V-shaped portable NMR sensor with a deep penetration depth and its application in assessing the aging level of turbine oils in power stations

Abstract

This paper presents a simple design for a nuclear magnetic resonance (NMR) sensor and its application for detecting turbine oil in two power stations. The magnet, which is composed of two identical cuboid permanent magnet blocks and two iron shimming sheets of a special shape, generates a relatively homogeneous static magnetic B₀ field(∼ 364 ppm) on a 10 × 10 mm² region of interest. In the vertical direction, it produces a constant gradient of ∼15.5 T/m within 5 mm which allows for self-diffusion measurements and 1 dimensional imaging. This NMR sensor can produce a deep penetration depth into the samples with relatively strong and uniform B₀ strength. The NMR sensor was specially designed for assessing the aging status of turbine oil in a power station, and a group of turbine oil of different service times was measured. Results demonstrate that an increase in the service time of the turbine oils clearly decreases transverse relaxation time T₂. This portable sensor can be used in fields and provide quantitative evaluation parameters of the aging status of turbine oil during periodic inspection.