2018 earthing - static.elektrum.lv · earthing systems earthing may 24, 2018 slide 6 lightning...

2018

Earthing An Overview of Earthing

Gary Blackshaw, Global Business Development Manager

History

Furse Overview

May 24, 2018 Slide 2

1893 2018

Founded b

y W

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e

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ally

as a

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1998

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1907

Re

loca

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to

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mp

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sis

on

En

gin

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rin

g

1912

Inco

rpo

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d a

s W

J F

urs

e &

Co

Ltd

1937

Will

iam

Jo

se

ph

Fu

rse

pa

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d a

wa

y

1950

Pre

mis

es b

uilt

at W

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rd R

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1987

Tw

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to

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1990

Acquired b

y E

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LC

1958

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by E

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1967

Acq

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by C

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1996

Acq

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125 years of history & experience!

125 years of reliability & trust!

1993

Ce

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2012

AB

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Divisions, business units & product groups

ABB Organization


Cable Ties, Metal Framing,

Duct, Cable Tray

Connectivity & Grounding

Cable Protection Systems

Emergency Lighting

Explosion Protection

Cable Apparatus

& Accessories

Solar Distribution

Solutions Building Products

Protection & Connection

Installation Products

Discrete Automation & Motion

Electrification Products

Process Automation

Power Grids

Group

Divisions

Business Units

Product Groups

Where we make a difference

Furse Overview


Oil & Gas / Petrochemical Utilities / Energy Cultural & Heritage

Data Centers Rail & Infrastructure High Tech & Industrial

The Furse Total Solution for all project types and industry sectors worldwide

Earthing Systems

Earthing


Earthing for Lightning Protection Systems

Applicable to Lightning Protection systems

IEC/BS EN 62305 Lightning Protection Standard

Generally simple

Power Earthing Systems

Applicable to Substations, Power Stations, Transformers, Transmission Lines,

Telecommunication Lines, Wind Farms, Solar Farms, Data Centres etc.

Various Standards

Generally very complex

Earthing Systems

Earthing


Lightning protection earthing systems are designed for high frequency applications. For example, a lightning current will typically reach peak value between 10 and 20

microseconds whereas power earthing systems are generally designed for applications operating at relatively low frequency and time spans from 0.2

milliseconds to 5 second duration

Lightning protection standards recommend a resistance to earth of 10 Ω or less in most cases

Power earthing systems will typically require far lower values, calculated for each

separate project

To achieve the low resistance values, designing a power earthing system requires much more thought, information, and application than just simply installing an array

of rods into the ground as is fairly common practice

—


Functions of the Earthing System



Safely & effectively dissipate the lightning current into the ground / earth

Earthing products for use in lightning protection systems are designed to safely & effectively dissipate lightning current to earth, whilst withstanding the stresses

placed on them

Equipotential bonding is equally vital to prevent dangerous sparking between the LPS and other components such as: metal installations, internal systems, external

conductive parts and lines connected to the structure. The products are designed to achieve equipotential bonding of metal parts within and around the structure

Basic Principles of Lightning Protection

Lightning Protection


1. Capture/intercept the lightning strike (air termination network)

2. Safely conduct the lightning current to earth (down conductor System)

3. Safely & effectively dissipate the lightning current into the ground (earth termination system)

4. Provide equipotential bonding & electrical insulation (separation distance) to prevent dangerous secondary sparking

5. Protect against the secondary effects of lightning caused by surges & transients (i.e. SPDs)

1

2

3

4

5

Earth Termination Systems

Lightning Protection Standard IEC/BS EN 62305

May 24, 2018 Slide 10

Recommended resistance of 10 Ohms or less in most situations

The standard recommends a single integrated earth termination system for a structure, combining lightning protection, power systems and telecommunication

systems

The main principle behind such a system is to ensure that all systems are at the same electrical potential in the event of a fault or lightning strike, thus

minimising and hopefully avoiding any risk of secondary flashing or arcing between the various electrically connected parts of the structure and the

equipment contained within

Note - Local electrical requirements and regulations may not permit the LP and power earthing systems to be interconnected

Earth Termination Arrangements

Lightning Protection Standard IEC/BS EN 62305

May 24, 2018 Slide 11

Type A arrangement

Vertical rods or horizontal radial electrodes

Connected to each down conductor

Type B arrangement

Unbroken ring conductor around perimeter of structure – depth >0.5m & 1m

from building edge

Foundation reinforcement – piles or raft

—

Power Earthing Systems

What Do We Mean By “Earthing”?

