Motor Operating-Point Shaft-Torque Worksheet
Calculate average shaft torque from documented shaft output power and speed, or estimate it from a complete balanced sinusoidal three-phase electrical operating point. Current alone does not determine motor torque.
Document the operating point
Every value must describe the same stable motor,connection,supply,load and speed. Use the direct shaft-power basis when applicable output power is known;the electrical basis adds uncertainty from power factor and efficiency.
Average shaft torque
Torque in lbf·ft
Shaft output power
Angular speed
Electrical active input
Electrical apparent power
Inferred losses
Calculation basis
Operating-state record
Equations,units and scope
| Osnova | Equations | Required evidence |
|---|---|---|
| Documented shaft output | ω=2πn/60 T=Pout·1000/ω | Pout in kW and n in r/min at the same steady operating point. |
| Balanced sinusoidal three-phase electrical state | S=√3 ULL IL/1000 Pin=λS Pout=ηPin T=Pout·1000/ω | Line-to-line RMS voltage,line RMS current,true power factor,efficiency and shaft speed for the same state. |
T is in N·m,ω in rad/s,and powers are in kW. The mechanical relation is general engineering arithmetic,not an “ISO torque-from-current formula.” For the electrical route,current is only one of five required measured or documented operating quantities.
Standards and source boundary
IEC Electropedia IEV 141-03-11 gives active power for a symmetric sinusoidal three-phase system. IEV 131-11-46 defines power factor as active power divided by apparent power. IEV 411-53-08 defines machine efficiency as output active power divided by input active power.
IEC 60034-1:2026,Edition 15 is the current rotating-machine rating/performance standard. IEC 60034-2-1:2024,Edition 3 covers standard methods for determining losses and efficiency from tests for most mains-fed machines. IEC 60034-2-3:2024,Edition 2 provides specific test methods for converter-fed AC motors. Exact clauses,test corrections and applicability are NEEDS_LICENSED_SOURCE unless the licensed documents and the test setup are available.
IEC 61800-2:2021,Edition 3 treats an adjustable-speed AC power drive as a complete system;generic constant-torque or field-weakening claims were therefore not used to infer torque. The SI unit relations follow the BIPM SI Brochure,9th edition.
Interpretation safeguards
- A current reading includes components that do not uniquely specify converted mechanical power. Voltage,true power factor,efficiency and speed must all apply to the same state for the electrical estimate.
- Nameplate efficiency or power factor at rated conditions may not represent a part-load,overload,temperature,frequency or converter-fed operating point.
- The direct basis is preferred when shaft output power has been established by an applicable torque/power test. Nameplate rated kW is a capacity/rating,not proof of actual output at an arbitrary current.
- Average shaft torque excludes torque ripple,torsional oscillation,acceleration torque and instantaneous electromagnetic torque.
- Measurement uncertainty can dominate the displayed numerical precision. Preserve the source readings and uncertainty;do not treat extra digits as extra accuracy.
Što je ispravljeno
The former page was titled “torque from current,”preloaded voltage,current,speed,power factor and efficiency,and supplied four unverified motor presets. It accepted power factor or efficiency above one in JavaScript,used a rounded 9549 factor,and presented generic starting-torque and VFD behavior as universal guidance.
The replacement starts blank,requires a source and state record,strictly accepts decimal point or decimal comma,and rejects nonfinite,nonpositive or out-of-range dimensionless values. It separates direct mechanical power from the conditional electrical estimate,uses P/ω without a rounded constant,and gives no starting,drive-control,air-gap or protection result.
