Documented Winding-Resistance Temperature-Correction Worksheet
Correct one measured winding resistance to a reference temperature using a documented material constant. Optionally compare three intended-equal winding values without turning an arithmetic spread into an automatic fault diagnosis.
Record the resistance measurement
The measured resistance,winding temperature and material constant must belong to the same conductor system and an applicable linear temperature range. Do not substitute ambient temperature for winding temperature without documented equilibrium evidence.
Corrected resistance
Correction factor
Resistance change
Implied coefficient at Tm
Temperature change
Material constant
Arithmetic mean
Rozsah
Range/mean
Maximum deviation from mean
Individual deviations
Selected comparison result
Equations and units
| Množstvo | Equation | Hranica |
|---|---|---|
| Temperature correction | Rs=Rm·(k+Ts)/(k+Tm) | Linear resistance-temperature model with documented k and applicable range;all temperatures in °C. |
| Implied local coefficient | α(Tm)=1/(k+Tm) | Derived from the same linear model;not an independent material property lookup. |
| Three-value descriptive spread |
mean=(R1+R2+R3)/3 range%=100(max−min)/mean |
Useful for reporting,but range/mean is not the AR100 “from average” criterion. |
| Deviation from average |
di=100|Ri−mean|/mean dmax=max(di) |
Compared with AR100 limits only under its repair scope and the selected winding construction. |
Ω,mΩ and µΩ are converted exactly by factors1,10−3 and10−6. A common temperature factor does not change dimensionless deviations,but all compared values still need the same valid reference state.
Standards and source boundary
ANSI/EASA AR100-2025 is the current freely downloadable recommended practice for repair of rotating electrical apparatus. Clause4.3.1 states resistance-unbalance limits of2% from the average for random windings and1% from the average for form-coil windings,and notes that some concentric windings may exceed2%. These comparisons do not replace manufacturer/customer specifications or specialized-machine requirements.
IEC60034-1:2026,Edition15 is the current rotating-machine rating/performance standard. IEC60034-2-1:2024,Edition3 covers loss and efficiency test methods for most mains-fed machines. IEEE112-2017 remains an active test procedure for polyphase induction motors and generators. Exact resistance-temperature clauses,constants,test corrections and applicability in those closed documents are NEEDS_LICENSED_SOURCE;this page does not label the general linear equation an IEC or IEEE formula.
The historical official U.S. Bureau of Standards Circular31,2nd edition documents the linear copper relationship and shows that the inferred zero varies with copper conductivity;−234.5°C corresponds to its100% conductivity copper entry. It is metrology evidence for why a universal copper preset is unsafe,not a current motor acceptance standard. Megger manufacturer guidance likewise stresses accurate winding temperature and trending;its “less than1% typical” statement is guidance,not used here as a universal pass/fail limit.
Measurement and interpretation safeguards
- Use an appropriate low-resistance method,typically a documented four-wire/Kelvin arrangement or verified lead compensation;record test current,stability and uncertainty.
- Measure winding temperature rather than assuming recently operated copper equals ambient. Thermal equilibrium requires evidence,not a universal30-minute idle rule.
- Direct winding,phase and terminal-to-terminal path resistances are different quantities for some wye/delta/internal connections. Record exactly what was accessible and compared.
- Resistance imbalance can arise from winding geometry,connections,lead paths,temperature or measurement error. Resistance alone does not prove shorted turns or winding degradation.
- For acceptance or repair decisions,use the applicable manufacturer/customer specification,licensed machine standard,winding construction and baseline/trend;more restrictive requirements can govern.
What was corrected
The former page preselected copper,k=234.5,25°C,75°C and2.45Ω;claimed generic IEEE/IEC support;used range/mean against invented1/2/5% “excellent/acceptable/problem/remove” bands;and diagnosed faults from that percentage. Its aluminum row combined α20=0.00403 with k=225,although the page’s own linear model gives α20=1/(225+20)=0.00408163.
The replacement starts blank,requires the applicable k and source,handles Ω/mΩ/µΩ,uses strict point/comma parsing and checks both temperature denominators. The optional comparison reports both range/mean and maximum deviation from the average,applies only the verified AR100-2025 random/form-coil limits when explicitly selected,and issues no fault or return-to-service decision. Unsupported material/resistivity tables,typical absolute motor values,hot-temperature insulation loading advice,presets,prefix parsing and unsafe HTML output were removed.
