Motor-Shaft Load Point & Candidate Capacity Worksheet
Convert one known shaft-power or shaft-torque point and compare it with a user-documented candidate rating. The worksheet does not select a motor,starter or VFD and does not create starting current,starting torque or “standard IEC size” data.
Document the shaft load point
All quantities refer to the motor shaft at one steady operating point. Convert driven-equipment data through the documented gearbox/coupling/transmission model before using this worksheet.
Angular speed
Shaft load power
Shaft load torque
Documented required output
Required torque at this speed
Candidate rated torque
Candidate capacity margin
Candidate utilization
Candidate comparison
Equations and units
| Input basis | Independent relation | Đầu ra |
|---|---|---|
| Known shaft power P in kW | T=P·1000/[2π(n/60)] | Mean shaft torque in N·m |
| Known shaft torque T in N·m | P=T·2π(n/60)/1000 | Mechanical shaft power in kW |
| Documented multiplier k | Preq=kP;Treq=kT | Arithmetic planning requirement at this same point |
The power–torque conversion is ordinary mechanics,not an IEC motor-selection formula. The multiplier is supplied by the user from controlled project/OEM evidence;the worksheet does not assign universal1.15/1.25/1.5 values.
Why one point cannot select a motor
- Selection requires the full driven-load torque–speed curve,breakaway torque,process transients,inertia,acceleration/deceleration time,starts per hour and duty cycle.
- Verify motor locked-rotor,pull-up,breakdown and accelerating torque against the load curve and supply/starter conditions;do not replace those curves with a universal multiplier.
- Check voltage,frequency,connection,ambient,altitude,cooling,enclosure,thermal class,permitted starts,overload and manufacturer tolerances.
- For variable speed,verify the complete motor-converter-load system across constant-flux,field-weakening,low-speed cooling,regeneration and overload regions.
- Oversizing is not automatically beneficial:it can worsen operating efficiency/power factor and does not by itself extend bearing life.
Standards and source boundary
IEC60034-1:2026,Edition15 is the current rotating-machine rating and performance standard and replaced2022. Exact duty,rating,tolerance and thermal requirements are NEEDS_LICENSED_SOURCE;they are not replaced by this worksheet.
IEC60034-12:2024,Edition4 has a specific scope for eight starting-performance designs of single-speed three-phase50/60Hz cage induction motors up to1000V,intended for DOL or star-delta starting and based on S1 duty. It does not justify one universal DOL/Y-Δ/soft-starter/VFD current or torque multiplier.
IEC61800-2:2021,Edition3 applies to adjustable-speed AC power-drive systems and provides criteria for selecting BDM/CDM/PDS performance and functional attributes. A VFD is a system selection,not a fixed1.2× current entry.
IEC60072-1:2022,Edition7 covers dimensions and output series for its stated industrial-machine scope. It does not prove that one hard-coded0.37–315kW list is available or suitable for every technology,duty,speed,mounting or manufacturer.
Nội dung đã hiệu chỉnh
The former calculator ignored its load-type selector,rounded the torque conversion through9550 and multiplied the result by unsourced service-factor presets. It then chose from a partial hard-coded list;requirements above315kW silently returned315kW,creating a direct undersizing path.
Starting current was derived from hidden400V and PF0.85 assumptions while omitting motor efficiency,and fixed current/torque multipliers were assigned to DOL,star-delta,soft starter and VFD without machine or system evidence. All automatic selection,starting estimates,standard-size tables and “always oversize” recommendations were removed.