Earthing

May 24, 2018 Slide 13

By “Earthing” we generally mean an electrical connection to the general mass of earth.

The mass of earth generally being a volume of soil/rock whose dimensions are very large in comparison to the electrical system being considered.

Functions of an Earthing System

Earthing

May 24, 2018 Slide 14

Earthing is generally provided for reasons of safety

To provide a definite path for fault currents from a fault point back to the associated system neutral

To provide a low impedance/resistance to ensure satisfactory protection system operation under fault conditions

To limit as far as it is practicable, the rise of earth potential under fault conditions to a value that can safely be transferred outside the site boundary to a third party

To eliminate persistent arcing ground faults To provide an alternative path for induced currents thereby minimising the electrical

noise in cables To ensure that a fault which develops between high and low voltage windings of a

transformer can be detected by primary protection systems

—

Standards

Standards -

Earthing

May 24, 2018 Slide 16

In Great Britain, earthing of an electricity supply system is governed by the: Electricity Safety, Quality and Continuity Regulations 2002

Electricity at Work Regulations 1989 Construction Design and Management (CDM) Regulations 1994

Breaches of the above constitute a criminal offence

BS EN 50522: 2011 – Earthing of power installations exceeding 1 kV a.c.

BS7430: 2011 - Code of practice for protective earthing of electrical installations

BS7354: 1992 - Design of high-voltage open terminal substations

BS7671: 2000 - Requirements for electrical installations

BS EN IEC 61936-1: 2001 - Power installations exceeding 1 kV a.c. – Part 1: Common rules

Standards – US

Earthing

May 24, 2018 Slide 17

IEEE Std 80 – 2000 - IEEE Guide for Safety in AC Substation Grounding

IEEE Std 81 – 1983 – Guide for measuring Earth Resistivity, Ground Impedance…..

IEEE Std 142 – 1991 – Grounding of industrial and commercial power

systems

IEEE Std 367 – 1996 – IEEE Recommended practice for Determining the Electric Power Station Ground Potential Rise and Induced Voltage from a

Power Fault

IEEE Std 665 – 1987 – IEEE Guide for Generating Station Grounding

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Soil Resistivity

Soil Resistivity

Earthing

May 24, 2018 Slide 19

One of the most important factors influencing the performance of an

earthing system

The resistance to earth of a given electrode depends upon the electrical resistivity of the earth i.e. the actual

soil where the earth electrodes will be positioned

The resistivity of soil can vary not only

geographically but across the same site, and quite dramatically at different

depths

Different layers of strata will affect the distribution of current passing through

the electrode

What Factors Influence Soil Resistivity?

Earthing

May 24, 2018 Slide 20

Type of soil

Moisture content

Temperature

Chemical composition

Compactness/Density

Seasonal variation

Artificial treatment

—

Soil Resistivity Measurement

Soil Resistivity Measurement

Earthing

May 24, 2018 Slide 22

The resistivity of soil can vary not only geographically but across the same

site, and quite dramatically at different depths

Different layers of strata will affect the

distribution of current passing through the electrode

Generally the soil is made up of varying

layers of material, different thickness’ therefore differing resistivity values

Soil resistivity measurements will

determine the soil resistivity for different depths

—

Earthing Materials and Connections

Earthing System

Dedicated Earthing

May 24, 2018 Slide 24

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Earth Electrode Types

Earth Electrode - Conductor

Earthing

May 24, 2018 Slide 26

Earthing conductors form an integral part of the single earthing arrangement, whether they provide the means of connection to the final earth electrode (earth rod or plate), or whether they comprise the earth electrode itself (through an earth grid or ring earth arrangement)

An earth conductor must be capable of carrying the maximum expected earth fault current and leakage current likely to occur at a structure. The size or minimum cross-sectional area of the conductor must therefore be calculated through the specification of fault current, duration, and jointing type.

