Torque measurements in synchronous generators using giant magnetoresistive sensor arrays via the Maxwell stress tensor

Power system oscillations arise from various sources. One contributor that is difficult to quantify during operation is the induced (air-gap) torque. This paper presents a new approach for measuring the instantaneous air-gap torque in real-time for synchronous generators. This is achieved through recent progress in nanowire giant magnetoresistive sensor (GMR) technology that now makes it possible to directly measure magnetic fields in the air-gap of operating electrical machinery. Results show that it is possible to compute the instantaneous air-gap induced electrical torque by evaluating a discretized form of the Maxwell stress tensor. This torque measurement can then be used to extract information on the operating condition of a synchronous generator in real-time. A prototype GMR sensor is evaluated. Analysis for generator diagnostics and detection of torsional oscillations is presented.