## electrical

### Transformer MCQ Objective Questions and Answers Page - 5

1.
 Transformer will operate at maximum efficiency when A Hysteresis loss = copper loss B Eddy current loss= copper loss C Copper loss= iron loss D Hysteresis loss = copper loss Answer : C Explanation :
2.
 Power transformers are designed to have maximum efficiency around _____full load. A Nearly B 70% of C 50% of D 25% of Answer : A Explanation :
3.
 The transformer efficiency will be maximum at a power factor of A 0.8 lead B Unity C 0.8 lag D 0.5 lead or lag Answer : B Explanation :
4.
 If P1 and P2 be the iron and copper losses of a transformer at full load and the maximum efficiency is at 75 % of the full load, then what is the ratio of P1 and P2? A 9/16 B 10/16 C 3/4 D 3/16 Answer : A Explanation :
5.
 What is load at which maximum efficiency occurs in case of a 100 kVA transformer with iron loss of 1 kW and full load copper loss of 2 kW? A 100 kVA B 70.7 kVA C 50.5 kVA D 25.2 kVA Answer : B Explanation :
6.
 A 500 kVA transformer has constant loss of 500 W and copper losses at full load are 2,000W. Then at what load, is the efficiency maximum? A 250 kVa B 500kVA C 1000kVA D 125kVA Answer : A Explanation :
7.
 A 2 kVA transformer has iron loss of 150 W and full load coper loss of 250 W. The maximum efficiency of the transformer would occur when the total loss is A 500w B 400w C 300w D 275w Answer : C Explanation :
8.
 A single-phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is A 86.7% B 88.26% C 88.9% D 87.8% Answer : D Explanation :
9.
 The all-day efficiency of a distribution transformer will be high with low A Copper losses B Iron losses C Operating temperature D Copper as well as iron losses Answer : D Explanation :
10.
 The all-day efficiency of a transformer depends primarily on A Its copper loss B The amount of load C The duration of load D Both (b) and (c) Answer : D Explanation :
11.
 A single-phase transformer is to be switched to the supply to have minimum inrush current. The switch should be closed at A Maximum supply voltage B Zero supply voltage C $\frac{1}{\sqrt{2}}$ maximum supply voltage D ½ maximum supply voltage Answer : A Explanation :
12.
 The desirable properties of transformer core material are A Low permeability and low hysteresis loss B High permeability and high hysteresis loss C  High permeability and low hysteresis loss D Low permeability and high hysteresis loss Answer : C Explanation :
13.
 The use of higher flux density in the transformer design A Reduces the weight per kVA B Increases the weight per kVA C Has no relation with the weight of transformer D Increases the weight per KW Answer : A Explanation :
14.
 What does the use of higher flux density value in a transformer design lead to A Increase in weight per kVA B Decrease in weight per kVA C Reduced iron losses D Reduced copper losses Answer : B Explanation :
15.
 The size of the transformer core depends upon A Frequency B Permissible flux density in the core material C Area of the core D Both (a) and (b) Answer : D Explanation :
16.
 Ferrite cores are employed in high frequency transformers due to their A Low resistance B High resistance C Low permeability D High hysteresis loss Answer : B Explanation :
17.
 What is the core loss in a high frequency ferrite core transformer used in SMPS power supply? A 10% of rated power B 5% rated power C 2% of rated power D 1% of rated power Answer : D Explanation :
18.
 The changes in volume of transformer cooling oil due to variations of atmospheric temperature during day and night is taken care of by which part of transformer? A Conservator B Breather C Bushing D Buchholz’s relay Answer : A Explanation :
19.
 An ideal transformer is one which has A No-load and magnetic losses B Interleaved primary and secondary windings C A common core for its primary and secondary windings D None of the above Answer : A Explanation :
20.
 When a given transformer is run at its rated voltage but reduced frequency, its A Flux density remains unchanged B Iron losses are reduced C Core flux density is reduced D Core flux density is increased Answer : D Explanation :
21.
 In an actual transformer the iron loss remains practically constant from no-load to full-load because A Value of transformation ratio remains constant B Permeability of transformer core remain constant C Core flux remains practically constant D Secondary voltage remains constant Answer : C Explanation :
22.
 An ideal transformer will have maximum efficiency at load such that A Copper loss= iron loss B Copper loss < iron loss C Copper loss > iron loss D None of the above Answer : A Explanation :
23.
 If the supply frequency to the transformer is increased, the iron loss will A Not change B Decrease C Increase D Any of the above Answer : C Explanation :
24.
 Negative voltage regulation is indicative that the load is A Capacitive only B Inductive only C Inductive or resistive D None of the above Answer : A Explanation :
25.
 Iron loss of a transformer can be measured by A Low power factor wattmeter B Unity power factor wattmeter C Frequency meter D Any type of wattmeter Answer : A Explanation :
26.
 When secondary of a current transformer is open-circuited its iron core will be A Hot because of heavy iron losses taking place in it due to high flux density B Hot because primary will carry heavy current C Cool as there is no secondary current D None of the above will happen Answer : A Explanation :
27.
 The transformer laminations are insulated from each other by A Mica strip B Thin coat of varnish C Paper D Any of the above Answer : B Explanation :
28.
 Which type of winding is used in 3-phase shell-type transformer? A Circular type B Sandwich type C Cylindrical type D Rectangular type Answer : B Explanation :
29.
