What would the differences of resistances be of shunt fields, series fields and armature circuits if the temperature was different? I remember in class they had us turn it on for about 5 minutes so it'd warm up for best possible reasons.... why?
And how would I use that to calculate a resistance at a different temperature? Say I have 242 ohm resistance for my shunt field at 20C, what would it be at 55C?
And how would I use that to calculate a resistance at a different temperature? Say I have 242 ohm resistance for my shunt field at 20C, what would it be at 55C?
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If this is just the DC resistance of a coil of copper wire,
Temperature Change in Resistance
Rt = Ro(1 + α∆T)
R = L/Aσ
σ = L/AR
σ is conductivity in 1/Ω-m
α is temperature coef in /ºC
α for copper is 0.0039 /ºC
Rt = Ro(1 + α∆T)
Rt = 242(1 + 0.0039•35) = 275 ohms
Temperature Change in Resistance
Rt = Ro(1 + α∆T)
R = L/Aσ
σ = L/AR
σ is conductivity in 1/Ω-m
α is temperature coef in /ºC
α for copper is 0.0039 /ºC
Rt = Ro(1 + α∆T)
Rt = 242(1 + 0.0039•35) = 275 ohms
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The windings on motors are usually copper, which has a significant temperature coefficient. It is always best to warm up power systems to measure their normal running characteristics. External shunt resistors will not change very much with temp as they use alloys of metal that have very low tempcos.