Basic of External Lightning Protection System (LPS)-(Part-4)

Material Combinations and Dimensions

• Required to use galvanically compatible metals in lightning protection system components and surface materials on which the components are mounted. For example, do not connect copper to aluminum.
• Do not use together metals that are not galvanically compatible. Bad matching accelerates their corrosion in the presence of moisture.
• With aluminum conductors, use only connection devices designed for aluminum. Make sure to use the right fastening torque.

Different Contact Material
Material	Suitable Contact Material
Copper	Nickel /Brass / Tin / Lead / Stainless steel / Monel (nickel–copper alloy)
Aluminum	Magnesium / Zinc / Galvanized steel / Stainless steel / Lead / Wrought iron / Galvalume (an aluminum-coated sheet steel product)

LPS Material

LPS Materials and Conditions of Use
Table-5 (IEC 62305-3)
Material	Use				Corrosion
	In Open Air	In Earth	In Concrete	Resistance		Increased by	May be destroyed by Galvanic Coupling with
Copper	Solid	Solid	Solid	Good in many environments		Sulphur compounds	–
	Stranded	Stranded	Stranded	–		Organic materials	–
	–	As coating	As coating	–		–	–
Hot galvanized steel123	Solid	Solid	Solid	Acceptable in air, in concrete, and in benign soil		High chlorides content	Copper
	Stranded 4	–	Stranded 4	–		–	–
Steel with electro-deposited copper	Solid	Solid	Solid	Good in many environments		Sulphur compounds	–
Stainless steel	Solid	Solid	Solid	Good in many environments		High chlorides content
	Stranded	Stranded	Stranded	–		–	–
Aluminum	Solid	Unsuitable	Unsuitable	Good in atmospheres containing low concentration of Sulphur and chloride		Alkaline solutions	Copper
	Stranded	–	–	–		–	–
Lead 5	Solid	Solid	Unsuitable	Good in atmospheres with high concentration of sulphates		Acid soils	Copper
	As coating	As coating	–	–		–	Stainless steel

Material Dimensions

• Several lightning protection system codes and standards define minimum dimensions for the components of a grounding system. These standards are designed to protect buildings and other inhabited or otherwise critical facilities.
• Practical minimums are based on field experience and indicate what is needed to protect the installed equipment in a cost-effective way during the foreseeable technical lifetime, typically a few decades, taking into account local regulations. To ensure proper operation of the grounding system, periodic inspection and maintenance is needed

Minimum Dimensions of Earth Electrode as per IEC 623053 

• Table 1 and Table 2 are based on standard IEC 62305-3 Ed 2. The tables list minimum dimensions for the lightning protection system equipment.
• The following table lists the different materials and shapes that are used in air terminals, down conductors, and ground electrodes, including the cross-sectional area.

Minimum Dimensions of Earth Electrodes
Table-7, IEC-62305-3
Material	Configuration	Dimensions
		Earth Rod Diameter	Earth Conductor	Earth Plate
Copper, Tin-plated copper	Stranded	–	50 Sq.mm (8 mm)	–
	Solid round	15 mm	50 Sq.mm (8 mm)	–
	Solid tape	–	50 Sq.mm (8 mm)	–
	Pipe	20 mm	–	–
	Solid plate	–	–	500 × 500 mm
	Lattice plate	–	–	600 × 600 mm
Hot-dipped galvanized steel	Solid round	14 mm	78 Sq.mm (9.96 mm)	–
	Pipe	25 mm	–	–
	Solid tape	–	90 Sq.mm (10.7 mm)	–
	Solid plate	–	–	500 × 500 mm
	Lattice plate	–	–	600 × 600 mm
	Profile	*	–	–
Bare steel (Shall be embedded in  concrete  for a minimum depth of 50 mm.)	Stranded	–	70 Sq.mm (9.4 mm)	–
	Solid round	–	78 Sq.mm (9.96 mm)	–
	Solid tape		75 Sq.mm (9.72 mm)
Copper coated steel	Solid round	14 mm	50 Sq.mm (8 mm)
	Solid tape		90 Sq.mm (10.7 mm)
Stainless steel	Solid round	15 mm	78 Sq.mm (9.96 mm)
	Solid tape		100 Sq.mm (11.28 mm)
Mechanical and electrical characteristics as well as corrosion resistance properties shall meet the requirements of the future IEC 62561 series.
In case of a type B arrangement foundation earthing system, the earth electrode shall be correctly connected at least every 5 m with the reinforcement steel.
* Different profiles are permitted with a cross-section of 290 mm2 and a minimum thickness of 3 mm, e.g. cross profile.

Minimum Cross-sectional Area of Air-termination Conductors

Minimum Cross-sectional Area of Air-termination Conductors
Table 6 (IEC 62305-3)
Material	Configuration	Cross-sectional Area	Comments
Copper, tin-plated copper	Solid tape	50 Sq.mm / 8mm *	2 mm min. thickness
	Solid round1	50 Sq.mm / 8mm *	8 mm diameter
	Stranded 1	50 Sq.mm / 8mm *	1.7 mm min. dia of each strand
	Solid round***	176 Sq.mm /15mm	16 mm diameter
Aluminum	Solid tape	70  Sq.mm*	3 mm min. thickness
	Solid round	50 Sq.mm / 8mm *	8 mm diameter
	Stranded	50 Sq.mm / 8mm *	1.7 mm min. dia of each strand
Aluminum alloy	Solid tape	50 Sq.mm / 8mm *	2.5 mm min. thickness
	Solid round	50 Sq.mm / 8mm *	8 mm diameter
	Stranded	50 Sq.mm / 8mm *	1.7 mm min. dia of each strand
	Solid round***	176 Sq.mm /15mm	16 mm diameter
Copper-coated aluminum alloy	Solid round	50 Sq.mm / 8mm *
Hot-dipped galvanized steel **	Solid tape	50 Sq.mm / 8mm *	2.5 mm min. thickness
	Solid round	50 Sq.mm / 8mm *	8 mm diameter
	Stranded	50 Sq.mm / 8mm *	1.7 mm min. dia of each strand
	Solid round***	176 Sq.mm /15mm	16 mm diameter
Copper-coated steel	Solid round	50 Sq.mm / 8mm *
	Solid tape	50 Sq.mm / 8mm *
Stainless steel	Solid tape	50 Sq.mm / 8mm *	2 mm min. thickness
	Solid round***	50 Sq.mm / 8mm *	8 mm diameter
	Stranded	70 Sq.mm / 9.5mm*	1.7 mm min. dia of each strand
	Solid round ***	176 Sq.mm /15mm*	16 mm diameter
* If thermal and mechanical considerations are important, these dimensions can be increased to 60 mm2 for solid tape and to 78 mm2 for solid round.
** The coating should be smooth, continuous and free from flux stains with a minimum thickness coating of 50 μm.
***Applicable for air-termination rods only. For applications where mechanical stress such as wind loading is not critical, a 10 mm diameter, 1 m long maximum air-termination rod with an additional fixing may be used.

Minimum values of the cross-section of the bonding conductors with different bonding bars

Minimum dimensions of conductors connecting internal metal installations to the bonding bar
Table-8 (IEC-62305-3)
Class of LPS	Material	Cross-section (mm2)
I to IV	Copper	16 Sq.mm
	Aluminum	25 Sq.mm
	Steel	50 Sq.mm

 

Minimum dimensions of conductors connecting internal metal installations to the bonding bar
Table-9 (IEC-62305-3)
Class of LPS	Material	Cross-section (mm2)
I to IV	Copper	6 Sq.mm
	Aluminum	10 Sq.mm
	Steel	16 Sq.mm

 

Table 10: Minimum thickness of metal sheets or metal pipes in air termination systems
(IEC/BS EN 62305-3 Table 3)
Class of LPS	Material	Thickness (1) t	Thickness (2) t’
I to IV	Lead	–	2 MM
	Steel (stainless, galvanized)	4 MM	0.5 MM
	Titanium	4 MM	0.5 MM
	Copper 5 mm 0.5 mm	5 MM	0.5 MM
	Aluminum 7 mm 0.65 mm	7 MM	0.65 MM
	Zinc – 0.7 mm	–	0.70 MM
Thickness t prevents puncture, hot spot or ignition
Thickness t’ only for metal sheets if it is not important to prevent puncture, hot spot or ignition problems

Minimum Dimensions

Air Terminal Minimum Dimensions
Material	Dimension
Copper, aluminum	Tube with a 16 mm diameter, minimum wall thickness of 2 mm
	8 mm (0.31 in) solid round
Steel	10 mm

 

Down Conductor Minimum Dimensions
Material	Dimension
Copper	25 mm2 solid or stranded wire or solid tape
Aluminum	35 mm2 in solid or stranded aluminum
Steel	35 mm2  solid steel or stranded wires

 

Minimum Thickness of Tapes
Material	Thickness
Copper	1 mm
Aluminum	2 mm
Galvanized steel	2 mm
Stainless steel	2 mm

 

Minimum Thickness of Strand Diameters in Stranded Cables
Material	Thickness
Copper	1 mm
Aluminum	1.6 mm
Steel	1.6 mm

 

Ground Rod Minimum Dimensions
Material	Thickness
Copper	Solid round 15 mm
	Pipe 20 mm diameter with a minimum wall thickness of 2 mm
Copper clad solid steel	14 mm
Galvanized steel	16 mm
Galvanized steel, pipe	25 mm diameter with a minimum wall thickness of 2 mm

 

Horizontal Ground Electrode Minimum Dimensions
Material	Thickness
Copper	25 mm2 solid/strand/tape with a minimum 2 mm thickness
Galvanized steel, round wire	50 mm2 with a minimum 8 mm diameter
Galvanized steel, stranded	50 mm2 with a minimum strand diameter of 1.7 mm
Galvanized steel, tape	50 mm2 with a minimum thickness of 2 mm

 

Installation Depth of Ground Electrode
Ground Electrode Type	Installation Depth
Ground rod	3 meter
Horizontal ground electrode	0.6 meter

 

Typical Ground Electrode Length and Spacing
Minimum values	Ground rod	Horizontal ground electrode
Length	Typically, 3 Meter	10 Meter to 30 Meter as per soil type dependent
Loop diameter	–	5 Meter to 6 Meter
Spacing	Min. 2 × rod length	–

Guideline for LPS System:

