Electrical Transformer Multiple choice Question (Electrical Mcqs) and Answer Part 6

        Electrical Engineering Objective Question and Answer 

101- If two transformer not having the same percentage impedance are connected in parallel for sharing a load,then ? 

        

        (A)   One of the transformer will be always fully loaded

        (B) One of the transformer likely to get burnt

        (C) load sharing of transformer will not be proportional to kVA ratings  

        (D) power factor of both the transformers will be lagging

       Answer: (C)

       102- Which value of flux is involved in the emf equation of the transformer ? 

        

        (A)Maximum Value  

        (B) Average Value

        (C) RMS Value  

        (D) Critical Value 

       Answer: (A)

       103- A 11 kV transformer is subjected to 1 minute, 50 Hz, lower frequency test voltage of? 

        

        (A) 11 kV Peak

        (B) 12 kV rms

        (C) 28 kV rms  

        (D) 110 kV rms

       Answer: (C)

       104- Harmonics current in transformer cause? 

        

        (A) Increased I^2*R Losses 

        (B) Increased Core Losses 

        (C) magnetic interference with protective relays  

        (D) all of the above 

       Answer: (D)
         

       105- Which of the following is the most likely source of harmonics in a transformer? 

        

        (A) Over load

        (B) Core saturation 

        (C) Poor insulation 

        (D) Loose connections 

       Answer: (B)

      106- The result of short circuit test on three 400 kVA, 11000/6600 V, 50 Hz transformers were as fallows:
      
      Transformer A - 360 V , 3000 W
      Transformer B - 400 V , 3200 W
      Transformer C - 480 V , 3250 W
      
       If the transformer are operating in parallel and a load of 300 kVA is to be applied, then
       
        (A) load of 100 kVA should be applied on each transformers  

        (B) entire load should be applied on transformer A

        (C) entire load should be applied on transformer C

        (D) transformer A should carry 100 kVA and C should carry 120 kVA load.

       Answer: (B)

       107- Two similiar 200 kVA, single phase transformer gave the following results when tested by back to back method:
        
         Mains wattmeter, W1 = 5 kW
         Primary series circuit watt meter.
         W2 = 7.5 kW 

         (at full load current)
         The efficiency of transformer at 50% full load and 0.8 p.f. loading will be nearly
  

        (A) 99%

        (B) 94%

        (C) 89%  

        (D) 84%

       Answer: (B)

       108- A 100 w 220 V incandescent bulb is connected in series with the primary of a 220 V, 20 kVA transformer , when the secondary of transformer is open circuited, the bulb will? 

        

        (A) Not glow

        (B) glow with less than normal brightness

        (C) glow with normal brightness 

        (D) glow with more than normal brightness 

       Answer: (B)

        109- In Scot connections the main transformer has center tap on ? 

        

        (A) Primary winding 

        (B) secondary winding 

        (C) both primary and secondary winding 

        
        Answer: (C)
        

        110- In Scott connections, the teaser transformer operates on 0.866 of its? 

        

        (A) rated current

        (B) rated voltage

        (C) rated power 

        (D) rated impedance 

        Answer: (B)

        111- Two single phase 100 kVA transformer, each having different leakage, impedance, are connected in parallel, when a load of 150 kVA at 0.8p.f lagging is applied? 

        

        (A) both transformer will operate at power factor more than 0.8 lagging  

        (B) both transformer will operate at power factor less than 0.8 lagging

        (C) one of the transformer will operate at p.f. more than 0.8 lagging and other will at p.f less than             0.8 lagging
         (D) both transformer will operate at identical power factor.

       Answer: (C)

       112- Two transformer T1 and T2 have identical ratings,Transformer T1 is designed for flux density of 1.15wb/m^2 and transformer T2 is designed for flux designed for flux density of 1.45wb/m^2,Form the above information it can be concluded that  ? 

        

        (A) Both transformer will operate at 0.8 p.f lagging

        (B) both transformer will have identical losses at full load   

        (C) The weight of the transformer T 1 will be more than that of transformer T 2.

        (D) The regulation of transformer T 1 will be better than that of transformer T2. 

       Answer: (C)

      113- A tap changer is used on a transformer for? 

        

        (A) adjustment in primary volatge

        (B) adjustment in secondary voltage

        (C) adjustment in both primary and secondary voltage 

        (D) adjustments in power factors 

       Answer: (B)

      114- Over currents in a transformer affect ? 

        

        (A) insulation life 

        (B) temperature rise 

        (C) mechanical stress

        (D) all of the above 

       Answer: (D)

      A 10 k VA, 2500/250 v, single phase transformer gave the following test results 
      Open circuit test : 250 V , 0.8 A , 50 W
      Short circuit test : 60 V, 3 A, 45 W

       115- From the test result it can be concluded that ? 

        (A) Open circuit test has been conducted on high voltage side

        (B) Short Circuit test has been conducted on high voltage side 

        (C) the transformer will have maximum efficiency at 0.8 p.f.lagging 

        (D) the efficiency at full load can not exceed 80%

       Answer: (B)

        116- The transformer has 50 watt 

        (A) hysteresis loss 

        (B) eddy current loss 

        (C) core loss

        (D) copper loss

       Answer: (C)

         117- In a transformer , the tappings are usually provided on ? 

        (A) Primary side

        (B) secondary Side

        (C) low voltage side

        (D) high voltage side 

       Answer: (D)

           118- A current transformer can be used with which of the following  instruments ? 

        (A) Ammeter 

        (B) Watt meter  

        (C) Watt hour meter 

        (D) Any of the above 

       Answer: (D)

        119- Voltage transformer of which class of accuracy can be used for precision testing in standard laboratories   ? 

        (A) 0.1 class 

        (B) 10 class 

        (C) 500 class 

        (D) 1000 class

       Answer: (A)

       120- A transformer has primary to secondary turn ratio of 10. Every single ohm of reactance on secondary winding when referred to primary will be same as  ? 

        (A) 0.1 ohm

        (B) 1 ohm

        (C) 10 ohm

        (D) 100 ohm

       Answer: (D)