Microcontroller-based power-angle instrument for a power systems laboratory

This paper presents the design and construction of a microcontroller-based instrument to measure the power angle, the rotor speed, and the terminal voltage frequency of synchronous machines. The instrument is suitable for both steady-state and transient measurements. It can be used as a stand alone instrument or connected to a personal computer. The instrument uses a 256-slit optical encoder and a signal transformer to detect the rotor position and the terminal voltage, respectively. Most of previous power-angle instruments require a laborious manual procedure to calibrate the power-angle zero reference each time the instrument is disconnected or turned off or the generator field is deenergized. This manual procedure affects the accuracy of the instrument. The instrument presented in this paper is self-calibrating, i.e., it is automatically self-calibrated by software. The power angle can be measured with a resolution of 0.0216 electrical degrees. To use the instrument with a personal computer, a special graphical user interface was designed.