Types Of Lightning Protection Systems LPS


In Article " 
 Introduction to Lightning System Design- Part One ", I listed all terms, abbreviations and Symbols used in lightning field and which will be used throughout Course EE-5: Lightning Protection Systems Design Calculations.

Also, in Article " Introduction to Lightning System Design- Part Two ", I answered the following questions:

  • What is Lightning? 
  • What are the types of Lightning flashes?
  • What is the shape of The Lightning Waveform?
  • How Lightning strikes can affect the electrical and/or electronic systems of a building?
  • What are the main effects of Lightning?


Today, I will explain the different Types of Lightning Protection Systems LPS.







What is the Lightning Protection Systems LPS?
  • 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.


Example of A Lighting Protection System (LPS)

  • So, A Lightning Protection System does not prevent lightning from striking; it provides a means for controlling it and prevents damage by providing a low resistance path for the discharge of the lightning energy.

  • A reliable Lightning Protection System LPS must encompass both structural lighting protection and transient overvoltage (electronic systems) protection. Simply stated, a structural lightning protection system cannot and will not protect the electronic systems within a building from transient overvoltage damage.








Why Using the Lightning Protection Systems LPS?

Lightning protection is essential for the protection of humans, structures, contents within structures, Transmission lines, and electrical equipment by controlling a variety of risks resulting from thermal, mechanical, and electrical hazards of the lightning flash current. These risks can be categorized as follows:

  1. Risk to persons (and animals),
  2. Risk to structures & internal equipment.


1- Risk to persons (and animals) include:

  • Direct flash,
  • Step potential,
  • Touch potential,
  • Side flash,
  • Secondary effects, such as:
  1. asphyxiation from smoke or injury due to fire,
  2. structural dangers such as falling masonry from point of strike,
  3. unsafe conditions such as water ingress from roof penetrations causing electrical or other hazards, failure or malfunction of processes, equipment and safety systems.


2- Risk to structures & internal equipment include:

  • Fire and/or explosion triggered by heat of lightning flash, its attachment point or electrical arcing of lightning current within structures,
  • Fire and/or explosion triggered by ohmic heating of conductors or arcing due to melted conductors,
  • Punctures of structure roofing due to plasma heat at lightning point of strike,
  • Failure of internal electrical and electronic systems,
  • Mechanical damage including dislodged materials at point of strike.









Popular Risks Definitions

1- Side flash:

All down-conductors have a resistance and, more importantly, inductance. 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:

  • 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; or
  • Bonding to the object to eliminate the potential difference (the object may carry a partial lightning current)



2- Step potential:

  • When lightning current is injected into the earth, a large voltage gradient builds up around the earth electrode with respect to a more distant point.


Touch and Step Potentials

  • This voltage differential experienced by a person bridging a distance of 1 m with the feet without contacting any other grounded object is called the step potential.
  • At the time of discharge being close to the earth electrode means the voltage differential across this distance can be large enough to be lethal depending upon circumstances such as condition of footwear, etc, substantial current can flow through one lower leg to the other.


The hazard is considered to be reduced to tolerable level if:

  • The probability of persons approaching, or duration of presence within 3 m of the down-conductor is very low – limiting access to the area can be a solution,
  • Step potential is reduced by use of 5 k ohm.m insulating barrier such as 50 mm of asphalt or 150 mm of gravel within 3 m of the electrode,
  • An equipotential earthing system such as mesh system is correctly used.


3- Touch potential:

  • Touch potential is due to a similar reason as step potential, but the voltage differential being considered is that which exists between the hand and (generally) feet.
  • The risk of electrocution due to touch potential is greater than for step potential, as the passage of current flows close to the heart region.


The hazard is considered to be reduced to tolerable level if:

  • The probability of persons approaching, or duration of presence is very low limiting access to the area can be a solution,
  • Natural down-conductors are used where extensive metal framework or steel work is interconnected,
  • A surface layer with 5 k ohm.m insulating barrier such as 50 mm of asphalt or 150 mm of gravel is used,
  • The down-conductor is insulated with at least 100 kV 1.2/50 μs impulse insulation (3 mm PVC).









What is The Effective Lightning Protection System?

The effective lightning protection system which eliminates the above risks must be designed to:

  • Intercept lightning flash (i.e. create a preferred point of strike),
  • Conduct the strike to ground safely through purpose designed down conductors,
  • Dissipate the lightning energy into the ground with minimum rise in ground potential,
  • Eliminate ground loops and hazardous potential differentials between LPS, structure and internal elements/circuits by creating low impedance, equipotential ground system,
  • Protect equipment from surges and transients on incoming power lines to prevent equipment damage and costly operational downtime,
  • Protect equipment from surges and transients on incoming telecommunications and signal lines to prevent equipment damage and costly operational downtime,
  • Not cause thermal or mechanical damage to the structure,
  • Not cause sparking which may cause fire or explosion,
  • Limit step and touch voltages to control the risk of injury to occupants.







