Lightning Arrestar

Lightening Arrester
Engr.Muhammad Younis (MSEES)

OBJECTIVE
What is Lightning
Mechanism of Lightning Discharge
Types of Lightning Strokes
Lightning Arresters
Types of Lightning Arresters

4
Lightning &
Transient Protection

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.

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

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 .

Lightning Discharge Diagram
Cloud Cloud
Fig.02
Return
streamer
Leader
Stepped
leader

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.
Engr.Muhammad Younis (MSEES) Fig : 03

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.

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. Engr.Muhammad Younis (MSEES) Fig:04

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.

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”.

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

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”.

Rod type lightning arrester
Line
Rod connected
to line
Rod gap
Rod connected
to earth
Transformer
tank
Transformer
Bushing
P
Fig.05

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”.

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.

Horn gap lightning arrester Diagram
Fig:06

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”.

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.

Multigap lightning arrester Diagram
Line
A
Shunted
resistance
Series gaps Shunted gaps
Series
resistance
Earth
B C
Fig:07

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.

Expulsion type arresters Diagram
Fig:08
Line
A
B
Rod gap
Internal gap
Fiber
tube
Earth
(1) (2)
Horn gap
Protector
tube

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 voltampere characteristics of the arrester it
is not suitable for protection expensive equipment.

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.

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

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.

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.

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

THANK YOU

Lightning Arrestar

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