Lightening Arrester.pptx

Explains Lightening phenomenon in details.

1. Lightening Arrester Submitted By : Indubhushan Kumar PhD*, M.Tech , B.Tech

2. CONTENTS Lightening arrester Surge Arresters / Surge absorber Numerical

3. Lightening Arrester

4. What is Lightning Arrester? The circuit which is protected from the strokes of lightning is known as lightning arrester. Here the lightning strokes are nothing but surges with high transient voltage, arcs of isolation, spark, and surge currents because of lightning, etc. Overhead lines can also be protected by using ground wire or shield wire from the direct strikes of lightning. The arrangement of these devices can be done on the towers, transmission poles and buildings to give a secure lane to the voltage & discharging current.

5. Lightening Arrester

6. Shield Wire or Earth Wire

7. Types of Lightning Arrester Horn Gap Arresters Rod Gap Arresters Expulsion type Arresters Valve-Type Arresters

8. Horn Gap Type The horn gap consists of two horn shaped rods separated by a small distance. One end of this is connected to the line and the other to the earth with or without a series resistance. The choke connected between the equipment to be protected and The horn gap serves two purposes: ( i ) The steepness of the wave incident on the equipment to be protected is reduced. (ii) It reflects the voltage surge back on to the horn.

9. Contd … There are two major drawbacks of the horn gap ( i ) The time of operation of the gap is quite large as compared to the modern protective gear. (ii) If used on isolated neutral the horn gap may constitute a vicious kind of arcing ground. For these reasons, the horn gap has almost vanished from important power lines.

10. Contd …

11. Rod Gap Arresters This arrester is very simple and is rugged in construction. C heapest among all the other arresters and requires no maintenance . It consists of two 1 inch metal rods that are placed at right angles to each other with a gap in between them. One rod is connected to the ground and the other rod is connected to the line circuit. The distance between the rod gap and the insulator should be 1/3 of rod gap lengths to avoid any damage to it.

12. The gap between the rods remains open under normal operating conditions. When a high voltage surge occurs on the line, the gaps spark over and it offers a low resistance path for the flow of surge current to the ground. 

13. Disadvantage of Rod Type The main drawback of this type of lightning arrester is it doesn't interrupt the power frequency follow current after the surge has disappeared or surge voltage becomes less than the breakdown value.  This causes a line to ground fault after every discharge of surge voltage by the arrester and initiates the breaker operation to de-energize the circuit to clear the flashover . There can be chances of damaging the rods due to heat produced by the spark between the gaps.

14. Expulsion Type Lightning Arrester   This type of arrester is also known as protector tube or expulsion gap . it is commonly limited to systems operating at voltages up to 33kV.

15. Contd .. It essentially consists of , A tube made of fiber is a very effective gas evolving material. An isolating spark gap. An interrupting spark gap, which is in series with the rod gap, is enclosed within the fiber tube. This interrupting spark gap is made up of two electrodes, in which the upper electrode is connected to the rod gap and the lower electrode is connected to the ground. There will be one expulsion arrester under each line conductor.

16. Contd .. When a surge voltage occurs on the line, the rod gap length will be increased and an arc is produced between the electrodes in the tube. Neutral gas is produced in the tube due to the vaporization of fibre of the tube walls. By the heat of an arc in a short span of time, high pressure will be built up by the evolved gas and the gas comes out of the tube . At the lower electrode, the gas which is coming out of the tube carries ionized air around the arc. The arc is extinguished at current zero. And due to the strong deionizing effect, the arc will not reestablish. As soon as, the gases have been expelled and the arc is extinguished, the tube is ready for a new operation.

17. Metal Oxide Lightning Arrester The metal oxide lightning arrester is the most commonly used arrester in modern power systems. It consists of a stack of series-connected metal discs made up of zinc oxide having highly non-linear resistance. Due to its high degree of non-linearity in resistance over a large current range, the arrester eliminates the use of a series gap . Hence the metal oxide arrester is also known as zinc oxide gapless lightning arrester.

18. Contd..

19. QUESTIONS What are BILS ? Explain their significance in power system studies. Explain clearly how the rating of a lightning arrester is selected. What is the best location of a lightning arrester and why ? Compare the relative performances of the following: ( i ) Rod gap; (ii) Expulsion gap; and ( iii) Valve type L.A . What is tower-footing resistance ? What are the methods to reduce this resistance ? Explain clearly how a lightning arrester is selected for protecting a power transformer.

20. THANK YOU……