A fault detection system for detection of line faults on an electrode line in an HVDC system wherein the electrode line comprises a first and second branch connected in parallel, the line fault detecting system comprising: a first pulse generation circuit having a trigger input and an output connectable to the first branch via a first injection line, the first pulse generation circuit arranged to generate a first electrical pulse at the output upon receipt of a trigger signal; a second pulse generation circuit having a trigger input and an output connectable to the second branch via a second injection line, the second pulse generation circuit arranged to generate an electrical pulse of opposite polarity to the first pulse at the output upon receipt of a trigger signal; a first current measuring device arranged to generate a signal indicative of electrical signals occurring in the first branch line; a second current measuring device arranged to generate a signal indicative of electrical signals occurring in the second branch line; and a monitoring device having a connection to the first and second current measuring devices, characterized in that the monitoring device is arranged to register: a first registered signal pattern, from the first current measuring device, the first registered signal pattern comprising signals occurring on the first branch line in response to the generation of an electrical pulse signal, and a second registered signal pattern, from the second current measuring device, the second registered signal pattern comprising signals occurring on the second branch line in response to the generation of an electrical pulse signal. a first pulse generation circuit having a trigger input and an output connectable to the first branch via a first injection line, the first pulse generation circuit arranged to generate a first electrical pulse at the output upon receipt of a trigger signal; a second pulse generation circuit having a trigger input and an output connectable to the second branch via a second injection line, the second pulse generation circuit arranged to generate an electrical pulse of opposite polarity to the first pulse at the output upon receipt of a trigger signal; a first current measuring device arranged to generate a signal indicative of electrical signals occurring in the first branch line; a second current measuring device arranged to generate a signal indicative of electrical signals occurring in the second branch line; and a monitoring device having a connection to the first and second current measuring devices, characterized in that the monitoring device is arranged to register: a first registered signal pattern, from the first current measuring device, the first registered signal pattern comprising signals occurring on the first branch line in response to the generation of an electrical pulse signal, and a second registered signal pattern, from the second current measuring device, the second registered signal pattern comprising signals occurring on the second branch line in response to the generation of an electrical pulse signal. a first registered signal pattern, from the first current measuring device, the first registered signal pattern comprising signals occurring on the first branch line in response to the generation of an electrical pulse signal, and a second registered signal pattern, from the second current measuring device, the second registered signal pattern comprising signals occurring on the second branch line in response to the generation of an electrical pulse signal.