• The following design guidelines need to be adhered to ensure safer installation of the external LPS.
• Air Terminal:
• Air terminal should be selected and provided only based on the protection angle or rolling sphere method
• Proper safety distance between the air terminal and any metallic object needs to be maintained as per the calculation mentioned earlier to avoid dangerous spark-overs.
• Different Material Jointing & Insulations:
• Wherever incompatible materials to be joined (Ex. Copper with Aluminum), suitable bi-metal connectors should be used.
• Suitable expansion joints must be provided on the horizontal conductors on top to take care of thermal effects.
• Special conductor holders of insulating type need to be provided on top of the terrace floor for routing the conductor to ensure electrocution impact does not happen in case of water stagnation.
• Equip potential Bonding:
• Required measures to ensure shielding, bonding / equipotential bonding techniques are handled properly to avoid LEMPs.
• Establishing connection for equipotential bonding with nearby metallic components need to be taken care of.
• Joints should be mechanically and electrically effective, should be protected against corrosion or erosion from the elements or the environment and should present an adequate contact area.
• Reinforcement Structure:
• In the case of using reinforcement in concrete structures as lightning down conductor details should be decided at the design stage, before building construction begins.
• Good contact between reinforcing bars to be ensured only by using connection clamps tested as per the requirement of IEC 62561-1
• Down Conductor:
• A down-conductor should be installed at each exposed corner of the structure where it is possible.
• The Down conductor should run as straight and vertical as possible so that they provide the shortest and most direct path of a low impedance from the air termination to the earth electrode so that the lightning current can be safely conducted to earth.
• The formation of loops in bring the down conductor shall be avoided, but where this is not possible the distance shall be maintained
• There should be a test joint arrangement to have separation between down conductor and earth termination for safety and for measurement of earth resistance.
• At least two down conductors are mandatory for any size of Building.
• The termination of the down conductor to an earth electrode should be done minimum of 1 meter away from the structure and minimum of 0.5m depth inside the ground.
• Earth electrodes for each down conductor shall be provided.
• Connection of down conductors to gutters or down-spouts even if they are covered by insulating materials.
• Usage of multiple connections with different materials should not be permitted.
• Insufficient conductor dimensions (non-complying material as mentioned in IEC 62305-3 Table – 5) should be strictly avoided.
• When the distance from down conductors to combustible materials cannot be assured, the cross section of the down conductor shall not be less than 100 mm²

Basic of External Lightning Protection System (LPS)-(Part-3)

COMPARISION OF VARIOUS PROTECTION METHOD

COMPARISION OF VARIOUS PROTECTION METHOD
Protection Method	Type of Structure
	Simple structure	Complex shaped structure	Plane Structure
Protection Angle	(*) YES	NO	NO
Mesh Method	NO	YES	YES
Rolling sphere Method	YES	YES	YES
(*) This method is not suitable for structure height more than radius of the rolling sphere relevant to the selected protection level of LPS

(2) Down Conductor system:

• In Air-termination systems, down-conductor systems and earth-termination systems should be harmonized to produce the shortest possible path for the lightning current.
• Down-conductors should preferably be connected to junctions of the air-termination system network and routed vertically to the junctions of the earth-termination system network.
• The function of a down conductor system is to conduct the lightning impulse from air-termination system to the earthing system. The down conductor system should be installed in such a way that the following points are ensured.
• (i) Several parallel current paths exist
• (ii) Length of current path is kept to minimum.
• (iii) Equipotential bonding to conducting parts is performed.
• Selection and installation of down conductors plays a major role in protecting electrical and electronic installations in a building. The number of down conductors to a typical building depends upon the class of LPS.
• A down conductor should be installed at each exposed corner of the structure and form a direct continuation of the air-termination conductors. Drown conductors are installed in such a way that they provide the shortest and most direct route to earth. Avoiding the formation of bends and loops is required.
• To reduce damage caused by lightning current, the down conductors are arranged so that the current path around the building’s perimeter is parallel and at equal distances.
• Even if the down conductor encased in insulating material, down conductors must not be installed in service shafts, gutters, or downspouts, as doing so invites severe damage during a lightning strike.
• Electrical insulation between LPS components and other metallic installation in the building are necessary to avoid flashover between different metal parts.
• Integration of down conductor with Building Natural Components:
• External down-conductors should be installed between the air-termination system and the earth-termination system. Wherever natural components (Steel reinforcement, metal framework structure) are available, they can be used as down-conductors.
• Down conductors are also integrated into structural steel reinforcement, metal framework of structure, steel roof, metal façade, handrails etc. is the best and practical solution for new and upcoming high raise buildings. In this integrated approach high safety is offered with no maintenance, long life, no influence on aesthetics. Separation distance need not be considered in this case.
• Down conductors can be embedded in RCC columns. In this case, bonding different metallic installations in the building is simple, thereby eliminating potential differences. This integrated method is not only cost-effective but has no negative effect on the building’s aesthetics. It also reduces the failure of electronic equipment inside the building from radiated lightning effects.
• Test joints are not required, and earth resistance measurements are not necessary in the location where the natural down conductors are terminated to foundation earthing.

• Number & distance between each Down Conductor:
• For each non-isolated LPS, the number of down conductors shall be not less than two and should be distributed around the perimeter of the structure to be protected. An equal spacing of the down conductors is preferred around the perimeter. The typical values of the distance between the conductors are shown below.

DISTANCE BETWEEN DOWN CONDUCTORS
(IEC/BS EN 62305-3 Table 4)
Class of LPS	Distance between conductors
CLASS I- (Very High Risk)	10 Meter
CLASS II- (High Risk)	10 Meter
CLASS III- (Moderate Risk)	15 Meter
CLASS IV- (Low Risk)	20 Meter

• If the distance between down-conductors is too large with the reference to the Table, the number of down-conductors should be increased to meet the required separation distance.
• As stated, a down-conductor should be installed at each exposed corner of the structure, where this is possible. However, an exposed each corner does not need a down conductor if the distance between this exposed corner to the nearest down-conductors complies with the following conditions:
• (i)the distance to both adjacent down-conductors is half the distance according to Tables or smaller.
• (ii) the distance to one adjacent down-conductor is one-quarter of the distance according to Tables or smaller.

• The number and position of down-conductors is important because if the lightning current is shared in several down-conductors, the risk of side flash and electromagnetic disturbances inside the structure is reduced. It follows that, as far as possible, the down-conductors should be uniformly placed along the perimeter of the structure and with a symmetrical configuration.
• The current sharing is improved not only by increasing the number of down-conductors but also by equipotential interconnecting rings.
• Down-conductors should be placed as far as possible away from internal circuits and metallic parts in order to avoid the need for equipotential bonding with the LPS., In cantilevered structures the separation distance should also be evaluated with reference to the risk of side-flashing to persons.
• If it is not possible to place down-conductors at a side, or part of a side, of the building because of practical or architectural constraints, the down-conductors that ought to be on that side should be placed as extra compensating down-conductors at the other sides. The distances between these down-conductors should not be less than one-third of the distances in Table.
• A variation in spacing of the down-conductors of ±20 % is acceptable as long as the mean spacing conforms to Table.
• In closed courtyards with more than 30-meter perimeter, down-conductors have to be installed.
• Insulation / Separation of LPS parts
• If it is not possible to make a straight connection because of large roof overhangs, etc. the connection of the air-termination system and the down-conductor should be a dedicated one and not through natural components like rain gutters, etc.
• It is permitted, where aesthetic consideration needs to be taken into account, to use a thin coating of protective paint or PVC covering over the external down-conductors.
• Down conductors, even if covered in insulating material, shall not be installed in gutters or waterspouts. The effects of moisture in the gutters lead to intensive corrosion of the down conductor.

Minimum Size of Down conductor
Protection level	Material	Section
I-IV	Steel	50 mm2
I-IV	Aluminum	25 mm2
I-IV	Copper	16 mm2

• For non-isolated LPS, down conductors are mounted directly onto the building (without separation distance) if the wall is made of flame resistant or normally inflammable material, the down conductors may be installed directly on or in the wall.
• Metal framework of a steel structure or the interconnected reinforcing steel of the structure can be used as a down conductor. Reinforcement of existing structure cannot be used as natural down conductor unless the reinforcement is safely interconnected. Separate external down conductors must be installed.
• Conductors on roofs and the connections of air-termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material.
• Recommended fixing centers for these conductors are shown in the Table.

Suggested fixing centers
Table E.1 IEC- 62305-3
Arrangement	Fixing centers for tape and stranded conductors (mm)	Fixing centers for round solid conductors (mm)
Horizontal conductors on horizontal surfaces	500 mm	1000 mm
Horizontal conductors on vertical surfaces	500 mm	1000 mm
Vertical conductors from the ground to 20 m	1000 mm	1000 mm
Vertical conductors from 20 m and thereafter	500 mm	1000 mm
NOTE: Assessment of environmental conditions (i.e. expected wind load) should be undertaken and fixing centers different from those recommended may be found to be necessary.

(3) Earth Termination:

• The purpose of the earth termination system is to provide a safe low-impedance path to high frequency lightning current into the ground.
• To minimize dangerous over voltage due to lightning, The shape and the dimension of the earth termination system are important.
• The earth termination system should be designed to have a resistance to earth of less than 10 ohms, as per the IEC/BS EN 62305 standards.
• There are two basic types of earth electrode arrangements are recommended in IS/IEC 62305 and NBC-2016 such as vertical /horizontal
• Type A arrangement: Horizontal earth electrodes or vertical earth electrodes installed outside the structure and connected to down conductors.
• Type B arrangement: Ring earth electrodes installed around the perimeter of the structure.
• POINTS NEED TO BE CONSIDER:
• Step Voltage: If earthing termination network is used in public access area, then the selection of suitable types of earth electrodes and safe distances from structure and from the external conductive parts in the soil (cables, metal ducts, etc.) are important. Hence special steps need to be taken for the protection against dangerous step voltages in the vicinity of the earth-termination networks.
• Earth resistance value: The recommended value of the overall earth resistance of 10 Ω is fairly conservative in the case of structures in which direct equipotential bonding is applied. The resistance value should be as low as possible in every case but especially in the case of structures endangered by explosive material. Still the most important measure is equipotential bonding.
• Depth of Electrode: The embedded depth and the type of earth electrodes should be such as to minimize the effects of corrosion, soil drying and freezing and thereby stabilize the equivalent earth resistance.
• It is recommended that the first half meter of a vertical earth electrode should not be regarded as being effective under frost conditions. Deep-driven earth electrodes can be effective in special cases where soil resistivity decreases with depth and where substrata of low resistivity occur at depths greater than those to which rod electrodes are normally driven.
• Mechanical Splitting / Stressing: When the metallic reinforcement of concrete is used as an earth electrode, special care should be exercised at the interconnections to prevent mechanical splitting of the concrete.
• If the metal reinforcement is also used for the protective earth, the most severe measure in respect of thickness of the rods and the connection should be chosen. In this case, larger sizes of reinforcement bars could be considered. The need for short and straight connections for the lightning protection earthing should be always recognized.
• In the case of pre-stressed concrete, consideration should be given to the consequences of the passage of lightning discharge currents, which may produce unacceptable mechanical stresses.

