viva voce slides.ppt
DESCRIPTION
These are slides of presentation at Master of Science Thesis defence in 2012.TRANSCRIPT
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LIGHTNING PROTECTION SYSTEM STUDY USING EARTH ELECTRODES AND
ENHANCEMENT MATERIALS
ByBuba, Sani Dahiru
GS25573Master of Science
Supervisors: Dr. Wan Fatinhamamah Wan Ahmad, Chair
Dr. Jasronita Jasni, Member Prof. Madya Dr. W. N. Wan Daud,
Member
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Presentation outline
Introduction Problem statement Objectives Methodology
Literature review
Installation of earthing systems/earth resistance measurements
Results and Findings
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Introduction
What is Earthing ?
‘The provision of permanent and continuous conductive
path to the ground having sufficient capacity to carry any
fault current liable to be imposed upon it, with sufficiently
low impedance to limit voltage rise above ground
potential, and be able to facilitate the operation of
protective devices’ Hinde (2009).
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Introduction contd.
Commonly used earthing structures includes single
horizontal wire, vertical rods, ring conductors,
multiple conductors forming triangular or
rectangular shapes and earthing grids, Liu (2004).
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Introduction continued
What is the purpose of earthing systems?
at power/low frequency is basically to provide a safe path/return for dissipation of stray/faults currents.
for transient/lightning protection is to dissipate transient charges, static charges, electromagnetic interference (EMI), and radio frequency interference (RFI).
for signal/high frequency systems, is to provide zero signal reference.
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Introduction contd.
Other purposes for which earthing is provided include;
to ensure safety of general public and personnel
against contact with energized circuits or systems.
protection of equipments against damage by
overvoltages
to provide safe and correct operation of power system both under normal, earth fault and transient conditions.
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Introduction contd.
Types of earthing
functional earthing system, specific to sensitive
electronic equipment and data networks, safety is
not a major concern
system earthing, neutral point of a transformer
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Introduction contd.
equipment earthing, connection of metallic
parts to earth
protective earthing refers to bonding of all
exposed metallic and extraneous conductive
parts
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Problem statement
The earth resistance of an electrode system consists of,
Resistance of the earth electrode
Contact resistance between the electrode and soil
Resistance of the soil surrounding the earth electrode
The first two resistances are negligible for most practical
purposes, IEEE Std 142-2007.
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Problem statement contd.
Resistance of the soil is therefore dependent on the soil resistivity.
Soil resistivity ρ varies with depth from the surface, type of soil,
concentration and type of soluble salts (chemicals) in the soil, moisture
content and soil temperature. In other words, the resistivity is that of
the electrolyte in the soil’, IEEE Std 142-2007.
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Objectives
Determine soil properties relevant to earthing systems
Install earthing systems using chemical
enhancement materials (CEM) and natural
enhancement materials (NEM).
Determine the best performed enhancement
material and earthing installation.
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Methodology
Selection of experiment sites Soil tests
Physical analysis Chemical analysis
Installation of soil parameter data loggers
Installation of earthing system using CEM and NEM
Earth resistance measurements
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Selection of experiment site
Site 1 Near Canteen Site 2 near guard house
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Results of soil tests
Results for Site 1 Results for Site 2
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Selection of site contd.
• BS7430-1998, recommends that where there is an option, the following types of soil should be chosen ,
wet marshy ground Clay, loamy soil etc.
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Literature Review
Chemical enhancement materials (CEM)
Soil resistivity may be reduced anywhere from
15% to 90% by chemical treatment of the soil,
(IEEE Std 142-2007).
Uman (2008), suggested that the resistivity of
soil can be reduced by adding chemicals to the
soil surrounding a grounding electrode.
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Literature review contd.
Brieals (1991), recommended the use of
common salting materials such as sodium
chloride (NaCl), magnesium chloride (MgCl2),
calcium chloride (CaCl2 ) and copper sulphate
(CuSO4 ) for soil enhancement purposes.
Wan Ahmad (2010), used NaCl, NH4Cl, CuSO4,
Na2S2O3, and MgCl2 around a circular trench.
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Literature review contd.
Natural enhancement materials (NEM)/backfill
BS7430-1998, Recommends replacement of soil
immediately around an electrode with a lower
resistivity material to improve earth electrode
contact resistance may be used in special or
difficult locations.
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Literature review contd.
Gomes et al. (2010), industrial wastes, bentonite and NaCl
Kumarasinghe (2008), paddy dust, coir peat, bentonite
Eduful et al. (2009), palm kernel fibre
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Reference diagram for CEM installation, (Megger manual)
CEM
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Cross section of circular trench and dimensions
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Installation of earthing systems contd.
CEM
Measure intervals and mark electrode positions
Drive earth electrode into the soil
Dig circular trench
Pour/place CEM inside circular trench
Backfill the trench with soil
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Grass clearing for installation of earthing system
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Earth electrode being driven into the soil
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circular trench marked out
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Completed circular trench
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Installation of earthing system contd.
‘Fourty to ninety pounds of chemical will initially be
required to maintain effectiveness of earthing system for
two to three years’, MIL STD HBK-419A, Vol. 1(1987).
1 pound = 0.453kg
40 pounds = 18.12kg assumed to be effective for 2 years
Experiment was designed for one year, the quantity of
CEM used was 18.12/2 = 9.06 kg rounded to 10kg.
