Every press of Start produces a starting-current event. Compare DOL and star–delta before examining the overload.
1 · Choose the experiment
DOL: approximately 60 A initially (6 × nameplate FLC), easing to running current over 4 simulated seconds.
A locked rotor does not accelerate. It draws high current until the overload trips or the starter is stopped.
Motor rated line current: 10 A. Relay senses supply-line current in both starter arrangements (not an inside-delta connection).
Use ×1–4 to watch start/changeover. Increase to ×20–60 to watch delayed tripping and cooling.
Repeated starts: Press Stop and Start again. The model retains its thermal history until New trial.
2 · Follow the protective action
Motor line current
0.0 A
10 A rated line FLC
Relay thermal index
0%
100% = model trip
Elapsed
0 s
Simulated time
Starter stage
OFF
No trip recorded
Starts: 0Last start peak: —Method: DOL
QShort-circuit
KContactor
OLOverload
MMotor
Ready. Predict the start current and trip response, then press Start.
3 · Follow the starting current and heat
Line current (A)Relay thermal index (% of trip)Trip threshold (100%)Start / changeover
4 · Discussion prompts
Choose normal. Compare DOL starting peak with the star starting peak. Why is star–delta suitable for some loads but not others?
Does 15 A after starting cause a delayed overload trip? What changes if the relay dial is 14 A?
What happens if the rotor is jammed during star, then changes over to delta?
Stop and restart twice. Does the starting surge recur each time? What happens to thermal memory?
Why can a star–delta transition still produce a current spike?
Educational model — not a relay or motor design tool. Values are illustrative: 10 A rated line FLC; DOL starting 60 A; star starting approximately 20 A; star period 6 s; open changeover 0.5 s; illustrative delta re-energisation peak 35 A. Real start current, changeover transients and acceleration depend on motor/load, design and timing; star torque is also reduced (approximately one third of direct delta starting torque for a suitable motor). The thermal index uses a simplified I² integrator, not a measured winding temperature or certified device trip curve. No short-circuit/phase-loss simulation is provided. Consult manufacturer data, device coordination and applicable AS/NZS 3000 requirements.