A good earth conductor must also:

Be able to withstand mechanical damage

Be compatible with the material of the earth electrode

Resist the corrosive effect of local soil conditions

Earth Electrode - Rods

Earthing

May 24, 2018 Slide 27

Copperbond Rod

Molecularly bonding 99.99% pure electrolytic copper on to a low carbon steel core (not sheathed type)

No interface or gap between the two metals due to the bond at molecular level which means a dissimilar metal reaction cannot occur and the copper cannot be separated from the steel

Highly resistant to corrosion

High tensile strength steel core means they can be driven to great depths

Copperbonded / Solid Copper / Stainless Steel


Earthing

May 24, 2018 Slide 28

Solid Copper Rod

99.99% pure copper

Offers greater resistant to corrosion

Ideally used in applications where soil conditions are very aggressive, such as soils with high salt content

Lower strength



Earthing

May 24, 2018 Slide 29

Stainless Steel Rod

Stainless Steel


Used to overcome many of the problems caused by galvanic corrosion which can take place between dissimilar metals buried in close proximity

High strength


Earth Electrode - Comparing Copperbonded & Galvanised Steel Rods

Earthing

May 24, 2018 Slide 31

Copper is resistant to corrosion in most soils

Zinc is sacrificial in most soils and with respect to most metals

Corrosion protection mechanisms are different;

The copper coating is designed to prevent corrosion of the steel core

The zinc coating will delay corrosion of the steel core by providing a sacrificial barrier


Earthing

May 24, 2018 Slide 32

¾” Galvanised Steel Earth Rod

5/8” Copperbonded Steel Earth Rod

Earth Electrode Rods excavated after 12 years

The loss of zinc on the galvanized steel earth rod resulted in

excessive corrosion of the steel

The copperbonded steel earth rod showed minimal corrosion


Earthing

May 24, 2018 Slide 33

Galvanised Earth Electrode Rod excavated after 11 years

Galvanised Steel Earth Rod

The loss of zinc resulted in excessive corrosion of the steel. One area is reduced from a ¾”

diameter to approximately a ¼” diameter due to the corrosion

The eventual failure could result in a potential, critical earthing

system collapse!

Corrosion

Earthing

May 24, 2018 Slide 34

Copper is one of the better and commonly used materials for earth electrodes. Solid copper is particularly suitable and recommended where high fault currents are

expected

Corrosion

Earthing

May 24, 2018 Slide 35

Earth electrodes, being directly in contact with the soil, shall be made of materials capable of withstanding corrosion. The factors associated with the corrosion of metals

in contact with soil that should be considered are;

The chemical nature of the soil pH value (acidity/alkalinity)

Salt content Differential aeration / drainage

Presence of bacteria

The material has to resist the mechanical influences during their installation as well as those occurring during normal service

Earth Electrode - Plates & Mats

Earthing

May 24, 2018 Slide 36

Difference in voltage potential minimized through use of earth mat

Voltage potential curve Image is for illustration purposes only

100V

600V

400V Difference

50V

50V Difference

1000V

Earth Electrode - Plates & Mats

Earthing

May 24, 2018 Slide 37

Copper Earth Plates

99.99% pure copper


Alternative style of electrode where there is high resistivity soil or where rock conditions prohibit the driving of rods

Copper Earth Lattice Mat

99.99% pure copper


Designed to minimize the danger of exposure to high step and touch voltages to operators in situations such as high voltage switching

Earth Electrode – Connections / Joints

Earthing

May 24, 2018 Slide 38

It is critical that the earth electrodes connections / joints are conductively and mechanically stable and reliable

Mechanical (compression, bolted etc.) connections / joints rely on surface contact and physical pressure to maintain connection

Exothermic welded connections / joints form permanent, high quality electrical connections

Compression Connection Mechanical Connection Exothermic Connection

Earth Electrode – Connections / Joints

Earthing

May 24, 2018 Slide 40

FurseWELD Exothermic Welding offers the following advantages;

Connections are designed to have a larger cross-sectional area than the conductors being joined

Equivalent or greater current carrying capacity

Joints can therefore handle higher fault currents than using mechanical clamps or brazing

Better corrosion properties

Permanent connections that will not loosen

Where to use it?

