Govt. Exams
Entrance Exams
Slip s = (Ns - Nr)/Ns = 0.04. Therefore, Nr = Ns(1-s) = 1500(1-0.04) = 1440 RPM.
Copper loss PCu = I²R is proportional to current squared. It is minimum when load current is zero (no-load condition).
For standard induction motors, slip at full load is typically 0.5% to 2%, ensuring minimal speed variation and high efficiency.
Synchronous speed Ns = 120f/P = (120 × 50)/6 = 1000 RPM, where f = frequency and P = number of poles.
Back EMF in DC motor: Eb = PΦN/60, which depends on flux (Φ) and speed (N). It is independent of armature current and load torque.
Copper loss (I²R loss) occurs in both primary and secondary windings. Core losses occur only in the magnetic core.
The commutator rectifies the alternating EMF induced in the armature coils to produce unidirectional (DC) output.
Core loss depends on frequency and flux density but is independent of load current. It remains constant at rated voltage.
Induction machines are AC machines, not DC machines. DC machines include generators and motors.
Synchronous speed Ns = 120f/P = 120×50/4 = 1500 rpm
