A Multiplexing Optical Partial Discharge Sensing System for Power Transformer using a Single Photodetector
Abstract : Optical ultrasonic sensor multiplexing for partial discharge (PD) detection based on a single photodetector is a challenging task. In this paper, we propose a novel multiplexed optical ultrasonic sensing system based on swept frequency interferometry. Optical ultrasonic sensor multiplexing is achieved using different carrier frequencies that depend on the length differences between the sensing fibers and the reference fiber. Only one photodetector is required for multiple-point optical fiber ultrasonic sensing. The experimental results indicate that the ultrasonic signals generated by a partial discharge defect model can be simultaneously detected. Then, the PD defect was accurately localized based on the arrival times of an ultrasonic signal at the multiplexed sensors.
? After performing the measurements which showed the existence of partial discharge sources, the works preceding the prototype system installation were carried out.
? First, the power transformer was turned off and disconnected from the HV transmission lines.
? Then, the oil excess was drained to the level enabling opening the revision hole in the upper tank cover.
? For this purpose, the comparative research, during which PRPD patterns were simultaneously registered with a standard partial discharges detector type Doble PD-Smart and monitoring system under test.
? The biggest problem of the AE detection method for localizing the PD source in the transformer is its signal sensitivity.
? The UHF method may have a strong anti-electromagnetism interference capability, but the PD UHF quantitation problem has not been thoroughly solved.
? The chemical methods are the fact that there can be a long time delay between the initiation of a PD source and the evolution of enough gas to be detectable.
? Hence, it is important that the partial discharge activity being studied and monitored to detect incipient insulation problems, to prevent catastrophic failures, and to prevent extensive costs.
• Therefore, in many research centers, the works on the elaboration of the antenna not only of compact dimensions but also of high gain and wide bandwidth, which covers the frequency band of the EM signals generated by PD in oil-paper insulation system are carried out.
• For this purpose, a standard LDC-5 PD calibrator (dDoble Engineering Company, Marlborough, USA) was used, which allowed to inject pulses with an apparent charge of 500 pC and duration of 50 ns into the primary circuit.
• The waveforms of the calibration pulses induced in the secondary circuit of the HFCT sensor were registered using an oscilloscope
? Many modern systems use a combination of these techniques, because electrical detection is a proven technology, combining it with modern techniques gives the conformity and the advantage of modern digital signal processing.
? In this paper, we are discussing different type of PD measurement techniques especially in the area of modern measurement techniques using fibre optic sensor with their advantages.
? The advantage of such system is the immunity to electromagnetic field, high flexible, high sensitive and large bandwidth.
? A further advantage is the very fast rise time (response characteristic) to register the discharges and a very low dark current.
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