Contactless surge sensor using a distributed closed loop detector

The paper proposes a contactless measuring method for surge current and voltage waveforms on an overhead transmission line. Travelling waves on the overhead line are detected as induced voltages or currents to a closed loop, which is a contactless measuring sensor consisting of two distributed lines parallel to the overhead line and two lumped resistances. Transfer functions between the overhead line and the contactless sensor are obtained analytically based on a Z-parameter theory in the frequency domain. Transient responses of the voltages and currents on the overhead line are numerically estimated by dividing the detected voltages or currents by the transfer function in the frequency domain and transforming into the time domain. An experimental result using the proposed method in a scaled circuit shows sufficient accuracy in comparison with a result by direct measurement. The proposed method is applied to a simulation of a surge characteristic measurement on a 500 kV untransposed horizontal line in Japan, and the reasonable accuracy of the proposed method is confirmed. The proposed method is simple in its structure and advantageous in an insulation design of the measuring circuit