A Complete Field Analysis of Substation Ground Grid By Applying Continuous Low Voltage Fault

IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems

“…The grounding system impedance may be measured with injected test currents taken from the power system lowvoltage network, see [9], [B25], [B44], and [B40]. However, interference voltages present on the grounding conductors and induced on the test conductors will modify the measured currents and potentials.…”

“…Or, if the substation has a ground source (for example from a grounded wye-delta transformer bank), the fault can be initiated either at the remote end of a radially-fed line or by energizing the line with one phase solidly grounded at the remote substation. Or, a power transformer can be installed temporarily and energized from a lower voltage bus with its high side connected to the out-of-service transmission line used during the staged test, see [9], [B18], [B25], and [B44]. Calculations should be made of expected current through the transformer so as not to exceed its short-time thermal rating or its short-circuit winding strength.…”

“…2) Saturation in steel overhead ground wires can increase the conductor GMR by a factor 10 between I and 30 A, thus effecting the shielding efÞciency, see [9]. 3) Corroded hardware may require 10 V or more to achieve conduction (very evident when using rusty probes and battery clips to make Wennet measurements).…”