Motor Starting Simulator

Compare Across-the-Line, Reduced Voltage Auto-Transformer, Soft Starter, and VFD starting methods on live current, speed, and torque curves — with configurable HP, inertia, NEMA design class, and voltage from 208 V to 4160 V.

AVAILABLEAUTOMATED CHECKS ONLYSTANDARDS-AWAREINTERMEDIATEIEEEWHAT DO THESE STATUSES MEAN?

4 STARTING METHODS1–500 HP · 208–4160 VNEMA A / C / DLIVE TORQUE CURVES

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Overview

Motor starting is one of those topics where the stakes are high — voltage dip, inrush, torque adequacy, cable sizing, protection coordination — but the interaction between starting method, motor characteristics, and load inertia is hard to reason about without seeing the curves move. This simulator runs a dynamic motor starting model for four methods: Across-the-Line (DOL), Reduced Voltage (Auto-Transformer, including 50/65/80% tap), Soft Starter (with configurable initial voltage and ramp time), and VFD (with configurable ramp time and current limit). Inputs include motor horsepower (1–500 HP), supply voltage (208 V to 4160 V MV), NEMA design class (A, C high-torque, D high-slip), shaft speed (900–3600 RPM), and load inertia multiplier. Live charts show current vs. time, speed vs. time, and motor/load torque vs. speed. The Compare tab puts two starting methods side by side with a comparison summary. The Profiles tab shows a library of preset motor/load combinations. The VFD Lab tab allows detailed VFD parameter exploration. A Tests tab simulates motor starting acceptance test observations. A Quiz tab reinforces core concepts.

App preview

A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

Inside the lab

Example data — not a real field report

Dashboard tab with live current, speed, and torque plots during a motor start — Dashboard — the primary run screen. Set HP, voltage (208 V–4160 V), NEMA design class, shaft speed, and load inertia, pick a starting method (DOL, RVAT, Soft Starter, VFD), and hit start. Live current-vs-time, speed-vs-time, and motor/load torque-vs-speed plots update as the machine accelerates.

Compare tab with two starting methods overlaid side by side — Compare — run two starting methods on the same motor and load, side by side. Inrush magnitude, acceleration time, and voltage dip are shown in a summary table so you can see, for example, exactly how a 65% auto-transformer tap trades starting torque for reduced inrush versus DOL.

VFD / Soft Starter Lab tab with ramp time and current limit controls — VFD / SS Lab — a dedicated workspace for tuning VFD and soft starter parameters: initial voltage, ramp time, current limit. Watch how a longer ramp eliminates inrush at the cost of longer acceleration, and how the current-limit setting flattens the current profile.

Challenges tab with preset motor and load scenarios — Challenges — guided scenarios (high-inertia fan, loaded conveyor, MV pump, weak bus) that ask you to pick a starting method to hit voltage-dip and starting-torque targets. Great for reinforcing method selection under realistic constraints.

Quiz tab with conceptual questions on motor starting — Quiz — short-answer questions covering inrush, locked-rotor current, NEMA design class differences, and when each starting method is the right pick. Use it as a fast self-check after a lab session.

Self-Test tab simulating motor starting acceptance test observations — Self-Test — simulates the observations you would record during a real motor-starting acceptance test: peak inrush, voltage dip at the bus, acceleration time, and final steady-state current. Handy for teaching test-report interpretation.

Learn tab with theory content on motor starting methods — Learn — the reference material behind the simulator: how induction machine slip and torque relate, why locked-rotor current is 6–8× FLC, how auto-transformer taps scale current and torque, and how VFDs decouple starting torque from inrush.

What you'll do

01Compare inrush current magnitude and duration for DOL, reduced voltage, soft starter, and VFD starting methods
02Explain how auto-transformer tap selection (50%, 65%, 80%) trades off inrush reduction against starting torque
03Predict the effect of load inertia on acceleration time and starting current duration
04Describe how a VFD eliminates inrush by controlling voltage and frequency throughout the ramp
05Interpret a current vs. time and speed vs. time chart from a motor starting test
06Select a starting method given constraints on voltage dip, starting torque, and cable size

Try a guided scenario

Start a motor across the line and then with reduced-voltage starting.

Motor starting behaviour · Motors & Transformers

No sign-in required. Progress is saved on this device.

What this lab is not

Not a design document, stamped calculation, or approval record.
Not a substitute for engineering analysis by a licensed professional.
Not connected to live equipment and not a safety device.

Calculation basis

References IEEE. Results are computed from the entered inputs and cited back to the referencing clause or table number — no code text or table is reproduced verbatim.

Simplifying assumptions are stated in the lab itself; where a model is intentionally conceptual, the lab says so rather than implying study-grade accuracy.

Standards basis: Standards-aware. Validation state: Automated checks only (last checked 2026-08-15).