Circular No. 16/2020/TT-BTTTT Issuing the "National Technical Regulations on Lightning Protection for Telecommunication Stations and Peripheral Telecommunication Cable Networks"

CIRCULAR

Issuing the "National Technical Regulation on Lightning Protection for Telecommunication Stations and Outside Cable Network"

_______________________

Pursuant to the Law on Standards and Technical Regulations dated June 29, 2006;

Pursuant to the Law on Telecommunications dated November 23, 2009;

WHEREAS, Decree No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing and guiding the implementation of certain provisions of the Law on Technical Standards and Regulations;

Pursuant to Decree No. 78/2018/NĐ-CP dated May 16, 2018 of the Government amending and supplementing some articles of Decree No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing the implementation of certain provisions of the Law on Standards and Technical Regulations;

Pursuant to Decree No. 17/2017/NĐ-CP dated February 17, 2017, issued by the Government, on the functions, tasks, powers, and organizational structure of the Ministry of Information and Communications;

Pursuant to the proposal of the Director of the Science and Technology Department,

The Minister of Information and Communications issues this Circular stipulating the National Technical Regulation on Lightning Protection for Telecommunication Stations and Outside Cable Network.

Article 1. Attached herewith is the National Technical Regulation on Lightning Protection for Telecommunication Stations and Outside Cable Network (QCVN 32:2020/BTTTT).

Article 2. Effective Date

1. This Circular takes effect from April 1, 2021.

2. The National Technical Regulation on Lightning Protection for Telecommunication Stations and Outside Cable Network, with code QCVN 32:2011/BTTTT, as stipulated in Clause 10, Article 1 of Circular No. 10/2011/TT-BTTTT dated April 14, 2011 of the Minister of Information and Communications, which details national technical regulations on telecommunications, shall cease to be effective from April 1, 2021.

Article 3. The Heads of the Office, Department of Science and Technology, Heads of agencies and units under the Ministry of Information and Communications, Directors of Provincial Departments of Information and Communications, and relevant organizations and individuals are responsible for implementing this Circular./.

SOCIALIST REPUBLIC OF VIET NAM

Independence - Freedom - Happiness

-----------------------------

QCVN 32:2020/BTTTT

NATIONAL TECHNICAL REGULATION ON LIGHTNING PROTECTION FOR TELECOMMUNICATION STATIONS AND OUTSIDE CABLE NETWORK

HANOI - 2020

QCVN 32:2020/BTTTT replaces QCVN 32:2011/BTTTT

Table of Contents

Foreword

The technical requirements and calculation methods in QCVN 32:2020/BTTTT are based on IEC 62305 parts 1, 2, 3 (2010), and ITU-T Recommendations K.39 (1996), K.40 (2018) and K.47 (2012).

QCVN 32:2020/BTTTT was compiled by the Institute of Post and Telecommunications Science and Technology, reviewed by the Department of Science and Technology, examined by the Ministry of Science and Technology, and issued together with Circular No. 16/2020/TT-BTTTT dated July 17, 2020 of the Minister of Information and Communications.

ON LIGHTNING PROTECTION FOR TELECOMMUNICATION STATIONS

AMENDMENT 1:2025 QCVN 07:2023/BXD
AND OUTSIDE CABLE NETWORK
This standard applies to telecommunication stations and outside cable networks to minimize damage caused by lightning, ensuring safety for people and the ability to provide telecommunication services and telecommunication application services.

HANOI - 2020

Chapter 1. GENERAL PROVISIONS

1.1. Scope of Application

Telecommunication stations referred to in this standard include the following works:

Switching centers, transmission centers;

Data centers;

Fixed wireless communication base stations used in fixed wireless communication, mobile communications, aviation, maritime, navigation, positioning, satellite, broadcasting, amateur services;

Radio stations, television stations.

This national technical regulation specifies:

Permissible damage risk caused by lightning to telecommunication stations and outside cable networks;

Calculation method for the frequency of damage caused by lightning to telecommunication stations and outside cable networks;

Lightning protection measures to protect telecommunication stations and outside cable networks.

1.2. Referenced documents

QCVN 9:2016/BTTTT, National Technical Regulation on Grounding for Telecommunication Stations.

TCVN 8071:2009, Telecommunication Works - Lightning Protection and Grounding Practices.

1.3. Explanation of terms and abbreviations

1.3.1. Risk area

The area surrounding a telecommunication work where a lightning strike could pose a danger to the telecommunication work.

1.3.2. Lightning current

A pulse of low-frequency electrical current that appears without a regular cycle, surges to its peak value, then decreases to zero. The characteristics of the lightning current are:

Peak (amplitude) value of the pulse, I;

Time to reach the peak value on the leading edge, T;

Time to decrease to half the peak value on the trailing edge, T2;

Waveform shape of the pulse current, T1/T2

Figure 1 illustrates the standard waveform of the lightning current and how to determine the parameters of the lightning current.

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1.3.3. Surge voltage

Pulse voltage with characteristic features similar to those of the pulse current. Figure 2 illustrates the standard waveform of the lightning voltage and how to determine the parameters of the lightning voltage.

Figure 2 - Standard waveform of lightning voltage

1.3.4. Failure current (for cable)

The smallest lightning current that causes damage to telecommunication cables, resulting in service interruption.

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1.3.5. Sheath breakdown current (cable)

The smallest current flowing through the metal sheath of a cable causing a breakdown voltage between the metal components in the cable core and the metal sheath, leading to cable damage.

1.3.6. Test current

The smallest current flowing through the metal sheath of a cable causing damage to the cable due to mechanical or thermal effects.

1.3.7. Electric current junction (for optical cable)

The smallest current flowing through the connecting components of an optical cable causing damage to the cable due to mechanical or thermal effects.

1.3.8. Breakdown voltage

The pulse voltage causing a breakdown between the metal components in the cable core and the metal sheath of the cable.

1.3.9. Outside telecommunication cable network

The part of the telecommunication network mainly located outside the telecommunication station, including all suspended, directly buried, conduit-laid, and tunnel-laid telecommunication cables.

1.3.10. Ground flash density

The number of lightning strikes per unit area of ground in a year (taken as 1 km²).

