Motor Circuit Analysis Concept and Principle

Low voltage Motor Circuit Analysis (MCA) techniques involve the collection and analysis of resistance, impedance, inductance, phase angle, current/frequency response and insulation to ground faults. Output voltage of the test instruments are less than 9 Vac, sinusoidal output. The resulting low level alternating magnetic fields excite the dielectric dipoles and surrounding magnetic steel dipoles, in both the stator and rotor. Winding defects, including developing shorts, cause changes to the dielectric and resulting dipolar ‘spin,’ which changes the capacitance of the winding circuit at the point of defect. The resulting change effects the phase angle and current/frequency response in the corresponding phase, causing a difference when comparing phase, or coil grouping, to phase. As the defect progresses, the changes to the insulation system continue, allowing trending of the defect over time. The purpose of this paper is to cover the concepts and principles in the physical changes to the windings in winding short and winding contamination faults.