(A) Type-A Earthing (Embedded Earth Electrode)

• This is the conventional type of LPS Earthing System where earthing rodsare used to form the earth electrode and connected each down conductor to an earth rod. The earth electrodes installed outside the structure.
• The type A earth-termination system is suitable for low structures (family houses ,Low rise building).
• This type of arrangement comprises horizontal or vertical earth electrodes connected to each down-conductor.
• Where there is a ring conductor, which interconnects the down-conductors, in contact with the soil, the earth electrode arrangement is still classified as type A, if the ring conductor is in contact with the soil for less than 80 % of its length.
• The total number of earth electrodes in Type A arrangement shall not be less than two.
• Type-A earthing suitable for:
• The type A earth termination arrangement is suitable for low structures (Houses), (below 20 meters in height)
• existing structures or an LPS with rods or stretched wires or for an isolated LPS.
• It is suitable for locations with low fault currents and provides safety and functional grounding.
• commonly used in residential and commercial settings.
• Type A earthing system depends upon the soil resistivity and class of LPS.
• Each down conductor shall have a vertical earth electrode with a minimum length as per the table. In case of horizontal electrode, the length shall be double.
• The earth electrodes shall be installed at a depth of upper end at least 0.5 m in soil if an earth chamber is not used.
• In general, a low earthing resistance (if possible lower than 10 Ω when measured at low frequency) is recommended for type A earthing if the specific length cannot be ensured.
• The minimum length of each earth electrode at the base of each down-conductor is specified in BS EN 62305 and the table below.

Horizontal & Vertical electrode Length for Type A & Type-B earth electrode (based on soil resistivity)
IEC- 62305-3
Class of LPS	<500 Ωm			<1000 Ωm		<2000 Ωm		<3000 Ωm
	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)		Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1	Horizontal electrodes (l1)	Vertical electrodes 0.5 x I1
I	5 Meter	2.5 Meter	20 Meter		10 Meter	50 Meter	25 Meter	80 Meter	40 Meter
II	5 Meter	2.5 Meter	10 Meter		5 Meter	30 Meter	15 Meter	45 Meter	22 Meter
III	5 Meter	2.5 Meter	5 Meter		2.5 Meter	5 Meter	2.5 Meter	5 Meter	2.5 Meter
IV	5 Meter	2.5 Meter	5 Meter		2.5 Meter	5 Meter	2.5 Meter	5 Meter	2.5 Meter

• The minimum length of each earth electrode at the base of each down-conductor is l1 for horizontal electrodes, or 0.5 x l1 for vertical (or inclined) electrodes,
• where l1 is the minimum length of horizontal electrodes. For combined (vertical or horizontal) electrodes, the total length shall be considered.
• Reduction of earthing resistance by the extension of earth electrodes is practically convenient up to
• 60 m. In soil with resistivity higher than 3000 Ωm, the use of type B earth electrodes or earthing enhancing compounds is recommended.

• Radial and vertical earth electrodes
• Each down-conductor should be provided with an earth electrode.
• Radial earth electrodes should be connected to the lower ends of the down-conductors by using test joints.
• During installation it is necessary to measure the earthing resistance regularly. Additional electrodes can then be installed in more suitable locations.
• The earth electrode should have sufficient separation from existing cables and metal pipes in the earth. The separation distance depends on the electrical impulse strength and resistivity of the soil and the current in the electrode.
• In the type A arrangement, vertical earth electrodes are more cost-effective and give more stable earthing resistances in most soils than horizontal electrodes.
• In some cases, it may be necessary to install the earth electrodes inside the structure, for example in a basement or cellar.
• Advantages:
• If there is a danger of an increase in resistance near to the surface, it is often necessary to employ deep-driven earth electrodes of greater length. Radial earth electrodes should be installed at a depth of 0,5 m or deeper. A deeper electrode ensures that in countries in which low temperatures occur during the winter, the earth electrode is not situated in frozen soil (which exhibits extremely low conductivity).
• An additional benefit is that deeper earth electrodes give a reduction of the potential differences at the earth surface and thus lower step voltages reducing the danger to living creatures on the earth surface. Vertical electrodes are preferred to achieve a seasonally stable earthing resistance.
• Limitation:
• When the type A earthing arrangement is provided, it is necessary to all electrodes are at equal equalization. This can be achieved by bonding all conductors by bonding bars. Special care also needs to be cared to control step voltage.

(B) Type-B Earthing (Foundation /Ring Earthing)

• Type B Earthing consists of either a Ring conductor external to the structure to be protected (in contact with the soil for at least 80% of its total length) or a Foundation earth electrode forming closed loop.
• Type-B Earthing is also done by combination of both Ring earthing and Foundation earthing.
• Foundation earthing is done using conductors embedded in foundation of the building.
• Foundation earthing also serves as protective and functional earthing. This is the most efficient earthing system to protect electronic equipment. Materials used and construction techniques availed must fulfil various mechanical, electrical and chemical requirements to provide long life for the installation.
• Connection of a Lightning Protection System to the steel in the concrete foundation can be done for all new constructions since this steel is usually good for equipotential bonding. A dedicated Earth Rod can also be installed in the foundation but then these Earth Electrodes would need to be bonded to the steel in the concrete.
• Earth-termination systems should serve the following three purposes.

1. conduction of the lightning current into the earth.
2. equipotential bonding between the down-conductors.
3. potential control in the vicinity of conductive building walls.

• The foundation earth electrodes and the type B ring-type earth electrodes meet all these requirements.
• Type A radial earth electrodes or deep-driven vertical earth electrodes do not meet these requirements with respect to equipotential bonding and potential control.
• The structure foundations of interconnected steel-reinforced concrete should be used as foundation earth electrodes. They exhibit very low earthing resistance and perform an excellent equipotentialization reference. When this is not possible, an earth-termination system, preferably a type B ring earth electrode, should be installed around the structure.
• Type-B Earthing Suitable for:
• Structures built on rocky ground
• Structures housing sensitive electronics/equipment
• Large structures
• It is used in areas with high fault currents, such as critical infrastructure and industrial facilities, to provide enhanced protection against surges and transients, often resulting from lightning or equipment malfunctions.
• The type B earth-termination system is preferred for meshed air-termination systems and for LPS with several down-conductors.
• Type B is recommended for buildings with electrical and electronic installations and buildings in high soil resistivity.
• Type B earth electrodes also perform the function of potential equalization between the down conductors at ground level, since the various down-conductors give different potentials due to the unequal distribution of lightning currents due to variations in the earth resistance and different lengths in the above ground conductor current paths. The different potentials result in a flow of equalizing currents through the ring earth electrode, so that the maximum rise in potential is reduced and the equipotential bonding systems connected to it within the structure are brought to approximately the same potential.
• In some Area it is not possible to install a ring earth electrode that will fully surround the structure Where structures belonging to different owners are built closely to each other or common for both. In this case the efficiency of the earth-termination system is somewhat reduced, since the conductor ring acts partly as a type B electrode, partly as foundation earth and partly as an equipotential bonding conductor.
• Where large numbers of people frequently assemble in an area adjacent to the structure to be protected, further potential control for such areas should be provided. More ring earth electrodes should be installed at distances of approximately 3 m from the first and subsequent ring conductors. Ring electrodes further from the structure should be installed more deeply below the surface i.e. those at 4 m from the structure at a depth of 1 m, those at 7 m from the structure at a depth of 1,5 m and those at 10 m from the structure at a depth of 2 m. These ring earth electrodes should be connected to the first ring conductor by means of radial conductors.
• POINTS NEED TO BE CONSIDER:
• If it is not possible to close the ring, a connection must be made inside the buildingusing conductive metallic equipment such as pipes.
• Ring shall be at least 0.5meter below the surface
• Ring shall be maintained at least 1 meter from the structure / from the external walls.
• It is recommended that 80% of the length of the ring shall be in contact with natural soil. Thus, no more than 20% of the total length may be in the basement of the structure instead of in direct contact with the soil.
• If the radius of the ring electrode is less than the length of vertical or horizontal earth electrodes required for Earthing, then additional horizontal or vertical earth electrodes can be connected to the ring.
• Bonding of different metallic installations in the building avoid dangerous potential differences and flashover
• Ring earth electrode Radius length: For the ring earth electrode (or foundation earth electrode), the mean radius (re) of the area enclosed by the ring earth electrode (or foundation earth electrode) shall be not less than the horizontal electrodes value (l1)
• re ≥ l1
• When the required value of l1 is larger than the convenient value of re, additional horizontal or vertical (or inclined) electrodes shall be added with individual lengths lr (horizontal) and lv (vertical) given by the following equations:
• lr = l1 – re (2) and lv = (l1 – re) / 2
• It is recommended that the number of electrodes should be not less than the number of down-conductors, with a minimum of two.
• The additional electrodes should be connected to the ring earth electrode at points where the down-conductors are connected and, for as many as possible, equidistantly.
• EARTH TERMINATION SYSTEM IN LARGE AREAS:
• An industrial plant typically comprises a number of associated structures, between which a large number of power and signal cables are installed. The earth-termination systems of such structures are very important for the protection of the electrical system. A low impedance earth system reduces the potential difference between the structures and so reduces the interference injected into the electrical links.
• A low earth impedance can be achieved by providing the structure with foundation earth electrodes and additional type B and type A earth arrangements.
• Interconnections between the earth electrodes, the foundation earth electrodes and the down conductors should be installed at the test joints. Some of the test joints should also be connected to the equipotential bars of the internal LPS.
• Internal down-conductors, or internal structural parts used as down–conductors, should be connected to an earth electrode and the reinforcement steel of the floor to avoid step and touch voltages. If internal down-conductors are near expansion joints in the concrete, these joints should be bridged as near to the internal down-conductor as possible.
• The lower part of an exposed down-conductor should be insulated by PVC tubing with a thickness of at least 3 mm or with equivalent insulation.
• When the area adjacent to the structure is covered with a 50 mm thick slab of asphalt of low conductivity, sufficient protection is provided for people making use of the area.