1.3.11. Keraunic level

The average number of thunderstorm days in a year, taken from the total number of thunderstorm days in a continuous 12-year solar activity cycle at a meteorological observation station.

1.3.12. Thunderstorm day

A day characterized by meteorological conditions where thunder can be clearly heard by observers.

1.3.13. Lightning

1.3.13. Lightning

The phenomenon of electrical discharge accompanied by sparks and a bang in the air can occur within clouds, between two clouds with opposite charges, or between a charged cloud and the ground. Telecommunication facilities during operation are affected by lightning as follows:

Direct lightning strike impact: the impact of a direct lightning strike on telecommunication facilities;

Secondary lightning impact due to propagation and induction: the secondary impact of lightning caused by static, electromagnetic, and combined electromagnetic effects;

1.3.14. Frequency of damage (number of damages due to flashes)

The average number of lightning strikes per year causing damage to telecommunication facilities.

1.3.15. Surge protective device (SPD)

A device that limits overvoltage and diverts surge currents.

1.3.16. Transfer impedance (combined impedance) of the metal shielding of cables (metal shielded external communication cables transfer impedance)

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The transfer impedance (combined impedance) of the metal shielding of cables is the ratio of the voltage drop from inside to outside the metal shielding of the cable to the total current flowing through the metal shielding.

1.3.17. Lightning protection zone (LPZ)

An area divided within a telecommunication station characterized by the severity of the electromagnetic field and the impact of lightning.

1.3.18. Damage probability (damage probability)

The probability of a single lightning strike causing damage to a telecommunication station and its peripheral communication cable network.

1.3.19. Risk (R)

The average possible annual loss value (in terms of human life and service) due to lightning, corresponding to the total value (in terms of human life and service) of the protected object.

1.3.20. Acceptable risk (Rr)

The maximum acceptable risk value for the protected object.

1.3.21. Lightning protection level (LPL)

A figure related to a set of lightning current parameters corresponding to the probability that the largest and smallest design values will not be exceeded in natural lightning phenomena.

1.3.22. Protective measures (protective solutions)

Measures applied to the object to be protected to reduce risk.

1.3.23. Lightning protection system (LPS)

A complete system used to reduce physical damage caused by lightning strikes to telecommunication stations and their peripheral communication cable networks.

1.3.24. External lightning protection system

Part of the lightning protection system including the lightning rod system, the down-conductor system, and the grounding electrode system.

1.3.25. Internal lightning protection system

Part of the lightning protection system including equipotential bonding and/or insulation connections with the external lightning protection system.

1.3.26. Lightning rod system (air-termination system)

A part of the external lightning protection system using metallic components such as rods and mesh wires to capture lightning strikes.

1.3.27. Down-conductor system

A part of the external lightning protection system designed to carry lightning current from the lightning rod system to the grounding electrode system.

1.3.28. Grounding electrode system (earth-termination system)

A part of the external lightning protection system designed to carry and distribute lightning current into the ground.

1.3.29. External conductive parts

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Metallic parts entering or exiting the telecommunication station and peripheral communication cable network requiring protection, such as pipe systems, metal cables, metal conduits, which may carry part of the lightning current.

1.3.30. Equipotential bonding

Connections to the lightning protection system of separate metallic parts, directly or through surge protective devices, to reduce potential differences caused by lightning.

1.3.31. Shielding wire

A metallic wire used to reduce physical damage caused by lightning strikes on telecommunication lines.

1.3.32. System of measures to protect against electromagnetic surges caused by lightning (LPMS)

A complete system of measures to protect against electromagnetic surges caused by lightning (LEMP) for internal installations.

1.3.33. Telecommunication station

An area comprising one or more telecommunication buildings containing telecommunication equipment, high antenna towers, and auxiliary equipment to provide telecommunication services and applications. The telecommunication station does not include houses and subscriber equipment.

1.3.34. Telecommunication plant

Construction works including passive telecommunication infrastructure (buildings, stations, poles, ducts, tanks) and network equipment installed therein.

1.3.35. Telecommunication building

A building housing telecommunication equipment systems.

1.3.36. Abbreviations

LPZ Lightning Protection Zone (Lightning Protected Zone)

LPL Lightning Protection Level (Lightning Protection Level)

LPMS LEMP protection measures system (System of measures to protect against electromagnetic surges caused by lightning)

1.4. Risk management process for lightning damage

The determination of the need to equip telecommunication stations and peripheral communication cable networks with lightning protection measures must go through a risk management process as follows:

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Figure 3 - Risk management process for lightning damage

1.5. Basic criteria for lightning protection

1.5.1. Lightning protection level

This standard specifies four levels of lightning protection. For each LPL, a set of lightning current parameters is defined.

The maximum value of the lightning current parameter corresponding to LPL I will not exceed with a probability of 99%.

The maximum value of the lightning current parameter corresponding to LPL I will decrease to 75% for LPL II and 50% for levels III and IV.

Table 1 - Values of lightning current parameters according to LPL

The maximum and minimum values of the lightning parameter for different levels of lightning protection in Table 1 are used to design components of the lightning protection system (for example, conductor cross-sectional area, thickness of metal sheathing, surge current withstand capability of SPDs, isolation distance to prevent dangerous sparks).

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The minimum values of the lightning current amplitude for different LPLs are used to determine the rolling sphere radius to define the LPZ 0B protected area where direct lightning strikes cannot approach (see 1.5.2 and Figure 4). The minimum values of the lightning parameters together with the corresponding rolling sphere radii are given in Table 2. These data are used to locate the lightning rod electrode systems and determine the LPZ 0B lightning protection zone (see 1.5.2).

Table 2 - Minimum values of lightning current and corresponding rolling sphere radius for LPL

15.2. Lightning Protection Zone

Measures such as LPS, shielding wires, electromagnetic shielding, and SPDs will determine the lightning protection zones. The distinction between lightning protection zones is characterized by significant differences in electromagnetic pulses caused by lightning at these zones.

Depending on the degree of lightning impact, lightning protection zones are defined as follows:

LPZ 0A Is the area at risk of direct lightning strikes and the entire electromagnetic field generated by lightning. Systems within this area may be subjected to the full or partial surge current.

