Electrical Safety – Innovative Methods for Measurement of Earthing / Grounding Systems
The faults in any electrical system are unavoidable. Every electrical equipment, appliance or 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.
Electricity most often kills 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 to be fatal. Under the provisions of Indian Electrical Rules, Electrical installation of the licensees, consumers are inspected every year by the Electrical Inspectorate wing under the guidance of Chief Engineer (Electrical) P.W.D. for observance and for enforcement of safety measures for working on electrical equipment installation. During the inspection of installations, overhead lines, transformers, etc. if any defects are observed, then instructions are given to the concerned for compliance of the same. Also all the electrical accidents are investigated by the electrical Inspectorate wing to check the observance of electrical measures and recommendations are given for compliance.
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 and time-consuming methods or handy instruments are not available. Many a time, 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 work. In case of HT consumers, the meters behave erratic as unbalance voltages are recorded due to poor earthing or no earthing. To ensure proper monitoring of earthing, it is necessary to give a handy and easy to use equipment to the field staff.
Hazards Happening Everyday Due To Improper Earthing
Major Accidents happen due to improper earthing and leakage current passed through human body or through hazardous materials causing fatality or loss. A few case studies go like this:
Person dies after touching the pole. It was observed that the pole was not earthed & lamp wire inside was with deteriorated insulation and came in contact with inside pole.
In a sugar factory a person was stacking sugar bags by climbing on steel ladder. He took support of roof truss and got shock. The fitting erected on truss was short & leakage passed to labor.
A person on the roof is electrocuted as he touches the TV / Disc antenna. In TV phase directly goes to internal circuit & neutral connected to chassis. Antenna circuit is also connected through capacitor. As phase position changed & phase comes directly in contact with chassis: circuit is completed but as a capacitor of antenna gets shorted & leakage transfers from chassis to metallic part of antenna.
Whenever electrical Installation is to be completed, its non-conducting parts should be connected firmly to earth electrodes. Every Electrical Installation should have proper earthing.
Earthing provides protection against dangerous potential under fault conditions. It is also important to take precautions against leakage of current. Insulation Resistance values should be checked periodically. It is also necessary to maintain Earthing properly of all electrical Installations. At the same time, it is also very important to check the earthing at regular intervals, and if required repair improper earthing.
Importance of Proper Earthing / Grounding System
Every electrical equipment or appliance must be ‘Earthed’ or‘Grounded’ for the safety of equipment, network as a whole and operating personnel.
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.
Every Overhead line / Sub-station / Generator station which is exposed are liable to cause injury from lightning.
The 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.
Earthing plays an important role in Generation, Transmission & Distribution for safe and proper operation of electrical system.
Every Earthing should be tested / checked at regular intervals so as to ensure that the resistance of Earth connection is minimum.
Proper records should be maintained. If results are poor, action should be taken to improve the earthing.
Old Measurement Method 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 is to be checked.
Measurement Of Earthing / Grounding – The Most Neglected Subject Today !
Old Measurement Methods Are :
- Crude & Strainful
- Time Consuming
- Require Shut – Downs
- In-Accurate
- Limitation due to paver block, cement concrete, limited space, terrace, etc
MECO Clamp-On Earth / Ground Resistance Tester
Now Latest Handy Instruments are available to measure Ground / Earth Resistance and Leakage Current by just Clamping to the grounding lines without disconnecting the circuit or Driving auxiliary electrodes. MECO 4680 Series with option of Jaw opening 23/38/55/65mm, can measure Ground Resistance & AC current (load/leakage) by just clamping to the Earthing Pit / Strips, Grounding lines without disconnecting the circuit or driving Auxiliary Electrodes. This is based on an unique principle in which a predefined current is injected in the ground circuit under test and then the induced magnetic current thereby generated in the circuit is measured at a high frequency by use of special Clampon Current Transformer in the instrument.
“The objective of Maintaining Proper Earthing is to obviate hazards, but the road ahead is very long, rough and tardy but with the cooperation and strong will, nothing is impossible.”
Article by Haren Shah
Haren Shah is Senior Marketing Executive at Meco Instruments Pvt. Ltd.
He has been with Meco for over 30 years.