This simulator follows the sensing elements, bimetal linkage and trip contacts of a generic thermal overload relay through normal operation, a locked-rotor event, cooling and reset — showing how thermal memory, not instantaneous current, decides when the relay trips.
• A real-time 3D cutaway — finned motor frame, stepped shaft, cooling fan, fan shroud/endshields, six-terminal connection box, main contactor K1, overload relay and trip contacts, dynamometer/load absorber, flexible coupling, three heater/bimetal elements and a trip bar/reset latch — with home view, focus-selected-part, full-enclosure toggle, exploded view, auto-rotate, expand and selectable labeled components. • Motor & controller settings: line-to-line supply voltage (200–460 V RMS), supply frequency (40–60 Hz), pole count (2/4/6), load torque at base speed, load law (constant or fan/pump demand), combined inertia, relay current setting (10–25 A), cold trip time at 7.2× setting (5–20 s), de-energized cooling time constant (30–300 s) and a "lock the shaft" checkbox, plus Start motor, Stop/coast, Reset trip, Apply locked rotor and Release shaft actions. • A Curves & measurements tab with the teaching thermal-trip characteristic chart, a current-and-thermal-memory history chart, the full model equations, and live snapshot readouts of line current, thermal utilization, rotor speed, current-squared integral, rotor copper loss and elapsed time since start. • An Experiments tab with four guided scenarios (a normal loaded run, a locked-rotor trip, a longer 20 s cold-calibration comparison, and observing thermal memory by tripping, unlocking and attempting an immediate reset) plus a Run model checks verification bench and a timestamped event log with trial-report export. • A Learn & assess tab with four guided lessons, a two-question knowledge-check quiz and a written model-scope statement with an external reference link.
The motor itself uses the same generic fundamental-frequency equivalent circuit as the other motor labs (Rs = 0.65 Ω, R2′ = 0.45 Ω, Xs = X2′ = 1.1 Ω, Xm = 28 Ω at 50 Hz). On top of that, a first-order thermal accumulator tracks relay thermal utilization θ: the thermal target is (I/Isetting)²/1.15², and dθ/dt = (target − θ)/τ, where τ is chosen so a cold start at 7.2× the current setting trips at the selected cold trip time. The relay trips when θ reaches 1.
When the supply is removed, utilization decays exponentially, θ(t) = θ0·exp(−t/τcool), using the configured cooling time constant. Reset trip is blocked above 35% thermal utilization, which is why an immediate reset attempt right after a trip fails — you have to let the relay cool first. Overload protection here only opens the control circuit so the contactor removes supply; it is explicitly not a short-circuit interrupting device.
The teaching thermal-trip characteristic chart shows how the accumulated thermal state responds to sustained overcurrent, calibrated to one fixed reference point (cold trip time at 7.2× setting) that you set directly. A hot restart — one where the accumulator hasn't fully cooled — has less remaining thermal margin than a cold start, which the "observe memory and reset" experiment demonstrates directly.
Per the model's scope statement, this calibration is not a certified IEC trip-class implementation or a winding-temperature estimator: real thermal overload relays have defined tolerances, test conditions and additional functions. Short-circuit protection and phase-loss sensitivity are separate functions not modeled here, and the underlying motor equivalent circuit excludes iron loss, saturation, unbalance, harmonics, detailed bearing dynamics and subcycle switching transients.
Reset trip is blocked above 35% thermal utilization in this model. After a trip the accumulated thermal state must cool — following an exponential decay set by the configured cooling time constant — before reset permission is restored, mirroring how real thermal overload relays retain thermal memory.
No. The relay is modeled purely as a thermal-memory device that opens a control contact so the main contactor removes supply on sustained overcurrent. Short-circuit interruption and phase-loss sensitivity are treated as separate protective functions outside this model.
It sets the single reference point used to derive the thermal time constant τ for the first-order accumulator: a cold start at 7.2 times the relay current setting will trip at exactly that configured time. Changing it reshapes how quickly the whole thermal-trip characteristic responds, not just that one point.
It is a teaching approximation, not a certified IEC trip-class curve or a winding-temperature estimator. It excludes short-circuit protection, phase-loss sensitivity, manufacturer trip tolerances, and the underlying motor equivalent circuit excludes iron loss, saturation, supply unbalance, harmonics and subcycle switching transients.