What is earthing and their methods.

Earthing:- In electrical supply systems, an earthing system defines the electrical potential of the conductors relative to the earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply. Earthing's main purpose is to provide a common point of reference between various source of electrical energy, i.e.
               Different power systems- Public utilities, on-site generation, battery systems.
               Different voltage system- 132kv,220kv,11kv etc.
               Different energy sources- Electrical energy, lightning, static electricity, RF energy.

          Earthing is, in essence, the control of abnormal voltages or currents through the proper application of Ohm's law   E=IR

          Earthing is the control or minimization of R in order to reduce the effects of E and I. Improper earthing can cause more harm than no earthing. Misunderstood earthing often leads to the installation of improper earthing systems that are either ineffective, or even worse dangerous. earthing purpose is a lot more than providing a common point of reference. It is the key of safety. That is, the protection of personnel, equipment, facilities.
           When considering protection of personnel equipment and facilities against electrical hazards, there is a need to consider both earthing and overcurrent protection and how they relate. They go hand in hand. A facility's electrical protection systems are intended to:- Electrocution, Fire, Protect equipment and facility from failure and fire.
             Protect electrical electrical circuit from cable failure, For the protection system to do as intended, they must first work; and second they must work fast enough to eliminate or at least minimize damage. This is where proper earthing caomes to play.


Need of earthing:-

  1. To protect the operating personnel from danger of shock in case they come in contact with the charged frame due to defective insulation.
  2. To maintain the line voltage constant under unbalanced load condition.
  3. To protect the equipments.
  4. To protect large buildings and all machines fed from overhead lines against lighting.
Methods of earthing:-
  • Plate Earthing:- In this method, a Copper plate of 720mm*720mm*31.8mm or a GI plate of the size 720mm*720mm*63.5mm is used for earthing. The plate is placed vertically down inside the ground at a depth of 3900mm and is embeded in alternate layer of coal and salt for a thickness of 150mm. In adition, water is poured for keeping the earth electrode resistance value well below a maximum of 5 ohms. The earth wire is securely bolted to the earth plate. A cement masonry chamber is built with a cast iron cover for easy regular maintenance.

  • Pipe earthing:- Earth electrode made of a GI (Galvanized iron) pipe with 38 mm diameter and length of 2000mm (depending on the current) with 12mm holes on the surface is placed upright at a depth of 4750 mm in a permanently wet ground. To keep the value of the earth resistance at the desired level, the are (150 mm) surrounded the GI pipe filled with a mixture of salt and coal. The efficiency of the earthing system is improved by pouring water through the funnel periodically. The GI earth wires of sufficient cross-sectional area, run through a 12.7 mm diameter pipe(at 600 mm below) from the 19 mm diameter pipe and secured tightly at the top.

              When compared to the plate earth system, the pipe earth system can carry larger leakage currents as a much larger surface area is in contact with the soil for a given electrode size. The system also enables easy maintenance as the earth wire connection is housed at the ground level.

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