LPZ 0B Is the area protected from direct lightning strikes but still threatened by the entire electromagnetic field generated by lightning. Systems within this area may be subjected to partial surge currents.

LPZ 1 Is the area where the surge current is limited due to current division and SPDs at the boundary. Spatial shielding can reduce the electromagnetic field generated by lightning.

LPZ 2, ..., n are areas where the surge current is further limited due to additional current division and SPDs at the boundary. Additional spatial shielding can further reduce the electromagnetic field generated by lightning.

NOTE 1: Generally, the higher the level of an LPZ, the lower the electromagnetic environment parameters.

The general principle of protection is that the object to be protected must be located within an LPZ whose electromagnetic characteristics are compatible with the object's ability to withstand damage caused by lightning (physical damage, damage to electrical and electronic systems due to overvoltage).

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Figure 4 - Illustration of LPZ lightning protection zoning at a telecommunications station

Chapter 2. TECHNICAL PROVISIONS

2.1. Requirements for Lightning Risk

2.1.1. Requirements for Telecommunications Stations

Telecommunications stations must be equipped with protective measures so that the risk value does not exceed the acceptable risk value as follows:

Table 3 - Acceptable risk values for telecommunications stations

2.1.2. Requirements for Peripheral Telecommunications Cable Networks

Peripheral telecommunications cable networks must be equipped with protective measures so that the risk value does not exceed the acceptable risk value as follows:

Table 4 - Acceptable risk values for peripheral telecommunications cable networks

NOTE: For peripheral telecommunications cables, human loss risk is not considered.

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The method for calculating the risk caused by lightning for telecommunications stations and peripheral telecommunications cable networks is presented in 2.2.

2.2. Method for Calculating Lightning Risk

2.2.1. Calculation of Lightning Risk for Telecommunications Stations

The risk caused by lightning for telecommunications stations is calculated according to the following formula:

R{ij} = L{p{ij}}\Sigma F{i} \quad (2.1)

Where:

F: Frequency of damage caused by lightning to the station, due to direct lightning strikes on the station, lightning strikes on adjacent antenna towers, lightning strikes near the station, and lightning surges through incoming lines; calculated according to 2.2.1.1.

L: Weighting factor representing the extent of loss in a single damage event caused by lightning to the station.

For human loss risk: L = 1;

For service loss risk: L = 2.74 x 10^-3

Pij: Probability of reducing minor human losses due to protective measures in Tables 8 and 9.

2.2.1.1. Calculation of Lightning Damage Frequency for Telecommunications Station Areas

The frequency of damage (F) at a telecommunications station with regional lightning density (Ng) considering the effectiveness of inherent or supplementary protective measures is determined by the following formula:

F = N g ( A d . D d + A n . D n + A s . D s + A a . D a ) ( 2.3 )

Where:

Ng: Lightning density in the station area, calculated based on geographic region, see Table E1, Appendix E.

p: Various probability factors of damage reduction depending on existing protective measures aimed at reducing the frequency of damage (F), see 2.2.1.2;

F₀ = N₀A₀P₀ - Frequency of direct lightning strikes on the station (d);

F{n} = N{g}A{n}.p{n} - Frequency of lightning strikes near the station area causing ground potential rise affecting the station (n);

Fs = Ng.As.ps - Frequency of damage caused by lightning strikes on cables or adjacent areas leading into the station (s);

F{a} = N{g}.A{a}.p{a} - Frequency of damage caused by direct lightning strikes on nearby objects, such as metal-connected antenna towers near the telecommunications station (a).

A4 - Area at risk of direct lightning strikes on the telecommunications station,

$A_{d}=(9\pi h^{2}+6ah+6bh+ab)\times10^{-8}\,\mathrm{km^{2}}$ (2.5)

Where:

a: Width of the telecommunications station, m;

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b: Length of the telecommunications station, m;

h: Height of the station building, m.

In cases where the area at risk of direct lightning strikes on an antenna tower covers part of the area at risk of direct lightning strikes on the station, the area A d is reduced by the covered portion.

An - Area at risk of lightning strikes near the telecommunications station causing ground potential rise affecting the station. An is calculated as the area of a region formed by a circle centered at the station with a radius d = 500 m, minus the area at risk of direct lightning strikes on the station A_d.

Where there are nearby structures such as other tall buildings (e.g., antenna towers, high-rise buildings) and cables leading into the station, the area A_n will be reduced by the covered area risk of those structures, as illustrated in Figure 5.

As - Area at risk of lightning strikes on incoming cables (information, power) to the telecommunications station. In general, incoming cables to the telecommunications station include overhead and buried types, the area As is calculated by the formula:

$A{s}=2\sum d{i}$ (2.6)

Where:

I: Length of each overhead or buried cable segment, m;

II: Corresponding distance for each segment, m;

For aerial cables, d = 1000 m;

For underground cables, d = 250 m;

n: Number of buried or suspended cable segments;

A: Direct lightning strike risk area on the antenna mast connected to the base station by metal;

For antenna masts in tower form, area A is calculated similarly to A1;

For circular, triangular, or quadrilateral antenna masts with guy wires and small dimensions, A_a is calculated as the area of a circle with radius 3h (h being the height of the antenna mast);

$A_{a}=\pi(3h)^{2}$

The direct lightning strike risk area for the telecommunications station zone is described in Figure 5.

Figure 5 - Description of the direct lightning strike risk areas for the telecommunications station zone

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2.2.1.2. Determination of damage probability factors p

Each damage probability factor p reflects the ability to reduce lightning damage through the natural protective characteristics of the installation structure (building materials, overhead or buried cable networks) and protective measures for the building or interfaces, as well as other internal and external protection measures (lightning protection systems, cable shielding grids, insulation techniques, etc.). In lightning protection design, applying a protective measure will slightly reduce the corresponding lightning damage probability, expressed through the p factors.

If several protective measures are applied to an object, the actual probability factor will be the product of the individual values, meaning:

$pt=\prod pi,(withpi\le1)$

The values of the p factors are presented in Tables 5 to 9.

