Lightning Arrestar

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1. fkhereri Engr.Muhammad Younis (MSEES)

2. Presented by Engr.Muhammad Younis (Msees01133015) Rehman Ali (Bsec01101007) Allah Rakh ( Bsec01101024) Engr.Muhammad Younis (MSEES)

3. OBJECTIVE Engr.Muhammad Younis (MSEES)

4. 4 Lightning & Transient Protection Engr.Muhammad Younis (MSEES)

5. What is Lightning “An electric discharge between cloud and earth or between the charge centers of the some cloud is known as Lightning”. Lightning is a huge spark and take place when cloud are charged to such a high potential (+ ve or – ve ) With respect to earth. Engr.Muhammad Younis (MSEES)

6. Engr.Muhammad Younis (MSEES) Clouds Play a major role in lightning formation

7. Mechanism of Lightning Discharge During the up rush of warm moist air from earth ,the friction between the air and tiny particles of water causes the building up charges. When drop of water are formed, the large drop become positively charged and smaller drop become negatively charge. When the Drop of water accumulate, they form Clouds and hence cloud may be posses Fig.01 Engr.Muhammad Younis (MSEES)

8. cont… either a positive or negative charge, depending Upon the charge of drop of water they contain. the charge on a cloud may become so great that It may discharge to another cloud or earth . we call this discharge as lightning . The thunder which accompanies lightning is due to the fact that lightning suddenly heats up the air , thereby causing it to explain. the surrounding air pushes the explained air back forth causing wave motion of air which we recognize as thunder . Engr.Muhammad Younis (MSEES)

9. Lightning Discharge Diagram Fig.02 Return streamer Leader Stepped leader Cloud Cloud Engr.Muhammad Younis (MSEES)

10. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Negative stepped leader Positive answering leaders Return stroke _ _ _ _ _ _ _ _ _ _ _ _ _ _

11. Cont… As the charge acquired by the cloud increases, the potential between cloud and earth increases and therefore ,gradient in the air increases. when the Potential gradient is sufficient (5kv/cm to 10kv/cm) to Break Down the surrounding air, The lightning stroke starts. Fig : 03 Engr.Muhammad Younis (MSEES)

12. Types of Lightning Strokes There are two main ways in which a lightning may strike the power system (e.g. overhead line or tower, sub-station etc.) 1. Direct stroke 2. Indirect stroke Direct stroke: In the direct stroke, the lightning discharge is directly from cloud to the subject equipment, like overhead line or other surface. The overvoltage set up due to the stroke may be large enough to flashover this path directly to the ground. Engr.Muhammad Younis (MSEES)

13. Indirect stroke Indirect stroke: Indirect strokes result from the electro statically induced charges on the conductors due to the Presence of charge clouds. A positive charge cloud is above the line and induces a negative charge on the line by electrostatic induction This negative charge , however , will be only On that portion of the line right under the cloud and the portion of the line away from, it will be positive charge. When the cloud discharge to earth or an other cloud ,the negative on the wire is isolate as it cannot floe quickly to earth over the isolator. Fig:04 Engr.Muhammad Younis (MSEES)

14. Lightning Arresters “ A lightning arrester is a protective device which Conducts the high voltage surges on the power system to the ground”. The earthing screen and ground wires can well protect the electric system against direct lightning strokes but the fail to provide protection against traveling waves which may be reach the terminal apparatus. the lightning arresters or surge diverters provide protection against such surges. Engr.Muhammad Younis (MSEES)

15. Working of lightning arrester Power circuit R Non-linear resistor Spark gap Lightning arrester Fig:04 Fig. o4 show the basic of a surge diverter. It consists of a spark gap Is series with a non-linear resistor. one end of the diverter is connect to The terminal of equipment to be Protected and the other end is effectively Grounded. The length of gap is so set that normal line voltage is not enough To cause an are across the gap but a Dangerously high voltage will break down The air insulation and from an arc. “The property of the non-linear Resistant is that its resistance decreases as the voltage or current Increases”. Engr.Muhammad Younis (MSEES)

16. Types of Lightning Arresters There are several type of lightning arrester in general use. They differ only in constructional details but operate the same principle viz. providing low resistant path for surge to ground. We shell discuss the following types. 1. Rod gap lightning arrester 2. Horn gap lightning arrester 3. Multigap lightning arrester 4. Expulsion type lightning arrester 5. Valve type lightning arrester Engr.Muhammad Younis (MSEES)

17. 1. Rod gap lightning arrester Rod gap lightning arrester. It is a very simple type of diverter and consist of two rods. One is connected to the line and other on to earth. the distant between gap and insulator must not be less then one-third of the gap length so that the arc may reach the insulator and damage it. “Under normal operating conditions, the gap remains non-conducting . On the occurrence of a high voltage surge on the line , the gap sparks over and the surge current is conducted to earth .in this way ,excess change on the line due to the surge is harmlessly conducted to earth”. Engr.Muhammad Younis (MSEES)

