PROJECT TITLE :

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

ABSTRACT:

Because of the electromagnetic induction between transmission lines and also the associated grounding wires, power frequency current causes flow into the bottom network via the metallic tower, which could 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) technique has been proven to be effective in managing power frequency interference. But, the check equipment based on the VF methodology is often deactivated when the external interference voltage exceeds a preset level so as to avoid false readings. This paper aims at tackling the problem by introducing a reverse phase cancellation (RPC) technique, which acquires and processes the interference signal before generating a cancelling signal with the identical 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 methodology since it retains the advantages of VF and avoids the trip-out of check equipment thanks to excessive interference.