VIVA VOCE SLIDES.ppt

LIGHTNING PROTECTION SYSTEM STUDY USING EARTH ELECTRODES AND ENHANCEMENT MATERIALS By Buba, Sani Dahiru GS25573 Master of Science

Supervisors: Dr. Wan Fatinhamamah Wan Ahmad, Chair Dr. Jasronita Jasni, Member Prof. Madya Dr. W. N. Wan Daud, Member

Presentation outline  Introduction  Problem statement  Objectives  Methodology

 Literature review  Installation of earthing systems/earth resistance measurements  Results and Findings

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).

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).

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.

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.

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

Introduction contd.

 equipment earthing, connection of metallic parts to earth

 protective earthing refers to bonding of all exposed metallic and extraneous conductive parts

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.

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.

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.

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

Selection of experiment site Site 1 Near Canteen

Site 2 near guard house

Results of soil tests

Results for Site 1

Results for Site 2

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.

Literature Review  Chemical enhancement materials (CEM)  Soil resistivity may be reduced anywhere from 15% to 90% by chemical treatment of the soil, (IEEE Std 1422007).  Uman (2008), suggested that the resistivity of soil can be reduced by adding chemicals to the soil surrounding a grounding electrode.

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.

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.

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

Reference diagram for CEM installation, (Megger manual)

CEM

Cross section of circular trench and dimensions

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

Grass clearing for installation of earthing system

Earth electrode being driven into the soil

circular trench marked out

Completed circular trench

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.

Typical CEM placed in circular trench CEM

A typical circular trench backfilled with soil

Earth electrode

Typical PVC earth chamber placed on earthing installation

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

Cross section of earthing installation using NEM as infill, Chen (2009).

Drilling hole for installation of earthing system using NEM

Hole drilling equipment

Water pump

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.

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.

Table 1 Results and Findings for CEM installations

Results for CEM contd.

Link to tables of percentage reduction of earth resistance for CEM

Table 2 Results and Findings for NEM installations

Results for NEM contd.

Link to tables of percentage reduction of earth resistance for NEM

Table 3 comparison between CEM and NEM

Table 4 soil condition before and after experiment

Comparison contd.

 Environmental condition after 365 days

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.

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.

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.

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.

Conclusion contd.

 In NEMs category, comparison between different earthing installations in terms of earth resistance readings, and percentage reduction of earth resistance indicated performed.

that

bentonite

installation

is

the

best

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.

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.

Table 5 List of Publications

THANK YOU

Graphs

 Soil parameter graphs  Different angles of measurement

References [1]

Hinde, S., Overhead Line Guidelines, British Columbia Safety Authority Information Bulletin No: BE30903121, 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.

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.

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.

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

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, MILHDBK-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.