A hybrid protection scheme based on integrated impedance for ±800kV UHVDC transmission line

This paper proposes a hybrid protection scheme for UHVDC transmission line. The proposed hybrid protection scheme consists of a single-ended protection, a pilot protection and faulty pole identification unit. The single-ended protection is based on the attenuation of dc filter and smoothing reactor on high frequency components, while the pilot protection is using the differences of voltage and current fault components between internal fault and external fault. Voltage fault component is used for faulty pole identification. A ±800kV UHVDC system model is built in PSCAD/EMTDC and simulation test results show that the hybrid protection scheme can not only distinguish internal fault from external fault accurately, but can also identify the faulty pole correctly. Finally, the influence of fault impedance on performance of the protection scheme is discussed.