• Foundation Earth Electrodes are simply concrete reinforced foundations – they are considered to be Type B Earthing. For these Foundation Earth Electrodes, there should be at 50mm of concrete covering the electrode to minimize corrosion.
• The type B earthing is recommended as either a ring conductor outside the perimeter of the structure which it’s recommended should be in contact with the soil for at least 80% of its total length.
• The alternative is to use a foundation earth electrode which can be in a mesh form.
• The reinforced concrete floor slab can be used around the structure.
• If the required resistance cannot be achieved by this method the vertical or radial earthing electrodes can be added to the network.
• For ease of testing after installation an inspection pit with an earth bar should be installed where the legs of the ring and conductor routing onto the ring from each test clamps join
• FOUNDATION EARTHING / NATURAL CONDUCTORS AS PART OF THE LPS
• The building’s natural components, metal roof, rebar, steelwork etc. can be considered as part of the LPS
• The reinforcing bars within the concrete structure can be used as a natural component of the LPS provided they are electrically continuous by either welding or clamping the joints.
• The re-bars are considered as electrically continuous provided that a major part of interconnections of vertical and horizontal bars are welded or otherwise securely connected by clamps conforming to BS EN 50164 standards.
• Forming:
• Foundation grounding is one of the most healthy grounding methods. Foundation grounding of buildings must be started at the beginning of construction, i.e. foundation stage. It is performed by installing a galvanized conductor between the reinforcing bars in the foundation. This conductor is connected to reinforcing bars at certain distances. The ends of the grounding conductor are taken out from some specified points and left as the connection bud. Once these ends are connected to the equipotential grounding bus bars, the grounding is completed by connecting all systems to be grounded to these buses.
• Foundation grounding must be performed in the form of a closed ring and placed in the foundation of the external walls of the building, or the foundation platform. In buildings with a large perimeter, foundation grounding rods must be divided into sections of 20x20m. Connection must be established with reinforcing bars every few meters.
• Foundation earthing can be accomplished in various ways, such as by using cable or flat conductor, connected to earth rods or by surrounding the foundation with conductor that enters the foundation through an earth terminal. Grounding standards, such as IEEE 80 Standard, provide guidelines for the design and installation of earthing systems, including those for foundations.
• For the foundation earthing’s connection with a lightning rod, a conductor is placed inside the pillars before the concrete placement, ending on the building’s rooftop.
• Circumferentially on the rooftop, an aluminum or copper conductor is placed on braces, in spots that include chimneys, solar water heaters, etc. Then spikes are placed, and the construction of the lightning rod is complete

• The connecting rebar must overlap and be clamped using rebar clamps or welded to a minimum of 20 times the diameter of the rebar a (Welding to be done on either side of the rebars.)
• The concrete used for the foundations of buildings has a certain conductivity (relative comparison) and, in general, “a large contact area” with the ground. It is highly recommended to use bare metal electrodes completely embedded in concrete (to a minimum depth of 5 cm) for grounding purposes, as they are highly protected against corrosion, usually for the entire life of the building according to IEC 60364
• It is recommended to use a foundation earth electrode embedded in concrete during the construction of the building (itself) to obtain a lower earth resistance value.
• Materials for Earth-Termination Systems
• The foundation earth electrode has to be made of
• Round steel (min. diameter 10 mm) or
• Strip steel (min. dimension 30 mm x 3.5 mm) which has to be galvanized (or black) for laying in concrete, or for laying in soil.
• Advantages:
• Does not require additional excavation work.
• Provides good contact with the ground.
• It extends over virtually the entire surface of the building foundation and results in minimum ground electrode impedance that can best be achieved with this surface.
• It also provides an optimal grounding arrangement for the lightning protection system.
• It is erected at a depth that is normally free from negative influences resulting from seasonal weather conditions.
• Step voltage elimination
• Equipotential connections
• Corrosion resistant

Basic of External Lightning Protection System (LPS)-(Part-2)

(B) ROLLING SPHERE METHOD: (Suitable for complex shape building)

•  The rolling sphere method should be used to protect the areas of a structure when there is design limitation to use the protection angle method.
• The rolling sphere method is recommended as the main method to be used in the design of lightning protection system with location of air terminals for structures with complex shapes.
• This method is more accurate, and complex compared to other lightning protection schemes, because it specifies the exact number of spikes needed for each building and considers the worst-case scenarios, in which a lightning strike hits the side of the building.
• Position of Air Termination Rod:
• In this method, the positioning of the Air-Termination system is adequate so that no point of the structure to be protected comes in to contact with a sphere with radius ‘r’ depending on the class of LPS (see table) rolling around on top of the structure in all possible directions. In this way, the sphere only touches the air termination system (see figure).
• Radius of Sphere:
• The rolling sphere lightning protection method assumes the electrically charged field that produces a lightning strike has a radius “r” and the sphere with that radius rolling over the surface of the building. Any place the sphere touches the building is a location where lightning can strike the building.  By installing air terminals, the sphere cannot touch the building because electrical charges flow through the lightning protection system into the ground.
• The radius of the rolling sphere is correlated with the peak value of the current in the lightning that strikes the structure: r = 10xIx0.65 where I define as kA.
• In the rolling sphere method, the radius of the sphere is selected in such a way that its radius is equal to the striking distance. Since the striking distance is a function of the prospective return stroke current, the radius of the sphere “r” is defined as a function of the probable return stroke current according to the relationship between the lightning striking distance and the peak return stroke current.
• The lightning stroke depends on the degree of risk considered.  So, for a high-risk facility, the sphere radius is at its smallest, e.g. 20meter or a 40meter diameter ball. The smallest size ball means the amount of protection installed will be at its highest. Thus, lowering the risk profile and increasing the protection afforded.
• For a low-risk scenario method, the sphere radius is at its largest distance, 60 meters (120-meter diameter ball), which means a lot less hardware to install.
• The radius r of the rolling sphere depends on the class of LPS as per given Table.

RADIUS OF THE ROLLING SPHERE
Class of LPS	Rolling sphere radius, r (m)
CLASS I- (Very High Risk)	20 Meter
CLASS II- (High Risk)	30 Meter
CLASS III- (Moderate Risk)	45 Meter
CLASS IV- (Low Risk)	60 Meter

• Figure shows the application of the rolling sphere method to different types of structures. The sphere of radius r is rolled around and over all the structure until it meets the ground plane or any permanent structure or object in contact with the ground plane which can act as a conductor of lightning.
• A striking point could occur where the rolling sphere touches the structure and at such points protection by an air-termination conductor is required.
• Any part of the structure that is in contact with the sphere is considered to be vulnerable to a direct lightning strike; the untouched volume defines a lightning protected zone.

• When the rolling sphere method is applied to the structure, the structure should be considered from all directions to ensure that no part protrudes into an unprotected zone a point which might be overlooked if only front, side and plan views on drawings are considered.

PENETRATION DISTANCE:

• The distance between the two air terminals should be chosen in such a way that protection is provided for all the objects placed on the surface to be protected.
• The protection of the objects placed on the surface can be ensured by calculating the penetration distance of the rolling sphere.
• The distance between the level of air terminals and the least point of sphere in the space between the air terminals is called penetration distance.

• Let us consider an object of height ‘h’ placed on the surface to be protected. Let ‘ht’ be the height of the air terminal, ‘p’ be the penetration distance and ‘d’ be the distance between the two terminals.
• In this case, the penetration distance ‘p’ should be less than the physical height of the air-termination rods above the reference plane minus the height of the objects to be protected.
• P<(ht-h)

DISTANCE BETWEEN TWO AIR TERMINALS:

• The penetration distance of the rolling sphere below the level of conductors in the space between the conductors can be calculated by using the below formula (IS 62305-3).
• p=r-√(r^2-(d/2)^2 )
• Were,
• p : penetration distance
• r : radius of rolling sphere
• d: distance between the air terminals
• For attaining a particular penetration distance, we can derive the required distance between the air terminals from the above equation.
• d=2x√(2 x p x r-p^2 )
• If there are no objects protruding from the structure to be protected, then the penetration distance can be increased up to the height of the air terminal to provide maximum protection. At this condition, the distance can be calculated by substituting the value of height of air terminal (ht) in place of penetration distance (p).
• d=2x√(2 x ht x r-ht^2 )
• The distance between the air terminals(d) in rolling sphere method depends on two factors.
• Height of the air terminal and
• Radius of the rolling sphere
• Among these two factors, the radius of rolling sphere is a constant value which depends on the class of LPS as specified by IS/IEC 62305-3. Hence for particular class of LPS, the distance between the air terminals purely depends on the height of air terminal.

Distance between Air Terminals (Meter)
Height of Air Terminal (ht)	Radius of Rolling Sphere(r)
	LPS-I	LPS-II	LPS-III	LPS-IV
	r=20 Meter	r=30 Meter	r=45 Meter	r=60 Meter
0.5 Meter	8.8	10.9	13.37	15.45
1 Meter	12.48	15.36	18.86	21.81
1.5 Meter	15.2	18.7	23	26.66
2 Meter	17.43	21.5	26.53	30.72
3 Meter	21.07	26.15	32.31	34.36
4 Meter	24	29.9	37	43
6 Meter	28.56	36	44	52.3

• Example:
• Conclude the equipment installed on Terrace is whether protected by LPS System or not by LPS system installed on Building (Calculate penetration height) having following details.
• LPS Level is -IV (Low Risk).
• The maximum height of equipment is 1 meter from Terrace Floor.
• The distance between the two Air terminals is 10 meters.
• Height of Air Terminal is 2 Meter.
• Calculation:
• First, we calculate the maximum distance between two Air terminal according to LPS level.
• Here Height of Air terminal (ht)= 2Meter.
• Height of equipment (h)=1 Meter
• According to LPS-IV Radius of rolling sphere (r) = 60 meter
• Distance between two Air terminals (d) =2√(2*ht*r-ht^2 )
• Distance between two Air terminals (d) =2√(2x2x60-2^2 )
• Distance between two Air terminals (d) =30.72 Meter
• Distance between actual installed Air terminals is 10 meter which is less than maximum calculated distance between two Air terminals.
• Now to calculate penetration height.
• penetration height (p)=r-√(r^2-(d/2)^2 )
• penetration height (p)=60-√(60^2-(10/2)^2 )
• penetration height (p)=0.20 Meter.
• Now Height of Air terminal (ht)-Height of equipment(h) = 2-1 =1Meter.
• Check condition of P< (ht-h)
• Here 0.2 <1 meter
• Hence equipment installed on terrace which height is 1 meter is protected from installed LPS System.

