Lightning Discharge and

Fundamentals of lightning

Protection

Presented By

Chittaranjan Behera

EEE-B

Contents:-

Introduction

Fundamentals of Lightning

General Principles lightning protection

Lightning Parameters

Measurements Of Peak currents

Advanced Approaches to Lightning Protection

Summery and Conclusion

References

Introduction

The principles of modern lightning protection technology

emphasize the protection, comprehensive treatment and

successive lines of defence. External lightning protection facilities

shall be installed for the external of buildings, and corresponding

lightning protection devices shall be installed for systems inside

buildings. Thunder and lightning is one of the Most destructive

natural disasters. Therefore, lightning protection is an important

systematic work. Only the lightning protection is carried out well for

a long term, the effects of lightning protection and disaster

reduction can be truly realized by some modernised protection

system

Lightning Flash:-

Lightning is the visible discharge of static electricity within a cloud, from cloud to

cloud, or between the earth and a cloud.

It can be divided into two types

1. lightning Discharge

2. lightning strokes

Lightning Discharge

Lightning flashes to earth (discharges) lead to a neutralization of charge between

the cloud charges and the electrostatic charges on the ground.

Two types of lightning Discharge

Downward flashes (cloud-to-earth flashes)

Upward flashes (earth-to-cloud flashes)

Downward flash:-

Flash starts from cloud and moves towards ground

Downward flashes are of two types:-

1. –ve Discharge

2. +ve Discharge

Upward Flash:

Flash starts from earth and move towards cloud

It is also of two types

1. –ve flash

2. +ve flash

Lightning waveform

General principle Of lightning Protection

There are generally two aspects of Lightning Protection

1. Diversion and shielding, primarily intended for

structural protection but also serving to reduce the lightning

electric and magnetic fields within the structure

2. The limiting of currents and voltages on electronic, power, and communication systems via surge

protection

Lightning Protection System:-

A Lighting Protection System (LPS) is the system that provides a means by which a lightning discharge

may enter or leave earth without passing through and damaging personnel, electrical equipment, and

non-conducting structures such as buildings

Ground based Structure:-

Properly structural lightning protection systems for ground-based structures serve to provide lightning

attachment points and paths for the lightning current to follow from the attachment points into the

ground without harm to the protected Structure

It basically composed of three elements

Air terminals

Down conductors

Grounding electrodes

Side Flash:-

During the lightning flash the rapid rate of current

rise can cause the inductive voltage rise of the

conductor to reach a magnitude where sufficient

voltage exists for the conductor to flashover to a nearby conductive and earthed object

Side flashing can be controlled by:

1. Using a number of parallel down-conductors to

reduce the current in each, ensuring the

separation distance between the two objects is

sufficient not to break down the intervening

medium

Lightning ParametersThere are four important parameters which can cause damage due to lightning

1. Peak current

2. Maximum rate of change of current

3. Integral of current over time

4. Action integral

Peak current:-

For resistive impedance

Ohm’s law

V=RI

If a peak current of 30 KA injected through a long power line phase conductor with a resistance

of 400 ohm then it produces a line voltage of 6MV

Maximum rate of change of Current:-

For inductive loads voltage is proportional to rate of change of current by the relation

V = L dI/dt

Integral of Current over Time:-

The severity of heating or burn-through of metal sheets such as airplane wing surfaces and

metal roofs is proportional to the lightning charge transferred which is in turn proportional to

the energy delivered to the surface.

Large no of charge is transferred due to longer duration of time and due to this heating and

burning will be occur

Action Integral:-

The time integral of joule heating power (I2(t) R) cause melting and explosion of poorly conducting material

The produced heat vaporises the internal material and the resultant gas pressure causes

explosion

It also cause some mechanical effects such as causing of hollow metal

Current induces due to electromagnetic fields from lightning

1.the peak values of electric and magnetic field

2.max rate of change of fields

Lightning Protection Standard:-

>CIGRE distribution

>IEEE distribution

For the CIGRE distribution, 98% of peak currents

exceed4 kA, 80% exceed 20 kA, and 5% exceed 90

kA

For the IEEE distribution, the “probability to exceed”

values are given by the following equation

Advanced Approaches to Lightning Protection

Electrogeometrical Model(EGM):-

Striking distance:-

The striking distance can be defined as the distance

from the tip of the descending leader to the object to

be struck at the instant when an upward connecting

leader is initiated from this object

>The geometrical construction of this surface can be

accomplished simply by rolling an imaginary sphere of

radius equal to the assumed striking distance across

the ground and across objects on the ground

Striking Distance

I=peak current(KA)

rs=striking distance(meters)

>The main application of the rolling sphere method is positioning air terminals on an ordinary structure,

so that one of the terminals, rather than a roof edge or other part of the structure, initiates the upward

leader that intercepts the descending leader and, hence, becomes the lightning attachment point

Objectives:-

To force the current to flow to ground

To reduce the hazardous potential

The distance between an LPS down-conductor and the protected object in air should be greater than Dair given in meters by

Dair=Distance b/w air terminal and protected object

Z=impedance of LPS grounding system

L=distance b/w LPS grounding system and point of intrest

Bonding vs isolation approaches in lightning protection:-

The distance between the LPS grounding system and buried metallic services should be

greater than Dsoil given by

I=Lightning Peak current

Z=impedance of LPS grounding system

Eb=Breakdown electric field

CONCLUSION:-

Any design of Direct Lightning Stroke Shielding depends on the probabilistic nature of

lightning phenomena. There is no method available to provide 100% shielding against

direct lightning stroke of the substation equipment and bus structures.

EGM method is more appropriate for large and important substations at 230 kV and

above voltage level. In order to arrive at some practical solutions, many assumptions are made in the different design techniques

References

A.M. Mousa, The Applicability of Lightning Elimination Devices to Substations and Power

Lines, IEEE Trans. on Power Delivery, Vol. 13, No. 4, October 1998, pp. 1120-1127.

D. W. Zipse, Lightning Protection Systems: Advantages and Disadvantages, IEEE Trans. On

Industry Applications, Vol. 30, No. 5, Sept/Oct. 1994, pp. 1351-1361.

IEEE Std. 998-1996, Section 6, pp. 42-43.

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