Fiber optics temperature/vibration and moisture monitoring in power transformers

Abstract

In most aging transformers, windings failures are caused by the deterioration of the insulation, leading to arcing and short circuits. Vibrations in a transformer are generated by different forces appearing in the core and winding during the operation. Winding vibrations result from the electromagnetic forces that are generated by the interaction of the current in a winding with leakage flux. These forces are proportional to the square of the load current, and therefore vibration is always there. VibroFibre™ technology was invented to monitor the vibration of the end windings. It works according to optical interference, i.e., when subjected to vibration, the signal reflected off the sensor is interpreted as intensity changes resulting from the change in the length of a fiber Bragg grating-based cavity. However, as temperature rises, the fringes also move making it necessary for other control measures to track this temperature rise. These counter measures effectively constitute indirect temperature measurement during this vibration monitoring. The same technology is now adapted to be applied to diagnose transformers. The special sensors are based on the advanced fiber optic vibration sensing technology, where up to 50 vibration sensors can be connected in series along a single optical fiber. These sensors are made thinner so they can be embedded between the windings and are best installed by the manufacturer of the transformers. These vibration sensor arrays will generate temperature information concurrently and will work up to 250 degrees C.