ABSTRACT
Induction machines undergo transients when voltage, current, and (or) speed undergo changes. Turning on or off the power grid leads to transients in induction motors. Reconnecting an induction machine after a short-lived power fault (zero current) is yet another transient. Bus switching for large power induction machines feeding urgent loads also qualifies as large deviation transients. Sudden short-circuits, at the terminals of large induction motors, leads to very large peak currents and torques. On the other hand, more and more induction motors are used in variable speed drives with fast electromagnetic and mechanical transients. So, modeling transients is required for power-grid-fed (constant voltage and frequency) and for PWM converter-fed IM drives control. Modeling the transients of induction machines may be carried out through circuit models or through coupled field/circuit models (through FEM). We will deal first with phase-coordinate abc model with inductance matrix exhibiting terms dependent on rotor position. Subsequently, the space phasor (d-q) model is derived. Both single and double rotor circuit models are dealt with. Saturation is included also in the space-phasor (d-q) model. The abc-dq model is then derived and applied, as it is adequate for nonsymmetrical voltage supplies and for PWM converter-fed IMs. Reduced order d-q models are used to simplify the study of transients for low and large power motors, respectively. Modeling transients with the computation of cage bar and end-ring currents is required when cage and/or end-ring faults occur. Finally the FEM coupled field circuit approach is dealt with. Autonomous generator transients are left out as they are treated in the chapter dedicated to induction generators.
