This simulator isolates the starting-current behavior of a direct-on-line squirrel-cage induction motor, letting you compare how supply voltage, load inertia and a locked rotor each change the current envelope and torque during acceleration from standstill.
• 01 / Motor laboratory: a real-time 3D test bench (housing, stator, windings, rotor, shaft, bearings, fan, guard, six-terminal box, main contactor K1, isolator, flexible shaft coupling, dynamometer/load absorber, a load-inertia flywheel and a starting-current clamp) with home view, focus-selected-part, cutaway, exploded view, auto-rotate and expand/hide-labels controls, start, stop/coast, reset trip, apply locked rotor and release-shaft actions, run/pause toggle, 0.02 s and 0.2 s step buttons, and playback speed from 10x slow motion to 20x faster. • Settings: line-to-line supply (200-460 V), supply frequency (40-60 Hz), motor poles (2/4/6), load torque, load law (constant vs quadratic fan/pump), combined inertia, applied supply fraction (40-100%) and a lock-the-shaft checkbox. • 02 / Curves & measurements: a torque/load/operating-point chart and a speed-and-current history chart, the underlying model equations, and live snapshot readouts of rotor speed, line current, highest fundamental RMS current reached, electromagnetic torque, the current-squared (I²t) integral and rotor copper loss. • 03 / Experiments: four guided scenarios (normal direct start at full voltage, a high-inertia load extending the high-current period, a reduced 65% supply voltage that can stall a loaded start, and a locked-rotor failed-acceleration test), plus a Verification bench of automated model checks and a timestamped event log with a copyable trial report. • 04 / Learn & assess: four lessons (the rotor initially has full slip, high inertia extends the start, voltage reduction reduces torque faster, I²t measures exposure not complete damage), a two-question knowledge-check quiz, and a scope-and-references statement linking to a Microchip AC induction motor application note.
The motor uses the same generic balanced fundamental-frequency induction-motor equivalent circuit as the other labs in this set (Rs=0.65 Ω, R2′=0.45 Ω, Xs=X2′=1.1 Ω, Xm=28 Ω at 50 Hz on a star-equivalent base, reactances scaling with frequency). At standstill, slip s=1 makes the rotor branch impedance R2′/s small, driving a high input-current demand; as speed rises and slip falls, that branch impedance grows and current falls toward its running value. Mechanical speed integrates J dω/dt = Te − Tload − 0.012ω, so the same net torque accelerates a larger inertia more slowly, extending the high-current period.
Applied supply fraction is imposed directly on the model rather than solved from a network — it represents a weak-grid or intentionally reduced-voltage condition. Because current at fixed slip is proportional to voltage while torque is approximately proportional to voltage squared in this unsaturated model, reducing voltage cuts torque faster than it cuts current, which is why a 65% voltage reduction can leave a loaded motor unable to accelerate even though its current has fallen.
The speed-and-current history chart shows the current envelope decaying as rotor speed rises during a normal start, versus persisting near its stalled value when the rotor is locked or a reduced-voltage start cannot produce enough torque to accelerate a loaded flywheel. The I²t readout accumulates a current-squared-time integral useful for comparing relative thermal exposure between starts, and rotor copper loss shows where energy is dissipated during high-slip operation.
Per the model's stated scope: starting-current readings are the fundamental RMS envelope, not the first asymmetric instantaneous current crest that a real fault-current calculation would use. Supply-voltage fraction is imposed, not solved from network impedance, so this model does not simulate voltage sag caused by the starting motor itself. Iron loss, saturation, unbalance, harmonics, bearing dynamics and subcycle switching transients are not solved, and I²t here is a comparative exposure metric, not a complete insulation-temperature or protection-coordination model.
At standstill the rotor has full slip (s=1), which makes the rotor-branch impedance R2′/s small and drives a high input-current demand. As the rotor accelerates and slip falls, that impedance grows and current falls toward its running value.
Not necessarily. In this unsaturated model, current at fixed slip scales with voltage while torque scales with voltage squared, so torque falls faster than current. The Experiments tab includes a 65% voltage scenario where a loaded start can stall even though current is lower.
Higher inertia means the same net accelerating torque produces slower acceleration, which extends the time the motor spends in its high-current, high-slip region. The high-inertia experiment demonstrates this directly.
I²t is a current-squared-time integral used to compare relative thermal exposure between different starts — it is not a complete insulation-temperature or protection-coordination calculation. The model also uses the fundamental RMS current envelope rather than the instantaneous asymmetric current crest, and supply-voltage fraction is imposed rather than solved from network impedance.