SIDE FLASHES IN TALL STRUCTURE

• On all structures higher than the rolling sphere radius “r”, flashes to the side of structure may occur. Each lateral point of the structure touched by the rolling sphere is a possible point of strike. However, the probability for flashes to the sides is generally negligible for structures lower than 60 meters.
• For taller structures, a major part of all flashes will hit the top, horizontal leading edges and corners of the structure. Only a few percentages of all flashes will be to the side of the structure.
• The probability of flashes to the sides decreases rapidly as the height of the point of strike on tall structures when measured from the ground.
• Therefore, consideration should be given to install a lateral air-termination system on the upper part of tall structures (typically the top 20 % of the height of the structure). In this case the rolling sphere method will be applied only to the positioning of the air-termination system of the upper part of the structure.

(1) Buildings Taller Than 120-meter High

• For structures taller than 120 meters, the standard recommends that all parts above 120 meters be protected. It is expected that due to the height and nature of such a structure, it would require a design to LPL I or II (99% or 97% protection level).
• For tall buildings, the actual risk of flashes to the side are estimated by the industry to be less than 2%, and typically these would be the smaller lightning flashes, e.g., from branches of the downward leader. Therefore, this recommendation would only be appropriate for high-risk locations or structures.

(2) Buildings Above 60-meter High

• In the IEC standards, for buildings above 60-meter, protection is required to the sides of the upper 20% of height. The same placement rules used for roofs should apply to the sides of the building.
• While the mesh method is preferable, particularly if using natural components, protection is permitted using horizontal rods and rolling sphere method. However, horizontal rods on most structures are impractical due to window washing access equipment, etc.

(3) Buildings Less Than 60-meter High

• Note that for structures less than 60 meters high the risk of flashes to the sides of the building is low, and therefore protection is not required for the vertical sides directly below protected areas.

(4) Buildings Taller Than 30 meters:

• For buildings taller than 30 m, additional equipotential bonding of internal conductive parts should occur at a height of 20 m and every further 20 m of height. Live circuits should be bonded via SPDs.

(C) THE MESH METHOD (Suitable for all flat surface building)

• The mesh method is the simplest and most flexible method for LPS because it does not depend on the height of the structure. However, it requires flat but non curved surfaces. The Flat surface may be horizontal or vertical surfaces.
• It is mostly used for simple Building like domestic households, mainly for perfectly square or rectangular buildings.
• In the mesh method, a mesh is created by a flat conductor and placed on the structure. The separation distance of the conductors is based upon the class of protection determined during the risk assessment.
• Mesh Size:
• According to IEC 62305, mesh conductor size is based on the selected class of LPS and that is totally dependable on user requirements.
• In the Mesh method, a conducting mesh with a cell size determined by the minimum return stroke current that is allowed to strike the protected structure.
• In order to avoid a direct strike, the mesh has to be located at a critical distance above the flat surface to be protected. This procedure is called “protective mesh method”.
• The maximum mesh size should be in accordance with the table below.

Mesh Size
Class of LPS	Mesh Size (M)
CLASS I-(VERY HIGH RISK)	5 X 5 METER
CLASS II-(HIGH RISK)	10X 10 METER
CLASS III-(MODERATE RISK)	15 X 15 METER
CLASS IV-(LOW RISK)	20 X 20 METER

• The following conditions shall be considered while selecting the Mesh Method.
• (a) Air-termination conductors are positioned, on roof edge lines, on roof overhangs, on roof ridge lines, if the slope of the roof exceeds 1/10.
• (b) The mesh dimensions of the air-termination network are not greater than the values given in Table.
• (c) The network of the air-termination system is constructed in such a way that the lightning current will always encounter at least two distinct metal routes to earth-termination.
• (d) No metal installation protrudes outside the volume protected by air-termination systems.
• (e) The air-termination conductors follow, as far as possible, the shortest and most direct
• Location of Mesh
• The corners and edges of roofs are most susceptible to damage due to lightning. Therefore, designers and installers should place the conductors as close to the edge of the roof as possible.
• IEC 62305 allows for the use of conductors under the roof of a structure. Thus, the natural components of a structure can be used as part of the mesh grid, or even the whole grid. These components may be the rebar structure underneath the roof or dedicated lightning protection conductors, but they must be connected to the air termination rods that are mounted above the roof.
• For structures, with a protruding metallic structure, the Protective Angle Method is generally used as a supplement to the Mesh Method

•  Mesh Method with combination of other Methods:
• For Medium to large scale buildings mesh can be implemented, but due to its limitations, it does not come alone. It must be merged with other types of LPS, either protection angle or rolling sphere, subject to the suitable class number of each type.
• Air termination conductors and down conductors should be inter-connected by means of conductors at the roof level to provide sufficient current distribution over the down conductors.
• Conductors on roof and the connections of air termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material. The fixing centers shall be minimum 1 meter apart.
• For each non-isolated LPS, the number of down conductors shall be not less than two. A down conductor should be installed at each exposed corner of the structure, where this is possible.

• Limitations:
• The mesh method is suitable for horizontal and inclined roofs with no curvature.
• The mesh method is suitable for flat lateral surfaces to protect against side flashes.
• If the slope of the roof exceeds 1/10, parallel air-termination conductors, instead of a mesh, may be used provided the distance between the conductors is not greater than the required mesh width.

Basic of External Lightning Protection System (LPS)-(Part-1)

Introduction:

• A lightning protection system does not attract or prevent a lightning strike. but the lightning protection system provides a low impedance path to lightning currents to flow from Lightning striking Point to the ground to prevent dangerous flashovers and lightning-caused fires.
• Lightning protection systems are designed to protect structures, equipment or people from the damaging effects of lightning strikes. These systems create pathways for lightning strikes to travel safely from the top of a structure to the ground with a lightning conductor. They protect the internal electrical components of a building by preventing fires or electrocution for that all metallic installations in the building must be made at equal potential.
• The basic goal of LPS is to prevent thermal, mechanical, and electrical effects that can cause damage to the protected structure or to humans via touch or step voltages within the structure.

Lighting Protection Standards:

• There are various lighting protection standards. Widely use are
• IEC 62305
• IS 2309
• NFPA 780
• NBC-2016

 IEC:62305 -Part 1 to 5:

COMPARISON BETWEEN IEC AND IS STANDARD FOR LPS: 

Comparison between IEC and IS standard for External LPS
Description	LPS as per IEC 62305	LPS as per IS 2309	ESE (Early Streamer Emission)
Coverage area	Real, Calculated and approved design as per building type complying to IEC 62305-3.	Real, Calculated and approved design as per building type complying to IEC 62305-3.	Imaginary – no proof available, Not complying and national or international standard.
Approvals / Applicability of latest standard	IEC 62305-3 – International standard, Released in 2010	IS 2309 & IS 3043 – National standard, Released in 1989	Approved only in France which is their local standard
Insurance cover	Yes.	Yes.	No. Not approved by IS & CEA
Height limitation	No height limitation as the LPS is based on horizontal air terminal	No height limitation as the LPS is based on horizontal air terminal	Height restriction is applicable surrounding the airport area as ESE is based on Vertical air terminal.
Air Termination Design	Rolling sphere method	Protective Angle method & Mesh method	Not as per any international method.
LPS for Type of Building	Any type of complex building.	Simple and Flat /Slopped Building
Material for Air terminal & down conductor.	8mm Aluminum round, which is easier to install, bend & needs less conductor holder.	25X3 GI is used which is difficult to install, bend & needs twice the amount of conductor holder.	Not as per any international method.
Material compatibility	Taken care using bi-metal connector	No specific mention in the standard.	Not taken care.
Expansion /contraction of metal in summer/winter	Taken care of using Expansion pieces.	Not taken care	Not applicable as it is based on vertical air terminal.
No of Down Conductor.	More than one down conductor to dissipate the Lightning current to the ground (Multiple Dissipation)	Less number of down conductors when compared to IEC 62305	In most of the sites, only one down conductor is installed.
Current sharing Path	Many Parallel paths. LEMP has minimal effects	Few parallel paths	Maximum 2 Parallel paths. High LEMP can damage electronic equipment.
Design of LPS	based on LPL 1 to 4 backed up by IEC 62305	Based on Experience & old IEC, BS standards.	Not as per any international method.
Experience	Used for many decades without any problem.	Used for many decades without any problem.	Approximately 15 years old. In Some country many buildings with ESE were damaged.
Grounding	Type B as per IEC 62305-1	Ring earthing as per IS 3043	Recommended only for small residences (not even apartments) where electronic equipment is not available.
Installation	time consuming but effective	time consuming but effective	less time consuming but ineffective

Lighting Protection Levels:

• Lighting Protection Level are divided into four categories. For each category, a set of maximum and minimum lightning current parameters is fixed (LPL I to IV).
• The maximum values of lightning current parameters are used to design lightning protection components (e.g. Cross section of conductors, thickness of metal sheets, current capability of SPDs and Separation distance against dangerous sparking).
• The minimum values of lightning current amplitude for the different LPL are used to derive the Rolling Sphere Radius to define the Lightning Protection Zone (LPZ0B) which cannot be reached by direct strike.

RELATION BETWEEN LPL AND CLASS OF LPS
Table-7, IEC- 62305-3
LPL	RISK LEVEL	CLASS OF LPS
CLASS I	Very High Risk	I
CLASS II	High Risk	II
CLASS III	Moderate Risk	III
CLASS IV	Low Risk	IV

 

CLASSIFICATION OF LPS
Table-4, IEC- 62305-1
CLASSIFICATION OF LPL	Maximum Current (KA)	Minimum Current (KA)
CLASS I- (Very High Risk)	200 KA	3 KA
CLASS II-(High Risk)	150 KA	5 KA
CLASS III-(Moderate Risk)	100 KA	10 KA
CLASS IV-(Low Risk)	100 KA	16 KA

Types of Lighting Protection System (LPS):

• There are two types of Lightning Protection System
• External Lighting Protection
• Internal Lighting Protection.
• External lightning protection
• External lightning protection protects buildings in case of a direct lightning strike. It basically intercepts direct lightning flashes to the structure and conduct the lightning current from the point of strike to the ground and creates a protective sheath around the building which prevents it from catching fire and protects the people within.
• The External LPS also disperses this current into the earth without causing damage to the structures or causing unsafe potential rise / sparking.

