B4.2 - Novel Fiber-Optical Accelerometer for Monitoring Tasks of Power Generators

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
B4 - Mechanical Sensors II
M. Villnow, M. Willsch, T. Bosselmann - Siemens AG, Erlangen (Germany), B. Schmauss - Universität Erlangen (Germany)
277 - 282


Due to the increase in energy demand modernizations of electric power plant installations become more and more important. To prevent damages and to verify optimization measures, sensors and monitoring systems are particularly essential. Therefore a novel fiber-optical acceleration sensor has been developed and proposed. The Siemens Fiber Optical Accelerometer (SFOA) is based on the intensity modulation of light. The end surface of a bare multimode fiber is placed towards a tilted mirror. Thereby the fiber is mounted to a fiber ferrule in a way that a defined length of the fiber sticks out at the end of the ferrule like a cantilever bar. When the fiber is illuminated by a light source, the light leaves the waveguide at its end surface, is reflected by the mirror and partially coupled back into the fiber. When the sensor head is exposed to acceleration, the protruding fiber end carries out a relative motion with respect to the mirror. In consequence of the geometric configuration of the tilted mirror, the distance between fiber end surface and mirror changes due to the motion. Based on these distance changes the intensity of the reflected and coupled light is modulated according to the occurring acceleration. Several investigations have been made to find out the best sensor configuration containing the effective beam angle, the distance between fiber end and mirror, the resonance frequency and the sensitivity of the sensor.

The fiber-optical accelerometer was characterized considering a wide range of acceleration of up to 100 m/s², heating tests, fiber bending tests and magnetic compatibility tests. The sensor head consists of nonmetallic materials like GRP (glass fiber reinforced plastic), Teflon, ceramic and epoxy resin so it can be used for measurements under harsh conditions, e.g. high temperatures of up to 150°C and strong magnetic fields that prevail in power generators. In addition a signal interrogation unit was developed to realize a complete sensor system. As a result the sensor was used to measure vibrations of the generator end windings. Therefore several sensors were mounted to the end winding connectors and directly onto the conductive bars, to measure the radial and tangential component of the vibrations due to magnetic forces caused by current forces and the rotor stray field. By placing sensors - arranged around the circumference of the end windings - a modal analysis can be determined in order to specify the vibration modes. In this paper the sensor principle and configuration is described and several investigation and measurement results are shown.