Types of Lightning Protection Systems LPS







Types of Lightning Protection Systems LPS





Lightning protection systems for buildings and installations may be divided into three principal types as follows:

  1. LPS for Protection for buildings and installations against direct strike by lightning,
  2. LPS for Protection against overvoltage on incoming conductors and conductor systems,
  3. LPS for Protection against the electromagnetic pulse of the lightning.








First: LPS for Protection for buildings and installations against direct strike by lightning

This type of LPS protects the building from damage by direct strike lightning but doesn’t prevent the lightning striking the building.

This type of LPS can be divided into:-

  1. Conventional lightning protection system,
  2. Non-Conventional lightning protection system.








1- Types of Conventional Lightning Protection System

The Conventional Lightning Protection System includes (2) different types as follows:

  • Franklin Rod LPS,
  • Franklin/Faraday Cage LPS.


  





2- Types of Non-Conventional Lightning Protection System

The Conventional Lightning Protection System includes (2) different types as follows:

1- Active Attraction LPS, which includes:

  • Improved single mast system (Blunt Ended Rods),
  • Early streamer Emission System.


2- Active Prevention/Elimination LPS, which includes:

  • Charge Transfer System (CTS),
  • Dissipation Array System (DAS).






Notes on different Types of Lightning Protection Systems LPS

Each system’s design requires the following:

  • The air terminal or strike termination device must be positioned so that it is the highest point on the structure.
  • The lightning protection system must be solidly and permanently grounded. Poor or high resistance connections to ground are the leading cause of lightning system failure for each one of these systems.
  • None of these systems claims to protect against 100% of the possibility of a lightning stroke arriving near protective area. A compromise must be made between protection and economics.








1- Conventional Lightning Protection System






Conventional Lightning Protection System

Properly designed conventional 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.


Conventional Lightning Protection System


Such systems are basically composed of three elements:

  1. Air terminals at appropriate points on the structure to intercept the lightning,
  2. Down conductors to carry the lightning current from the air terminals toward the ground, and
  3. Grounding electrodes to pass the lightning current into the earth.


The three system components must be electrically well connected.

Notes:

  • Many national and international standards like NFPA 780 describe conventional lightning protection systems and the efficacy of the conventional approach has been well demonstrated in practice.
  • The conventional lightning protection technique has proven its effectiveness as evidenced by the comparative statistics of lightning damage to protected and unprotected structures.


Other names for Conventional Lightning Protection System:

1- Passive Neutral Systems:

The Conventional Lightning Protection System is labeled as Passive Neutral Systems since the air terminal or strike termination devices themselves aren’t considered to be any more attractive or unattractive to the lightning stroke then the surrounding structure. They are positioned where they should be the first conductor in any path that the lightning strike takes to the structure.

2- Traditional Lightning protection systems:

The Conventional Lightning Protection System is labeled as Traditional Lightning protection systems since these systems are the used ones in industry over 200 years ago.








Types of Conventional Lightning Protection System

The Conventional Lightning Protection System includes (2) different types as follows:

  1. Franklin Rod LPS,
  2. Franklin/Faraday Cage LPS.








1- Franklin Rod LPS

Other names for this type of Conventional Lightning Protection System are:

  1. Sharp pointed rods,
  2. Single mast system,
  3. Franklin Cone / protective Angle cone.



Franklin Rod LPS

  • A pointed lightning rod or air terminal or a single mast will help prevent lightning from striking in the immediate vicinity because it will help reduce the difference in potential between earth and cloud by "bleeding off" charge and therefore reducing the chance of a direct strike.
  • This lightning rod or air terminal or a single mast will provide a cone shaped zone of protection with angle of 45 degree forming a circular base on the ground around a building or part of a building.
  • Many decades of experience shows that by combining Franklin rods located at critical points on a structure with a proper down conductor and grounding system the damage due to lightning could be reduced significantly.


 Note:

This system is generally limited to buildings less than 20 m high.








2- Franklin/Faraday Cage LPS

A faraday cage is an enclosure fixed to the outside of the building made of conductors laid out on a grid pattern to produce an external mish. If the building is steel formed, the job can be made considerably easier as the steel frame itself can be used as part of the cage, but air termination devices are needed if the upper external surface of the roof is not metal and continuous with the steel frame.



Franklin/Faraday Cage Principle


Advantages of The faraday cage LPS:

  1. The faraday cage, if designed correctly, will form an electromagnetic shield. This means that there will be no electric fields inside the cage resulting from currents flowing to earth on the surface of the cage.
  2. Each one of numerous down conductors will be earthed to ground.
  3. The air termination network can easily be made suitably extensive.
  4. This is the type of protection which is likely to be the most reliable in terms of lightning protection.






In the next Article, I will explain the Conventional Lightning Protection System LPS Components. Please, keep following.




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