LPS for Rooftop PV Systems Use - pqrs.co.za

14/12/2020

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Lightning Protection Systems (LPS) for Rooftop Solar PV

Safe and effective Lightning Protection Systems (LPS) for Rooftop Solar PV

General principles & statistics Lightning formation and characteristics Lightning damages and statistics Simplified risk assessment methodologies

What is an effective LPS Air-termination systems (ATS) Down-conductor system (DCS) Earth-termination system (ETS) Lightning equipotential bonding (LEB) Separation distances

Update from SABS SANS 10142-1-2 SANS 10313 Certification of installations

Practical examples Structures without LPS Structures with isolated

LPS Structures without

isolated LPS

The formation of lightning

Down‐ward leaders and up‐ward streamers

Interesting facts and figures

The formation of lightning

Designing effective & safe lightning protection systems (LPS)

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Formation of Lightning

Downward Leaders & Upward Streamers

Downward Leaders & Upward Streamers

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Reasons for Lightning Damage

Lightning Safety

Electrothermal Effects• Direct strike• Contact Potential (Touch Voltage)• Side Flash• Step Voltage• Upward Streamer Current

Direct Strike Side Flash Upward Streamer

Step Potential

Contact / Touch Potential

Lightning Safety

Blunt Force Trauma

• Barotrauma

• Concussive Injury

• Musculoskeletal Injury (Muscle Contraction) - falling

Concussive, Explosive Barotrauma• Also called secondary missile injury.

• Injuries caused by flying shrapnel resulting from a direct lightning strike to an object.

• Lightning`s pressure blast can tear or rip off clothing, fracture bones, cause Tympanic Membrane rupture and cause lung concussions

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Lightning Safety

Lightning Fatalities

Step Potential50‐55%

Side Flash30‐35%

Upward Streamer10‐15%

Touch Potential3‐5%

Direct Strike3‐5%

Blunt Injury?

Are You Safe?

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WHY?

Are You Safe?

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Are You Safe?

WHY?

Build the Plane

Faraday Cage

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Direct lightning strike damages

Indirect lightning strike damages

Insurance survey results

Lightning damages & statistics


Direct Lightning Strike Damages

source: DEHN

source: DEHN

Indirect Lightning Strike Damages

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Sources of Damage to PV Systems

Technical Failure 6% Marten Bite 3%

Malevolence 3%

Theft 2%

Fire 2%

Lightning and Surges

26%

Miscelaneous 32%

Snow Loading 14%

Storms 9%, 9%

The principle of a Risk Assessment

Lightning collection area (new concept)• Solar rooftop vs. Building LPS

Critical vs. Cumulative line length for d.c. & a.c lines• Lightning ground flash density (NG)

Simplified risk methodologies


Risk Assessment Principles

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Lightning Collection Area

• The erection of solar systems on or at buildings does not changethe lightning strike risk to the building, which means the equivalentcollection area of the building (Abuilding) remains the same.

• The risk to the solar system can be estimated by calculating theequivalent collection area of the solar system (Asolar) then to usethe formula below to calculate the risk to the solar system only.

𝑹𝒔𝒐𝒍𝒂𝒓 𝑹𝒃𝒖𝒊𝒍𝒅𝒊𝒏𝒈𝑨𝒔𝒐𝒍𝒂𝒓

𝑨𝒃𝒖𝒊𝒍𝒅𝒊𝒏𝒈

• The method of risk assessment is based on the evaluation of the critical length Lcrit and its comparison with L the cumulative length of the d.c. lines.

