EM Field Survey

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EM Field Survey

Fault current flowing through the EHV, and HV lines in the power system results in a sudden rise in the line current and an earth potential rise (EPR) at the points where the fault current is conducted into and out of the earth. Generally, a sudden rise in the current flow through an EHV line may create the following failures in critical buildings.

  • High amount of conducted and radiated EMI inside the building resulting in the failure of the malfunctioning communication system.
  • High fault current flow to the tower's foundation due to reasons such as an insulator failure or lightning in the EHV, and HV lines, could generate EPR (earth potential raise). This EPR will not have any direct influence on the electrical system, however, EMI can be coupled into the communication system, resulting in failures.

The values of EPR and EMI depend on the following aspects:

  • Rating of the fault current
  • Type of earthing in power system
  • Earthing resistance of the high-voltage substation
  • Current-earthing coefficient of the fault point
  • Soil resistivity
  • Layout of the earthing device
  • Environmental conditions
  • Transmission mode of transmission lines

The recommended exposure to human beings (general public) from magnetic flux density is about 2 x 10-4 T. However, for sensitive electronic installations, the magnetic field shall be reduced to a limit of less than 1.2 µT.

The best EMI mitigation techniques as recommended in IEC 61000 and ITU standards are to be followed.