Table 5 - Values of p for building materials of telecommunications stations

Table 6 - Values of p for external protective measures for telecommunications stations

NOTE: p% is the probability factor causing human injury

Table 7 - Values of p for protective measures on cables entering the telecommunications station

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Installing isolation transformers at the low-voltage network interface (with impulse voltage greater than 20 kV) (as specified in A.1.2) | 0.1

Selecting and installing surge protection devices that are well coordinated with the equipment's withstand capability, with quality installation techniques (as specified in A.1.2) | 0.01

Table 8 - Values of p for internal protective measures for telecommunications stations

Table 9 - Values of p for different floor surface layers to reduce touch and step voltages

2.2.2. Calculation of risks caused by lightning strikes on peripheral telecommunications cable networks

Considering the general case, the cable line (metallic or optical fiber cable with metallic components) includes buried and suspended segments. The damage risk (R) to be considered is the annual service loss due to direct lightning strikes. The damage risk is calculated using the formula:

Where:

Fpa: Damage frequency for suspended cable segments;

Fpb: Damage frequency for buried cable segments;

Fps: Damage frequency due to direct lightning strikes on structures where cables enter;

La: Loss per direct lightning strike on suspended cable;

Lb: Loss per direct lightning strike on buried cable;

Ls: Loss per direct lightning strike on structures where cables enter.

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For metallic cable lines:

$La=2\times10^{-3}$

$Lb=3\times10^{-3}$

$Ls=2\times10^{-3}$

For optical fiber cable lines:

$La=Lb=Ls=10^{-3}$

2.2.2.1. Frequency of damage for suspended and buried cable segments

The frequency of damage for suspended and buried cable segments is calculated using the formula:

Fpa=2xNgx[L-3(Ha+Hb)]xDxp(la)xCd×10^-6, (damage/year)

Fpb = 2 x Ngx[L-3(Ha + Hb)] x D x p(Ia) x Cd x Kd x 10^-6, (damage/year) (2.8)

Where:

L: Cable length (m)

Ha: Height of the elevated structure at end "a" of the cable, (m);

Hb: Height of the elevated structure at end "b" of the cable, (m);

p(la): Probability factor of damaging current, calculated using the formula:

p(i) = 10^2 e^(a-b)i with i >= 0

a = 4.005 and b = 0.0117 with I ≤ 20 kA

a = 5.063 and b = 0.0346 with I > 20 kA

Cd: Position coefficient;

Table 10 - Position coefficient for installation

a) Experience shows that telecommunications cables installed at the top of hills in rural areas often suffer more direct lightning strikes than those installed in flatlands. Telecommunications cables installed along hill slopes in rural areas are similar.

b) High-rise buildings over 20 m.

Ng: Lightning density, (km².year⁻¹) (see Appendix E)

D: Lightning strike distance, (m);

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For buried cables:

D = 0.482 (p) ^{1/2} with p ≤ 100 Ω.m;

D = 2.91 + 0.191 (ρ) ^ {1/2} with 100 Ω.m < ρ < 1000 Ω.m;

D = 0.283 (ρ) ^ {1/2} with ρ > 1000 Ω.m;

For suspended cables:

D = 3H, (m); H is the cable suspension height (usually between 4 m to 15 m);

la: Damaging current, (kA) (see Appendix C.1);

Kd: Damage correction factor;

Kd = 2.5 for unshielded buried cables;

Kd = 1.0 for shielded buried cables;

2.2.2.2. Frequency of damage due to direct lightning strikes on structures where cables enter (Fps)

The frequency of damage due to direct lightning strikes on structures affecting cables is calculated using the formula:

Fds=NgAd,p(a)·Cd(damage/year); (2.9)

Where:

Ad: Risk area for direct lightning strikes on structures, calculated using the formula:

$Ad=(9\pi h^{2}+6ah+6bh+ab)10^{-6}(km^{2})$

Where: a = length, (m);

b = width, (m);

c = height, (m);

p(Ia): Probability of lightning amplitude creating a damaging current on structures;

la: Damaging current for cables, see Appendix C.2.

3. MANAGEMENT PROVISIONS

Telecommunications stations and peripheral telecommunications cable networks within the scope of Article 1.1 must comply with the technical requirements set forth in this Standard.

4. RESPONSIBILITIES OF ORGANIZATIONS AND INDIVIDUALS

4.1. Organizations and enterprises with telecommunications stations and peripheral telecommunications cable networks are responsible for:

Ensuring that telecommunications stations and peripheral telecommunications cable networks comply with the Standard during design, installation, operation, and maintenance.

Implement the declaration of conformity for lightning risk criteria such that the lightning risk level at telecommunications stations must be less than or equal to the corresponding levels stipulated in this Standard. The declaration of conformity shall be carried out in accordance with Circular No. 28/2012/TT-BKHCN dated December 12, 2012, issued by the Ministry of Science and Technology, and Circular No. 02/2017/TT-BKHCN dated March 31, 2017, amending and supplementing certain provisions of Circular No. 28/2012/TT-BKHCN dated December 12, 2012.

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4.2. The Telecommunications Administration shall be responsible for receiving declarations of conformity, managing, guiding, and inspecting the declaration of conformity.

Chapter 5. ORGANIZATION OF IMPLEMENTATION

5.1. The Telecommunications Administration and Provincial Departments of Information and Communications shall be responsible for guiding and organizing the implementation of management of telecommunications stations and peripheral telecommunication cable networks in accordance with this Standard.

5.2. This Standard replaces QCVN 32:2011/BTTTT "National Technical Regulation on Lightning Protection for Telecommunications Stations and Peripheral Telecommunication Cable Networks."

5.3. In cases where the provisions set forth in this Standard are changed, supplemented, or replaced, they shall be implemented according to the latest document.

5.4. During the process of implementing this standard, if any issues arise or difficulties occur, relevant organizations and individuals shall reflect them in writing to the Ministry of Information and Communications (Department of Science and Technology) for guidance and resolution.

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ANNEX A

Product Name, Goods According to QCVN

Measures for protecting telecommunications stations from lightning

A.1. Measures for protecting telecommunications stations from lightning

To reduce the risk of damage to an acceptable level as specified in 2.2.1, it is necessary to apply some or all of the following protective measures:

A.1.1. External LPS System (Direct Lightning Strike Protection)

The external LPS system (direct lightning strike protection) must include the following basic components:

Lightning rod system;

Down-conductor system;

Grounding system;

Supporting structure.

a) Lightning Rod System

Lightning rods must be installed and positioned in such a way that they create a protective coverage area completely enveloping the object to be protected. The installation positions of the lightning rods are determined using the following methods:

+ Protection angle method, suitable for simple-shaped buildings but limited in height;

+ Rolling sphere method, suitable for all cases;

+ Mesh method, suitable for protecting flat surfaces.

