Assessment of analysis techniques used in determining grounding system potential rise from the fall of potential method

The prevalent method used to determine the ground potential rise (GPR) of an earthing or grounding system is to perform a fall of potential (FOP) test undertaken during a grounding system current injection test. Determining the test GPR requires analysis of FOP test data due to the FOP response´s nonconservative asymptotic behaviour. This paper assesses achievable tolerance by FOP test analysis including recognised and alternative methods. Susceptibility to voltage and distance measurement noise is examined by application to a grounding system model to establish minimum error bounds and method estimation variation on GPR estimates. The applicability of the FOP test `rule of thumb´ termination condition, to take three to four readings beyond the `knee´ of the FOP response, is also examined. In particular, the question of whether appropriate information is gathered when this condition is met is discussed