This paper presents a novel algorithm to determine the location of DC line faults in an HVDC system with a mixed transmission media consisting of overhead lines and cables, using only the measurements taken at the rectifier and inverter ends of the composite transmission line. The algorithm relies on the travelling wave principle, and requires the fault generated surge arrival times at two ends of the DC line as inputs. With accurate surge arrival times obtained from time synchronized measurements, the proposed algorithm can accurately predict the faulty segment as well as the exact fault location. Continuous wavelet transform coefficients of the input signal are used to determine the precise time of arrival of travelling waves at the DC line terminals. Two possible input signals, the DC voltage measured at the converter terminal and the current through the surge capacitors connected at the DC line end, are examined and both signals are found to be equally effective for detecting the travelling wave arrival times. Performance of the proposed fault-location scheme is analyzed through detailed simulations carried out using the electromagnetic transient simulation software PSCAD®. The impact of measurement noise on the fault location accuracy is also studied in the paper.
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