Details of these methods are provided in Appendix B. The values of the protection angle, rolling sphere radius, and mesh size corresponding to each level of LPS are specified in Table A.1.

Table A.1 - Maximum Values of Rolling Sphere Radius, Mesh Size, and Corresponding Protection Angle for Each Level of LPS

NOTE:

1. Not applicable for values greater than those marked by •

2- H is the height of the lightning rod above the reference plane of the protected area.

3- The protection angle does not change with H values below 2 m.

Figure A.1 - Determination of the Protection Angle Corresponding to Each Level of LPS

Lightning rods can take various forms: bars, wires, mesh, and combinations thereof.

Natural lightning rods can be formed from metallic parts of structures covering the area to be protected, such as metal roof components, metal pipes, and metal containers, provided they meet the following conditions:

+ Continuous and durable electrical conductivity;

+ Not covered by insulating materials;

+ Do not pose dangerous situations when punctured or overheated by lightning strikes.

Lightning rods may have supporting structures that are part of the object to be protected; If columns are used as supporting structures, they must be made of materials ensuring mechanical durability and suitable for climatic conditions.

b) Down-Conductor System

Down-conductors must be distributed around the perimeter of the building to be protected such that the distance between two conductors does not exceed 30 meters. In all cases, there must be at least two down-conductors.

Down-conductors must be connected to the grounding system.

Down-conductors must be installed straight and vertically, creating the shortest and most direct path to ground and avoiding the formation of loops. They should not be installed in locations posing danger to people.

c) Grounding System

The grounding system includes electrodes, connections between electrodes, and grounding cables.

The grounding system must be designed and have a grounding resistance value as prescribed in QCVN 9:2016/BTTTT.

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The type of grounding electrode and the layout structure of the electrodes must be selected to suit the actual terrain conditions where grounding is installed.

The grounding electrode system must be interconnected with other grounding systems (if any) as prescribed in QCVN 9:2016/BTTTT.

d) Materials

The materials and dimensions of materials chosen for the direct lightning strike protection system must ensure that the system will not be damaged by the effects of electric and electromagnetic currents, corrosion, and other mechanical forces.

e) Lightning rods and down-conductors must be securely fixed and interconnected to prevent breakage, disconnection, or loosening due to electrodynamic or other mechanical forces. Connections must be ensured through welding, screwing, bolting, and kept to a minimum number.

A.1.2. Protection Against Lightning Spread from Outside the Station Building

Electronic equipment inside the telecommunications station may be damaged by lightning spread and induction through metal communication and power lines entering the station. To limit these impacts, the following measures must be applied:

a) Protection Measures for Communication Lines Entering the Station

Select communication cables leading into and out of the station with shielding having low transmission impedance or optical cables without metallic components; the cable shielding must be equipotentially bonded as prescribed in QCVN 9:2016/BTTTT.

Install surge protection devices (SPDs) on communication lines at the interface between the line and equipment according to TCVN 8071:2009 Telecommunication Works - Lightning Protection and Grounding Practices.

b) Protection Measures for Power Lines Entering the Station

Install surge protection devices on power lines at the point where the lines enter the station according to TCVN 8071:2009 Telecommunication Works - Lightning Protection and Grounding Practices.

Use a separate low-voltage transformer to supply power to the station.

A.1.3. INTERNAL LIGHTNING PROTECTION SYSTEM (TO PREVENT SPARKING AND CONTACT LIGHTNING INSIDE THE TELECOMMUNICATIONS STATION)

a) EQUIPOTENTIAL BONDING

IMPLEMENT equipotential bonding at the boundaries between lightning protection zones (LPZ) for metallic components and systems (metal pipes, cable racks, equipment racks).

b) INTERNAL SHIELDING MEASURES

CONNECT the metallic components of the building to each other and to the direct lightning strike protection system, such as the roof, metal surfaces, reinforcing bars, and metal door frames of the building.

USE shielded cables or cables run in low impedance metal conduits. The shielding cover or metal conduit must be equipotentially bonded at both ends and at the boundaries between lightning protection zones (LPZ). Cable conduits must be divided into two parts by a metal partition, one part containing communication cables, the other part containing power cables and bonding conductors.

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c) CONFIGURATION AND GROUNDING IN THE TELECOMMUNICATIONS STATION

INTERNAL configuration and grounding within the telecommunications station must comply with QCVN 9:2016/BTTTT.

A.2. LIGHTNING PROTECTION MEASURES FOR PERIPHERAL CABLE NETWORKS OF TELECOMMUNICATIONS

A.2.1. GENERAL PRINCIPLES

A telecommunication line's ability to withstand direct lightning strikes without damage depends on the magnitude of the lightning current. This capability is defined by the protection factor (Kp), which is the ratio of the number of damages caused by lightning strikes to the total number of lightning strikes. Similarly, the protection factor is also defined for structures connected to the line.

From its definition, the protection factor Kp is a number between 0 and 1. A value of Kp=0 means that the line or structure can withstand lightning strikes without damage, while Kp=1 means every lightning strike causes damage. Selecting appropriate cables and/or applying protective measures reduces the protection factor.

The protection factor depends on minimizing the lightning current causing damage to the line and the rational distribution of the lightning current.

K{0}=p(l{a})\quad(A.1)

la, is the damaging current, KA

p(I_{a}): Probability factor of damaging current

Of which

The damaging current (Ia) is the minimum value of the lightning current causing damage to the telecommunication line. If Ia is too small, then Kp = p(I_a) ≈ 1 and every lightning strike damages the line. Figure A.2 illustrates the protection factor as a function of the damaging current.

