Earth potential rise due to induced current from 3-phase high voltage transmission lines
#Transmission line, #HV lines, #Induced current, #Ground wire, #Magnetic fields, #Comsol Multiphysics
Challenge
A power utility experienced stray current in the soil around earthing systems, at a 400kV powerline. The resulting earth potential rise led to undesired impact on a production facility in the proximity of the powerline, and Upvious was involved in trying to explore the causes.
Upvious Contribution
After discussions on potential scenarios and causes of the effects observed, Upvious constructed first a 2D model of the different power line configurations involved. By defining actual phase currents in the dual three phase systems (in complex terms involving current magnitude and phase angle), the induced current in the ground wire as function of the phase currents was calculated.
Secondly a 3D model of the soil was created to couple the current sources (sections of ground wire between transmission towers carrying induced current) with the load being the resistivity of the soil. The coupling was done in Comsol Multiphysics, where current sources were defined as electric circuits coupled to the soil via the earthing impedances of each of the transmission towers. By doing so, the impact of the many different involved factors could be investigated, including powerline phase configuration, load currents, active and reactive power, transmission grid layout, soil resistivity, earthing system geometry, etc.
Results
The results of the modelling effort demonstrated how the configuration of HV transmission lines, and the imbalance of power flow (active and reactive) to grid junction points can result in the injection or extraction of ground currents – finally leading to the observed earth potential rise.
The simulation effort, process and results were thoroughly explained to the customer, enabling such knowledge to be included in future designs of power stations and transmission grid layout.
