This document discusses different types of lightning arresters used to protect electrical equipment from surges due to lightning strikes. It describes horn gap, rod gap, expulsion type, and metal oxide arresters. Horn gap arresters consist of two horn shaped rods separated by a small gap. Rod gap arresters are the simplest and consist of two metal rods placed at right angles with a gap between. Expulsion type arresters contain a fiber tube that produces gas to extinguish the arc when surged. Metal oxide arresters are the most common today, using a stack of zinc oxide discs with highly nonlinear resistance to eliminate the need for a series gap.

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

2. CONTENTS
o Lightening arrester
o Surge Arresters / Surge absorber
o 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.
 Cheapest 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,
1. A tube made of fiber is a very effective gas evolving material.
2. An isolating spark gap.
3. An interrupting spark gap, which is in series with the rod gap, is enclosed
within the fiber tube.
4. 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
1. What are BILS ? Explain their significance in power system studies.
2. Explain clearly how the rating of a lightning arrester is selected. What is
the best location of a lightning arrester and why ?
3. Compare the relative performances of the following: (i) Rod gap; (ii)
Expulsion gap; and (iii)Valve type L.A.
4. What is tower-footing resistance ? What are the methods to reduce this
resistance ?
5. Explain clearly how a lightning arrester is selected for protecting a power
transformer.

20. THANK YOU……