Sag online monitoring system of power transmission line

The invention provides a sag online monitoring system of a power transmission line, which comprises a fiber grating strain sensor, a fiber grating temperature sensor, a demodulation module, a transmission module and a calculation module, wherein the fiber grating strain sensor is fixed on the surface of a wire of the power transmission line and used for measuring the wire strain capacity of the power transmission line and obtaining a first optical signal for reflecting the wire strain capacity; the fiber grating temperature sensor is fixed on the surface of the wire of the power transmission line and used for measuring the temperature of the power transmission line and obtaining a second optical signal for reflecting the temperature; the demodulation module is used for demodulating the first optical signal and the second optical signal; the transmission module is used for transmitting the demodulated wire strain capacity and the demodulated temperature into the calculation module; andthe calculation module is used for calculating the wire sag of the power transmission line according to the demodulated wire strain capacity and the demodulated temperature. The invention overcomes the problems that a weighing system for measuring the sag adopts a resistance strain gauge to measure the wire tension, the electrical-bridge balance of the resistance strain gauge is more difficult, and the wire sage is difficult to be measured enduringly and accurately in the prior art.