Figure A.2 - Protection Factor (Kp) as a Function of Damaging Current (Ia)

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A.2.2. MEASURES TO PROTECT AGAINST DIRECT LIGHTNING STRIKES ON CABLES

a) For buried cables, the following protective measures may be considered:

Using shielding wires, typically zinc-coated steel wire;

Using steel pipes, typically zinc-coated steel pipes.

b) For overhead cables, the following protective measures may be considered:

Using supporting wires as shielding wires (see section a, sub-section A.2.3);

Replacing with buried cable lines and applying protective measures as described in a).

c) For both overhead and buried cables, the following measures may be considered:

Replacing with non-metallic optical cables or wireless transmission (see section a, sub-section A.2.3);

Using cables with high impulse breakdown voltage (see section b, sub-section A.2.3);

Using cables with high flashover voltage (see section c, sub-section A.2.3).

A.2.3. CABLE SELECTION

a) Non-metallic Optical Fiber Cables

Non-metallic optical fiber cables will not suffer direct lightning strikes, thus using non-metallic optical cables results in Kp = 0.

b) Cables with High Impulse Breakdown Voltage

If the damaging current (Ia) is determined by the impulse breakdown current (Is), cables with higher impulse breakdown currents can be selected by:

Increasing the impulse breakdown voltage by choosing plastic insulating materials instead of paper or enhancing insulation at joints;

Reducing the outer layer resistance by using thicker metal sheaths.

The protection factor achieved when increasing the damaging current is calculated using formula A.2.

c) Cables with High Flashover Voltage

If the damaging current is determined by the test current (It), cables with higher test currents can be selected by:

Using shells with high mechanical strength (e.g., iron);

Using thicker metal sheaths.

The protection factor achieved when increasing the damaging current is calculated using formula A.2.

A.2.4. INSTALLATION OF SURGE PROTECTION DEVICES (SPD)

SPDs can be installed at the point where the line enters a structure susceptible to direct lightning strikes, to reduce the frequency of damage caused by lightning strikes on the structure (F_{ps}). SPDs must be connected between the conductors of the cable and the equipotential bonding bar of the structure.

Installing SPDs increases the impulse breakdown current of the cable Is (see Appendix C).

The protection factor achieved when increasing the cable's impulse breakdown current is calculated according to formulas A.2 and C.4 (see Appendix C).

A.2.5. INSTALLATION OF UNDERGROUND LIGHTNING PROTECTION WIRE FOR BURIED CABLES

To reduce the lightning current entering buried cables, use underground lightning protection wires made of metal laid above the cable route to attract part of the lightning current. Thus, the underground lightning protection wire increases the damaging current (Ia) and reduces the frequency of damage. The underground lightning protection wire must be laid along the entire length of the protected cable section and extended by a distance Y, with Y calculated as follows:

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Where:

ρ = Soil resistivity, Ω.m.

The new damaging current (I'a) is calculated using the formula:

$I{a}=I{a}n_{,(KA)}$ (A4)

Where n is an even factor, see Appendix D.

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Provisions on the HS Code of Terrestrial Mobile Radio Equipment and Terrestrial Radio Relay Equipment

Product Name, Goods According to QCVN

DETERMINING THE LOCATION FOR INSTALLATION OF LIGHTNING RODS

B.1. DETERMINING THE LOCATION OF THE LIGHTNING ROD SYSTEM USING THE PROTECTION ANGLE METHOD

The location of the lightning rod system is considered satisfactory if the object to be protected is completely within the protected area created by the lightning rod system.

To determine the protected area, the physical dimensions of the metallic lightning rod system must be considered.

B.1.1. PROTECTED AREA BY A SINGLE VERTICAL LIGHTNING ROD

The protected area by a single vertical lightning rod has the shape of a cone with its apex at the top of the lightning rod, with a vertex angle of α, depending on the level of the LPS and the height of the lightning rod, as shown in Table A.1. Examples of protected areas are illustrated in Figures B.1 and B.2.

Code

Radius of the protected area;

Height of the lightning rod above the reference plane, in the protected area;

Protection angle according to Table A.1

Diagram B.1 - Protected area by a vertical lightning rod with physical height of a lightning rod

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NOTE: Protection angle α1 corresponds to the height h1 of the lightning rod, which is the height relative to the roof surface of the protected object; protection angle α2 corresponds to the height h2 = h1 + H, with the ground being the reference plane;

Diagram B.2 - Protected area by a vertical lightning rod

B.1.2. Protected area by a linear lightning rod

The protected area by a linear lightning rod is defined as the set of protected areas of successive vertical rods whose peaks lie on the line. See the example in Diagram B.3.

Diagram B.3 - Protected area by a linear lightning rod

B.1.3. Protected area by a grid-type lightning rod system

The protected area by a grid-type lightning rod system is defined as the set of protected areas by each individual conductor.

An example of the protected area by a grid-type lightning rod system is shown in Diagrams B.4 and B.5.

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Diagram B.4 - Protected area by a separate grid-type lightning rod system, determined by the protection angle method and the rolling sphere method

NC 210205

NOTE: H = h

Diagram B.5 - Protected area by a non-separate grid-type lightning rod system, determined by the mesh method and the rolling sphere method

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B.2. Determining the position of the lightning rod system using the rolling sphere method

Applying this method, the positioning of the lightning rod system is appropriate when there is no point in the protected area that touches a rolling sphere with radius r, dependent on the level of the LPS (see Table A.1), rolling around and over the top of the structure in all directions. Thus, the sphere only touches the lightning rod system (see Diagram B.6)

NOTE 1: The radius of the rolling sphere must comply with the selected LPS level (see Table A.1)

NOTE 2: H=1

Diagram B.6 - Design of the lightning rod system using the rolling sphere method

On structures higher than the radius of the rolling sphere, it may occur that lightning strikes hit the body of the structure. Each point on the side of the structure where the rolling sphere touches will be a potential strike point. However, this probability can be disregarded for structures lower than 60 meters.

For taller structures, most lightning strikes will hit the top, major horizontal edges. Only a small number of strikes will hit the body of the structure.

Furthermore, collected data show that the probability of lightning striking the body of the structure decreases rapidly as the height of the strike point increases on tall structures when measured from the ground. Therefore, lightning rods must be installed at the upper part of the structure (usually at the top 20% of the structure's height). In this case, the rolling sphere method is only applied to locate the lightning rods of the upper part of the structure.