• Internal Lighting Protection:
• An Internal LPS protects equipment against transient voltages and currents.
• Internal Lighting Protection / Surge protection provides safety within the building. It keeps surges which might enter the house via power supply cables / Power Line and protect electrical /electronic devices of house (which would otherwise be at risk via these routes).

Types of External LPS System

• There are two types of External LPS System
• Non-Conventional System / Early Streamer Emission (Isolated System)
• Conventional System (Non-Isolated System)
• Non-Conventional / Early Streamer Emission (Isolated System):
• Non-Conventional System / Isolated System does not mean that the system is electrically isolated from earth (a common misconception). It just means of physical distance achieved between the lightning current and the item being protected.
• In Non-Conventional / Isolated System, Lightning conductor does not directly attach to the structure or asset being protected. There is little or more separation between Structure and Lightning system.
• This can be achieved with free-standing masts (or poles) which stand someway off the item being covered at highest Point. Or, in some cases, separation can be achieved by using non-sparking conductors.
• Lightning Rods are installed at the highest point of protected building with sufficient separation distance to each other electrically and physically. Separate (Isolated) Lighting Rod provides conductive path to lighting current to the earth.
• Conventional (Non-Isolated System):
• In Conventional / Non-isolated System is typically attached conductor arrangements directly to the structure or asset being protected with little or no separation.

Components of External Lighting Protection System:

• An external Lightning Protection System has following parts

1. Air terminal system= Intercept a lightning flash to a structure
2. The down conductor system =provides the safest path to the lightning current towards the earth.
3. Earthing system =Disperse the lightning current into the earth.

• These individual elements of an LPS should be connected using appropriate lightning protection components. This will ensure that in the event of a lightning current discharge to the structure, any potential damage to the structure protected will be minimized.
• In most cases, the external LPS may be attached to the structure to be protected. An isolated LPS is preferred for areas at risk of explosion and fire.

(1) Air Termination System:

• The role of an air termination system is to capture the lightning discharge current and dissipate harmlessly to earth via down conductor and earth termination system. Therefore, it is very important to use a correctly designed Air-termination system.
• Air Termination System can be composed of any combination of the following elements.
• (i) Rods (including free standing masts)
• (ii) Catenary wires (suspended wires)
• (iii) Meshed conductors that may lie in direct contact with the roof or be suspended above it.

AIR TERMINATION SYSTEM DESIGN

•  As per considering Class of Lighting Protection System, the air-termination system shall be design by following methods.
• All methods should be used, independently or in any combination to ensure that the protection zones by different parts of the air-termination overlap and ensure that the structure is entirely protected.
• Methods for the air-termination for Lighting Protection System is
• (A) Protection Angle Method
• (B) Rolling Sphere Method and
• (C) Mesh Method
• All three methods may be used for the design of an LPS. The choice of the method depends on a practical evaluation of its suitability and the vulnerability of the structure to be protected.
• The major difference in Air Termination methods is as below.
• (i) The protection angle method is suitable for simple structures or for small parts of bigger structures. It also has limitations on the height of the air terminal. This method is not suitable for structures higher than the radius of the rolling sphere relevant to the protection level of the LPS.
• (ii) The rolling sphere method is suitable for complex shaped structures. This method is mostly used in all the cases.
• (iii) The mesh method is for general purposes, and it is particularly suitable for the protection of plane surface.

(A) PROTECTION ANGLE METHOD (Suitable for Simple-Shaped building)

• The Protection Angle method is wider used compared to mesh method, because it can be installed at simple structure, on not smooth/not flat surface, on protruding metallic structure.
• This method is used for structures that do not exceed 15 Meter in height.
• For structures less than 7.5 Meter in height, a Protection angle shall be 60 degrees, or 1:2, angle is permitted.
• For structures over 7.5 Meter but not in excess of 7.5 Meter a Protection angle shall be 45 degrees, or 1:1, angle is used. This is illustrated in Figure
• The Protective Angle Method is generally used as a supplement to the Mesh Method.
• Air-termination rods should be positioned so that all the parts of the structure, including metallic equipment installed on the roof like HVAC units, PV panels to be protected inside the envelope generated by the air-termination rods.
• In this method several air terminals are placed at the highest points on top of buildings/structures at different locations. Each air terminal covers a certain angle of protection.
• The degree of protection can be selected based on the height of terminal from base to tip. For example, if class I is selected, this means that the angle of protection is 70 degrees, considering 2 meters height of the terminal.
• In the case of installing metallic equipment’s, like HVAC Unit, PV panels at roof, sufficient distance among the equipment and air terminals shall be considered to avoid sparking, as well as selecting the appropriate protection angle.
• The real physical dimension of metal Air-termination shall be considered to calculate area protected by Lighting terminal. Typically, if the air rod is 5 meters tall, then the zone of protection offered by this air terminal rod would be based on 5 meters and the relevant class of LPS.
• If the building height is less than 30 meters, 45-degree cone of protection can be used. For building height more than 30 Meters, 30-degree cone of protection shall be considered

Volume protected by a vertical rod air-termination system

• Air-termination conductors, rods, masts and wires should be positioned so that all parts of the structure to be protected are inside the envelope surface generated by projecting points on the air-termination conductors to the reference plane, at an angle α to the vertical in all directions.
• The volume protected by a vertical rod is assumed to have the shape of a right circular cone with the vertex placed on the air-termination axis, semi-apex angle α, depending on the class of LPS, and on the height of the air-termination system as given in Table.

• The protection angle should confirm to the table mentioned below, with h being the height of the air-termination above the surface to be protected.

Height of Air Termination Rod-Protection Angle & Protection Distance
Height of Air termination rod in meter	LPS-CLASS-I		LPS-CLASS-II		LPS-CLASS-III		LPS-CLASS-IV
	Angle	Protection Distance in Meter	Angle	Protection Distance in Meter	Angle	Protection Distance in Meter	Angle	Protection Distance in Meter
1	71	2.9	74	3.49	77	4.33	79	5.14
2	71	5.81	74	6.97	77	8.66	79	10.29
3	66	6.74	71	8.7	74	10.46	76	12.03
4	62	7.52	68	9.9	72	12.31	74	13.95
5	59	8.32	65	10.72	70	13.74	72	15.39
6	56	8.9	60	11.28	68	14.85	71	17.43
7	53	9.29	58	12.12	66	15.72	69	18.24
8	50	9.53	56	12.8	64	16.4	68	19.8
9	48	10	54	13.34	62	16.93	66	20.21
10	45	10	52	13.76	61	18.04	65	21.45
11	43	10.26	50	14.08	59	18.31	64	22.55
12	40	10.07	49	14.3	58	19.2	62	22.57
13	38	10.16	47	14.95	57	20.02	61	23.45
14	36	10.17	45	15.01	55	19.99	60	24.25
15	34	10.17	44	15	54	20.65	59	24.96
16	32	10	42	15.45	53	21.23	58	25.61
17	30	9.81	40	15.31	51	20.99	57	26.18
18	27	9.17	39	15.1	50	21.45	56	26.69
19	25	8.26	37	15.39	49	21.86	55	27.13
20	23	8.49	36	15.07	48	22.21	54	27.53
21			35	15.26	47	22.52	53	27.87
22			36	16.71	46	22.78	52	28.16
23			32	15	47	24.66	53	30.52
24			30	14.43	44	23.18	50	28.6
25			29	14.41	43	23.31	49	28.76
26			27	13.76	41	22.6	49	29.91
27			26	13.66	40	22.66	48	29.99
28			25	13.52	39	22.67	47	30.03
29			23	12.73	38	22.66	46	30.03
30					37	22.61	45	30
31					36	22.52	44	29.94
32					35	22.41	44	30.9
33					35	23.11	43	30.77
34					34	22.93	42	30.61
35					33	22.73	41	30.43
36					32	22.5	40	30.21
37					31	22.23	40	31.5
38					30	21.94	39	30.77
39					29	21.62	38	30.47
40					28	21.27	37	30.14
41					27	20.89	37	30.9
42					26	20.48	36	30.51
43					25	20.05	35	30.11
44					24	19.59	35	30.81
45					23	19.1	34	30.35
46							33	29.87
47							32	29.37
48							32	29.99
49							31	29.44
50							30	28.87
51							30	29.44
52							29	28.82
53							28	28.18
54							27	27.51
55							27	28.02
56							26	27.31
57							25	26.58
58							25	27.05
59							24	26.27
60							23	25.47

• Air termination conductors and down conductors should be inter-connected by means of conductors at the roof level to provide sufficient current distribution over the down conductors.
• Conductors on roof and the connections of air termination rods may be fixed to the roof using both conductive or non-conductive spacers and fixtures. The conductors may also be positioned on the surface of a wall if the wall is made of non-combustible material. The fixing centers shall be minimum 1 meter apart.
• For each non-isolated LPS, the number of down conductors shall be not less than two.
• A down conductor should be installed at each exposed corner of the structure, where this is possible.

Limitation:

• The protection angle method has geometrical limits and cannot be applied if Building height (H) is larger than the rolling sphere radius (r).
• The angle will not change for values of Building height (H) below 2 meters.

Lighting Arrester

Lighting and Voltage Surge

• Lightning can create voltage surges in several of the following ways. Lightning can score a direct hit on your house. It can strike the overhead power line which enters your house, or a main power line that is blocks away from your home. Lightning can strike branch circuitry wiring in the walls of your house. Lightning can strike an object near your home such as a tree or the ground itself and cause a surge. Voltage surges can be created by cloud to cloud lightning near your home. A highly charged cloud which passes over your home can also induce a voltage surge.
• Voltage surges can also be caused by standard on and off switching activities of large electric motors or pieces of equipment. These surges can be created by a neighbor, or by a business or manufacturing facility some distance from your house. These surges are insidious and for the most part are silent. They can occur with little or no warning.

