Motor Sizing & VFD — validation & limitations

What it calculates

• IEC 60072-1 frame selection: smallest standard IEC frame, from 0.25 kW to 250 kW, that covers the design power with the specified service factor — a design power above the top of the series is refused with an explanation, never silently capped at the largest frame
• Starting-torque check on every application type: locked-rotor torque against the peak run-up demand (load torque plus acceleration torque), with an extra 1.6× breakaway margin required for hoists
• Frame comparison table with separate breakaway (locked-rotor torque vs steady load) and run-up (peak demand vs that frame's pull-out torque) verdicts on every candidate size
• Speed-torque characteristic (Kloss formula) with constant-torque, quadratic fan/pump and linear compressor load curve overlays, and automatic operating-point detection
• VFD energy savings and CO₂ reduction by speed band — cube law for centrifugal fans and pumps, linear law for conveyors — with simple payback period
• Thermal derating for altitude above 1000 m and ambient temperature above 40 °C, common manufacturer practice built on the IEC 60034-1 reference site conditions, plus a winding-temperature estimate taken at the design's own load (or at the nameplate service-factor load when no design load is set)
• IE efficiency class comparison (IE1 through IE4) with annual energy-cost table
• Starting analysis: DOL, star-delta, soft-starter and VFD starting current and torque comparison
• IEC duty-type rating factor for S1 continuous, S2 short-time, S3 intermittent and S6 continuous-periodic duty — intermittent and short-time duty permit an up-rating — S2 by the thermal-time-constant equivalence (capped at 2.0); S3/S6 by a rough, conservative thermal rule that credits the reduced cooling of a stopped self-ventilated motor (S3) and the no-load losses of an idling one (S6), never above 1/√CDF and capped at 1.6 — confirm the S3/S6 rating with the motor manufacturer
• Every panel validates its inputs: an unrecognised enclosure, insulation class, duty type or supply voltage, or an efficiency, power factor, torque, speed or service factor outside its physical range, is refused rather than returned as a plausible-looking number

Standards this tool applies

• IEC 60034-1 — IEC-style frame selection from a rated-power series, rated torque, full-load current, rule-of-thumb thermal derating (altitude + ambient), Kloss speed-torque curve, VFD affinity-law energy savings, IE1–IE4 efficiency comparison (rough values) and S1/S2/S3/S6 duty derating (rough model) — with PDF report.

Validation evidence — independent reference cases (0)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

No independent reference case is registered for this tool yet. Its engine is covered by the regression suite, but no published worked example has been reproduced end to end.

Limitations

Not checked by this tool

• Supply voltage drop during starting and cable sizing — Check the cable and the starting voltage dip with the supply data (IEC 60364-5-52)
• Motor protection (overload relay, breaker, fuse coordination) — Select protection per IEC 60947-4-1 with the maker's starting current and time
• Inverter effects: harmonics, bearing currents and insulation stress — Not assessed; follow IEC/TS 60034-25 and the drive maker's guidance
• Enclosure (IP) and hazardous-area (Ex) suitability — Select IP per IEC 60034-5 and Ex equipment per IEC 60079
• Torsional vibration and the coupling of the drive train — Check the coupling with /couplings and torsional modes separately
• Self-ventilation loss at low VFD speed (constant torque below base speed) — Not derated; take the maker's VFD torque-derating curve or fit a separately driven fan (IEC/TS 60034-25)
• Starts per hour for S4 / S5 intermittent duty with starting — Not computed (S4/S5 are refused); confirm the permitted starts per hour and load inertia with the motor maker
• Hoist holding brake and overhauling (lowering) load — Not checked; size the brake torque and the regenerative / braking resistor for the lowering load per the hoist standard