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We present an optical-fiber voltage sensor for 170-kV gas-insulated high-voltage switchgear. The sensor is based on the converse piezoelectric effect of quartz. The full voltage is applied to a cylinder-shaped quartz crystal. The resulting alternating piezoelectric deformation of the crystal is sensed by an elliptical-core dual-mode fiber, which is wound onto the circumferential crystal surface. The fiber is interrogated by low-coherence interferometry. We address the dielectric design of the sensor and verify its dielectric reliability under ac overvoltages and lightning impulse voltages. We then investigate the sensor performance, including accuracy, dynamic range, bandwidth, and temperature dependence.

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A versatile technology based upon the fiber Fabry-Perot interferometer (FFPI) is proving its merit in industrial sensing applications. The FFPI consists of two internal mirrors separated by a length L of single-mode optical fiber. A sensor head is designed such that the measurand of interest (e.g., pressure, strain, acceleration, magnetic field, temperature) affects the optical length of the interferometer. A signal conditioning unit that performs multiplexing and signal processing functions is capable of monitoring many sensors with a single distributed feedback laser and digital signal processor. An alternative monitoring scheme using a white light interferometry with a lowcoherence light source has also been demonstrated. Applications include monitoring gas pressure in engines, liquid pressure in pumps, strain in civil structures, defects in bearings, and vibration in rotating machinery. In extensive field tests, the engine pressure sensor has shown an unprecedented combination of accuracy and durability at high temperatures. Other advantages over competing technologies include high sensitivity, immunity from electromagnetic interference, small size, the ability to locate sensors far from monitoring equipment, and the potential for least-cost implementation through multiplexing and networking. CWR3 5:15 pmBidirectional Brillouin/erbium fiber ring laser and its application to current sensing