.
In olden days, the term “lightning arrester” was used in power system which is replaced by the new term as “surge arrester”. This is because the main reason for most of over voltages was lightning when the power system design was not that much complicated. In most advanced designs, load shading, sudden change in high power in load, and disconnector switching in EHV substation causes over voltage where surge arrester are used in a substation instead of lightning arrester which provides protection against all of the above mentioned surges. In LV/MV transmission and distribution lines, a new term as “line arrester” is also used for lightning / surge arresters.
Lightning Arrester is a protective device used to protect the circuit from lightning strokes having high transient voltage surges, surge currents due to lightning, spark and isolation arcs etc.
It is used to protect the power system by redirecting the high voltage surges to the ground. Although, the earthing or ground wire also protects the overhead lines and power system from direct lightning strikes but it may fail to protect against traveling waves which may reach to the terminal connected devices and equipment. For this reason, surge diverters or lightning arresters are used to protect the power system against such produced surges by faults or lightning stokes.
Lightning arresters are installed on the peak height of a structure i.e. transmission poles and towers and building to provide a safe path to the discharging current and voltage caused by the lighting strokes to the ground to protect the system form lightning induced problems.
A lightning rod (also known as lightning conductor) is a metal rod (copper or aluminium or other conducting materials) installed on the top of the structure ( transmission and distribution towers , buildings etc) to protect it from the direct lighting strikes.
Lightning is the electrostatic discharge between clouds and earth. If they hit the power lines directly, the system voltage may rise to a dangerous level which may harm the electrical installation and equipment. For this reason, a lightning rod is used to protect the electrical installation, equipment and devices from direct hit of lightning strokes.
Lightning rod is cheaper than surge arrester which is mounted on the top surface of a building or power lines tower which provides a safe path to the high value electrostatic charges and lightning currents to the ground (it must be properly earthed to the grounding system as well).