Method to Suppress Lighting and Voltage Surge:

• When a voltage surge is created, it wants to equalize itself and it wants to do it as quickly as possible. These things seem to have very little patience. The surges will do whatever it takes to equalize or neutralize themselves, even if it means short circuiting all of your electronic equipment.
• The method of providing maximum protection for equipment is quite simple. Create a pathway for the voltage surge (electricity) to get to and into the ground outside your house as quickly as possible. This is not, in most cases, a difficult task.
• The first step is simple. Create an excellent grounding system for your household electrical system. The vast majority of homes do not have an excellent grounding system. Many homes have a single grounding rod and /or a metallic underground water pipe which are part of the electrical grounding system. In most cases, this is inadequate. The reason is somewhat easy to explain. Imagine putting a two inch fire hose into your kitchen sink and opening the nozzle to the full on position. I doubt that the drain in your sink could handle all of the water. Your grounding system would react in the same way to a massive voltage surge. Just as the water jumps out of the sink, the electricity jumps from the grounding system and looks for places to go. Frequently it looks for the microchips in your electronic devices. They are an easy target. They offer a path of least resistance.
• Voltage surges want to be directed to the grounding system, and when they do, they want to get into the ground around your house in a hurry. You can achieve this by driving numerous grounding rods into virgin soil around your house. These rods should be UL approved and connected by a continuous heavy solid copper wire which is welded to each grounding rod. This solid copper wire begins on the grounding bar inside of your electrical panel and terminates at the last grounding rod. Avoid using clamps if at all possible. Over time, the connection at the clamp can corrode or become loose creating tremendous resistance. This will act as a roadblock to the electricity trying to get into the ground around your home.
• The grounding rods should be at least ten feet apart from one another. They should be located in soil which readily accepts electricity. Moist clay soils are very desirable. Rocky, sandy, or soils with gravel generally have high resistance factors. Electricity has a tough time dissipating into them. Resistance readings should be in the range of 10 to 30 ohms. The lower the better.
• The second step in household surge protection is to install a lightning arrester inside of your electric service panel. These devices can be extremely effective in intercepting large voltage surges which travel in the electric power lines. These devices capture the voltage surges and ‘bleed’ them off to the grounding wire which we just spoke of. If for some reason you do not have a large enough grounding wire, or enough ground rods, the arrester cannot do its job. It must be able to send the surge quickly to the ground outside of your house. Almost every manufacturer of circuit breakers makes one to fit inside their panel. They can be installed by a homeowner who is experienced in dealing with high voltage panels. If you do not have this capability, have an experienced electrician install it for you.
• The final step in the protection plan is to install ‘point of use’ surge suppression devices. Often you will see these called ‘transient voltage surge suppressors’. These are your last line of defense. They are capable of only stopping the leftover voltage surge which got past the grounding system and the lightning arrester. They cannot protect your electronic devices by themselves. They must be used in conjunction with the grounding system and the lightning arresters. Do not be lulled into a false sense of security if you merely use one of these devices!
• The ‘point of use’ surge suppression devices are available in various levels of quality. Some are much better than others. What sets them apart are several things. Generally speaking, you look to see how fast their response time is. This is often referred to as clamping speed. Also, look to see how high of a voltage surge they will suppress. Make sure that the device has a 500 volt maximum UL rated suppression level. Check to see if it has an indicator, either visual or audio, which lets you know if it is not working. The better units offer both, in case you install the device out of sight. Check to see if it offers a variety of modes with respect to protection. For example, does the device offer protection for surges which occur between the ‘hot’ and neutral, between ‘hot’ and ground, as well as between neutral and ground. There is a difference! Check to see if it monitors the normal sine waves of regular household current. Surges can cause irregularities in these wave patterns. Good transient surge suppression devices ‘devour’ these voltage spikes. Finally, check the joule rating. Attempt to locate a device which has a joule rating of 140 or higher. Electrical supply houses often are the best place to look for these high quality devices.
• Some devices can also protect your phone equipment at the same time. This is very important for those individuals who have computer modems. Massive voltage surges can come across phone lines as well. These surges can enter your computer through the telephone line! Don’t forget to protect this line as well. Also, be sure the telephone ground wire is tied to the upgraded electrical grounding system.

What is a surge arrester?

• Surge arresters are devices that help prevent damage to apparatus due to high voltages. The arrester provides a low-impedance path to ground for the current from a lightning strike or transient voltage and then restores to a normal operating conditions.
• A surge arrester may be compared to a relief valve on a boiler or hot water heater. It will release high pressure until a normal operating condition is reached. When the pressure is returned to normal, the safety valve is ready for the next operation.
• When a high voltage (greater than the normal line voltage) exists on the line, the arrester immediately furnishes a path to ground and thus limits and drains off the excess voltage. The arrester must provide this relief and then prevent any further flow of current to ground. The arrester has two functions; it must provide a point in the circuit at which an over-voltage pulse can pass to ground and second, to prevent any follow-up current from flowing to ground.

Causes of over voltages

• Internal causes
• External causes

Internal causes

• Switching surge
• Insulation failure
• Arcing ground
• Resonance
• Switching surge: The over voltages produced on the power system due to switching are known as switching surge.
• Insulation failure: The most common case of insulation failure in a power system is the grounding of conductors (i.e. insulation failure between line and earth) which may cause overvoltage in the system.
• Arcing ground: The phenomenon of intermittent arc taking place in line to ground fault of a 3phase system with consequent production of transients is known as arcing ground.
• Resonance: It occurs in an electrical system when inductive reactance of the circuit becomes equal to capacitive reactance. under resonance , the impedance of the circuit is equal to resistance of the circuit and the p.f is unity.

Types of lightning strokes

• Direct stroke
• Indirect stroke

(1) Direct stroke

• In direct stroke, the lightning discharge is directly from the cloud to the subject equipment. From the line, the current path may be over the insulator down the pole to the ground.

(2) Indirect stroke

• Indirect stroke results from the electro statically induced charges on the conductors due to the presence of charge clouds.

Harmful effects of lightning

• The traveling waves produced due to lightning will shatter the insulators.
• If the traveling waves hit the windings of a transformer or generator it may cause considerable damage.

Protection against lightning

• Different types of protective devices are:-
• Earthing screen
• Overhead ground wires
• Lightning arresters

(1)The Earthing screen

• The power station & sub-station can be protected against direct lightning strokes by providing earthing screens.
• On occurrence of direct stroke on the station ,screen provides a low resistance path by which lightning surges are conducted to ground.
• Limitation:
• It does not provide protection against the traveling waves which may reach the equipments in the station.

(2)Overhead ground wires

• It is the most effective way of providing protection to transmission lines against direct lightning strokes.
• It provides damping effect on any disturbance traveling along the lines as it acts as a short-circuited secondary.
• Limitation:
• It requires additional cost.
• There is a possibility of its breaking and falling across the line conductors, thereby causing a short-circuit fault.

(3)Lightning Arresters

• It is a protective device which conducts the high voltage surge on the power system to ground
• The earthing screen and ground wires fail to provide protection against traveling waves. The lightning arrester provides protection against surges.

AC Power Surge Arrester

Type 1 Surge Protectors

• Type 1 surge protectors are designed to be installed where a direct lightning strike risk is high, especially when the building is equipped with external lightning protection system (LPS or lightning rod).
• In this situation IEC 61643-11 standards require the Class I test to be applied to surge protectors : this test is characterized by the injection of 10/350 μs impulse current in order to simulate the direct lightning strike consequence. Therefore these Type 1 surge protectors must be especially powerful to conduct this high energy impulse current.

Type 2 surge protectors

• Type 2 surge protectors are designed to be installed at the beginning of the installation, in the main switchboard, or close to sensitive terminals, on installations without LPS (lightning rods).
• These protectors are tested following the Class II test from IEC61643-11 based on 8/20 μs impulse current injection.

Type 3 surge protectors

• In case of very sensitive or remote equipment, secondary stage of surge protectors is required : these low energy SPDs could be Type 2 or Type 3. Type 3 SPDs are tested with a combination waveform (1,2/50  μs – 8/20 μs) following Class III test.

Types of Lightning Arrestors according to Class:

1.     Station Class

• Station class arrestors are typically used in electrical power stations or substations and other high voltage structures and areas.
• These arrestors protect against both lightning and over-voltages, when the electrical device has more current in the system than it is designed to handle.
• These arrestors are designed to protect equipment above the 20 mVA range.

2.     Intermediate Class

• Like station class arrestors, intermediate class arrestors protect against surges from lightning and over-voltages, but are designed to be used in medium voltage equipment areas, such as electrical utility stations, substations, transformers or other substation equipment.
• These arrestors are designed for use on equipment in the range of 1 to 20 mVA.

3.     Distribution Class

• Distribution class arrestors are most commonly found on transformers, both dry-type and liquid-filled.
• These arrestors are found on equipment rated at 1000 kVA or less.
• These arrestors are sometimes found on exposed lines that have direct connections to rotating machines.

4.     Secondary Class

• Secondary class lightning arrestors are designed to protect most homes and businesses from lightning strikes, and are required by most electrical codes, according to, Inc., an electrical power protection company.
• These arrestors cause high voltage overages to ground, though they do not short all the over voltage from a surge. Secondary class arrestors offer the least amount of protection to electrical systems, and typically do not protect solid state technology, or anything that has a microprocessor.

Choosing the right AC Power Surge Arrester

• AC power surge protectors is designed to cover all possible configurations in low voltage installations. They are available in many versions, which differ in:
• Type or test class (1 , 2 or 3)
• Operating voltage (Uc)
• AC network configuration (Single/3-Phase)
• Discharge currents (Iimp, Imax, In)
• Protection level (Up)
• Protection technology (varistors, gas tube-varistor, filter)
• Features (redundancy, differential mode, plug-in, remote signaling…).
• The surge protection selection must be done following the local electrical code requirements (i.e.: minimum rating for In) and specific conditions (i.e. : high lightning density).

Working Principle of LA:

• The earthing screen and ground wires can well protect the electrical system against direct lightning strokes but they fail to provide protection against traveling waves, which may reach the terminal apparatus. The lightning arresters or surge diverts provide protection against such surges. A lightning arrester or a surge diverted is a protective device, which conducts the high voltage surges on the power system to the ground.
• The earthing screen and ground wires can well protect the electrical system against direct lightning strokes but they fail to provide protection against traveling waves, which may reach the terminal apparatus. The lightning arresters or surge diverters provide protection against such surges. A lightning arrester or a surge diverted is a protective device, which conducts the high voltage surges on the power system to the ground.

