TRANSFORMER part-4

1. The type of oil, which is suitable as transformer oil is
    (a) Crude oil                                  (b) Organic oil
    (c) Mineral oil                                (d) Animal oil. 

  Ans.c

2. The chemical used in breather is
    (a). asbestos fiber                           (b). silica sand
    (c). sodium chloride                       (d). silica gel 

 

 Ans.d 

3. Which winding in a transformer has more number of turns?

     (a). Low voltage winding               (b). High voltage winding

     (c). Primary winding                      (d). Secondary winding 

 Ans.b

4. For a transformer, the condition for maximum efficiency is

    (a)  Hysteresis loss = eddy current loss

    (b)  Core loss = hysteresis loss

    (c)  Copper loss = Iron loss

    (d)  Total loss = 2/3 copper loss. 

 Ans.c

5. Core lifting of a transformer is done after a period of

    (a) 3 yrs.                                           (b) 4 yrs.

    (c) 5 yrs.                                           (d) 6 yrs. 

 Ans.c

6. Short circuit test on transformers is conducted to determine

   (a). hysteresis losses                          (b). copper losses

   (c). core losses                                   (d). eddy current losses 

 Ans.d

7. Transformers placed in a room enclosed from all the four sides, the minimum

    spacing between the walls and the transformer should be

   (a) 0.5 m                                            (b) 0.75 m

   (c) 1 m                                               (d) 1.25 m 

 Ans.d

8.  The efficiency of a transformer will be maximum when

   (a). copper losses = hysteresis losses         (b). hysteresis losses = eddy current losses

   (c). eddy current losses = copper losses    (d). copper losses = iron losses 

 Ans.d

9. The secondary winding of which of the following transformers is always kept

    closed?

   (a). Step-up transformer                            (b). Step-down transformer

   (c). Potential transformer                          (d). Current transformer 

 Ans.d

10. The power factor in a transformer

     (a) Is always unity

     (b) Is always leading

     (c) Is always lagging

     (d) Depends on power factor of load.

 Ans.d

TRANSFORMER part-3

1. A no-load test is performed on a transformer to determine

(a). Core loss                            (b). Copper loss

(c). Efficiency                      (d). Magnetising current and loss 

Ans.d 

2. For a transformer, the condition for maximum efficiency is

(a) Hysteresis loss = eddy current loss

(b) Core loss = hysteresis loss

(c) Copper loss = Iron loss

(d) Total loss = 2/3 copper loss. 

Ans.c

In Transformer maximum efficiency =2*Iron loss
So here Iron loss = to Copper loss
(Max,Efficiency=Cu loss+Iron loss)

3. In a transformer the tappings are generally provided on

(a). primary side                       (b). secondary side

(c). low voltage side                  (d). high voltage side 

Ans.c

4. Transformer oil shall be free from

 (a) Odour                                (b) Gases

 (c) Temperature                      (d) Moistur

Ans.d

5. The colour of fresh dielectric oil for a transformer

 (a) Pale yellow                          (b) Dark brown

 (c) White to grey                       (d) Colourless 

Ans.d

6. The function of breather in a transformer is

(a). to provide oxygen inside reduced load 

(b). to cool the coils during reduced load

(c). to cool the transformer oil 

(d). to arrest flow of moisture when outside air enters the transformer 

Ans.d

7. The maximum efficiency of a distribution transformer is

(a). at no load                       (b). at 50% full load

(c). at 80% full load              (d). at full load 

Ans.b

8. Material used for construction of transformer core is usually

(a). Wood                              (b). copper

(c). Aluminium                       (d). silicon steel 

Ans.d

9. An open-circuit test on a transformer is conducted primarily to measure

(a). Insulation Resistance      (b). Copper loss

(c). Core loss                         (d). Total loss 

Ans.c

10. A Buchholz relay can be installed on

(a). auto-transformers           (b). air-cooled transformers

(c). welding transformers      (d). oil cooled transformers 

Ans.d

TRANSFORMER part-2

1.While testing transformer oil the gap between electrodes is kept at a distance of

(a) 1 mm (b) 2 mm

 (c) 3 mm (d) 4 mm 

Ans: d

2.The short circuit test of a transformer gives

(a) Copper loss at full load

(b) Copper loss at half load

(c) Iron loss at any load

(d) Sum of iron loss and copper load

Ans: a

3.What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV? (a) 4KVA   (b)0.25KVA  (C) 16KVA (d) 8KVA Ans: c 4.Which test is conducted on all transformers in a manufacturing concern  (a) Routine test (b) Type test (c) Special test (d) All above  Ans: a 5.The ratio of kW to kVA is known as  (a) Voltage regulation (b) power factor (c) Transformation ratio (d) None above Ans: b 6.A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10  load. What is the efficiency of the transformer? (a) 88%  (b) 90% (c) 92%  (d) 95% Ans: b Pin = 120*0.3=36W. Pout = 18*18/10=32.4. efficiency = Pin/Pout. = (32.4/36)*100. = 90%. 7.The dielectric strength of transformer oil is expected to be a. 1 kV b. 33 kV c. 100 kV d. 330 kV Ans: b 8.A common method of cooling a power transformer is a. natural air cooling b. air blast cooling c. oil cooling d. any of the above  Ans: c 9.The transformer ratings are usually expressed in terms of a. Volts b. amperes c. kW d. kVA  Ans: b 10.The thickness of lamination used in a transformer is usually a. 0.4mm to 0.5 mm b. 4 mm to 5 mm c. 14mm to 15mm d. 25mm to 40 mm  Ans: a

TRANSFORMER part-1

1.The BDV of transformer oil should be

 (a) 20 kV (b) 30 kV

 (c) 40 kV (d) 50 kV 

b-Answer

2. The open circuit test of transformer determines

(a) Iron loss

(b) Copper loss at full load

(c) Copper loss at half load

(d) Total losses. 

a-Answer

3.Transformers placed in a room enclosed from all the four sides, the minimum spacing between the walls and the transformer should be

 (a) 0.5 m (b) 0.75 m

(c) 1 m (d) 1.25 m 

d-Answer

4.The path of a magnetic flux in a transformer should have

a. high resistance b. high reluctance

c. low resistance d. low reluctance

d-Answer 

5.At an atmospheric temperature of 45 deg C and keeping in view the working condition, the winding temperature of the transformer should not exceed

 (a) 80 deg C (b) 95 deg C

(c) 110 deg C (d) 130 deg C 

b-Answer

6.Primary winding of a transformer

a. is always a low voltage winding 

b. is always a high voltage winding

c. could either be a low or high voltage winding

d. none of the above 

c-Answer

7.Efficiency of a power transformer is of the order of

a. 100 percent b. 98 percent

c. 50 percent d. 25 percent

b-Answer

8.The maximum efficiency of a distribution transformer is

a. at no load b. at 50% full load

c. at 80% full load d. at full load 

b-Answer

9.A transformer transforms

a. voltage b. current

c. power d. frequency 

c-Answer

10.Transformer breaths in when

a. load on it increases b. load on it decreases

c. load remains constant d. none of the above 

b-Answer