18. Rod type lightning arrester Line Rod connected to line Rod gap Rod connected to earth Transformer tank Transformer Bushing Fig.05 P Engr.Muhammad Younis (MSEES)

19. Limitations of rod type The rod may malt or damaged due to excessive heat produced by the are. The climatic conditions (e.g. rain, humidity, temperature etc.) affect the performance of rod gap arrester. The polarity of surge also affected the performance of this arrester. “Due to the above limitations the rod type arrester is only used as a ‘ Back-up’ protection in case of main arrester”. Engr.Muhammad Younis (MSEES)

20. 2.Horn gap lightning arrester It consist two horn shaped metal rod A and B separated by a small air gap. the Horns are so constructed that distance between them gradually increased. one end is connected to the line through resistance R and choke coil L while the other is connected to effectively grounded .The resistance R helps in limiting in follow current to a small value. the choke coil is designed that it offers small reactance at normal power frequency but a very high reactance at transient frequency. Engr.Muhammad Younis (MSEES)

21. Horn gap lightning arrester Diagram Fig:06 Engr.Muhammad Younis (MSEES)

22. Advantages The arc is self clearing. therefore this type of arresters does not cause short circuiting of the system after the surge is over in the case of rod gap. Series resistance helps in limiting the follow current to a small value. Note : “This type of arrester is not reliable and can only be used a second line of defense like the rod gap arrester”. Engr.Muhammad Younis (MSEES)

23. 3.Multigap lightning arrester It consist of series of metallic cylinders insulated from one another and separated small intervals of air gaps. First cylinder A in series is connected to the line and other to be ground through series resistance. the series resistance limits the power arc. By the inclusion of series resistance the degree of protection against travelling wave is reduced. In order to overcome this difficulty some of gap(B to C) are shunted by resistance. such type arresters can be employed where system voltage does not exceed 33kv. Engr.Muhammad Younis (MSEES)

24. Multigap lightning arrester Diagram Line A Series gaps Shunted gaps Shunted resistance Series resistance Earth B C Fig:07 Engr.Muhammad Younis (MSEES)

25. 4.Expulsion type arresters This type of arrester is also called “protector tube "and is commonly used on system operating up to 33kv. It is essentially consist of rod gap AB in series with a second gap enclosed in a fiber tube. this gap in the fiber tube is formed by two electrodes. The upper electrode is connected to rod gap and lower is earthed. One expulsion arrester is placed under each line conductor. Engr.Muhammad Younis (MSEES)

26. Expulsion type arresters Diagram Fig:08 Line A B Rod gap Internal gap Fiber tube Earth (1) (2) Horn gap Protector tube Engr.Muhammad Younis (MSEES)

27. Advantages They are not very expensive. They can easily installed. They are improved form of rod gap arrestor as they block flow of power frequency follow currents. Limitations this type of arrester can not be mounted in an enclosed equipment due to discharge of gases during operation. due to poor volt\ampere characteristics of the arrester it is not suitable for protection expensive equipment. Engr.Muhammad Younis (MSEES)

28. 5.Valve type arrestor Valve type arrester incorporate non linear resistor and extensively used on system , operating at high voltages. It consist of two assemblies (1)series spark gap (2)non linear resistor disc in series The non linear elements are connected in series with the spark gaps and earth. Engr.Muhammad Younis (MSEES)

29. Valve type arrestor Diagram Line Spark gaps and Grading resistors Set of non-linear Resistors (1) (2) Fig:09 Current terminal Porcelain housing Spark gaps Non-linear resistor Engr.Muhammad Younis (MSEES)

30. Working On the occurrence of an over voltages, the break down of series spark gap takes place and the surge current is conducted to earth via non linear resistor. Since the magnitude of surge current is very large the non linear elements offer a very low resistance the passage of surge. The result, surge will rapidly go to earth instead go back over the line. When surge is over the non linear resistor to stop flow of current. Engr.Muhammad Younis (MSEES)

31. Advantages They provide very effective protection (especially for transformers and cables) against surges. They operate very rapidly less than second. Applications Station type used for protection of important power station operate on up to 220kv Line type arrester station handling voltage up to 66kv. Engr.Muhammad Younis (MSEES)

32. Ultimate test of varistors and arrester: Independenttype testing, IEC 60099-4 Surge Arrester Type Testing Insulation withstand tests Residual voltage tests Long duration current withstand test Operating duty test Power frequency voltage versus time curve Short circuit (pressure relief) test Partial discharge testLatest edition of IEC 60099-4released 2006 Engr.Muhammad Younis (MSEES)

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