Towards the development of a downhole optical voltage sensor for monitoring electrical submersible pumps

In this paper a novel design of a downhole, three-phase optical voltage sensor for monitoring electrical submersible pumps (ESPs) is presented. In the proposed approach, voltage applied across a piezoelectric transducer is converted to strain that is measured using a fiber Bragg grating sensor. A novel design introduces strain amplification at the grating location which enhances the measurement resolution. Finite element electrostatic modeling software is used to evaluate the electric field distribution around the sensor components, and improvements are incorporated at the design stage to minimize the possibility of electrical breakdown in the prototype device. The operation and performance of a 3-phase device is evaluated by means of tests at voltages up to 10 kV. Results show that the new sensors exhibit measurement accuracies of better than 0.5% full scale and thus, with further development and ruggedization, will be suitable for the ESP monitoring application.