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B.3. Locating the lightning rod system using the mesh method

For the purpose of protecting flat surfaces, a grid-type lightning rod is considered to protect the entire surface if all of the following conditions are met:

a) Lightning conductors are placed at:

The edges of the roof;

Small extensions above the roof;

At the lines on the roof peak, if the roof slope exceeds 1/10.

NOTE

The mesh method is suitable for flat or sloping roofs without curvature;

The mesh method is suitable for flat surfaces at the edge of the structure to protect against lightning strikes to the body of the structure;

If the roof slope exceeds 1/10, parallel lightning conductors can be used instead of a grid, provided that the distance between the conductors does not exceed the width of the mesh as required.

b) The size of the mesh must not exceed the values given in Table A.1.

c) The grid-type lightning rod system must be installed such that the lightning current always flows through two separate conductors down to the grounding electrode system.

d) There must be no metallic parts outside the protected area by the lightning rod system.

e) Lightning conductors must follow the shortest and straightest paths.

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Annex C

Product Name, Goods According to QCVN

Determining the damaging current for metal cables and optical cables with metal components

C.1. Determining the damaging current for buried and overhead cables in the event of direct lightning strikes to the cable

C.1.1. Damaging current for metal cables

The damaging current for metal cables, la, is determined as follows:

Where:

1. Current time

s. Penetration current (see Section B.3);

C.1.2. Damaging current for optical cables with metal components

The damaging current for optical cables with metal components, la, is determined as follows:

(if |n|<2Ic and |t|<2Is)

$I{a}=\{2I{c}\text{ if }2I{c}<1\text{ and }2I{c}<2I_{s}\}$ (C.2)

(2ls if 2ls < l, and 2ls < 2Io

Where:

1. Same,

c. New current;

I_s: Penetration current (for optical cables with metal components in both the sheath and core) (see C.3).

NOTE

The value of current I is considered in the case of optical cables with metal components in both the sheath and core,

The value of current I, I is determined in laboratory tests and can be provided by the cable manufacturer.

C.2. Determining the damaging current, I_a, for cables entering a structure struck by lightning

When lightning directly strikes a structure through which cables pass, causing damage to the cables, the damaging current, I_a, is determined based on the following assumptions:

50% of the lightning current flows into the building's grounding system;

The remaining 50% of the lightning current is divided among n service cables entering the building (telecommunication cables, power cables, water pipes);

All of the lightning current through telecommunication cables will flow into the sheath of shielded cables or be divided among the cores of unshielded cables.

For lightning strikes to a structure through which telecommunication cables pass, the damaging current is calculated as follows:

For shielded metals:

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For unshielded metals:

$I{a}=2\pi mI{c}$ (C.4)

Where:

Is is the penetration current determined according to Section C.3;

Io is the current flowing into each strand

+ For unshielded cables without SPD, I0 = 0;

+ For unshielded cables with SPD, Ic = 8.Sc [kA]

Where Sc is the cross-sectional area of the conductor, measured in mm².

For optical cables:

2.n.ls if ls < la

$l_{a}=\{0,5\}$

2n if l < ls

Where:

n: Number of pipes and metal cables entering the structure (telecommunications, electricity, water...);

C.3. Determining the penetration current of cables, ls/Ic

The formula for calculating the surge current through the metal sheath of the cable in this Appendix applies to cables with a single-layer metallic sheath. For common telecommunications cables, the surge voltage values are presented in Table C.1.

Table C.1 - Surge Voltage Values for Symmetrical Cables

The surge current through the metallic sheath or optical cable (with metallic components in both the sheath and core) buried underground is calculated using the following formula:

Where:

K = 8 : Waveform factor of the lightning surge (waveform 10/350 μs), (m/Ω)^(1/2)

R : Resistance per unit length of the cable sheath, Ω/km;

Uw: Surge voltage between the shielding sheath and the cable conductor, kV;

p : Resistivity of the soil, Ω.m;

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Table C.2 - Typical Surge Current Values for Cable Sheaths (kA) (Regulation)

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Appendix D

Calculate the shielding factor of the underground lightning protection wire protecting the buried communication cable

The shielding effect of the underground lightning protection wire depends on its installation location and is evaluated by the shielding factor n.

The shielding factor η is determined by the ratio of the currents on the cable sheath when there is (I'sh) and when there is not (Ish) an underground lightning protection wire as follows:

r= 'sh/lsh

D.1. Shielding Factor of One Underground Lightning Protection Wire

The shielding factor of one underground lightning protection wire is determined by the expression:

$r=ln(x/s)/ln(x^{2}/s.r) \quad (D.1)$

Where (see Figure D.1 a):

r. Average radius of the cable sheath;

S: Radius of the underground lightning protection wire;

X: Distance between the axes of the cable and the underground lightning protection wire.

Tables D.1 and D.2 provide shielding factor values for various sizes of conductors and different distances between conductors and underground lightning protection wires.

Table D.1 - Shielding Factor with r = 10 mm

Table D.2 - Shielding Factor with r = 20 mm

D.2. Shielding Factor of Multiple Underground Lightning Protection Wires Arranged in a Circle Around the Cable

D.2.1. Case Using Two Underground Lightning Protection Wires

See Figure D.1 b.

Table D.3 - Shielding Factor of Two Underground Lightning Protection Wires

D.2.2. Case Using Three Underground Lightning Protection Wires, with Distance x = 0.25 m See Figure D.1 c.

Table D.4 - Shielding Factor of Three Underground Lightning Protection Wires (x = 0.25 m)

D.2.3. Case Using n Underground Lightning Protection Wires Symmetrically Arranged Around the Cable, with Distance x = 0.25 m

See Figures D1d, D1e, D1f.

Table D.5 - Shielding Factor of n Underground Lightning Protection Wires Symmetrically Arranged

Figure D.1 - Arrangement of Underground Lightning Protection Wires Around the Cable

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Appendix E

(For reference)

Characteristics of Lightning in Vietnam

Table E.1 - Lightning Density in Provinces and Cities of Vietnam

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The lightning density data is based on information collected by the Institute of Geophysics and published in Table 5.1 of QCVN 02: 2009/BXD National Technical Regulations for Natural Conditions Used in Construction.