FurseWELD Exothermic Welding

May 24, 2018 Slide 41

Infrastructure projects

Utility projects

Power plants

Substations

Rail

Windfarms

Solar farms

OHL

Telecoms

—

Earth Electrode Backfill Materials

Earth Electrode Backfill Materials – Typical Application

Earthing

May 24, 2018 Slide 43

An earth electrode backfill material may be used to reduce the contact resistance and increase the effective size of earth electrodes, e.g. as a

backfill for earth rods installed in drilled holes or as a layer encapsulating horizontal earth conductors buried in a trench.

Earth Electrode Backfill Materials – Bentonite

Earthing

May 24, 2018 Slide 44

Bentonite is a moisture retaining clay consisting largely of sodium montmorillonite, which when mixed with water swells to many times its dry volume. Its main advantage as far as earthing is concerned, is that it has the ability to hold its moisture content for a considerable period of time and to

absorb moisture from the surrounding soil.

Earth Electrode Backfill Materials – Bentonite

Earthing

May 24, 2018 Slide 45

Bentonite will absorb up to five times its weight in water and swell up to thirteen times its dry volume. At six times its dry volume it is a very dense, pasty clay that can hold its own shape and will adhere to any

surface it touches. These two characteristics solve the compaction and soil to rod contact problems

Bentonite hydrates chemically, holding water in its structure. The material is a natural clay formed years ago by volcanic action. It is non-

corrosive, stable and will not change characteristics as time elapses

The resistivity of Bentonite varies from about 3 Wm upwards depending on its moisture content (BS7430 clause 8.5)

Generally not used in very dry or free draining locations

Earth Electrode Backfill Materials – FurseCEM

Earthing

May 24, 2018 Slide 46

FurseCEM is a granulated electrically conductive aggregate that replaces normal concrete fine aggregates such as sand, permitting electrically

conductive concretes to be designed by applying conventional concrete technology

—

Step and Touch Potential

Step and Touch Potential

Earthing

May 24, 2018 Slide 48

When the human body is accidentally introduced into the circuit between live (faulted) metalwork and earth a current may flow that could be lethal

Current flow is dependant on many factors such as duration, body impedance,

footwear impedance, surface resistivity etc.

The evaluation of ‘step’ and ‘ touch’ potentials are required by most international earthing standards

Most earthing standards set tolerable limits for step and touch potentials which are

determined by the product of allowable body current and the impedance of the electrocution circuit model

Definitions of voltage limits varies between standards

Step Potential

Earthing

May 24, 2018 Slide 49

Step Potential is the difference in surface potential experienced by a person’s feet bridging a distance of 1m without contacting any other grounded surface

Step Potential can be controlled by the use of a properly designed ground electrode

system (grid) or the use of insulating ground coverings such as rock chips

50% Voltage drop between feet Same potential between feet

Touch Potential

Earthing

May 24, 2018 Slide 50

Touch Potential is the potential difference between EPR and the surface potential at the point where a person is standing, while at the same time having hands in

contact with a grounded structure

Touch Potential is controlled by proper bonding and protective systems, such as personnel safety mats and insulating ground coverings (rock chippings)

No Protection Same potential as tower

—

Earthing Design Overview

Design Overview

Earthing

May 24, 2018 Slide 52

A vital first part of the earthing design is the accurate measurement and interpretation of Soil Resistivity

Accurate soil resistivity data together with other system design information are of

vital importance as the inputs to complex computer modelling processes

This data is used to determine “Rise of Earth Potential” values under system fault conditions

The data is also used to calculate values of potentially hazardous touch, step and

transfer voltages and determine the “Hot” or “Cold” nature of the site

Hot Site – A site where the rise of earth potential, under the maximum earth fault current condition, can exceed the

value either 430 V or 650 V depending upon the fault clearance time Cold Site – A site that has a earth potential rise below the telecommunication authorities limits (430 and 650 volts @

50Hzs)

Design Overview – Earthing System

Earthing

May 24, 2018 Slide 53

Using the soil model and taking account of the power system bonding requirements, an economical earthing system layout can be developed and analysed