 During open circuit test of a transformer A Primary is supplied rated voltage B Primary is supplied full-load current C Primary is supplied current at reduced voltage D Primary is supplied rated kVA Answer : A Explanation :
30.
 Open circuit test on transformers is conducted to determine A Hysteresis loss B Copper losses C Core losses D Eddy current losses Answer : C Explanation :
31.
 Short circuit test on transformers is conducted to determine A Hysteresis losses B Copper losses C Core losses D Eddy current losses Answer : B Explanation :
32.
 For the parallel operation of single-phase transformers, it is necessary that they should have A Same efficiency B Same polarity C Same kVA rating D Same number of turns on the secondary side Answer : B Explanation :
33.
 The transformer oil should have ………. volatility and ………. Viscosity A Low……. low B High………. high C Low………. high D High………. low Answer : A Explanation :
34.
 The function of breather in a transformer is A To provide oxygen in a tank 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 Answer : D Explanation :
35.
 The secondary winding of which of the following transformers is always kept close A Step-up transformer B Step-down transformer C Potential transformer D Current transformer Answer : D Explanation :
36.
 The size of transformer core will depend on A Frequency B Area of the core C Flux density of the core, material D (a) and (b) Answer : D Explanation :
37.
 Natural air cooling is generally restricted for transformers up to A 1.5 MVA B 5 MVA C 15 MVA D 50 MVA Answer : A Explanation :
38.
 The core and windings of a transformer are put in a steel tank in order to A Make it suitable for outdoor operation B Provide protection against mechanical damages and provide additional cooling C Improve its appearance D All the above Answer : B Explanation :
39.
 conservator (for transformer) is used A to take up the expansion of oil due to temperature rise B to act as an oil storage C for better cooling of transformer D none of the above Answer : A Explanation :
40.
 In a large power transformer, a conservator drum is provided above the completely oil filled transformer tank and connected to it by a a short pipe. The conservator drum is linked to external air through a breather. What is the purpose of providing the conservator? A To store reserve oil to make up oil losses due leakage B To prevent explosion due to rise in oil pressure inside the tank during a fault C To accommodate change in oil level during the load cycle of the transformer load D To expert additional pressure by the conservator oil on the oil inside the main tank to prevent disintegration of oil at high temperature Answer : C Explanation :
41.
 Sludge formation in transformer oil is due to which one of the following? A Ingress of dust particles and moisture in the oil B Appearance of small fragments of paper, varnish, cotton and other organic materials in the oil C Chemical reaction of transformer oil with the insulating materials D Oxidation of transformer oil Answer : D Explanation :
42.
 In a power transformer, the breather is provided in order to A Filter transformer oil B Prevent ingress of moisture with air C Provide oxygen to the cooling oil D Provide fresh air for increasing cooling effect Answer : B Explanation :
43.
 The chemical used in breather of a transformer should have quality of A Absorbing moisture B Joining air C Cleansing the transformer oil D None of the above Answer : A Explanation :
44.
 Malfunctioning of the Buchholz relay may be caused due to A Heavy external short circuits B Improper breather action C Dropping of oil level below the relay level during operation D  excessive overheating Answer : C Explanation :
45.
 Which of the following statements associated with Buchholz relay is not TRUE? A It is a voltage sensitive device B It is used only on oil cooled transformers C It is usually not provided on transformers of ratings below 500kVA D Its operating time is of the order of 0.1 second Answer : C Explanation :
46.
 A Buchholz relay is used for A Protection of a transformer against all internal faults B Protection of a transformer against external faults C Protection of a transformer against both internal and external faults D Protection of induction motors Answer : A Explanation :
47.
 If a transformer is switched on to a voltage more than the rated voltage A Its power factor will deteriorate B Its power factor will increase C Its power factor will remain unaffected D Its power factor will be zero Answer : A Explanation :
48.
 Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is A Approximately equal to one B Less than one C Great than one D None of the above Answer : A Explanation :
49.
 Minimum voltage regulation occurs when the power factor of the load is A Unity B Lagging C Leading D Zero Answer : C Explanation :
50.
 In a step-down transformer, there is a change of 15 A in the load current, this result in change of supply current of A Less than 15 A B More than 15 A C 15A D None of the above Answer : A Explanation :
51.
 The efficiency of transformers compared with that of electric motors of the same power are A About the same B Much smaller C Much higher D Somewhat smaller Answer : C Explanation :
52.
 The short-circuit voltage of a transformer mainly depends upon the A Magnitude of leakage flux B Ohmic resistance of primary winding C Ohmic resistance of secondary winding D Cross-sectional area of the iron core Answer : A Explanation :
53.
 In a transformer, electric power is transferred from one coil to the other coil in a transformer A Magnetically B Electromagnetically C Physically D Electrically Answer : B Explanation :
54.
 In an ideal transformer, on no-load, the primary voltage is balanced by A The primary induced e.m.f B The secondary induced e.m.f C The secondary voltage D The drop across resistance and reactance Answer : B Explanation :
55.
 As per name plates of a transformer, the secondary normal voltage is 220 Which of the following statement is correct A 220 V is the no-load voltage B The no-load voltage is more than 220 V C The secondary voltage increases with the increasing load D At a load which draws the rated current the voltage becomes less than 220 V Answer : B Explanation :
56.
 A transformer is working at its maximum efficiency. Its iron loss is 1 KW. Its copper loss will be A 0.2 kW B 0.25 kW C 0.5 kW D 1 kW Answer : D Explanation :