Demonstrative Video
Equivalent Circuit of an IM
2-winding Transformer:
\(I_0\) is 1% of the F.L Current
Reason: magnetic flux is confined completely in the steel core of low reluctance, hence \(I_\mu\) is small, as a result \(I_0\) is small
Induction Motor:
presence of air-gap (high reluctance) necessitates a large \(I_\mu\), hence \(I_0\) is very large (40-50 % of F.L Current)
Although, stator and rotor operates at different frequency, but represented in the same vector diagram because magnetic field relative to them are synchronous with each other
When motor is loaded, rotor current is given by \[I_{2}=s\dfrac{E_{2}}{\sqrt{R_{2}^{2}+\left(sX_{2}\right)^{2}}}=\dfrac{E_{2}}{\sqrt{\left(R_{2}/s\right)^{2}+X_{2}^{2}}}\]
From above equation, rotor circuit consists of
a fixed \(R_2\) and variable \(sX_2\) (proportional to slip) connected across \(E_r = sE_2\), or
Fixed reactance \(X_2\) connected in series with a variable \(R_2/s\) (inversely proportional to slip) and supplied with constant \(E_2\)
\[\begin{aligned} \dfrac{R_{2}}{s} & =R_{2}+R_{2}\left(\dfrac{1}{s}-1\right)\\ \Rightarrow R_{2} & =\mbox{represents the rotor Cu loss}\\ \Rightarrow R_{L}&=R_{2}\left(\dfrac{1}{s}-1\right) \\ & =\mbox{electrical equivalent of the mechanical load} \end{aligned}\]
The exciting current may be transferred to the left because inaccuracy involved is negligible and calculations is very much simplified
