On the Feasibility of Monitoring Power Transformer’s Winding Vibration and Temperature along with Moisture in Oil Using Optical Sensors

Abstract

Despite major progress in the design of power transformers, the Achilles’ heel remains the insulation system, which is affected by various parameters including moisture, heat, and vibrations. These important machines require extreme reliability to guarantee electricity distribution to end users. In this contribution, a fiber optic sensor (FOS), consisting of a Fabry–Perot cavity made up of two identical fiber Bragg gratings (FBGs), is proposed, to monitor the temperature and vibration of power transformer windings. A phase shifted gratings recoated sensor, with multilayers of polyimide films, is used to monitor the moisture content in oil. The feasibility is investigated using an experimental laboratory transformer model, especially fabricated for this application. The moisture contents are well correlated with those measured by a Karl Fisher titrator, while the values of temperature compare well with those recorded from thermocouples. It is also shown that the sensors can be used to concurrently detect vibration, as assessed by sensitivity to the loading current. The possibility of dynamically measuring humidity, vibrations, and temperatures right next to the winding, appears to be a new insight that was previously unavailable. This approach, with its triple ability, can help to reduce the required number of sensors and therefore simplify the wiring layout.

Fibre Bragg Grating Sensors for Condition Monitoring of High-Voltage Assets: A Review

“…When subjected to 24 h cyclic loading, the water activity varied (due to cyclic absorption of moisture by the cellulose) which was detected by both the FBG array and a moisture probe. The authors of [84] exposed transformer oils to saturated humid air and obtained perfect correlation between wavelength shifts and water content for the ranges tested: 50-300 ppm in mineral oil and 5-30 ppm in ester oil. The high accuracy demonstrated in these studies suggests that PI-coated FBG sensors have the potential for development of online moisture monitoring in transformers.…”

Effect of Multiple Reclosing Time Intervals on Axial Vibration of Winding

“…In the reclosure-failure case the winding experiences a cumulative superposition effect of multiple impulses over a short time period, when the previous impulse is not eliminated and the subsequent impulse occurs [4]. This effect leads to greater deterioration of the winding [5]. When the short circuit is removed, the transformer structure fails to fully recover, and the insulating pad between copper disks is deformed by vibration [6].…”