• SPDs shall be installed on the d.c. side of the installation:

𝑳 𝑳𝒄𝒓𝒊𝒕

DC Lines ‐ Critical Length

AC Lines ‐ Critical Length

• A method of general risk assessment is described in IEC 61662. An essential simplification of this method has been accepted. It is based on the critical length dc

• Protection is required if:

• d is the conventional length in km of the supply line of the considered structure (Max. 1km)

• dc is the critical length; of the incoming lines and the level of consequences

𝒅𝒄𝟏𝑵𝑮

𝒅 𝒅𝒄

𝒅𝒄𝟐𝑵𝑮

consequences to groups of individuals, e.g. large residential buildings, churches, offices, schools;

consequences to individuals, e.g. residential buildings, small offices.;

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Lightning Ground Flash Density (NG)

• Notes:

• Single station in SA

• NG of Irene => 7‐8

Operator: SA weather services

Stations (n) : 25

NG of Irene: 11.2 (>50% increase)

Operator: CSIR

Stations (n): 1

NG of Irene: 7.4

What it an effective & safe LPS?

External lightning protection systems• ATS, DCS & ETS

Internal lightning protection systems• LEB, SPD, Routing & Shielding

What is an Effective & Safe LPS?


Total Lightning Protection System

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External Lightning Protection System

Internal Lightning Protection System

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Rolling Sphere Method

The rolling sphere method is the universal method of design and is recommended for geometrically complicated applications.

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Rolling Sphere Method

Rolling Sphere Method – 3D Modeling

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Combination of Air Termination Methods

Final Striking Distance

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Natural Air Terminals



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• Care must be taken to avoid using steel roof sheeting where

there is a risk of fire – hot spots could cause ignition of the

wooden roof trusses.

Down Conductor System

Links Air Termination System to Earth Termination System

In order to reduce the probability of damage due to lightning current flowing in the

LPS, the down‐conductors shall be arranged in such a way that from the point of

strike to earth:

a) several parallel current paths exist;

b) the length of the current paths is kept to aminimum;

c) The number of down conductors shall not be less than two per LPS and

should be distributed around the perimeter of the structure, this is

subject to architectural and practical constraints.

d) A down conductor should be installed at each exposed corner of the structure, where possible.

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Down Conductor System

Down Conductor Spacing

Maximum Spacing of Down Conductors Depends on Lightning Protection Level

Down Conductors Dimensions

• Copper, aluminium and galvanized steel are generally used as down conductor materials, the minimum dimension as shown below:

• When the separation distance from a down conductor to a conductive element cannot be assured, the use of HVI conductors should be considered.

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Types of Down Conductors

Type 1: External Down Conductors Type 2: Natural Down Conductors• Purpose built down conductors installed on

the outside of the structure.

• Copper, aluminium and galvanized steel are generally used as external down conductors.

External down conductors are subject to the maintenance of separation distances

• Natural elements such as structural steelwork, concrete steel reinforcing, metallic facades and welded rainwater downpipes should be utilized as natural down conductors.

Care must be taken to ensure electrical continuity across all‐natural down conductors.

Natural Down Conductors

Natural Down Conductors

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Earth Termination System

Safe Dissipation of Lightning Current

General

The shape and dimension of the lightning protection earthing system are important when dealing with safe dispersion of the lightning current into the ground.

In order to minimize any dangerous overvoltage's a low resistance earthing system is recommended –if possible lower than 10 Ohms.

A single integrated earthing system is preferable, which is suitable for all purposes (i.e. lightning protection, power systems, telecommunications systems and data systems).

Alternatively all earthing systems shall be equipotentially bonded together.

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Soil Resistivity Measurement

Soil Resistivity Measurement

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Types of Earth Termination Systems

Selection of Type of Earth Electrode

Type A: Individual Earth Electrodes• Recommended for:

‐ Lightning protection level III and IV systems‐ Structures with low soil resistivity values‐ Retrofits where Type B electrodes are unpractical.

Type B: Ring Earth Electrodes• Recommended for:

‐ Lightning protection level I and II systems‐ Integrated earthing systems‐ Bare solid rock sites (only Type B)‐ Structures with extensive electronics‐ Structures with a high risk of fire

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Earth Electrode Dimensions

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Lightning Equipotential Bonding

Prevents Dangerous Sparking Inside The Structure

Equipotentialization is performed to prevent dangerous sparking within a structure due to lightning current flowing in the external

LPS or any conductive parts of a structure.

