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.