Electrical Machines Practice Test 10

1. Which of the above are correct for an auto transformer when compared to the identical rating two winding transformer?

I. KVA rating : 1/(1-k)
II. Losses : (1-k)
III. Impedance drop = 1/(1-k)

2. The statements which support the points that auto transformers are disadvantageous as compared to 2-winding transformer?

I. Weight of conductor reduces
II. Direct electrical contacts
III. Leakage reactance reduces
IV. Lower short-circuit current

3. A 2000/1000/500 three winding transformer is to be used as auto transformer with supply of 3000 V. Two loads of 1050 kVA at 3500V and other one at 180 kVA at 1000V. The total kVA supplied will be?

4. The efficiency of a 20 KVA, 2000/200 V, single phase transformer at unity pf is 98%. The given total losses at full load is 200 W. The pu resistance is?

5. If the pu impedance of a single phase transformer is 0.01+j0.05, then its regulation at p.f. of 0.8 leading will be?

6. From the above graph of the core losses per cycle is, the hysteresis losses per phase for a transformer at a operating frequency of 40 Hz is?

7. A V-V connected transformer can be connected in parallel to delta-delta connected transformer but not to ___________

8. Which of the statements made here are incorrect regarding the transformer?

I. Maximum voltage regulation occurs at the leading p.f.
II. Maximum voltage regulation occurs when load p.f. angle and 
impedance angle of the leakage impedance are same.
III. V.R. at zero p.f. is always zero.
IV. V.R. of a transformer may be negative at leading p.f.

9. Which of the following mentioned losses occur in a transformer?

10. Identify the phasor diagram for the negative voltage regulation from the below diagrams.