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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
illia
m J
oseph F
urs
e
Ori
gin
ally
as a
Ste
ep
leja
ck c
om
pa
ny
Ce
leb
ratin
g 1
25
ye
ars
in
bu
sin
ess
1998
Acq
uir
ed
by T
ho
ma
s &
Be
tts
1907
Re
loca
ted
to
Tra
ffic
Str
ee
t
Mo
re e
mp
ha
sis
on
En
gin
ee
rin
g
1912
Inco
rpo
rate
d a
s W
J F
urs
e &
Co
Ltd
1937
Will
iam
Jo
se
ph
Fu
rse
pa
sse
d a
wa
y
1950
Pre
mis
es b
uilt
at W
ilfo
rd R
oa
d
1987
Tw
o b
uy-o
uts
to
ok p
lace
1990
Acquired b
y E
ast M
idla
nds E
lectr
icity P
LC
1958
Acq
uir
ed
by E
V H
old
ing
s
1967
Acq
uir
ed
by C
row
n H
ou
se
1996
Acq
uir
ed
by C
inve
n L
td
125 years of history & experience!
125 years of reliability & trust!
1993
Ce
leb
rate
d 1
00
ye
ars
in
bu
sin
ess
2012
AB
B a
cq
uir
ed
Th
om
as &
Be
tts
Divisions, business units & product groups
ABB Organization
May 24, 2018 Slide 3
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
May 24, 2018 Slide 4
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
May 24, 2018 Slide 5
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
May 24, 2018 Slide 6
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
—
Earthing for Lightning Protection Systems
Functions of the Earthing System
Earthing for Lightning Protection Systems
May 24, 2018 Slide 8
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
May 24, 2018 Slide 9
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
—
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
—
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
Earth Electrode - Rods
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
Copperbonded / Solid Copper / Stainless Steel
Earth Electrode - Rods
Earthing
May 24, 2018 Slide 29
Stainless Steel Rod
Stainless Steel
Highly resistant to corrosion
Used to overcome many of the problems caused by galvanic corrosion which can take place between dissimilar metals buried in close proximity
High strength
Copperbonded / Solid Copper / Stainless Steel
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
Earth Electrode - Comparing Copperbonded & Galvanised Steel Rods
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
Earth Electrode - Comparing Copperbonded & Galvanised Steel Rods
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
Highly resistant to corrosion
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
Highly resistant to corrosion
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)
IEC/BS EN 62561-4:2011 Lightning protection system components (LPSC)
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)
IEC/BS EN 62561-7:2011 Lightning protection system components (LPSC)
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
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