Transcript Roadhsow Introduction and Six PP

GROUNDING
3. Dissipate the energy into a low impedance
grounding system.
4. Bond all ground points together to eliminate
ground loops and create an equipotential plane.
Why do we ground?
• Personnel Safety
- Reduce potential differences between non-current carrying
parts (enclosures) and between non-current carrying parts and
Earth.
• System stability
- Operate over current device during a ground fault.
• Protect equipment
- Over voltage control.
- Lightning Dissipation
- ESD (Electrostatic Discharge)
• Reliability of Equipment
- Noise Control (Computer Grounding, SRG)
Guidelines / Rules
International Electro technical Commission (IEC)
Underwriters Laboratory (UL)
National Fire Protection Association (NFPA)
American National Standards Institute (ANSI)
British Standards (BS)
Mine Health Safety Health Administration (MSHA)
Institute of Electrical & Electronic Engineers (IEEE)
Occupational Safety Health Administration (OSHA)
Telecommunication Industry Association (TIA)
European Committee for Electro Technical
Standardization (CENELEC)
What is a good
ground?
Ideally, zero ohms resistance
• Some standards require a single electrode, of specified
dimensions
• Others want a figure below a specified value
• NEC
< 25
• Telecom < 5
• Power
< 1
• Combination of the above
Goal is practical and dependant on governing factors
• Physical limitations of the site
• An economic solution
Characteristics
A good grounding system:
• has a low resistance path into ground.
• The lower the resistance the more likely
lightning, surge and fault currents will flow
safely to and dissipated to ground
• does not deteriorate over time.
• A grounding system must resist corrosion
and be capable of repeatedly carrying high
currents.
Typically, a life in excess of 30 years!
Grounding
Design
When designing the grounding system, we
must consider each of the components as
part of a chain:
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•
•
•
•
Soil
Electrode to soil
Electrode
Connector
Ground Conductor
Grounding
Chain
SOIL
• Soil resistivity must be carefully considered, including
moisture content temperature and seasons.
• Resistivity is measured to determine information
necessary to design and build an electrode system
• Bore samples confirm sub-strata composition
• Usually measure resistivity using the Wenner method
(developed in 1915 by Frank Wenner)
Grounding Design
For any design, we need to establish the
parameters:
• Required ground resistance;
• From standard or specified by client
• Soil resistivity;
• At least 2 measurements at 90 degrees
• Many measurements at different spacings
• Bore hole survey of site
• Site area and limitations (drawings)
• Property outline
• Existing structures, paved areas
• Buried pipes and services
Resistivity
Also known as specific resistance:
• Physical characteristic of the material
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•
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Copper = 1.72 x 10-8 ohm.m
GEM = 0.12 ohm.m
Bentonite = 2.5 ohm.m (typical)
Concrete = 30 to 90 ohm.m
Sand (moist) = 300 ohm.m
Gravel (moist) = 500 ohm.m
Sand (dry) = 1000 ohm.m
Stoney soil = 30,000 ohm.m
Grounding
Chain
ELECTRODE TO SOIL
Grounding
Chain
GROUND ENHANCEMENT
• Chemicals (salts)
• Calcium Chloride or Sodium Chloride
• Bentonite
• Hydrous Aluminium Silicates
• GEM ® & E-Gel
• Proprietary Formulations
Grounding
Chain
CHEMICALS (SALTS)
• Leach into environment (pollution)
• Accelerate corrosion
• Maintenance replacement issue
Grounding
Chain
BENTONITE
•
•
•
•
Requires moisture to form electrolyte
Effective when wet
Low initial cost
May pull away from rod or soil when it dries
Grounding
Chain
GEM
•
•
•
•
Very effective - conducts wet or dry
20 times more conductive than Bentonite
Provides seasonal stability – sets hard
Easy to use
• 12 kilogram bags
• Install wet or dry
GEM Calculator
• Design software available
Grounding
Chain