• Fig shows the basic form of a surge diverter. It consists of a spark gap in series with a non-linear resistor. One end of the diverter is connected to the terminal of the equipment to be protected and the other end is effectively grounded. The length of the gap is so set that normal voltage is not enough to cause an arc but a dangerously high voltage will break down the air insulation and form an arc. The property of the non-linear resistance is that its resistance increases as the voltage (or current) increases and vice-versa. This is clear from the volt/amp characteristic of the resistor shown in Fig
• The action of the lightning arrester or surge divert er is as under:
• (i) Under normal operation, the lightning arrester is off the line i.e. it conducts no current to earth or the gap is non-conducting
• (ii) On the occurrence of over voltage, the air insulation across the gap breaks down and an arc is formed providing a low resistance path for the surge to the ground. In this way, the excess charge on the line due to the surge is harmlessly conducted through the arrester to the ground instead of being sent back over the line.
• (iii) It is worthwhile to mention the function of non-linear resistor in the operation of arrester. As the gap sparks over due to over voltage, the arc would be a short-circuit on the power system and may cause power-follow current in the arrester. Since the characteristic of the resistor is to offer low resistance to high voltage (or current), it gives the effect of short-circuit. After the surge is over, the resistor offers high resistance to make the gap non-conducting.

Type of LA for Outdoor Applications:

• There are several types of lightning arresters in general use. They differ only in constructional details but operate on the same principle, providing low resistance path for the surges to the round.
• 1. Rod arrester
• 2. Horn gap arrester
• 3. Multi gap arrester
• 4. Expulsion type lightning arrester
• 5. Valve type lightning arrester

(1) Rod Gap Arrester

• It is a very simple type of diverter and consists of two 1.5 cm rods, which are bent at right angles with a gap in between as shown in Fig.
• One rod is connected to the line circuit and the other rod is connected to earth. The distance between gap and insulator (i.e. distance P) must not be less than one third of the gap length so that the arc may not reach the insulator and damage it. Generally, the gap length is so adjusted that breakdown should occur at 80% of spark-voltage in order to avoid cascading of very steep wave fronts across the insulators.
• The string of insulators for an overhead line on the bushing of transformer has frequently a rod gap across it. Fig 8 shows the rod gap across the bushing of a transformer. Under normal operating conditions, the gap remains non-conducting. On the occurrence of a high voltage surge on the line, the gap sparks over and the surge current is conducted to earth. In this way excess charge on the line due to the surge is harmlessly conducted to earth

Limitations:

• (i) After the surge is over, the arc in the gap is maintained by the normal supply voltage, leading to short-circuit on the system.

• (ii) The rods may melt or get damaged due to excessive heat produced by the arc.

• (iii) The climatic conditions (e.g. rain, humidity, temperature etc.) affect the performance of rod gap arrester.

• (iv) The polarity of the f the surge also affects the performance of this arrester.

• Due to the above limitations, the rod gap arrester is only used as a back-up protection in case of main arresters.

(2) Horn Gap Arrester:

• Fig shows the horn gap arrester. It consists of a horn shaped metal rods A and B separated by a small air gap. The horns are so constructed that distance between them gradually increases towards the top as shown.
• The horns are mounted on porcelain insulators. One end of horn is connected to the line through a resistance and choke coil L while the other end is effectively grounded.
• The resistance R helps in limiting the follow current to a small value. The choke coil is so designed that it offers small reactance at normal power frequency but a very high reactance at transient frequency. Thus the choke does not allow the transients to enter the apparatus to be protected.
• The gap between the horns is so adjusted that normal supply voltage is not enough to cause an arc across the gap.

• Under normal conditions, the gap is non-conducting i.e. normal supply voltage is insufficient to initiate the arc between the gap. On the occurrence of an over voltage, spark-over takes place across the small gap G. The heated air around the arc and the magnetic effect of the arc cause the arc to travel up the gap. The arc moves progressively into positions 1, 2 and 3.
• At some position of the arc (position 3), the distance may be too great for the voltage to maintain the arc; consequently, the arc is extinguished. The excess charge on the line is thus conducted through the arrester to the ground.

(3) Multi Gap Arrester:

• Fig shows the multi gap arrester. It consists of a series of metallic (generally alloy of zinc) cylinders insulated from one another and separated by small intervals of air gaps. The first cylinder (i.e. A) in the series is connected to the line and the others to the ground through a series resistance. The series resistance limits the power arc. By the inclusion of series resistance, the degree of protection against traveling waves is reduced.
• In order to overcome this difficulty, some of the gaps (B to C in Fig) are shunted by resistance. Under normal conditions, the point B is at earth potential and the normal supply voltage is unable to break down the series gaps. On the occurrence an over voltage, the breakdown of series gaps A to B occurs.
• The heavy current after breakdown will choose the straight – through path to earth via the shunted gaps B and C, instead of the alternative path through the shunt resistance.

• Hence the surge is over, the arcs B to C go out and any power current following the surge is limited by the two resistances (shunt resistance and series resistance) which are now in series. The current is too small to maintain the arcs in the gaps A to B and normal conditions are restored. Such arresters can be employed where system voltage does not exceed 33kV.

(4) Expulsion Type Arrester:

• This type of arrester is also called ‘protector tube’ and is commonly used on system operating at voltages up to 33kV. Fig shows the essential parts of an expulsion type lightning arrester.
• It essentially consists of a rod gap AA’ in series with a second gap enclosed within the fiber tube. The gap in the fiber tube is formed by two electrodes. The upper electrode is connected to rod gap and the lower electrode to the earth. One expulsion arrester is placed under each line conductor. Fig shows the installation of expulsion arrester on an overhead line.

• On the occurrence of an over voltage on the line, the series gap AA’ spanned and an arc is stuck between the electrodes in the tube. The heat of the arc vaporizes some of the fiber of tube walls resulting in the production of neutral gas. In an extremely short time, the gas builds up high pressure and is expelled through the lower electrode, which is hollow. As the gas leaves the tube violently it carries away ionized air around the arc. This de ionizing effect is generally so strong that the arc goes out at a current zero and will not be re-established.

Advantages:

• (i) They are not very expensive.

• (ii)They are improved form of rod gap arresters as they block the flow of power frequency follow currents

• (iii)They can be easily installed.

Limitations:

• (i)An expulsion type arrester can perform only limited number of operations as during each operation some of the fiber material is used up.

• (ii) This type of arrester cannot be mounted on enclosed equipment due to discharge of gases during operation.

• (iii)Due to the poor volt/am characteristic of the arrester, it is not suitable for protection of expensive equipment

(5) Valve Type Arrester:

• Valve type arresters incorporate non linear resistors and are extensively used on systems, operating at high voltages. Fig shows the various parts of a valve type arrester. It consists of two assemblies (i) series spark gaps and (ii) non-linear resistor discs in series. The non-linear elements are connected in series with the spark gaps. Both the assemblies are accommodated in tight porcelain container.
• The spark gap is a multiple assembly consisting of a number of identical spark gaps in series. Each gap consists of two electrodes with fixed gap spacing. The voltage distribution across the gap is line raised by means of additional resistance elements called grading resistors across the gap. The spacing of the series gaps is such that it will withstand the normal circuit voltage. However an over voltage will cause the gap to break down causing the surge current to ground via the non-linear resistors.
• The non-linear resistor discs are made of inorganic compound such as thyrite or metrosil. These discs are connected in series. The non-linear resistors have the property of offering a high resistance to current flow when normal system voltage is applied, but a low resistance to the flow of high surge currents. In other words, the resistance of these non-linear elements decreases with the increase in current through them and vice-versa.

Working.

• Under normal conditions, the normal system voltage is insufficient to cause the break down of air gap assembly. On the occurrence of an over voltage, the breakdown of the series spark gap takes place and the surge current is conducted to earth via the non-linear resistors. Since the magnitude of surge current is very large, the non-linear elements will offer a very low resistance to the passage of surge. The result is that the surge will rapidly go to earth instead of being sent back over the line. When the surge is over, the non-linear resistors assume high resistance to stop the flow of current.

(6) Silicon carbide arresters:

• A great number of silicon carbide arresters are still in service. The silicon carbide arrester has some unusual electrical characteristics. It has a very high resistance to low voltage, but a very low resistance to high-voltage.
• When lightning strikes or a transient voltage occurs on the system, there is a sudden rise in voltage and current. The silicon carbide resistance breaks down allowing the current to be conducted to ground. After the surge has passed, the resistance of the silicon carbide blocks increases allowing normal operation.
• The silicon carbide arrester uses nonlinear resistors made of bonded silicon carbide placed in series with gaps. The function of the gaps is to isolate the resistors from the normal steady-state system voltage. One major drawback is the gaps require elaborate design to ensure consistent spark-over level and positive clearing (resealing) after a surge passes. It should be recognized that over a period of operations that melted particles of copper might form which could lead to a reduction of the breakdown voltage due to the pinpoint effect. Over a period of time, the arrester gap will break down at small over voltages or even at normal operating voltages. Extreme care should be taken on arresters that have failed but the over pressure relief valve did not operate. This pressure may cause the arrester to

(7) Metal Oxide Arrestor:

• The MOV arrester is the arrester usually installed today
• The metal oxide arresters are without gaps, unlike the SIC arrester. This “gap-less” design eliminates the high heat associated with the arcing discharges.
• The MOV arrester has two-voltage rating: duty cycle and maximum continuous operating voltage, unlike the silicon carbide that just has the duty cycle rating. A metal-oxide surge arrester utilizing zinc-oxide blocks provides the best performance, as surge voltage conduction starts and stops promptly at a precise voltage level, thereby improving system protection. Failure is reduced, as there is no air gap contamination possibility; but there is always a small value of leakage current present at operating frequency.
• It is important for the test personnel to be aware that when a metal oxide arrester is disconnected from an energized line a small amount of static charge can be retained by the arrester. As a safety precaution, the tester should install a temporary ground to discharge any stored energy.
• Duty cycle rating: The silicon carbide and MOV arrester have a duty cycle rating in KV, which is determined by duty cycle testing. Duty cycle testing of an arrester is performed by subjecting an arrester to an AC rms voltage equal to its rating for 24 minutes. During which the arrester must be able to withstand lightning surges at 1-minute intervals.
• Maximum continuous operating voltage rating: The MCOV rating is usually 80 to 90% of the duty cycle rating.

Installation of LA:

• The arrester should be connected to ground to a low resistance for effective discharge of the surge current.
• The arrester should be mounted close to the equipment to be protected & connected with shortest possible lead on both the line & ground side to reduce the inductive effects of the leads while discharging large surge current.

Maintenance of LA:

• Cleaning the outside of the arrester housing.
• The line should be de-energized before handling the arrester.
• The earth connection should be checked periodically.
• To record the readings of the surge counter.
• The line lead is securely fastened to the line conductor and arrester
• The ground lead is securely fastened to the arrester terminal and ground.