31
| Date post: | 15-Jan-2017 |
| Category: |
Documents |
| Upload: | badami-shantha-kumar |
| View: | 627 times |
| Download: | 2 times |
[email protected] | +91 9845834712
Statistical Data on Insurance Claims
Burglary29%
Flood5%
Fire6%Lightning
21%
Storm1%
Others14%
Misoperation24%
[email protected] | +91 9845834712
US National Space & Science Technology Centre
Two instruments were used to gather data for the aerial map. The Optical Transient detector was launched aboard NASA's Microlab satellite in 1995 and the Lightning Imaging Sensor is fitted to a joint NASA-Japan satellite launched in 1997 to measure tropical rainfall levels. The sensors gathered lightning data over
periods of five and three years respectively.
[email protected] | +91 9845834712
Typical formation of Lightning - Step 1
Negative electrical charges build up within clouds
Electric field intensification
Positive charges gather on ground
Air breakdown leads to stepped leader
[email protected] | +91 9845834712
Typical formation of Lightning - Step 2
Continuation of downward step leader
Further electric field intensification
Strong upward positive streamer generation
Streamer racing towards downward step leader
[email protected] | +91 9845834712
Typical formation of Lightning – Step 3
Positive upward streamer meets the downward step leader
Conducting path forms
Potential is equalised by the "return stroke“
Visible lightning flash
[email protected] | +91 9845834712
Typical characteristics of Lightning Pulse
LONG TAIL=> flow
HIGH ENERGY
HIGH VOLTAGEdi & dvdt dt
VERY FASTRISE TIME
Typical50 kA
[email protected] | +91 9845834712
Typical Lightning StrikeInstantaneous Power : Over one Megawatt
Total Energy : Over 250 Kilojoules
Sound Pressure : 90 Atmospheres at 500m away
Temperature : 30,000°K+ (5 times Sun Surface)
Rise Time : 0.1 to 5 Microseconds
Average Current : 35 kA
Duration : 300 Microseconds + Repeats
Channel Length : 5 km
[email protected] | +91 9845834712
How Transients enter your Equipment
Capacitive coupling is where the transient voltage is coupled due to the inherent capacitance between two circuits
Magnetic coupling occurs when magnetic field of a current carrying conductor induces lightning current on to an adjacent conductor
Galvanic coupling is a direct electrical connection
[email protected] | +91 9845834712
4 Step ApproachIncludes:Definition and provision of area protection direct strike
Creation of a bonded earthing system
Protection of power lines
Protection of signal, data and communication lines
[email protected] | +91 9845834712
Risk AssessmentMany standards have essential risk assessment methods
AS1768
IEC61024
NF C 17-102
[email protected] | +91 9845834712
Electrical Field Modelling
Originally developed by AJ Ericksson
CAD software forms three dimensional representation of the structure to be protected and the air terminals to be used.
Based on this representation the software determines if protection is achieved to the required level of risk.
[email protected] | +91 9845834712
Electric Field Modelling
Striking distance is influenced by geometry and dimensions such as height, width, radius and altitude all have effect.Corners and edges cause an up-leader to be launched when the down-leader is at a greater distance than flat surfaces. This striking distance is calculated for all directions from the terminal and from the structure resulting in two surfaces.
[email protected] | +91 9845834712
Electrical Field Modelling
The software determines if coverage is successfully achieved based on the relative distances between the surfaces and typical leader velocities based on the site & location conditions
[email protected] | +91 9845834712
Why Grounding?By CODE Required
Personnel Safety ( Touch and step potential)
Equipment Protection (Operate over current device during a ground
fault 50/60Hz event)
Lightning Dissipation (5kHz - 50kHz)
Electro-Static Discharge (ESD)
Noise Control (Computer Grounding)
[email protected] | +91 9845834712
Objective of Lightning Protection Earth
To dissipate the lightning energy with minimum voltage rise that may affect
people or equipment
[email protected] | +91 9845834712
Earth Potential Rise
Consider only REarth potential rise: Ve = 1 x R
= 50000 x 10= 500 kV
[email protected] | +91 9845834712
Lightning Frequency: 5 – 50KHz
SHUNT CONDUCTANCE Gis related to soil conductivity pand contact resistance
CHARACTERISTIC IMPEDANCE
Z0 = R+jwLG+jwC
We want: Z low = R low, L low, C high
[email protected] | +91 9845834712
Types of Lightning Earth
Regular earthing Bi-polar earthing Radial earthing
[email protected] | +91 9845834712
Earthing System
Combination ofhorizontal strip andvertical rods - Linea - Radial
Optimum spacingL > 2 x D
[email protected] | +91 9845834712
Thank You!
NO 33 9TH MAIN ROAD, MC LAYOUT, VIJAYANAGAR, BENGALURU 560040
KARNATAKACALL: 08023303592 | 9845834712 | 07760850152
E-MAIL: [email protected]
