Lightning Arresters:

Presented By:

K. Shruthi

09251A0228

Contents:• Introduction• How does the lightning occur?• Lightning arresters

• Construction of lightning arrester• What exactly does a lightning arrester do?• How does it divert the lightening?• Ideal characteristics of lightning arrester• Installation and maintenance• Types of lightning arresters• Conclusion

How does the lightning occur??

Lightning:An electric discharge

between cloud and earth, between clouds or between the charge centres of the same clouds

Lightning arresters

• Protects Power system and other equipment from lightning and switching surges.

• Conducts the high voltage surges to the ground.

• Can also protect the system from traveling waves.

Construction of Lightning Arrester:

Length of the gap is so set that the normal line voltage is not enough to cause an arc across the gap but an dangerously high voltage will breakdown the insulation and form an arc.

What exactly does a lightning arrester do?

• Diverts the lightning to ground• Limits the voltage produces by lightning• Protects equipment in parallel with it.

But,• Does not stop the lightning• Does not absorb the lightning

How does it divert the lightning?

• During over voltage, the air insulation across the gap breaks down and the arc is formed providing a low resistance path to the ground.

• The non linear resistance offers low resistance during the lightning period.

Ideal characteristics of lightning arresters:

Ideally, it should• Enter into conduction at some voltage above

arrester rating.• Hold the overvoltage surge for small period.

Installation & Maintenance:Installation:• The arrester should be

connected to ground to a low resistance for effective discharge of the surge current.

• The arrester should be mounted close to the equipment to be protected & connected with shortest possible lead on both the line & ground side to reduce the inductive effects of the leads while discharging large surge current.

Maintenance:• Cleaning the outside of the arrester

housing.• The line should be de-energized

before handling the arrester.• The earth connection should be

checked periodically.• Record the readings of the surge

counter.• The line lead is securely fastened to

the line conductor and arrester• The ground lead is securely fastened

to the arrester terminal and ground.

Types of Lightning Arresters:

• Rod gap arrester• Horn gap arresters• Multi gap arresters• Expulsion type arresters• Valve type arresters

Rod Gap Arresters:Limitations:• After the surge is over, the arc in

the gap is maintained by the normal supply voltage, leading to a short- circuit on the system.

• The rods may melt or get damaged due to excessive heat.

• The climatic conditions affect the performance of rod gap arrester.

• The polarity of the surge also affects the performance of this arrester

Horn Gap Arresters:

Advantages:• The arc is self-clearing. • Series resistance helps in

limiting the follow current to a small value

Limitations:• The bridging of gap by

some external agency can render the device useless

• Corrosion or pitting adversely affects the performance of the arrester.

• The time of operation is comparatively long

Multi Gap Arresters:

Expulsion Type arrester:

Advantages:• Not expensive.• Improved form of rod gap

arresters• Easily installed

Limitations• Can perform only limited number of operations• Cannot be mounted in enclosed equipment• Not suitable for protection of expensive

equipment

Valve Type Arrester:Advantages: • Provide very effective protection

against surges• Operate very rapidly• The impulse ratio is practically

unity

Limitations: • May fail to check the surges of

very steep wave front from reaching the terminal apparatus

• Adversely affected by the entry of moisture into the enclosure

Metal Oxide Varistor:Advantages:• Residual depression• Fast response time (25ns)• Freewheeling.• Safe and Reliable• Commonly used in the

current power supply system products

Drawbacks:• Leakage current

Conclusion:

By proper selection of type and rating of lightning arrester, all the electrical equipment can be protected from lightning and voltage surges

References:

• Principles of Power Systems by V. K. Mehta and Rohit Mehta

• www.seminarpaper.com• www.arresterworks.com

Thank You

Any Queries?