1. LIGHTENING PROTECTION USING LFA-M
By: D.S.P. Edirisinghe
080096T
Department of EE

2. Outline. Introduction Types of lightening strokes
Lightening protection system
What is LFA-M?
Block Diagram
Design of LFA-M
How LFA-M protects the system?
Advantages
Disadvantages

3. Lightening… What is it…? Types of Lightening Strokes...
Takes place when clouds are charged to a high potential
Electrical discharge between a cloud and earth
A huge spark...
Types of Lightening Strokes...
Direct stroke
Indirect stroke

4. Lightening - Direct Stroke
Lightening discharge is directly from a cloud to overhead line.
From the line, current path may be over at the ground.
The over voltage setup due to the stroke may be large enough to flashover this path directly to the ground.

5. Lightening - Indirect Stroke
Results from electro statically induced charges on the conductors.
(+ve) ly charged cloud induces (-ve) charge right under the cloud on the line and (+ve) charge away from it.
When cloud discharges to earth, (-ve) charge rushes along both directions in form of travelling wave.
++++++
- - -

6. Lightening protection system
A system designed to protect a structure from damage due to lightening strikes.
Intercepts such strikes and safely passes their extremely high voltage currents to “ground".
Provides a low-impedance path for the lightning current to lessen the heating effect.

7. Lightening protection system...
Traditional Designs...
Majority of nowadays- traditional “Franklin System”-providing low impedance path
“Franklin System”-A system of
lightning protection conductors
lightning rods -installed on the roof of the building to intercept any lightning before it strikes the building.
This has 3 main parts.
The roof circuit
Interconnection to grounding electrodes
Grounding electrodes

8. Lightening protection system...
Non-traditional Designs...
Aim is to reduce the number of air terminals required by a traditional Franklin-type system.
Reduce the overall cost of the protection system.
Mainly in two categories.
Systems that provide an increased zone of protection
Systems that eliminate lightning strikes altogether.

9. Non-traditional protection designs..
Early streamer emission
Radioactive rod systems
Laser induced systems
Charge transfer systems

10. LFA-M....? What is it..? Long flashover arrestors.
Devices which capture the high voltage sparks resulting out of lightening.
‘M’ indicates that it is for the protection of medium overhead transmission lines.
Can be applied for protection of distribution lines.

11. LFA-M....?
Induced over voltages can be counteracted by installing a single arrestor on an overhead line support.
For direct lightening -arrestors are connected between poles and all the phase conductors in parallel with the insulators.

12. Block Diagram....
a) block diagram b) electric schematic c) arrester testing

13. DESIGN OF LFA-M
An LFA-M arrester consists of two cables like pieces. Each cable piece has a semi conductive core of resistance R
The cable pieces are arranged so as to form three flashover modules 1,2,3.
Semi conductive core 1 2 3

14. How LFA-M protects the system?
(1)A lightning impulse causes a spark over of the spark gaps
(4)All three modules are assured of creeping discharges into a single long flashover channel.
(2)Resistance carries a high potential U
(3)Same resistance applies a 0 potential

15. LFA Loop type....

16. Advantages....
LFA-Ls help avoid both conductor burnouts and overhead power lines outages caused by lightning induced over voltages.
Extend the working life of high voltage circuit breakers.
Protect electric networks against arc over voltages.

17. Advantages.... (cntd)
Cannot be destroyed by lightning currents as metal oxide arresters, gapped silicon carbide arresters or expulsion tubes since currents are flowing outside of LFAs.
Are not stressed by operational voltage and do not require maintenance.
It protects from 0.4 to 10 kV power distribution

18. Disadvantages....
Efficiency can only be increased by number of flash over modules.
Cost of installation.

19. QUESTIONS.....