Direct Stroke Lightning Protection (DSLP)

Lightning Stroke

When the electric field becomes strong enough, an electrical discharge occurs within clouds or between clouds and the ground is called lightning stroke.

Lightning Stroke

Effect of Lightning Strokes

Assumption: No Shielding and No Lightning Mast Possible Insulation Flashover (depends primarily

on the stroke current magnitude) Damage to Major Substation Equipment Substation Outage Cost

Effects of Lightning Stroke Assumption: With Shielding and Lightning Mast

Devices

Minimize the possibility of direct lightning strike to bus and/or major equipment in the substation and hence, the outage and possible failure of major electrical equipment.

Lightning Conductor

Lightning conductor consists of the lightning receiver projecting above the object to be protected, the earthing grid and the conductor which connects the receiver with the earthing grid and carry the lightning current safely to the ground.

Type of Lightning Conductor

In substations we use two type of

lightning media:

Lightning Masts

Ground Wires (Shield Wire)

Lightning MastA column or narrow base structure containing a vertical conductor from its tip to earth. Its purpose is to intercept lightning strokes so that they do not terminate on objects located within its zone of protection.

Shield Wire

A wire suspended above the phase conductors to protect phase conductor, objects from lightning strike located within its protective zone.

Methods use for Lightning Protection• Lightning Masts• Shield Wires• Combination of Masts & Shield WiresCalculation Dr. Razevig’s Method Fixed Angles Method: 45/60 degrees Electrogeometric methods IEEE Std. 998-1996

Protective ZoneThe space around a lightning conductor in which the probability of lightning stroke is small is called protective zone.

Active Height

Projection of height of the lightning conductor above the height of the object to be protected is called the active height of the lightning conductor.H1=H-hH1 is active height

Experimental Determination of Protective

Zone

IVG-Impulse Voltage generator1- Electrode(For Discharge)2- Model of the lightning Conductor3- Grounded metallic plane

Lightning Protection By Lightning Mast

H= Height of Diodeh= Height of Lightning RodR= Radius of Zoner=radius of Protective Zoneh1= Height of object to be protected

Lightning Protection By Shield Wire

H= Height of Diodeh= Height of Lightning RodB= Radius of Zoneb=radius of Protective Zone

Protective Zones of the Lightning Masts

If h1<2/3hRadius of protective zone is r1=1.5h(1-h1/0.8h)h1 object heighth LM heightIf h1>2/3hr1=0.75h(1-h1/h)

if height of Lightning Mast h>30mt. Then r1 must be multiplied by the coefficient p=5.5/√h

Protective Zone Calculation for more than 1 LM

For 2 LM Distance between two LM a<=7(h-h1) h-h1 is active height of LM h1=h-a/7 For 3 LM a circle of diameter D is passing

through the tips of the LM D=8(h-h1)

Protective Zone Calculation for more than 1 LM

Minimum active height of LM 1,2,4 is h2=60/8=7.5mt (h2 is active height) Minimum active height of LM 2,4,5 is h2=55/8=6.9mt Minimum active height of LM 1,3,4 is h2=50/8=6.4mt Minimum active height of LM 4,5,7,8 is h2=57/8=7.2mtLM of Active height =7.5mt is able to protect the area.Maximum height of equipment to be protected is 11mtSo height of LM h=7.5+11=18.5mt

Protective Zones of the Shield Wire

If h1<2/3hRadius of protective zone is b1=1.2h(1-h1/0.8h)

If h1>2/3hb1=0.6h(1-h1/h)

Fixed Angles Method

X= (B-A)Tan60 or X= (B-A) Tan α

Electrogeometric Method(EGM)

S=8kIs0.65

S is strike distanceIs stroke current in kAk is coefficient k=1 for shield wirek=1.2 for Lightning Mast

Electrogeometric Method(EGM)The Protective area of shield wire or mast depends on the amplitude of the stroke current Is.

Allowable stroke current :Is=2.2(BIL)/Zs

Is is allowable stroke current in kAZs is surge impedance of the conductor through which the surge is passing in ohms.

Application of EGM by Rolling Sphere Method

Shield Mast Protection for Stroke Current Is

Shield Mast Protection for stroke current Is1 > Is

Shield Mast Protection for stroke current Is1 < Is

Multiple Shielding Electrodes

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