What does a good grounding of the Power Substation and Switching Station really mean? Earthing For SafetyProvision of adequate grounding in a substation and switching stations are very important for the safety of operating personnel as well as electrical devices do not rise above tolerablethresholds and that the earth connection is rugged to dissipate the fault to the earth.What does a good grounding of the power substation and switching station really mean?The importance of an effective, durable and a dependable earth for ensuring safety from electrical hazards does not require to be elaborated upon more.By earthing, connecting the electrical equipment to the general mass of the earth, this has a very low resistance.1. Requirements Of a Good Substation EarthingThe object of an earthing system in a substation is to provide under and around the substation a surface that shall be at a uniform potential and near zero or absolute earth potential as possible.
The provision of such a surface of uniform potential under and around the substationensure that no human being in the substation subject in shock of injury on the occurrence of a short circuit or development of other abnormal conditions in the equipment installed in the yard.The primary requirements of a good earthing system in a substation are:1.It stabilizes circuit potentials with respect to ground and limits the overall potential rise.2.It protects life and property from over voltage.3.It provides low impedance path to fault currents to ensure prompt and consistent operation of protective devices during ground faults.4.It keeps the maximum voltage gradient along the surface inside and around the substation within safe limits during ground fault.2. Maximum Permissible Resistance Of Earthing SystemLarge Power Station0.5 ohmMajor Sub-Station1.0 ohmSmall Sub-Station2.0 ohmsIn all other cases5.0 ohms3. Touch Voltage (E-TOUCH)Definition – The potential difference between a ground metallic structure and a point on the earth’s surface separated by a distance equal to the normal maximum horizontal reach of a person, approximately one meter as shown infigure 1.
Figure 1 – Touch voltage at a grounded structure4. Step Voltage (E STEP)Definition – The potential difference between two points on the earth surface separated by distance of one pace that will be assumed to be one meter in the direction of maximum potential gradient as shown in figure.Figure 2 – Step voltage at a grounded structure
5. Earthing System In a SubstationThe earthing system comprises of earthing (or) grid, earthing electrodes, earthing conductors and earth connections.5.1 Earth Mat or GridThe primary requirement of earthing is to have a very low earth resistance.