Engr.Muhammad Younis (MSEES)
Lightening Arrester
Engr.Muhammad Younis (MSEES)
OBJECTIVE
What is Lightning
Mechanism of Lightning Discharge
Types of Lightning Strokes
Lightning Arresters
Types of Lightning Arresters
Engr.Muhammad Younis (MSEES)
4
Lightning &
Transient Protection
Engr.Muhammad Younis (MSEES)
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 cloudare charged to such a high potential (+ve or –ve)
With respect to earth.
Engr.Muhammad Younis (MSEES)
Engr.Muhammad Younis (MSEES)
Play a major role in lightning formation
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)
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)
Lightning Discharge Diagram
Fig.02
Returnstreamer
Leader
Steppedleader
Cloud Cloud
Engr.Muhammad Younis (MSEES)
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
Negative stepped leader
Positive answering leaders
Return stroke
_ _ _ _ _ _ _ _ _ _ _ _ _ _
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 : 03Engr.Muhammad Younis (MSEES)
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)
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:04Engr.Muhammad Younis (MSEES)
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 divertersprovide protection against such surges.
Engr.Muhammad Younis (MSEES)
Working of lightning arrester
Power circuit
RNon-linearresistor
Sparkgap
Lightningarrester
Fig:04
Fig. o4 show the basic of asurge 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 effectivelyGrounded. The length of gap is so setthat normal line voltage is not enough
To cause an are across the gap but a Dangerously high voltage will break downThe air insulation and from an arc.
“The property of the non-linear Resistant is that its resistancedecreases as the voltage or current
Increases”.
Engr.Muhammad Younis (MSEES)
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)
1. Rod gap lightning arresterRod 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)
Rod type lightning arresterLine
Rod connectedto line
Rod gap
Rod connectedto earth
Transformertank
TransformerBushing
Fig.05
P
Engr.Muhammad Younis (MSEES)
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)
2.Horn gap lightning arresterIt 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)
Horn gap lightning arrester Diagram
Fig:06Engr.Muhammad Younis (MSEES)
AdvantagesThe 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)
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)
Multigap lightning arrester Diagram
Line
A
Series gaps Shunted gaps
Shunted resistance
Seriesresistance
Earth
B C
Fig:07
Engr.Muhammad Younis (MSEES)
4.Expulsion type arrestersThis 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)
Expulsion type arresters Diagram
Fig:08
Line
A
B
Rod gap
Internal gap
Fibertube
Earth
(1) (2)
Horn gap
Protectortube
Engr.Muhammad Younis (MSEES)
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)
5.Valve type arrestorValve 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)
Valve type arrestor Diagram
Line
Spark gaps andGrading resistors
Set of non-linearResistors
(1)(2)
Fig:09
Currentterminal
Porcelainhousing
Spark gaps
Non-linearresistor
Engr.Muhammad Younis (MSEES)
WorkingOn 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)
AdvantagesThey provide very effective protection (especially for
transformers and cables) against surges.
They operate very rapidly less than second.
ApplicationsStation 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)
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)
THANK YOU
Engr.Muhammad Younis (MSEES)