A PC based ground impedance measurement instrument

A PC-based instrument for ground impedance measurements is presented. The instrument injects a transient electric current between the ground under measurement and an auxiliary ground, and it measures ground potential differences (GPDs) around the ground under measurement. The GPD measurements are processed with software which rejects external noise by the use of correlation methods. Estimation methods are used to extract the ground potential rise and ground impedance. The final result is the ground impedance versus frequency in a user-selected frequency range. The instrument has been constructed and field tested by three electric utilities.<>