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Shreyas • Mar 3, 2011

Modular Long Flashover Resistor Explained

About 30-40% of power outages around the world are caused due to the lightening. The transmission lines are subjected to both direct lightning strokes and induced over voltages. Of these, the contribution of lightning towards the disruption of power flow is more. To protect transmission lines from the lightning and induced over voltages, separate protective schemes are essential according to the conventional protective design. Surge absorbers protect the lines from induced over voltages whereas lightning arrestors are used to bypass the lightning stroke to ground. With the advent of Modular Long Flash over Arrestor or LFA-M, we no more need separate arrangements for the above two problems.

Flashover Resistor

The basic construction of other conventional lightning arrestor (LA) includes the installation of a nonlinear resistor in series with spark gap. During normal power system voltages, the resistance of non linear resistance is very high. Hence the arrestor is non operational. Now when the voltage across arrestor increases due to abnormal conditions, the resistance of the non linear resistance gradually decreases. Finally when the voltage exceeds flashover voltage of the LA, the spark gap breaks down and lightning overvoltage is discharged to ground. Thus the electrical installations are saved from the over voltage abnormalities.

LFA-M are applied for the protection for over head medium (1KV to 33KV) transmission lines only. The operation is based on creeping discharge principle. LFA-M consists of two cables having a core which is resistive in nature. Ring electrodes are mounted on the cable surface. Three flashover modules are formed by the arrangement of these cable pieces. Differential voltage is applied at each ends of the cable due to the resistive core. Resultantly, total voltage applied at the ends of the module make it ready for simultaneous initiation of discharge. The single channel is degenerated into smaller channels which flow over the surface of the cable through the ring electrodes connected serially.

The protective scheme using LFA-M is pretty extensive and encapsulates all types of towers, insulators and cables. LFA-M differs from conventional type of lightning arrestors in two aspects: path of lightning current and Arc Quenching mechanism. The path of lightning follow up current in case of LFA-M is over the surface of the arrestor cable. The arc is quenched by the long discharge path provided by the ring electrodes.

The recent trend is to mount LFA-Ms on the pole in parallel with each line insulator. The “lightning” thing about LFA-M is that they are protected from both lightning and power frequency follow up currents. Hence LFA-M does not go undergo erosion unlike metal oxide or expulsion gap electrode arrestors. The use of LFA-M can be extended to long transmission lines by increasing the number of modules. According to Georgij Podporkin and Acacio Wey,Streamer Electric Company, Russia, LFA-M have passed all the test to be employed on a commercial basis. The use of LFA-M, to counter power transmission failures in India, is expected to be on rise in near future.

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