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Typical CEM placed in circular trench
CEM
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A typical circular trench backfilled with soil
Earth electrode
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Typical PVC earth chamber placed on earthing installation
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Installation of earthing system using NEM
NEM
Bore/drill hole
Fill the hole with NEM and compress
Drive earth electrode at the middle
Cover the top with soil
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Cross section of earthing installation using NEM as infill, Chen (2009).
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Drilling hole for installation of earthing system using NEM
Hole drilling equipment
Water pump
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Earth resistance measurements
Earth resistance measurement was conducted using 3-point fall of potential method (Wenner method).
Earth Tester Megger DET3TC
Potential and current probe positions were fixed using rule of 62%
Measurements were conducted for different angles between current and voltage probes initially.
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Earth resistance measurements contd.
Zero degrees between potential and current
probes was chosen for simplicity and popularity.
Additional data recorded during measurements
includes, ambient temperature, ambient
weather, soil condition and humidity.
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Table 1 Results and Findings for CEM installations
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Results for CEM contd.
Link to tables of percentage reduction of earth resistance for CEM
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Table 2 Results and Findings for NEM installations
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Results for NEM contd.
Link to tables of percentage reduction of earth resistance for NEM
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Table 3 comparison between CEM and NEM
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Table 4 soil condition before and after experiment
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Comparison contd.
Environmental condition after 365 days
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Contributions of the study
The results from this study has revealed that, soil
treatment with suitable CEMs can significantly
reduce earth resistance.
Performance of CEM for reduction of earth
resistance was reported in terms of actual earth
resistance and percentage values.
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Contributions contd.
10kg of CEM is effective for one year in clay
loam type of soil.
Soil treatment with CEMs raises the pH from
acidic to alkaline which is good for plant growth.
Soil treatment with CEMs slightly changes the
soil texture from clay loam to sandy clay loam.
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Contributions contd.
Electrode encasement/enhancement using
biodegradable materials are effective for short
periods only.
Suitable maintenance period was recommended.
Performance of CEMs in clay loam type of soil
was reported.
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Conclusion
It is concluded from the study that;
In terms of earth resistance readings,
comparison between different earthing
installations in the CEM category indicated that
CaCl2 is the best performed CEM.
In terms of percentage reduction of earth
resistance, NaCl is the best performed CEM.
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Conclusion contd.
In NEMs category, comparison between different
earthing installations in terms of earth resistance
readings, and percentage reduction of earth
resistance indicated that bentonite installation is
the best performed.
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Conclusion contd.
When the performances of CEM and NEM
installations are compared, it was found that CEM
installations performed better than NEM
installations both in terms of earth resistance
readings and percentage reduction of earth
resistance.
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Conclusion contd.
Therefore CEMs such as CaCl2, NaCl, MgCl2, and
Na2S2O3 are considered effective in reduction of
earth resistance in clay loam type of soil.
Similarly, NEMs such as bentonite and palm
kernel fibre are also considered an effective
backfill materials for reduction of earth
resistance.
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Table 5 List of Publications
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THANK YOU
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Graphs
Soil parameter graphs
Different angles of measurement
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References
[1] Hinde, S., Overhead Line Guidelines, British Columbia Safety Authority Information Bulletin No: B- E30903121, 12th March, 2009.
[2] Liu, Y., Transient Response of Grounding Systems Caused by Lightning: Modelling and Experiments, PhD Dissertation from the Faculty of Science and Technology, University Uppsala, Sweden, November, 2004.
[3] IEEE STD 142TM: 2007, Recommended Practice for
Grounding of Industrial and Commercial Power Systems, Pp169.
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References contd.
[4] British Standard BS7430-1998, Code of Practice for Earthing.
[5] Uman, M. A., the Art and Science of Lightning Protection, Cambridge University Press, New York, 2008, Pp. 85.
[6] Briels, G., Chapter 4 of Electrical Hazards and Accidents, Van Nostrand Reinhold, New York, 1991, Pp. 72-73.
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References contd.
[7] Wan Ahmad, W. F., Abdul Rahman M. S., Jasni, J., Ab Kadir, M. Z., A., and Hizam, H., Chemical Enhancement Materials for Grounding Purposes, Presented at the 30thInternational Conference on Lightning Protection, ICLP 2010, Cagliari, Sardinia, Italy, 13-17 Sept.2010.
[8] Gomes, C., Lalitha, C., and Priyadarshanee, C., “Improvement of Earthing Systems with Backfill
Materials,” presented at the 30th International Conference on Lightning Protection, ICLP 2010, Cagliari, Sardinia, Italy, 2010.
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References contd.
[9] Kumarasinghe, N., “A Low Cost Lightning Protection System and its Effectiveness,” presented at the 20th International Lightning Detection Conference and 2nd International Lightning Meteorology Conference,
Tucson, Arizona, U. S. A, 2008.
[10] Eduful, G., and Cole, J. E., “Palm Kernel Oil Cake as an Alternative to Earth Resistance Reducing Agent,” presented at the Power Systems Conference and Exposition, Seattle, WA, 2009, p.2
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References contd.
[11] A Practical Guide to Earth Resistance Testing, www.megger.com/det
[12] Grounding, Bonding, and Shielding for Electronic Equipment and Facilities, Military Handbook,
MIL- HDBK-419A, Vol. 1, December 1987, Ch2. Pp 63.
[13] Chen, L. H., Chen, J. F., and Wang, W. I., “Research on Used Quantity of Ground Resistance Reduction Agent for Ground Systems,” European Transactions on Electrical Power, Online, Wiley Inter Science, 2009.