ELECTRODE-TO-SOIL
Ground rod resistance is affected by length, relative
placement, and most importantly, coupling integrity
where rods are joined for deep driving.
GROUND RODS (Electrodes)
Material Choices
GROUND RODS (Electrodes)
Materials are selected for corrosion resistance:
• Galvanised steel rods are cheap but
have a relatively short service life
• Solid copper and stainless steel
rods have a long service life but are
considerably more expensive
• Copperbonded earth rods are less
expensive than solid copper and
can be deep driven
GROUND RODS (Electrodes)
International standards require a minimum of
0.25 mm copper on a Copperbonded rod
ERITECH bonded rod
• Requirement of BS7430; UL467
• Copper specimens buried in 43 soil
types for 8-13 yrs
• Calculated average penetration in
30 years would be 0.17 mm in 41 of
the 43 different soils
• Base on this, 0.25 mm established as
minimum
Typical sheathed rod
GROUND RODS (Electrodes)
•
•
Ground rods can be coupled to achieve greater
depth, using either:
• Compression couplings
• Threaded couplings
A driving head can be used to prevent head
deformation.
GROUND RODS (Electrodes)
Comparison of life expectancy
Life Expectancy
50
45
50
40
45
35
30
35
Years 25
20
15
10
15
5
0
Zinc Galvanized
Copperbonded
Steel (10 mil )
Copperbonded
Steel (13 mil )
Stainless Steel
Grounding
Chain
CONNECTOR
Connections must maintain the integrity of the conductor
and the system as a whole for up to 40 years.
They must be of an appropriate material and mass to:
• carry prospective fault currents
• be able to resist corrosion
• maintain original low resistance
Grounding
Chain
MECHANICAL CONNECTOR
Although quick to apply, suffer
from the following
disadvantages:
• Tends to loosen
• Corrosion in the connection
interface
Introduction to
Cadweld
Molecular Bond
There is no
mechanical
interface in a
molecular
bond.
Molecular bonds guarantee
conductivity across the entire section
Introduction to
CADWELD
Mechanical joints will deteriorate
over time and if not maintained,
eventually fail.
Introduction to
Cadweld
Cadweld – a process to make exothermic
welded connections
Exothermic – a chemical reaction which gives off
heat as the reaction takes place
3Cu2O + 2Al  6Cu + Al2O3 + Heat (2537oC)
Cadweld provides a simple on site welding connection
without requiring external power, equipment or special
training normally associated with welding or brazing
Introduction to
Cadweld
Introduction to
Cadweld
Eliminate Connections
The process can be used to
splice conductors, make “T”
connections and “cross overs”
as well as connections to
ground rods, ladder trays,
rebar, rail and steel structure.
Introduction to
Cadweld
CADWELD
CONNECTION
Completely continuous
solid welded copper
connection
Introduction to
Cadweld
Life of the mold
A mold will generally last for 50
connections. However:
• RSA, NSW, Australia
70mm2 bonds to rail head
= 250 connections
• GV Kinsman, Australia
tramway bonds
= 300 connections
Extend mold life, clean only with soft natural bristle brush,
clean cloth, or newspaper.
Introduction to
Cadweld
The Process
• The weld metal is supplied in a
plastic canister. It contains a precise
measure by weight.
• Packed in the base of the canister is
also a measure of starting material.
• Weld metal does not age, it’s shelf
life is unlimited.
Note: No phosphorous is used in CADWELD.
Materials are harmless and non toxic.
Introduction to
Cadweld
How is a
CADWELD
Connection
done?
Introduction to
Cadweld
Technical Advantages
No de-rating - The current carrying capacity
(fusing) is equal to the conductor (see photos).
 Lasts the life of the conductor - The joint will not
deteriorate with age. It is permanent.
 Can not loosen - There is no mechanical interface.
The joint is a molecular bond.
 Does not corrode – The joint is unaffected by
corrosive products to the same degree as copper
 Resistance does not increase – The connection will
withstand repeated faults without deterioration

