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What is an Effective Grounding?

Effective grounding is essential to:

  1. Prevent the enclosure of an electrical equipment and its connected conductors rising to a potential dangerously above that of its surroundings or ground. If the environment has a risk of an explosion, there may be a danger of sparking from very small voltage differences.
  2. Allow sufficient ground fault current to safely flow to the grounding system to operate the protective devices without danger. This requirement may conflict with the necessity to keep potentials at a low level and restrict the available methods of protection. The "earth loop impedance" of the completed system to be measured in order to ensure protection operation is not compromised.
  3. Suppress dangerous earth potential gradients.

To ensure the benefits of effective grounding, it is necessary to determine the degree of grounding provided in the system by comparing the magnitude of ground-fault current to the system three- phase fault current. The higher the ground-fault current in relation to the three-phase fault current the greater the degree or effectiveness of grounding in the system.

IEEE Std 142 defines effectively grounded as

Grounded through a sufficiently low impedance such that for all system conditions the ratio of zero-sequence reactance to positive-sequence reactance ( X0 / X1 ) is positive and not greater than 3, and the ratio of zero-sequence resistance to positive-sequence reactance ( R0 / X1 ) is positive and not greater than 1.

Effectively grounded systems will have a line-to-ground short circuit current of at least 60% of the three-phase short-circuit value. In terms of resistance and reactance, effective grounding of a system is accomplished only when R0 ≤ X1 and X0 ≤ 3X1 and such relationships exist at any point in the system. The X1 component used in the above relation is the Thevenin equivalent positive-sequence reactance of the complete system including the sub-transient reactance of all rotating machines.

Other reading materials for effective grounding

A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia, and Professional Electrical Engineer (PEE - 1st Place April 1991) - Philippines with extensive experience in concept selection, front-end engineering, HV & LV detail design, construction, and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and wastewater pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).

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