Question

(a) List the factors that determine the maximum developed torque of the induction motor. (6)

(b) The primary and secondary windings of a 500 kVA transformer have resistances of 0.42 and 0.0019 respectively. The primary and secondary voltages are 11000 V and 415 V respectively and the core loss is 2.9 kW, assuming the power factor of the load to be 0.8. Calculate the efficiency on: (10)

(i) Full load.

(ii) Half load;

Answer 1

Part (a)

The maximum developed torque of an induction motor is determined by several factors, primarily derived from its equivalent circuit parameters and supply conditions. These factors include:

Stator Supply Voltage (V1): The maximum torque is directly proportional to the square of the stator supply voltage. A higher supply voltage leads to a significantly higher maximum torque.
Stator Resistance (R1): Higher stator resistance tends to reduce the maximum torque. It contributes to the overall impedance that limits current flow.
Stator Leakage Reactance (X1): Higher stator leakage reactance reduces the maximum torque. Leakage reactance represents the magnetic flux that does not link both stator and rotor windings.
Rotor Leakage Reactance (X2'): Higher rotor leakage reactance (referred to the stator) reduces the maximum torque. Similar to stator leakage reactance, it impedes the flow of rotor current and thus the torque production.
Supply Frequency (f): The maximum torque is inversely proportional to the supply frequency. This is because reactances (X = 2πfL) are directly proportional to frequency, and synchronous speed (ωs = 2πf/P) is also directly proportional to frequency.
Number of Poles (P): The maximum torque is directly proportional to the number of poles of the motor. This is due to its inverse relationship with the synchronous speed (ωs = 2πf/P).

✓ Verified Model Answer (Text Solution)

The maximum developed torque of an induction motor is determined by several factors, primarily derived from its equivalent circuit parameters and supply conditions. These factors include: