lightning slides

8/10/2019 Lightning Slides

1/24

MElec-Ch6 - 1

Chapter 6

Lightning Protection


2/24

MElec-Ch6 - 2

Overview

Characteristics of Lightning Principles of Protection

Precautions for Personnel

Precautions for Electronic Equipment


3/24

MElec-Ch6 - 3

Characteristics of Lightning

Static Electricity Ultra-High Voltage Generation

The Discharge

Surface Dispersion Basic Laws of Electricity


4/24

MElec-Ch6 - 4

Lightning

Static Electricity Separation and storage of electrical charge

A spark is an extremely small lightning discharge

Ultra-High Voltage Generation

Surface of earth is normally negatively charged

Top of storm clouds are positively charged

Forces nearby earth to become positively charged

Develops a multimillion-volt potential


5/24

MElec-Ch6 - 5

The Discharge

Clouds send negative charged leaders down

Earth sends positive leaders up

From grounded sharp metal objects

Conducting path when leaders meet

Unidirectional (DC) current flow

Voltage potential 100 to 1,000 million volts Current range 10,000 to 200,000 amperes

Duration from 1 microsecond to 1 second


6/24

MElec-Ch6 - 6

Anatomy of a Lightning Stroke

Electrons begin

zigzagging

downward in a

forked pattern.

This is the

stepped leader.As the stepped leader

nears the ground, it

draws a streamer of

positive charge upward.

As the leader and

streamer come together,

a powerful electrical

current begins flowing.

Current beginsthe return stroke,

an intense wave

of positive

charge traveling

upward about

60,000 miles per

second.


7/24MElec-Ch6 - 7

Surface Dispersion

Surface dispersion

Main portion of lightning bolt penetrates earth

Spurs find far-reaching paths along surface

Surface dispersion is deadly

Stay out of the water

Keep away from trees


8/24MElec-Ch6 - 8

Basic Laws or Electricity

Lightning creates magnetically inducedcurrent in all metal items within itsinfluence

The longer the wire, greater the current

The closer the strike, greater the current

Any impedance to current flow results in

Build up of high voltage at that location Resulting in arc-over to reach ground

Ignites flammable material

Vaporizes metal of insufficient cross-section


9/24MElec-Ch6 - 9

Principles of Protection

Cone of Protection

Lightning Protection System

Power Boat Applications Sail Boat Applications


10/24MElec-Ch6 - 10

Cone of Protection

Lightning rod protects areas within its cone

60 degree cone is 99% effective

45 degree cone is 99.9% effective

Less current flow from sharp pointed tip

More current flow from blunt or ball tip


11/24MElec-Ch6 - 11

Lightning Protection System

Air Terminal

Discharge Conductor

Water Terminal Bonding


12/24MElec-Ch6 - 12

Air Terminal

Also known as a Lightning Rod Traditionally inch copper rod

With sharpened point

Six inches above object to be protected


13/24MElec-Ch6 - 13

Discharge Conductor

Not less than #4 AWG Uninsulated stranded copper wire

Straight from Air Terminal to Water Terminal No sharp bends (bend radius of 1 foot)

Should be run outside of hull

Electrical wiring should be at right angles

#4


14/24MElec-Ch6 - 14

Water Terminal

Also known as a Ground Plate

External to hull Sailboats use metal keel

Area of one square foot

Not painted No water film between plate and hull

Use bedding compound

Size: 18 x 6 x


15/24MElec-Ch6 - 15

Bonding (Chapter 2)

Bonding is also for Lightning Protection

Purposekeep all metal surfaces at zero potential To prevent electrical shock

To prevent stray current corrosion

To prevent induced potential from lightning strike

Bonding conductor Cross section of #6 AWG

Strap not less than #20 gauge (0.032 inch thick)

Normally #6 bare copper wire


16/24MElec-Ch6 - 16

Powerboat Application

Fiberglass antennas provide NO protection

Add lightning rod on other side for protection e.g. grounded metal whip antenna

Ground the signal mast or Tuna Tower

Need a ground plate

Stay within the cone of protection


17/24

MElec-Ch6 - 17

Powerboat Application

Grounded metal whip provides protection

Grounded HF whip antenna with loading coil No protection above loading coil

Unless loading coil bypassed with large conductor


18/24

MElec-Ch6 - 18

Sailboat Application

Metal masts are grounded (bonded)Add discharge conductor to wood mast

Shrouds and stays grounded

Keel is ground plate


19/24

MElec-Ch6 - 19

Precautions for Personnel

Remain inside the boat Trust lightning protection system

Stay Out of the Water

Surface dispersion

Avoid contact with metal surfaces

Induced voltage

Handle only one metal control at a time


20/24

MElec-Ch6 - 20

Precautions for Electronics

Before a lightning storm

After a lightning strike


21/24


22/24

MElec-Ch6 - 22

Before Lightning Storm 2

If underway, keep operational One VHF radio

One GPS / chart plotter

Radar, if so equipped

Handhelds stored below


23/24


24/24

MElec Ch6 24

Summary

Tremendous energy in lightning strike

Lightning protection Based on cone of protection Components

Air terminal Discharge conductor (#4 AWG stranded) Water terminal (1 sq ft)

Bond all metal above deck Before lightning storm

Disconnect all unnecessary equipmentAfter lightning strike

First check people Then hull

May have to go to backup electronics

lightning slides

Documents