This simulator models a generic 480 V bus-fed motor control center (MCC) with two independent feeder buckets — a direct-on-line (DOL) starter with a thermal overload relay driving a fixed-frequency motor, and a variable-frequency drive (VFD) driving a separate belt-conveyor motor — so you can trace power and control paths, distinguish overload from short-circuit protection, and study drive speed ramping.
• A real-time 3D cutaway of the MCC main isolator and horizontal bus, the DOL starter bucket (branch breaker, contactor, arc barriers, coil), the thermal overload relay, the VFD bucket (rectifier, DC-link capacitors, heatsink, inverter legs), the control supply and terminal marshalling, the DOL motor and centrifugal load, the VFD motor and belt conveyor, and the vertical feeder bus/cable tray, with toggleable enclosure, auto-rotate, expand and selectable numbered components with callouts. • Eleven fixture controls: MCC main supply available, 24 V control power available, DOL run command, VFD run command, DOL mechanical loading (% reference), DOL overload current setting (A), VFD mechanical loading (% reference), drive frequency demand (Hz), drive frequency ramp (Hz/s), a locked-DOL-shaft jam fault, and a DOL branch short-circuit fault. • Direct actions: start/stop trial, command both motors ON, command both motors OFF, and reset the cooled starter protection. • A Curves & measurements tab with a feeder-current chart (DOL, VFD) and a shaft-speed chart (DOL, VFD), the underlying model equations, and live readouts including thermal memory (% of trip), contactor/drive enabled state, overload trip latch and DOL branch breaker state. • A Test & diagnose Experiments tab with four guided experiments (start both feeders, locked rotor, branch short circuit, missing control voltage) plus a Verification bench of automated model checks and a timestamped event log with report export. • A Learn & assess tab with four guided lessons, a two-question knowledge-check quiz, and a written model-scope statement with a manufacturer reference link.
The DOL branch draws a fixed 60 A starting/inrush current (72 A if the shaft is jammed at locked rotor) before settling to a running current of 4 + 10 × load-fraction amps. The thermal overload relay accumulates thermal memory according to dθ/dt = [(I/overload setting)² − θ] / 30 s, trips the starter once θ reaches 1.4, and only permits a reset once θ has cooled back below 0.7 — so a marginal overload takes time to trip and time to reset, unlike an instantaneous short-circuit device.
The VFD bucket instead solves an output-frequency envelope rather than PWM switching detail: a four-pole motor's synchronous speed is 30 × frequency (rpm), and the VFD's target shaft speed is 30f × (1 − 0.04 × load fraction), ramping toward the commanded frequency at the configured Hz/s rate with representative slip. Losing 24 V control power drops any run command immediately, even with the main bus still energized — restoring control power does not by itself restart a motor; a fresh run command is required. A DOL branch short circuit opens only that branch's breaker in this idealized, independently protected fixture, leaving the VFD feeder unaffected.
The feeder-current chart lets you watch DOL inrush decay as the motor accelerates versus the VFD's frequency-following current estimate, while the shaft-speed chart shows each motor's mechanical speed — useful for confirming that a locked DOL shaft never spins up while the independent VFD motor continues normally. Thermal memory is displayed directly as a percentage of the trip threshold so you can see an overload building well before it actually latches.
Per the model's scope statement, this uses generic 480 V MCC equipment and phenomenological motor/current envelopes, not an IEC trip-class curve or a manufacturer protection study. Short-circuit opening is idealized with no interrupting-rating calculation; there is no arc-flash model, PWM harmonics, regenerative torque or full induction-machine equivalent circuit; and shaft animation runs 30 times slower than the underlying numerical speed for visual clarity.
The thermal overload relay accumulates heat over time (dθ/dt = [(I/setting)² − θ]/30 s) and trips the starter on a sustained overload once θ reaches 1.4, requiring cooldown below θ = 0.7 before reset. The DOL branch breaker instead protects against a short circuit and opens directly and immediately in that scenario — they protect against different fault types on different time scales.
The two feeder buckets are independently protected on separate branch conductors. A locked DOL shaft drives high current into the DOL branch and its overload relay alone, while the VFD bucket and its motor are electrically and thermally unaffected and continue at their commanded frequency.
No. Losing 24 V control power drops any active run command immediately. Restoring control power alone does not reissue that command — you have to press a run command (or "Command both motors ON") again after control power returns.
It uses phenomenological current and thermal envelopes rather than an IEC trip-class curve or manufacturer protection study, idealizes short-circuit interruption with no interrupting-rating calculation, and excludes arc-flash energy, PWM harmonics, regenerative torque and a full induction-machine equivalent circuit. Shaft animation is deliberately slowed 30x relative to the numerical speed.