Anomalies in harmonic distortion and Concordia pattern analyses in induction motors due to capacitor bank malfunctions

It is a common practice in industries these days to incorporate properly sized capacitor banks across induction motors for several reasons including power factor correction, reducing distortions, increasing capacity, etc. Total harmonic distortion (THD) and power factor (PF) are used in such cases to quantify the improvements obtained through connection of the external capacitor banks. On the other hand, one of the methods for assessing the motor internal condition is by the use of Concordia pattern analysis. Though adequate precautionary measures are adopted, the capacitor banks may sometimes malfunction, leading to damage of one or more of the individual capacitors in the whole bank. Such a minor fault in the capacitor bank is often not apparently discernible. This may however, give rise to substantial degradation of power factor correction performance and may also damage the supply profile. The case is more severe with the fact that the Concordia pattern gets distorted due to such external capacitor faults, and can give anomalous results about motor internal fault analyses. The aim of this paper is to present laboratory and field test results to have a close look at the anomalies in harmonic distortion and Concordia pattern analyses in induction motors due to capacitor bank malfunctions.