Mr. Haren Shah, Senior Marketing Executive, Meco Instruments Pvt. Ltd.
Every electrical equipment’s, appliance, system must be Earthed or grounded to obtain a low resistance path for dissipation of current into the earth. Earthing plays an important role in Generation, Transmission & Distribution for safe and proper operation of any electrical installation. Ground fault current directly has an impact on human safety. Major accidents happen due to improper Earthing. Leakage current passes through human body and fatality occurs. Even every Overhead line / Sub station / Generator station which is exposed are liable to injury from lightning.
In electricity supply systems, an earthing or grounding system is circuitry which connects parts of the electric circuit with the ground, thus defining the electric potential of the conductors relative to the Earth’s conductive surface. In particular, it affects the magnitude and distribution of short circuit currents through the system, and the effects it creates on equipment and people in the proximity of the circuit. If a fault within an electrical device connects a live supply conductor to an exposed conductive surface, anyone touching it while electrically connected to the earth will complete a circuit back to the earthed supplyconductor and receive an electric shock.
Electricity most often hurts a man not causing extreme physical injuries but by merely shocking the life out of the body suddenly. This is due to life and electricity in minute form being closely inter-related so that a small current can prove fatal. When body is alive it is found to maintain a potential difference between its inside and outside.
Galvany in 1780 proved that all live muscles contract when electricity applied. When contraction due to electricity is more that will power contract and relaxes which brings to death due to electric shocks. The current affect heart muscles and when contract become too powerful, muscles bewildered and fall in state of flutter, called ventricular fibrillation, the heart stops functioning. It will be proper to know what current and potentials are safe to handle.
Importance of Proper Earthing / Grounding Systems.
- The main reason for proper earthing in electrical network is for the safety. When all metallic parts in electrical equipments are grounded then if the insulation inside the equipments fails there are no dangerous voltages present in the equipment case.
- If the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediately blow. When the fuse is blown then the dangerous voltages are away.
- Purpose of Earthing in an electric power system is to limit, with respect to the general mass of earth, the potential of current carrying conductors, which are part of the equipment, non-current carrying metal works, associated with the equipment, apparatus and appliances connected to the system.
- It is also important to take precautions against leakage of current. Insulation Resistance values should be checked periodically. It is also necessary to maintained Earthing properly of all electrical Installation. As the same time it is also very important at regular interval to check and if required unproper Earthing should be repaired. The records should be maintained if results are poor, action should be taken to be improved.
Measurement Of Earthing / Grounding – The Most Neglected Subject Today !
Old Measurement Methods with Four Spikes, hand generating are: Old Measurement Methods is called fall of potential method./ In this method earth grid is to be isolated from the earth electrode. Two auxiliary electrodes – one current electrode and another potential electrode are placed besides the electrode to be tested at equal distance in a straight line. A measured current is passed through the auxiliary current electrode. The potential difference developed between the auxiliary potential electrode and the electrode to be tested is measured. Resistance is calculated from the above current and voltage values. Normally in the site we use three lead digital earth testers for the measurement.
In the field the condition of earthing is so poor and normally earth resistance or leakage current is not measured either because of prevailing tedious & time consuming methods or handy instruments were not available. Many a times the important aspect of proper earthing is neglected resulting in complex problems associated with poor earthing. The Distribution Transformers fail because of earthing not being proper and lightening arrestors do not carry out their work. In case of HT consumers the meter behaves erratic as unbalance voltages are recorded due to poor earthing. To ensure proper monitoring of earthing it is necessary to give a handy and easy to use equipment to the field staff. Now Latest Handy Instruments are available to measure Ground / Earth Resistance and Leakage Current on Live Load By just clamping to the grounding lines without disconnecting the circuit or Driving auxiliary electrodes.
MECO Introduce Clamp-On Earth / Ground Resistance Tester Model 4680BL & 4680BLC, which can measure ground resistance from 0.099 Ohms ~ 1000 Ohms & Leakage Current from 80mA ~ 30A AC by just clamping to the grounding lines without disconnecting the circuit or driving Auxiliary Electrodes.
Suitable for Flat Strip (Jaw Size 65 mm), Data hold, Data Storing Memory, Auto power off & Continuity Loop Test are Key features of 4680BL / 4680BLC. It Is based on an unique principal in which a pre-defined current is injected in the ground circuit under test and then the induced magnetic current there by generated in the circuit is measured at a high frequency by use of special clamp -on current transformer in the instrument.
This is an extremely handy instrument especially at place where it is next to impossible to measure Earth /Ground Resistance by conventional methods. Substantial time saving and easy operating justify the investment in these instruments Regulations for earthing system vary considerably among countries and among different parts of electric systems. The objectives of Maintaining Proper Earthing is very good but the road ahead is very long, rough and tardy but with the cooperation and strong will, nothing is impossible.