A versatile dual sided spectrum analyzer for protective relaying and electric machine condition monitoring

Protective relaying is extremely important for reliable operation of power systems with minimal interruption. It saves equipment by limiting current, voltage and power variations due to faults. One essential component of protective relaying is symmetrical component analysis. This monitors the positive and negative sequence components of voltages and currents. These components are also important for condition monitoring of rotating electrical machines. It is shown in this paper that these components can easily be obtained from the double sided spectrum analysis of the complex valued signals. Apart from the standard fast Fourier transform (FFT), advanced techniques such as Park´s vector analysis and residual estimation can also be used in the detection of faults. Thus an on-line, realtime instrument that displays these quantities would be very useful. In this paper, the development of such an instrument is presented. It can monitor sequence quantities and locate various characteristic fault frequencies and signature patterns in single and three phase machines. It also has a user friendly interface that is based on MATLAB¹. The instrument was successfully tested on three-phase synchronous and induction machines. The performance is demonstrated by detecting eccentricity faults in salient pole synchronous machines. As commercially available spectrum analyzers cannot yet provide this level of functionality, this is a very useful instrument for practicing power engineers.