Step potential is nothing the potential developed between the two feet on the ground of a man or animal when short circuit occurs. What is not as well understood is that gpr and the associated step and touch potential can arise from deenergized lines due to electromagnetic coupling from parallel live lines. The maximum permitted values of step and touch potentials vary widely between the different standards. What is step and touch potential and reducing resistance to. Apr 24, 2016 step potential and touch potentials are very important in substations because during ground faults all the ground current returns to the substation transformer as the substation transformer is grounded. Sep 01, 2016 this video explains what is step potential and touch potential. Calculation of touch voltage and ground current can be performed on single phase or threephase systems. Step and touch voltage tests are a very important factor when it comes to ensuring human safety within the substation and surrounding areas, especially during an electrical fault. The current that returns through the earth can create a significant voltage gradient along the ground and between ground and conducting. Steppotential step potential is the potential difference between the feet of a person standing on the floor of the substation, with 0. This allows the step and touch voltages to be measured easily and quickly and simulates the bodys electrical resistance, as per the required standards. The safe parameters of grounding systems should include touch voltage, step voltage, and gpr. Thank you for your question regarding the calculation of step and touch voltages in a substation, it is our pleasure to help.
Awareness of step and touch potential, caused by earth potential rise, is important for anyone working on highvoltage power transmission and distribution systems above 1 kv. A person on the ground is subjected to the risk of injury during an electrical fault simply by attempting to move toward or away from the grounding point. Read more step potential and touch potential must read. Having passed both touch and step potential criteria, we can conclude that the earthing system is safe. At critical locations, such as the fence around your substation, hazardous step and touch voltages can occur. This chapter contains safety criteria according to ieee standards, step and touch voltage criteria, reduction factor, simplified equations for mesh and step. A new method and instrument for touch and step voltage measurements article pdf available in ieee transactions on power delivery 94. Step and touch voltages and grounding potential rise ieee and iec. A more certain technique to determine step and touch potential is to measure it directly.
What is step potential and touch potential and calculation. It is, therefore, crucial to measure step and touch voltage at locations in and around the substation in order to ensure safety for persons and animals. Three main techniques for mitigating step and touch. Simply drive the special ground rod about 15 feet from the tower, mount the instrument on the rod, and connect the probe to the tower using a standard hot stick. Touch potential is defined as the difference between the maximum earth potential rise epr. The importance of testing and designing a low resistance grounding system. The snt02 kit provides an easytouse method to continuously monitor and alarm step and touch potential. S 100 ohmmeters for surface resistivity of wet concrete floor. The maximum allowable step potential is 5,664v, which exceeds the step voltage calculated above and the earthing system passes the step potential criteria. Continuously monitor and alarm step and touch potentials.
Distribution of step and touch voltages at the typical hvmv. The open circuit handtofoot voltage during a ground fault. Step potential is the potential difference between the feet of a person standing on the floor of the substation, with 0. The value of maximum permitted touch potential has a dominant. In step potential, electricity spreads like ripples or rings over the surface of the ground away from the point of the contact. And, the minimum surface potential within a 1 m radius of the earthed plant. This has commonly been done using a standard voltmeter equipped with a high voltage probe. Methods to reduce step potential and touch potential in.
Three cables, wound on cable reels, 200 m long one mains synchronizer device, to synchronize the sts generation to the mains two test probes for the step and touch test one voltage meter, digital, type true rms, for the earth resistance and step and touch tests one resistor box for the step and touch test. Explanation on step potentials due to a direct lightning strike. It is equal to the difference in voltage between the object and a point. This document provides an overview of the electrical shock. Protection from hazardous differences in electric potential. A ground rod is driven approximately 15 feet from the tower, and the negative probe is connected to this ground reference point. Design and analysis of substation grounding grid with and. This document provides an overview of the electrical shock risks associated with touch and step potential. Insert the injector electrode at the approximate distance of the projected fault away from the grounding system and connect the z lead to it 3. Any cable between equipment will also have a difference in potential between the 2 x devices and then lightning surge currents will rather flow in the low resistance cables that in the ground, damaging equipment at both ends. For an actual layout of a grounding grid and secondary cables in a respective actual soil model, the maximum coresheath potential difference on the insulations of secondary systems can be analyzed if it is set as k% of gpr. How do you calculate the step and touch voltages in the. It also explains how to act when a fault occurs in a power station inorder to overcome the problems caused by step potential and.
Mesh voltage, metal to metal touch voltage and transferred voltage 6. As per ie rules one has to keep touch potential less than 523 volts step potential. Let us try to solve for the energy eigenstate without redoing all the work involved in solving for b and c in terms of a. For a safe design where step is the limiting condition we may assume the allowed step potential e. Step potential is the voltage between the feet of a person standing near an energized grounded object the electrode. Pdf study of step and touch voltages in resistivecapacitive. Design of earthing grounding system in a substation grid. The person should not get a shock even if the grounded structure is carrying fault current, i. Step and touch potential awareness step and touch instrument. A good grounding system should have the actual mesh and step voltages well below tolerable touch and step voltages respectively. Guzman, david guillermo, touch and step potential analysis at 23. Step potential is the voltage between two places that are a step apart on energized ground. If they step on one ring while their foot is on the other ring electricity will make up to difference in voltage through the body. For the step potential circuit, we have two feet in series, the contact resistance r1 is, therefore, equal to 6.