The equipotential bonding of the following elements to the external LPS is essential :

• Metal Installations• Power Supply Systems• Information Technology Systems

Types of Equipotential Bonding:

• Bonding via bonding conductors• Bonding via surge protection devices

Lightning Equipotential Bonding

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Separation Distance Principles

Separation Distances Prevent Uncontrolled Flashovers“An isolated external LPS should be used when the flow of the lightning current into bonded internal

conductive parts may cause damage to the structure or its contents.” – IEC 62305 Part 3

The uncontrolled entry of partial lightning currents into a structure

inadequate separation distances can lead to flashovers between the LPS and internal conductive elements of the

structure.

This can result in the risk of fire and damage to internal systems

The correct separation distance therefore must be maintained to prevent these

flashovers.

distance between two conductive parts at which no dangerous sparking can occur

=

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Isolated vs Non‐Isolated LPS

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Separation Distance Exceptions

Separation Distances Can Be Ignored If :

• Interconnected concrete reinforcing is utilised as natural down conductors – applies only to down conductors.

• Interconnected structural steel work is utilised as natural down conductors – applies only to down conductors.

• HVI (High Voltage Insulation) Conductors are utilised for Air Termination and Down Conductor Systems.

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Separation Distance Simulations

Separation Distance Simulations

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LPS for Rooftop PV Systems

Isolated LPS for Rooftop PV Systems

Isolated LPS for Rooftop PV Systems

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Non‐Isolated LPS for Rooftop PV Systems

Non‐Isolated LPS for Rooftop PV Systems

Scenario 1 – Structures without LPS

• Surge protection to PV system by means of Class 2 & 3 surge arresters• Equipotential bonding to electrical earthing system by means of 16mm² copper conductors.

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Scenario 2 – Structures with Isolated LPS

• Surge protection to PV system by means of Class 2 & 3 SPDs – Class 1 SPD in Main DB• Equipotential bonding to electrical earthing system by means of 16mm² copper conductors.

Equipotential Bonding

The bonding of the PV panels is carried out at the internal earth bar only.

No Bonding to the LPS is carried out for isolated LPS.

Isolated LPS

An isolated LPS is achieved when the calculated separation distance between the

LPS and the PV system is maintained.

Scenario 2 – Structures with Isolated LPS

Scenario 3 – Structures with Non‐isolated LPS

• Surge protection to PV system by means of Class 1 & 2 SPDs – Class 1 SPD in Main DB• Equipotential bonding to electrical earthing system by means of 16mm² copper conductors.

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Scenario 3 – Structures with Non‐isolated LPS

Equipotential BondingPV panels are bonded directly to the LPS and

the internal earth bar

Air termination rods and finials are mounted to PV

framework

SANS Update – Pending Changes

SANS 10313 Update

Addressing applications which SANS 62305 does not cover are:

Thatch, Solar Rooftop, Recreational facilities, Safe shelters and Mining applications

Update of the lightning ground flash data

Adoption of new innovations and technologies

Mandating the use of LPS Installation Safety Report – accountability and transparency


SANS 10142‐1‐2 / SANS 10313

• EGI Categories A1 and A2 are exempt from installing any external lightning protection systems. SANS 10313 recommends a minimum LPL III for Categories A2 and A3.

• A risk assessment, according to SANS 10313, shall be performed for EGI Category A3 (as per Section 4.5.1, Generator Categories by Capacity). If the risk profile shows a high risk, a full lightning protection system must be installed for the EGI.

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SANS Update – Lightning Ground Flash Index


SANS 10142‐1

External LPS must be bonded to the main

consumer earth‐terminal

When external lightning protection

systems are fitted a Type 1 SPD shall be

fitted in conjunction with a Type 2 SPD


SANS 10142‐1

Simple risk assessment to

determine the need for a surge

protective device (SPD)

How to select & wire the SPDs

correctly?

New SPD test report to be issued

as part of the supplementary COC

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SANS 10313 – Certification

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LPS for Rooftop PV Systems Use - pqrs.co.za

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