When an induction motor is supplied with unbalanced voltages, the voltage can be resolved into positive-sequence ($V_1$), negative-sequence ($V_2$), and zero-sequence ($V_0$) components using symmetrical components · The negative-sequence voltage produces a magnetic field rotating in opposition to the rotor, resulting in high negative-sequence current ($I_2$) due to the low negative-sequence impedance ($Z_2 \approx Z_{\text{locked-rotor}}$) · If the supply voltage unbalance changes, the ratio of $V_2 / V_1$ alters drastically, producing localized overheating that fixed protection relays set for a different unbalance condition cannot reliably detect.

In competitive exams like GATE and ESE, remember that a $1\%$ voltage unbalance can cause up to $6\% - 10\%$ current unbalance in induction motors due to low negative-sequence impedance ($Z_2$) · Always check negative-sequence relay protection ($46$ device) for unbalanced fault analysis.