Power Frequency Interference and Suppression in Measurement of Power Transmission Tower Grounding Resistance

Due to the electromagnetic induction between transmission lines and the associated grounding wires, power frequency current causes flow into the ground network via the metallic tower, which may interfere with grounding resistance measurements. This paper analyzes the mechanisms of this interference, and shows that power frequency interference becomes stronger at phase-wire transposition towers. Grounding resistance measurement by the variable frequency (VF) method has been proven to be effective in dealing with power frequency interference. However, the test equipment based on the VF method is always deactivated when the external interference voltage exceeds a preset level in order to avoid false readings. This paper aims at tackling the problem by introducing a reverse phase cancellation (RPC) method, which acquires and processes the interference signal before generating a cancelling signal with the same amplitude and frequency and a phase which is exactly opposite in polarity. This paper proves that the RPC method represents an excellent improvement over the VF method since it retains the advantages of VF and avoids the trip-out of test equipment due to excessive interference.