Distributed Fiber-Optic Strain Sensing for Real-Time Health Monitoring of Wind Turbine Gearboxes: Implications for Renewable Energy System Reliability

Abstract

Gearbox failures in wind turbines are one of the most important issues to address in wind turbine operation and maintenance (O&M) because it has a tremendous influence on the operation and maintenance costs and on wind power generation reliability. This paper examines the use of distributed fibre optic sensing (DFOS) using optical frequency domain reflectometry (OFDR) for the full and real-time strain monitoring of a 2 MW onshore wind turbine (OWT) gearbox. A single-mode optical fiber (175 ?m polyimide coated) was bonded around the circumference of the planetary ring gear (1.864 m diameter, first stage) of a 1P2H gearbox configuration enabling circumferential measurements of strain at 2.6 mm spatial resolution at 12.5 Hz sampling rate at approximately 2254 locations. The strain response was characterized by performing stepped load tests at six levels of torque: (17%, 33%, 50%, 66%, 83%, 100%) of rated torque. Results show a very good linear correlation between the torque applied and the peak-to-peak strain measured (R² = 0.9991) and a range of strains from 28 ? at 17% torque to 142 ?at 100% torque at all the locations monitored. The system was found to be able to detect all three planet gear positions in real-time, and the carrier was found to be rotating at 12.1 rpm. Additionally, the high sensitivity of DFOS to both mechanical strain and temperature allowed thermal monitoring, which showed a 14 °C temperature change during continuous operation. These results show that DFOS is a scalable, low installation-overhead approach to condition-based  maintenance (CBM) and has direct implications towards the levelized cost of energy (LCOE) reduction of wind power systems.

KEYWORDS: distributed fiber-optic sensing; DFOS; OFDR; wind turbine gearbox; planetary gear; strain monitoring; condition-based maintenance; renewable energy; O&M cost reduction; fault detection; structural health monitoring