Optical system with potential for remote health monitoring of subsea machinery

A prototype fibre optic sensing system is described with potential to remotely monitor the condition of 3 phase variable frequency sub-sea motors and electric submersible pumps. An indication that the integrity of a powerful electric motor may be compromised can be gained by spectral analysis of the stators drive current, the relative phases of the currents, the measurement of vibration at specific locations on the motor and the temperature of the bearings. The optical interrogation system is based on an imbalanced Mach Zehnder fibre interferometer, illuminated with a broad band source with FBG based current and vibration sensors. Signals from sensors operating at an effective distance of 7 km have been demonstrated.