ELECTRICAL GROUNDING AND EARTHING SYSTEMS Presented By: T.Sidharth Sankar Achary Regd No-1021106019 7th sem. Electrical Engg.
CONTENTS INTRODUCTION. DIFFERENCE BETWEEN GROUND AND NEUTRAL. TYPES OF EARTHING SYSTEMS. TYPES OF GROUNDING. USES. CONCEPT OF VIRTUAL GROUND. MULTIPOINT GROUND. CONCLUSION. REFERENCES.
INTRODUCTION In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It also ensures that in the case of an insulation fault, a high fault current flows, which will trigger an over current protection device (fuse, MCB) that disconnects the power supply. A functional earth connection serves a purpose other than providing protection against electrical shock.
DIFFERENCE BETWEEN GROUND AND NEUTRAL. Ground or earth in a mains (AC power) electrical wiring system is a conductor that exists primarily to help protect against faults and which in normal operation does not carry current. Neutral is a circuit conductor that may carry current in normal operation, and which is usually connected to earth. In house wiring, it is the center tap connection of the secondary winding of the power companys transformer. In a polyphase or three-wire AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, and similar phase spacing. By this definition, a circuit must have at least three wires for one to serve as a neutral. In the electrical trade, the conductor of a 2-wire circuit that is connected to the supply neutral point and earth ground is also referred to as the "neutral". This is formally described in the US and Canadian electrical codes as the "identified" circuit conductor.
TYPES OF EARTHING SYSTEMS International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT. The first letter indicates the connection between earth and the power-supply equipment (generator or transformer): T : direct connection of a point with earth (French: terre); I : no point is connected with earth (isolation), except perhaps via a high impedance.The second letter indicates the connection between earth and the electrical device being supplied: T : direct connection with earth, independent of any other earth connection in the supply system; N : connection to earth via the supply network.
TYPES OF GROUNDING In radio frequency communications In AC power wiring installations Circuit ground versus earth. In lightning protection
In radio frequency communications An electrical connection to earth for as a reference potential for radio frequency antenna signals. High frequency signals can flow to earth through capacitance, capacitance to ground is an important factor in effectiveness of signal grounds. An ideal signal ground maintains zero voltage regardless of how much electrical current flows into ground or out of ground. The resistance at the signal frequency of the electrode-to-earth connection determines its quality, and that quality is improved by increasing the surface area of the electrode in contact with the earth, increasing the depth to which it is driven, using several connected ground rods, increasing the moisture of the soil, improving the conductive mineral content of the soil, and increasing the land area covered by the ground system.
In AC power wiring installations In a mains (AC power) wiring installation, the ground is a wire with an electrical connection to earth, that provides an alternative path to the ground for heavy currents that might otherwise flow through a victim of electric shock. These may be located locally, be far away in the suppliers network or in many cases both. This grounding wire is usually but not always connected to the neutral wire at some point. The ground wire is also usually bonded to pipe work to keep it at the same potential as the electrical ground during a fault. Water supply pipes often used to be used as ground electrodes but this was banned in some countries when plastic pipe such as PVC became popular. This type of ground applies to radio antennas and to lightning protection systems.
Circuit ground versus earth In an electrical circuit operating at signal voltages (usually less than 50 V or so), a common return path that is the zero voltage reference level for the equipment or system. Voltage is a differential quantity, which appears between two points having some electrical potentials. In order to deal only with a voltage (an electrical potential) of a single point, the second point has to be connected to a reference point (ground) having usually zero voltage. This signal ground may or may not actually be connected to a power ground. A system where the system ground is not actually connected to earth is often referred to as a floating ground.
In lightning protection A ground conductor on a lightning protection system is used to dissipate the strike into the earth.
USES A power ground serves to provide a return path for fault currents and therefore allow the fuse or breaker to disconnect the circuit. Filters also connect to the power ground, but this is mainly to stop the power ground carrying noise into the systems which the filters protect, rather than as a direct use of the power ground. In Single Wire Earth Return (SWER) electrical distribution systems, costs are saved by using just a single high voltage conductor for the power grid. This system is mostly used in rural areas where large earth currents will not otherwise cause hazards. Signal grounds serve as return paths for signals and power at low voltages (less than about 50 V) within equipment, and on the signal interconnections between equipment.
VIRTUAL GROUND CONCEPT If two opposite power sources are connected each other by a conductive medium so that their opposite output quantities are superposed (summed), zero or reference level result referred to as virtual ground appears somewhere along the medium. In this "conflict" point, the efforts of the "fighting" sources are "neutralized". The process is associated with continuous energy wasting from both the sources as a result of a continuous energy flow through the medium. Shortly, virtual ground phenomenon is summing of opposite equal quantities associated with continuous energy wasting; virtual ground represents the result of summing two opposite equal quantities.
MULTI POINT GROUND A Multipoint Ground is an alternate type of electrical installation that attempts to solve the Ground Loop and Mains hum problem by creating many alternate paths for electrical energy to find its way back to ground. The distinguishing characteristic of a multipoint ground is the use of many interconnected grounding conductors into a loose grid configuration. There will be many paths between any two points in a multipoint grounding system, rather than the single path found in a star topology ground.
CONCLUSIONGrounding and Earthing systems form the first lineof defense in every type of electrical systems. Thesystem may be a generator/transformer/housinginstallation/generating station/etc. So it is strictlyadvised to know the basic concepts of grounding asfar as electrical engg. is concerned.