Temperature safety analysis and backup protection scheme improvement for overhead transmission line in power oscillation condition

The oscillating block module is usually adopted to avoid false action of distance protection of overhead transmission lines during power oscillation. However, this scheme ignores the safe operation of conductor temperature during oscillating block. This paper focuses on the conductor overheating problem and safety protection issue during power oscillation. Firstly, through analysis the differences in conductor temperature calculations under oscillating current, short-circuit current and normal load, a numerical iterative method of conductor temperature rise (CTR) calculation under power oscillating current is proposed using the transient thermal balance equation. Then, the safe operation scheme of transmission line is proposed by setting temperature alarm and temperature off-limit trip out. An improved backup protection based on the combination of temperature and impedance is proposed to avoid false action of distance protection, also provide overheating protection for transmission line during power oscillation. Finally, a two-source power system and the modified 29-bus system are adopted to verify the CTR calculation and the improved backup protection. Results indicate that the proposed scheme can provide effective evidence of safe operation and relay setting for transmission lines through excavating the tolerance ability of overcurrent and oscillating current.