Abstract
Transmission lines are affected by Aeolian vibration, which causes strands to break and eventually causes an entire line to break. In this paper, a method for monitoring strand breaking based on modal identification is proposed. First, the natural frequency variation of a conductor caused by strand breakage is analyzed, and a modal experiment of the LGJ-95/15 conductor is conducted. The measurement results show that the natural frequencies of the conductor decrease with an increasing number of broken strands. Next, a monitoring system incorporating a fiber Bragg grating (FBG)-based accelerometer is designed in detail. The FBG sensor is mounted on the conductor to measure the vibration signal. A wind speed sensor is used to measure the wind speed signal and is installed on the tower. An analyzer is also installed on the tower to calculate the natural frequencies, and the data are sent to the monitoring center via 3G. Finally, a monitoring system is tested on a 110 kV experimental transmission line, and the short-time Fourier transform (STFT) method and stochastic subspace identification (SSI) method are used to identify the natural frequencies of the conductor vibration. The experimental results show that SSI analysis provides a higher precision than does STFT and can extract the natural frequency under various wind speeds as an effective basis for discriminating between broken strands.
Highlights
Aeolian vibrations often occur on transmission lines when a steady wind blows toward the conductors
The maximum absolute change was 2.67 Hz, and the maximum relative change was 3.9%. These results indicate that strand breakage can be effectively monitored by monitoring the change in natural frequency
fiber Bragg grating (FBG)-based the analyzer, and Photovoltaic (PV) panels were installed on the cross arm of the tower towind measure speed sensor, the analyzer, and Photovoltaic (PV) panels were installed on the cross arm of the tower acceleration sensor
Summary
Aeolian vibrations often occur on transmission lines when a steady wind blows toward the conductors. Long-term vibration often causes a transmission line to break at the point of clamped contact [1,2]. The load current of transmission lines is variable, as is the magnetic field around them; these variations have a considerable influence on the magnetic induction or eddy current method These sensors must be installed above the broken strand position, and a broken wire may cause the sensor to loosen. When one strand is broken, the bending stiffness decreases, which leads to changes in modal parameters This technology, called modal identification, is applied to the structural monitoring of bridges [14,15] and wind turbines [16]. A broken strand detection method using modal identification is proposed This method is tested on an LGJ-15/95 transmission line. SSI analysis providers a higher precision than does STFT and can extract the natural frequency under various wind speeds
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