A three phase power transformer having a line voltage ratio of 400 V to 33 kV is connected in star-delta. The C.T.s on 400 V side have current ratio as 1000/5. What must be the C.T. ratio on 33 kV side. Assume current on 400 V side of transformer to be 1000 A.

Multiple choice questions: 1- A voltages of 50Hz transformer are 1500 V on primary and 600 V on the secondary. It has 1.5 V per turn. Then the number of turns on primary and secondary are ---------- a) 20 and 8 b) 100 and 10 c) 1000 and 120 d)1000 and 400 e) none of the previous. 2-A 600/200 V single phase transformer is supplying a load of 60 A at a p.f of 0.707 lag. The no load current is 3A at 0.2 P.f. lag. Then the primary current is ---- a) 63A b) 22.56A c) 69A d)24 e) 21.55 f) none of the previous. S 3- The silicon ratio in transformer iron cannot be increased greater than 5% because of- a) the iron loss will increase b) the hysteresis loss will increase c) the eddy current loss will increase d) none of the previous 4- If V1 = 400V and the wattmeter read 800W at no load test then the value of Ro is none of the previous a)100 b)4002 c) 200 d)160002 S

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A 100VA single-phase transformer inside a refrigerator has 100 turns in its primary coil and 20 turns in its secondary. A 120v ac source is connected to the primary. a. Is this an example of a step-up or a step-down transformer? b. What is the secondary voltage? c. Indicate why a transformer is needed in a fridge – why two different voltages are needed in a fridge, and indicate a part of the fridge that is powered by the secondary voltage of this transformer. d. Ifa 202 load is connected to the secondary, what percentage of its rated will the transformer supply? e. If the primary is reduced to 90 turns, what will the secondary voltage be with the same 120v primary source? power