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Fiber optical online monitoring for high-voltage transformers

The increasing significance of a current state dependent maintenance and the demand for a reliability and an economical operation of power industry devices led to a discussion about monitoring and diagnosis possibilities for high-voltage (h-v) transformers which are one of the most important valuable network components. In the area of high field devices only the use of optical measurement techniques offers the possibility to supervise the characteristic measurands, e.g. critical temperatures or the occurance of Partial Discharges (PDs). Therefore a temperature detector based on Fiber Bragg Gratings (FBG) is presented, who allows a semi-distributed measurement at the active part of the h-v transformer. In this connection some points dealing with cost-effective signal processing units and details about a succesful integration of the sensing elements are investigated and the experimental results are shown. Partial discharges at transformers mainly occure in the insulating oil and on oil-surfaces. Hereby the quantity and amplitude of the PDs are relevant to the actual assessment of the transformer. To analyze the reason for occurrence of PDs it is necessary to localize and characterize the PD source. For on-line detection of PDs the measuring equipment must be placed into the oil. For this application a potential free experimental setup, based on a fiber optical system, for PD detection is described. By using a Mach-Zehnder-Interferometer for acousto-optic measurement the existence of PDs can be detected. By using fiber optical sensors for temperature and PD detection it is possible to watch the operating conditions of h-v transformers and avoid critical states.