ELECTRIC SHOCK AND EARTHING Presentation by: Kishor Ghimire(222) Ramesh Adhikari(233)

ELECTRICAL SHOCKS Electric shock is the physiological reaction or injury occurs when the human body becomes part of the path through which current flows

BASIC CIRCUIT ANALYSIS

FACTOR DETERMINING SHOCK INTENSITY The current strength

FACTOR DETERMINING SHOCK INTENSITY CONTD.. The body resistance Frequency of current The path taken by the current Duration of the contact Area of contact

IMPLEMENTATION Execution by electrocution electric chair, employed as an official method of capital punishment developed throughout the 1880s Researchers found electroconvulsive therapy (ECT) to be more effective than the use of drugs to treat short-term depression

IMPLEMENTATION CONTD.. Electric Fencing

SAFETY

FIRST-AID CURE Mouth to mouth respiration Artificial respiration

EARTHING WHAT IS EARTHING? Connections of neutral parts of the electrical equipment to the general mass of the earth for immediate discharge of electric energy without danger.

OBJECTIVES Why ground at all? PERSONNEL SAFETY FIRST The PRIMARY goal is SAFETY. Why ground at all? PERSONNEL SAFETY FIRST EQUIPMENT PROTECTION SECOND

Deals with the Earthing of current carrying parts of the equipment SYSTEM EARTHING Deals with the Earthing of current carrying parts of the equipment EQUIPMENT EARTHING Deals with the Earthing of non- current carrying parts of the equipment

EARTHING SYSTEM Mostly used for: Lightning protection Simplest form is a single stake Mostly used for: Lightning protection Stand alone structures Back-up for utility ground The next slides are to bring the point out that there‘s a huge variety of ways of creating a ground system. For simplicity in the presentation we refer to ‘ground electrode‘ or ‘grounding system‘ to describe these different methods of grounding. It should be noted that there are many different types of grounding systems available. The type installed will depend on the local conditions and the required function of the grounding system The simplest form of grounding element is the ground stake, this can take many forms with a variety of lengths from a few feet to many feet long made of materials such as brass, galvanised or stainless steel, the size and material as required locally The simple ground rod can be used for lightning protection on stand-alone structures such as pole mounted transformers or radio towers, it can also be used as a back up to a utility ground. Ground rod

GROUND ROD GROUP typically for lightning protection on larger structures or protection around potential hotspots such as substations A group of connected rods will have a more complicated interaction, typically configurations like this are present around substation sites and sensitive buildings. A slightly more complicated version of the rod system is the ground rod group, this is typically for lightning protection on larger structures or protection around potential hotspots such as substations. Ground rod group

GROUND PLATE For areas where there is rock (or other poor conducting material) fairly close to the surface Ground plates are used widely in telecoms applciations. They are particularly good where the deeper ground has high resistivity. For areas where there is rock (or other poor conducting material) fairly close to the surface ground plates are preferred as they are more effective Ground plate

GROUND MESH A ground mesh consists of network of bars connected together, this system is often used at larger sites such as electrical substations. Ground meshes can be part of the foundations of structure. At substations and generating site the metal parts of the foundations will all be bonded together and form part of the overall grounding systems. At substation site an area of ground could be reserved at the start of the life of the substation with a ground mesh under the whole of the site. As the site grows over a period of years new equipment can easily be installed and grounded by the mesh. This ensures that the whole of the site remains at the same potential should a fault occur. Ground mesh

SOIL CHARACTERISTICS Soil type. Soil resistivity varies widely depending on soil type, from as low as 1 Ohmmeter for moist loamy top soil to almost 10,000 Ohm-meters for surface limestone.

STEP AND TOUCH VOLTAGES

Ground Testing Methods Resistivity Measurement ( Wenner method) Resistivity measurements are performed by using a four wire method. Used to determine which KIND of earthing should used, BEFORE placing earth stakes. Four stakes are used during resistivity testing. The distance between the stakes should be measured. This distance depends on the total area and the local resistivity. Typical distances are 6 and 12 feet, but if large areas have to be surveyed the distances may need to be larger, in that case it would be important to have oversized stakes, maybe even 3 to 6 feet long. Those types of surveys are more specialised. The outer two spikes inject test current and the inner two spikes measure voltage, a value of resistance is then derived

MEASUREMENT OF RESISTANCE The distance between the earth ground stacks is at least three times greater than the stake depth. The soil resistivity measurement are often corrupted by the existence of ground currents and their harmonics. It uses Automatic Frequency Control (AFC) system to prevent from it.

RESISTIVITY MEASUREMENT From the indicated resistance value RE, the soil resistivity is calculated according to the equation : E = 2  . a . RE   E ...... mean value of soil resistivity (W.m) RE ...... measured resistance (W) a ...... probe distance (m) Resistivity has to be calculated using the measured value Re. It becomes evident at this point that measuring the distances between the test spikes is important as it has an effect on the result achieved. Note the measurements and values refer to metres. All the tables of resistivity I’ve been able to find are in ohm metres although it’s possible to have ohm inches or ohm feet etc.

METHODS OF DECREASING GROUND RESISTANCE Decreasing the ground resistance of a grounding system in high resistivity soil is often a formidable task. Recently, some new methods have been proposed to decrease ground resistance.

BY INCREASING DEPTH OF EARTHING ELECTRODE

BY INCREASING THE NUMBER OF EARTHING ROD

RELATION OF SOIL RESISTIVITY WITH MOISTURE AND TEMPERATURE

CHEMICAL RODS Chemical rods are electrodes with holes along their length, filled with mineral salts. The rod absorbs moisture from both air and soil.

PRICE OF EARTHING WIRE IN NEPAL

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