Page 173 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

TASK 3 :Carry out blocked rotor test on 3Ф induction rotor
1 Connect the motor for blocked rotor test as per diagram Fig 3
2 Keep the autotransformer to zero voltage position
3 Switch on the ICTP.

4 Ensure safety precaution: do not supply rated voltage during blocked rotor test
5 Increase the output of the autotransformer gradually, and adjust current equal to full load current.
6 Read and record meter readings in Table.
7 Keep the auto transformer at zero output voltage position

8 Switch off the motor.
9 Switch off the supply and disconnect the circuit.
10 Tabulate the total copper losses in Table 3
Table 3

Total copper
Sl.No Line Voltage Line current Wattmeter 1 Wattmeter 1
loss(W1+W2)

Fig 3

TASK 4: Calculate the efficiency of 3Ф induction motor
1 Calculate the output of motor in watts, HP X 746 Watts
2 Total loss = Full load I2R loss + Constant loss (Blocked rotor wattmeter reading + constant loss)
3 Calculate the efficiency of motor, Efficiency =output / input = (output) / output + total losses
(Total losses = Blocked rotor wattmeter reading + Constant losses)

4 Tabulate the calculated result in Table 4
Table 4
A B C D E F G
Output (HP) Output (W) Full load Constant Total loss Input (B + E) Efficiency
(A x 746) copper loss(W) loss(W) (C+D) (B / F)

156

CITS : Power - Electrician & Wireman - Exercise 71