A 3-ph., 4-pole, 60Hz induction motor is supplied by a 660-V source. At a particular loading, the total power consumed is 65KW and the current drawn from supply is 70A (assume star connection). The rotor speed is 1760rpm. The stator iron losses are 1.2KW, the windage and friction losses are 1.8KW, and the resistance of stator winding per phase is 0.13 Ω Calculate:

Question

A 3-ph., 4-pole, 60Hz induction motor is supplied by a 660-V source. At a particular loading, the total power consumed is 65KW and the current drawn from supply is 70A (assume star connection). The rotor speed is 1760rpm. The stator iron losses are 1.2KW, the windage and friction losses are 1.8KW, and the resistance of stator winding per phase is 0.13 Ω Calculate:

i) Efficiency
ii) Load torque

Answer 1

To calculate the efficiency and load torque of the given induction motor, we need to find the input power and the output power.

i) Efficiency:
The efficiency of a motor can be calculated using the formula:

Efficiency = (Output Power / Input Power) * 100

Output Power = Total Power consumed - Stator Iron Losses - Windage and Friction Losses
Input Power = Total Power consumed (given)

Output Power = 65KW - 1.2KW - 1.8KW = 62 KW

Now, we can calculate the efficiency:

Efficiency = (62KW / 65KW) * 100 = 95.38%

Therefore, the efficiency of the motor is approximately 95.38%.

ii) Load Torque:
The load torque can be calculated using the formula:

Load Torque = (Output Power * 60) / (2 * π * Rotor Speed)

Where,
Output Power = 62 KW (calculated above)
Rotor Speed = 1760 RPM

We need to convert the rotor speed from RPM to rad/s:

Rotor Speed (in rad/s) = (Rotor Speed in RPM * 2 * π) / 60

Rotor Speed (in rad/s) = (1760 * 2 * 3.14) / 60 = 184.89 rad/s

Now we can calculate the load torque:

Load Torque = (62KW * 60) / (2 * 3.14 * 184.89) = 3.32 Nm

Therefore, the load torque of the motor is approximately 3.32 Nm.