Mechanical Connector
Crimp Connector
CADWELD Connection
Ontario
Hydro
Report
Introduction to
Cadweld
User Benefits
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

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
Simple to use – Minimal training is required. One
connection is sufficient operating under supervision.
Visual inspection – The quality of the joint can be
confirmed by eye. Every connection!
Light & portable - The components, including
accessories can be carried easily by one person.
No external power or heat – The reaction is self
contained. There are no hoses or leads to trail around.
Versatile – Used to weld copper, copper alloys, copper
bonded steel, steel alloys including stainless steel.
Introduction to
Cadweld
Use Cadweld when there is a need for:



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
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
Conductivity
Corrosion resistance
Overload withstand
Reliability and long life
Small space available
Large conductors
Compliance with IEEE80 & 837
A new system for delivering
CADWELD connections,
featuring
 Electronic ignition
 Prepackaged weldmetal
The
Process
CADWELD is Now Even Easier to
Use with the Latest Advancement
in the Continuing Evolution of
ERICO’s Exothermic Products
Simplified Method of Completing Exothermic
Welded Electrical Connections
The

Utilizes Integrated
Tamper Proof,
Disposable,
Moisture Resistant
Weld Metal Package

Weld Metal, Disk
and Ignition Source
are All Incorporated
into Weld Metal
Package
system
Part Numbers
CADWELD PLUS (F20)
Short
Video
Long Video
Grounding
Chain
Grounding Conductor
• Material (conductivity & corrosion resistance)
 Copper, Copperweld, galvanized steel,
 Aluminum (above ground and insulated)
• Size (cross sectional area / impedance)
 Sufficient to withstand maximum fault current
for maximum clearing time
Grounding
Chain
* Copper conductor, at 0.5 sec the
impact of connector choice is:
mm2
Cadweld
1083 C
Brazed
450 C
Pressure
350 C
Pressure
250 C
35
13.7kA
10.6
9.7
8.4
50
19.9
15.2
13.8
12.0
70
27.9
21.3
19.3
16.8
95
37.8
28.9
26.2
22.8
A
I=
K S
120
47.8
36.5
33.1
28.8
240
95.6
73.0
66.3
57.5
Grounding
Chain
* When the decision on conductor size is made,
the type of connector is part of that process
• Mechanical connectors passing IEEE 837 can be
rated equivalent to the conductor (1083 C)
• These connectors still fall short of Cadweld for
performance equivalent to the conductor. Refer:
Ontario Hydro Technologies Report C-95-EST-193-P
& Southern Electric International Project C94901
Grounding Design
Calculating resistance to ground from IEEE 142
Grounding Design
For a more complex design, we need to
advised of some additional parameters:
• Size of fault current;
• Clearing time of protection;
• Existing grounding systems
• Material and components preferences
• Standard conductor sizes
• Deep driven rods (bore hole)
• Horizontal radials extending outside
property line (acceptable?)
Field Data
Design Program – Win IGS
Can model soil conditions
• Based on measurements using
the Wenner 4 point method
• Requires survey of area
• 2 directions at 90 degrees
• More measurements is better
Soil Parameter Report
Design Program – Win IGS
Can model soil conditions
• A 2 layer soil resistivity model
is produced
• Parameters / level of confidence
in the result is noted
Plan View
Drawings developed
within WinIGS
According to the:
• area available,
• ground analysis and
• design calculations
3D model
Drawings developed
within WinIGS
According to the:
• area available,
• ground analysis and
• design calculations
Customer Drawings
CAD Drawings are
produced
More detail added:
• accessories (pits, etc)
• bill of materials
• installation notes
• expand design for poor
soil types covering
multiple sites
Wind Farm 1B
Expanded Designs II
Basic design, all towers
3B, 500 (40’)/ 1,000 ohm.m
Bill of Materials
Bond (Connect) Grounds
Together
4. Bond all ground points together to eliminate
ground loops and create an equipotential plane.
Bond
(Connect)
Grounds
Grounding Design
Together
Older designs, have
independent grounding
systems.
The more recent trend is
to bond all the ground
systems.
Addn risk of electromagnetic induction along route of internal earth lead
Multiple Point of Entry
Single Point of Entry
Bond (Connect) Grounds
Together
When normal operating conditions dictate
that equipment grounds remain isolated, a
Potential Equalisation Clamp (PEC) can
be used for this purpose.
QUESTION TIME