In view of the complexity of the control system of voltage source converter based HVDC (VSC-HVDC)

its insufficient fault tolerance ability

and low correct rate of line protection device

a novel pilot protection for VSC-HVDC transmission lines using the modulus model identification is proposed. According to this principle

the external fault is equivalent to a positive capacitance model

so the correlation coefficient between the differential current and differential voltage derivative is 1; while the internal fault is equivalent to a negative capacitance model

so the correlation coefficient between the differential current and differential voltage derivative is -1. So the internal faults and the external faults can be distinguished by judging whether the correlation coefficient is positive or negative. In practice

modules are used to reduce the interpole electromagnetic coupling disturbance in the VSC-HVDC bipolar system. Theoretical analysis and PSCAD simulation experiments show that the new principle

without compensating for transmission lines capacitor current

is simple

easy to implement

and is not affected by transition resistance and control characteristics

while capable of identifying internal faults and external faults reliably and rapidly.