Step and touch potential voltage earth potential rise. Step and touch voltage are used to derive the safety criteria for grounding grid design. When current is flowing from the tower to the earth ground, the ground potential rises at the tower and a voltage gradient will occur based on the resistivity of the soil, resulting in a potential difference between two points on the ground. Pdf a new method and instrument for touch and step. This video explains what is step potential and touch potential. Apr 24, 2016 reducing step and touch potential hazards one of the simplest methods of reducing step and touch potential hazards is to wear electric hazard shoes. It involves a fault current flow in the earth establishing a potential difference between the earth contact point and some nearby conductive structure or hardware. The maximum touch voltage experienced while standing within a mesh of a ground grid and touching a grounding object. What is step potential and touch potential and step potential and touch potential calculations step potential and touch potential.
The maximum touch voltage within a mesh of a ground grid. Pdf this paper aims to calculate step and touch voltages around transmission line tower foot. Step potential is the step voltage between the feet of a person standing near an energized grounded object. Each ring carries a different voltage as it travels into the ground. Step potential electricity will flow from higher voltage to lower voltage. Touch potential is a problem similar to step potential see figure 4. For example, if you are standing on energized ground, there could be a significant difference in voltage between where one foot and the other are placed, and an.
Figure 4 touch potential protection for step and touch potential is the use of switch operating platforms and. It is equal to the difference in voltage, given by the. Step and touch voltages and grounding potential rise ieee. This potential gradient may affect a person in two ways, either by steptostep contact or by touch contact. Difference in surface potential experienced by a persons feet bridging a distance of 1 meter 3 feet without. It is equal to the difference in voltage between the object and a point some distance away. However, the transmission line itself acts as a very large antenna, and can pick. Electrical step potential hazard avoidance step potential is the voltage difference between the feet of a person near an energized, grounded object. What is step and touch potential and reducing resistance. Pdf a new method and instrument for touch and step voltage. Maximum permissible touch and step voltages assessment in high voltage systems 1 kv 289. The open circuit foottofoot voltage during a ground fault. Also, there are cases where the touch potential could be nearly the full voltage across the earthed object. The snt02 kit provides an easytouse method to continuously monitor and alarm stepandtouch potential.
Step potential and touch potential must read electrical concepts. Step and touch potential voltage earth potential rise risk. Earth potential rise earth potential rise epr is caused by electrical faults that occur at electrical substations, power plants, or highvoltage transmission lines. Oct 26, 2015 awareness of step and touch potential, caused by ground potential rise, is important for anyone working on highvoltage power transmission systems. Touch potential touch potential is the voltage between any two points on a persons body hand to hand, shoulder to back, elbow to hip, hand to foot and so on. Step and touch potential resulting from ground potential rise gpr is well understood as a safety hazard in many situations involving energized power sources. In a typical snt application, the transmission line is deenergized and is bonded to the tower to be safe to work on. During broken pole or downed wire conditions, some really good conductors exist that provide a path to ground including metal fences, wet soil and puddles. The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. Now, the most important thing is to understand the physical meaning and significance of step potential and touch potential.
Human body impedance touch voltage thresholds are related to touch current thresholds by the bodys impedance according to ohms law. Touch potential is the touch voltage between the energized object and the feet of a person in contact with the object. Understanding step and touch potential incident prevention. Step potential and touch potential excellent explanation. Common practice better practice measure step and touch potential. Determine the expected fault current and multiply it by the resistance reading to get the step potential voltage. Distribution of step and touch voltages at the typical hv. For a safe design where step is the limiting condition we may assume the allowed step potential e step is equal to the fault induced step potential e s at the maximum design fault as one of the boundary conditions of the design. Step potential and touch potentials are very important in substations because during ground faults all the ground current returns to the substation transformer as the substation transformer is grounded.
Touch and step potential criteria open electrical, 2017 one of the objectives of a safe earthing grid is to protect people against lethal electric shocks in th e event of an earth fault. With the hgt1, step and touch voltage testing can be carried out quickly, easily and accurately, explains moritz pikisch, product manager at omicron. To understand step and touch potential, we first need to understand. Operational and safety considerations for light rail dc. When dry, properly rated electric hazard shoes have millions of ohms of resistance in the soles and are an excellent tool for personnel safety. Three main techniques for mitigating step and touch potential. Step and touch potential resulting from ground potential rise gpr is. Apr 27, 2018 step potential is the voltage between the feet i. Figure 1 also shows that workers are at risk from step and touch potentials. This voltage, gpr, is equal to the maximum grid current times the grid resistance. Explanation on step potentials due to a direct lightning. Step potential around power lines to understand step and touch potential, we first need to understand how energy dissipates across conductive objects. Maximum limit of allowable ground potential rise of.