Question

An armature has a resistance of 0.2 Ω at 150°C and the armature Cu loss is to be limited to 600 watts with a temperature rise of 55°C. If α0 for Cu is 0.0043/°C, what is the maximum current that can be passed through the armature?

Answer 1

$R_T=R_0(1+\alpha_0\Delta\>T)$

$P_{max}=I^2_{max}\>R_T$

$T_0=150°c$

$R_0=0.2\Omega$

$\alpha_0=0.0043/°c$

$P_{max}=600w$

$\Delta\>T=55°c$

$R_T=0.2(1+0.0043×55)$

$=0.2473$

$600=I^2_{max}×0.2473$

$I^2_{max}=2426.2$

$I_{max}=49.26A$