chapter  9
45 Pages

SKIN AND ON–LOAD SATURATION EFFECTS

So far we have considered that the resistances, leakage, and magnetization inductances are invariable with load. In reality, the magnetization current Im varies only slightly from no-load to full load (from zero slip to rated slip Sn ≈ 0.01 to 0.06), so the magnetization inductance L1m varies little in such conditions. However, as the slip increases towards standstill, the stator current increases up to (5.5 to 6.5) times rated current at stall (S = 1). In the same time, as the slip increases, even with constant resistances and leakage inductances, the magnetization current Im decreases. So the magnetization current decreases while the stator current increases when the slip increases (Figure 9.1).