Circuit distance I-segment protection method applicable to access of unified power flow controller

The invention belongs to the field of power system circuit relay protection, and particularly relates to a circuit distance I-segment protection method applicable to access of a unified power flow controller. A virtual similar triangle is built according to geometrical characteristic of a system voltage and current phasor after a fault, a novel fault distance solution equation is built to accurately solve out a fault distance, and an internal fault and an external fault are correctly distinguished by combining a fault distance measurement fluctuation auxiliary criterion. The method is free from the influence of a transition resistor, a fault position can be accurately positioned only by electrical quantity information of a single end, and the internal fault and the external fault can be reliably distinguished by combining the auxiliary criterion. Moreover, the method is applicable for distance components with various fault types and various action characteristics, has favorable universality and is not free fr