Ground potential rise

Ground Potential Rise (GPR) refers to the increase in electrical potential between the ground and a point of reference when a fault occurs on a power system. It is caused by lightning or high voltage ground faults. Under these conditions the potential of the soil surrounding the point of ground fault increases to dangerous levels.

In a power system, when a fault occurs, the current flowing through the fault can create a rise in electrical potential at the ground, which can create a hazard for people or equipment that are in contact with the ground. This rise in electrical potential can also result in damage to electrical equipment and increase the risk of flashovers and arcs, which can cause further damage to the power system and disrupt the supply of electricity.

GPR is an important consideration in the design of electrical power systems, particularly in industrial and high voltage applications, where high levels of fault current can flow. To minimize the risk of GPR, various mitigation techniques are employed, such as earthing systems, surge arrestors, and fault current limiters.

ground potential rise
Possible points of lightning strike that may lead to a ground potential rise in a residential installation.

How to mitigate ground potential rise?

There are several techniques that can be used to mitigate Ground Potential Rise (GPR) in an electrical power system:

  1. Proper earthing system design: The earthing system is an essential component of a power system, and a well-designed earthing system can help to reduce the level of GPR. A good earthing system should have low impedance and sufficient capacity to carry fault currents safely to ground.
  2. Surge arrestors: Surge arrestors are devices that protect electrical equipment from high voltage surges, including those caused by GPR. They work by diverting the surge current to ground, thus reducing the voltage at the point of protection.
  3. Fault current limiters: Fault current limiters are devices that limit the amount of fault current that flows in the system. By limiting the fault current, the GPR can be reduced, which can help to prevent damage to electrical equipment and reduce the risk of flashovers and arcs.
  4. Shield wires: Shield wires are conductors placed around high voltage cables to reduce the electric field around the cable. By reducing the electric field, the GPR can be reduced, which can help to prevent damage to electrical equipment and reduce the risk of flashovers and arcs.
  5. Protective relaying: Protective relaying is the process of detecting a fault and automatically disconnecting the faulted portion of the power system. By disconnecting the faulted portion of the system, the fault current can be limited, which can help to reduce the GPR.

It’s important to note that the best approach to mitigating GPR will depend on the specific circumstances of each power system and the level of risk that is acceptable. The selection of appropriate mitigation techniques should be based on a comprehensive analysis of the power system, including an assessment of fault current levels, earthing system design, and the electrical characteristics of the system components.

Additional reference:

“IEEE SA – 80-2013 – IEEE Guide for Safety in AC Substation Grounding”. Retrieved 2016-12-15.

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