In cases where QCVN 02:2009/BXD is revised and supplemented, the latest revised and supplemented version shall be used.

Table E.2 - Distribution of Main Characteristics of Ground Lightning

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Appendix F

(For reference)

Calculating Loss Risk for a Telecommunications Station

Calculating damage risk due to lightning for a telecommunications station in Tuy Hoà City, Phú Yên Province, with the following basic data:

Size and material of the station building: 5m x 3m x 3m; reinforced concrete;

Antenna height and distance from antenna to building: 80 m high, 4 m away from the building;

Characteristics and length of cables entering the station:

+ Power cable length 600m, without shielding, buried underground;

+ Communication cable length 1000m, without shielding, suspended;

Figure F.1 - Model of a Telecommunications Station with a Tall Antenna Column

F.1. Calculation of Risk Areas, A

The risk area for direct lightning strikes on the station building, in this case A_d = 0 (as the building is covered by the risk area of the antenna column);

The risk area for direct lightning strikes on the antenna column:

Aa = Π (3h)² = Π (3x80)² = 1800956 (m²) = 0.2 (km²);

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The risk area for lightning strikes on the communication cable:

Astele = 2.d1tele.Ltele - Aa/2 = 2x1000x1000 - 90000 = 1.91x10^-6 (m²) = 1.9 (km²) – (the risk area for lightning strikes on the cables is reduced due to coverage by the risk area for lightning strikes on the antenna column);

The risk area for lightning strikes on the power cable.

Answer = 2. d1power.Lpower - Aa/2 = 2 x 250 x 600 - 90000 = 0.21x10^8 (m²) = 0.2 (km²)

The risk area for lightning strikes near the station building, A_n, is reduced due to coverage by the risk area for lightning strikes on the antenna column and the risk areas for the cables, for each individual case we have:

+ Case covered by the communication cable:

$A{intele}=\pi d^{2}/2-A{o}/2=0.3(km^{2})$

+ Case covered by the power cable.

A{n}(power) = \Pi d^{2}/2 - A{a}/2 + (\Pi d^{2}/3 - 2d{1}.d{1}\sqrt{3}/2) = 0.5 (km²) - (the components in parentheses represent the area of a circular segment when d=2d_{1})

Figure F.2 - Risk Areas

F.2. Calculation of Damage Frequency

The lightning density of the area where the telecommunications station is located in Tuy Hoà City, Phú Yên Province, according to Table D.1, Appendix D is Ng = 3.7 times/km².year.

The damage frequency F depends on Ng, the risk areas just calculated above, and the corresponding probability damage factors for protective measures, with values taken from Tables 5 to 9.

Without any protective measures, only considering the shielding of the building structure and the grounding of the cable shielding connected to the station, the damage frequency will be:

Damage frequency due to direct lightning strikes on the station building:

F{d}=N{g}.A{d}.p{d}=0(d\sigma A_{d}=0)

Damage frequency due to lightning strikes near the station building:

F{n}=N{g}\cdot A{n}\cdot P{n}=N{g}\cdot(A{n}(tele)+A{n}(power))\cdot P{n} with p n = 0.1 because the building has a reinforced concrete structure (according to Table 5),

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F1 = 3.7 x (0.3 + 0.5) x 0.1 = 0.296 (times/year);

Fs = Ng · (As(telo) + As(power)) · Ps

with p s = 1 because there are no protective measures on the cables (according to Table 7):

F_s = 3.7 x (1.9 + 0.2) x 1 = 7.7 (times/year)

Damage frequency due to direct lightning strikes on the antenna column:

F{a}=N{g}\cdot A{a}\cdot P{a}

with p_a = 0.01 because the building has a reinforced concrete structure (according to Table 5) and assuming the cable is well grounded to the building's steel reinforcement:

F_{a}=3.7\times0.2\times0.01=0.0047(\text{times/year});

F.3. Calculation of Loss Risk

The loss risk to people inside the telecommunications station area is calculated according to formula 2.1, with the assumption that the floor surface layer is made of dry concrete (p_injury = 10^-3 according to Table 9):

Rinjury = L.Pinjury. ΣFI = 1.10⁻³ x (0.296 + 7.7 + 0.0047) = 8.10⁻³

This risk is too high compared to the allowable risk level (10⁻⁵), therefore additional protective measures need to be installed.

The service loss risk is calculated according to formula 2.2:

Ross = LZF = 247.10^-3 x 8 = 19,76.10^-3

The above risk is too high compared to the permissible risk standard (10^-3); therefore, additional protective measures must be installed.

From the above calculation, it can be seen that the highest frequency of losses caused by lightning strikes originates from telecommunications and power lines (Fs = 7,7 times/year). Therefore, protective equipment must be installed on these lines. If the installation method is of good quality, it will reduce Fn and F_s by a factor of p = 0,01. As a result, the frequency of losses will be:

ΣF = 3,7 x [0,8.10⁻¹.10⁻² + 2,1.10⁻² + 0,2.10⁻³] = 8,51.10⁻² (times/year)

Human loss risk can be reduced by equipping an external lightning protection system (pinjury = 0,1 according to Table 6) and covering the working surface with asphalt or wood material (pinjury = 10^-5). In this case, the human loss risk will be:

Rinjury = 8,51.10⁻².10⁻¹.10⁻⁵ = 8,51.10⁻⁸

This value meets the permissible standard. Therefore, the protective measures for humans mentioned above are sufficient.

Service loss risk.

Rloss = 8,51.10-2 . 2,74.10-3 = 23,3.10-5 = 0,233.10-3

This value meets the permissible standard. Therefore, the protective measures for services mentioned above are sufficient.

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References

[1] IEC 62305-1:2010, Protection against lightning – Part 1: General principles

[2] IEC 62305-2:2010, Protection against lightning – Part 2: Risk management

[3] IEC 62305-3:2010, Protection against lightning - Part 3: Physical damage to structures and life hazard

[4] ITU-T Recommendation K.39 (1996), Risk assessment of damages to telecommunication sites due to lightning discharges

[5] ITU-T Recommendation K.40 (2018), Protection against lightning electromagnetic pulses in telecommunication centres

[6] ITU-T Recommendation K.47 (2012), Protection of telecommunication lines against direct lightning flashes