Example of a 3D earth electrode layout consisting of vertical electrodes and horizontal interconnecting conductor tapes

Furse Earthing Design

C‐DEGS

Soil resistivity measurements

System design

Validation of existing designs

Step & touch potential calculations

Hot / Cold site parameters

—

Glossary

Glossary

Earthing

May 24, 2018 Slide 56

Earth Potential Rise – Voltage between an earthing system and reference earth Reference Earth (remote earth) – Part of the earth considered as conductive, the

electric potential which is conventionally taken as zero, being outside the zone of influence of the relevant earthing arrangement

Hot Site – A site where the rise of earth potential, under the maximum earth fault current condition, will exceed the value either 430 V or 650 V depending upon the

fault clearance time Cold Site – A site that has a earth potential rise below the telecommunication

authorities’ limits (430 and 650 volts @ 50Hz) Rise of Earth Potential (ROEP) - The radial ground surface potential around a earth

electrode referenced with respect to remote earth Local Earth – Part of the earth which is in electric contact with an earth electrode

and the electric potential of which is not necessarily equal to zero Foundation Earth Electrode – Conductive structural embedded in concrete which is

in conductive contact with the earth via a large surface

Glossary

Earthing

May 24, 2018 Slide 57

Earth Fault – Fault caused by a conductor being connected to earth or by the insulation resistance to earth becoming less than a specified value

Fault Level – The fault level in amps that may be expected to flow through the earth grid and on which calculations will be based

Earth Fault Current – Current which flows from the main circuit to earth or earthed parts at the fault location

Resistivity – The reciprocal of conductivity. It is the inherent resistive property of a material. Dimensionally it is resistance x length for a 1 metre cube in Ω/m

ABB Furse Quality Expectations

IEC/BS EN 62561 Lightning Protection Component Standard

—

Quality Expectations

IEC/BS EN 62561 Lightning Protection Component Standard

IEC/BS EN 62561 Recognised Manufacturing Product Standards

IEC/BS EN 62561

Lightning Protection System Components (LPSC)

Parts 1 – 7

Governing lightning protection components quality & performance

Introduced to be the direct replacement of BS EN 50164

IEC/BS EN 62561

Lightning Protection System Components (LPSC)

IEC/BS EN 62561-1:2012 Lightning protection system components (LPSC) Part 1: Requirements for connection components

IEC/BS EN 62561-2:2012 Lightning protection system components (LPSC)

Part 2: Requirements for conductors and earth electrodes

IEC/BS EN 62561-3:2012 Lightning protection system components (LPSC) Part 3: Requirements for isolating spark gaps (ISG)


Part 4: Requirements for conductor fasteners

IEC/BS EN 62561-5:2011 Lightning protection system components (LPSC) Part 5: Requirements for earth electrode inspection housings and earth

electrode seals

IEC/BS EN 62561-6:2011 Lightning protection system components (LPSC) Part 6: Requirements for lightning strike counters (LSC)


Part 7: Requirements for earth enhancing compounds

IEC/BS EN 62561 Recognised Manufacturing Product Standards

In order to comply with IEC/BS EN 62305 standard the components & materials used shall comply with the IEC/BS EN 62561 series

Governs lightning protection component quality and performance

Has fully replace BS EN 50164

LPSC which conform to this standard offers assurance that their design and manufacture is suitable for use in LPS installations.

IEC/BS EN 62561 Product Test Standards

IEC/BS EN 62561-1 Lightning protection system components (LPSC) Part 1: Requirements for connection components

A performance specification attempt to simulate actual installation conditions

Preconditioning or environmental exposure followed by three 100kA 10/350s electrical impulses (simulating lightning discharge)

IEC/BS EN 62561-1

Examples of components before and after testing

IEC/BS EN 62561-1

IEC/BS EN 62561-2 Lightning protection system components (LPSC) Part 2: Requirements for conductors and earth electrodes

A performance specification attempt to simulate actual installation conditions

Dimensional checks – radial copper thickness & adhesion

Preconditioning or environmental exposure

Bend testing

IEC/BS EN 62561-2

2018 earthing - static.elektrum.lv · earthing systems earthing may 24, 2018 slide 6 lightning...

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