Electrical Transformer Multiple choice Question (Electrical Mcqs) and Answer Part 11

      Electrical Engineering Objective Question and Answer 





201- The magnetizing current of a transformer is usually small because it has  


        (A) laminated silicon steel core 

        (B)small air gap 

        (C) fewer rotating parts 

        (D) large leakage flux 

       Answer: (B)


      202- In a dry type transformer , accumulation of dust on the winding and core is likely to cause   


        (A) corrosion of core metal 

        (B) short circuiting of primary winding 

        (C) short circuiting of secondary winding 

        (D) reduction in heat dissipation 

       Answer: (D)

      203- Which of the following connection of transformer will given the highest secondary voltage


        (A) Delta primary, delta secondary 

        (B) Delta primary, star secondary 

        (C) Star primary, star secondary 

        (D) star primary, delta secondary 

       Answer: (B)

     204- In a transformer , no load current :


        (A) Leads the applied voltage by 90°

        (B) Lags the applied voltage by 90°

        (C) Lags the applied voltage some what less than 90°

        (D) Leads the applied voltage some what less than 90°

       Answer: (C)

        205- A transformer has maximum efficiency when ( pi =core loss , Pc = copper loss) 


        (A) 0.5

        (B) 1

        (C) 1.5

        (D) 2

       Answer: (B)

      206- The voltage regulation of a transformer at full load 0.85 pF lagging is 5%, Its voltage regulation at full load 0.85 pF leading will be 


        (A) positive 

        (B) negative 

        (C) same 

        (D) reduce and may even became negative 

       Answer: (D)

       207- In an ideal transformer shown below, the resistance seen from the HV side is 



                                                                        Fig. 24

        (A) 50 ohm

        (B) 100 ohm

        (C) 200 ohm

        (D) 800 ohm

       Answer: (D)


      208- The efficiency of a transformer at full load 0.85 pF lag is 90%. Its efficiency at full load 0.85 pF lead is   


        (A) less than 90%

        (B) 90 %

        (C) More than 90%

        (D) None of above 

       Answer: (B)


       209- Two transformer are connected in parallel and share loads in the ratio of  their kVA ratings when their ohmic impedance 


        (A) Purely reactive 

        (B) equal 

        (C) In direct ratio of their ratings 

        (D) In inverse ratio of their rating 

       Answer: (D)

        210- Two transformer are connected in parallel and share loads in the ratio of  their kVA ratings when their ohmic impedance 


        (A) Purely reactive 

        (B) equal 

        (C) In direct ratio of their ratings 

        (D) In inverse ratio of their rating 

       Answer: (D)

        211- if R = equivalent resistance 
                     X= equivalent reactance 
                     Pi = core loss

           Then load current for maximum efficiency of operation in a transformer is  
           


        (A)  Pi/X

        (B) Pi/R

        (C) √Pi/R

        (D) √Pi/X

            Answer: (C)

      212- In an ideal transformer,impedance transforms from one side to other 


        (A) In direct ratio of turns 

        (B) In direct square ratio turns 

        (C) In verse ratio of turns 

        (D) In verse square ratio of turns 

       Answer: (B)

       213- A single phase transformer fed from a rated voltage supply operates at no-load. The core loss of the transformer is assumed to be negligible.The current drawn by the transformer from the supply will have the wave-form


                  
  

                                                                                    Fig. 25

       Answer: (B)

      214- The given figure represents a transformer with two winding 1 and 2 wound on the core as shown.By applying a voltage V1 across winding 1 , a Voltage V2 is induced across winding 2. In an idealized condition V2 would lag V1 by

            

                                                                                 Fig. 27


        (A) Zero degree 

        (B) 90 degree

        (C) 180 degree

        (D) 270 degree

       Answer: (C)


       215- Three single phase transformers are connected to form a 3 phase transformer bank. the transformers are connected in the following manner. The nomenclature of the above connection for phase sequence ABC is 

             
                                                                                      Fig. 26


        (A) Yd0

        (B) Yd6 

        (C) Yd11 

        (D) Yd 1.

       Answer: (A)


      216- The voltage regulation of transformer at full load and 0.8 power factor lagging is 2.5%. The voltage regulation at full load, 0.8 power factor leading will be   


        (A) -2.5%

        (B) zero

        (C) 1.0%

        (D) 2.5%

       Answer: (A)


       217- The series equivalent impedance of a single phase transformer referred to its secondary side is Ze2= Re2 + Jxe2. The voltage regulation of this transformer will be , zero when the power factor of the load is 


        (A) Unity  

        (B) I Xe2/Ze2 I

        (C)  I Xe2/Xe2 I lagging 

        (D)  I Re2/Ze2 I leading 

       Answer: (A)

         218- Consider the circuit shown in the figure. for maximum power transfer to the load , the primary to secondary turns ratio must be 

                    


                                                                                Fig.  28


        (A) 9 : 1

        (B) 3 : 1

        (C) 1 : 3

        (D) 1 : 9

       Answer: (A)

        219- If a saw cut is made in the iron core of a single phase transformer as shown in the given figure. with secondary terminal open, it will result in 
        
                      

                                                                                    Fig. 29  


        (A) no voltage across secondary terminals due to dis conductivity magnetic circuit 

        (B) Excessively large current drawn by primary  

        (C) no appreciable change in the operation of transformer

        (D) no transformer action and the primary current will be greatly reduced 

       Answer: (A)

       220-In a given figure, a delta-star Dy1 transformer is supplied from a star D connected alternator.
               The secondary voltage Vcn will be    
         
                         
                                                                          Fig. 30

        (A) in Phase with VCB

        (B) in phase with VBC

        (C) 30° lagging VCB

        (D) 30° leading VCB

       Answer: (A)

       221- An 11 kV/400 V, 1000 kVA, Y/Y tranformer is reconnected as Δ /Y transformer, with the high voltage side connected in Δ. The rating for the new combination will be 


        (A) 11/√3 kV/40V , 1000 kVA 

        (B) 11 kV/ 400V, 1732 kVA

        (C)  11√3 kV/400V, 1000 kVA

        (D)  11 kV/400 √3 V, 1000/√3 kVA

       Answer: (A)

        222- For the ideal transformer shown in the given figure,  

                   

                                                                                              Fig. 31 


        (A) v1 = nV2 , i2= -ni1

        (B) v2 = nv1 , i2 = ni1

        (C) v1 = nv2 , i1 = 1/n x i2

        (D) v1 = nv2, i2 = -1/n i1

          Answer: (A)

        223- A transformer has negative voltage regulation when its load power factor is  


        (A) Zero

        (B) leading 

        (C) unity 

        (D) lagging

         Answer: (B)


        223- The essential condition for parallel operation of two single phase transformer is that they should have the same  


        (A) voltage ratio

        (B) kVA rating 

        (C) polarity 

        (D) percentage impedance 

         Answer: (C)

       225-  When the impedance triangles of two transformers operating in parallel are not identical in shape and size, the two transformer will


        (A) Get heated unequally 

        (B) Share with load unequally 

        (C) Run with different power factor 

        (D) None of above 

         Answer: (C)


        226- A scott connected transformer can not be parallel with a

 (A) V-V transformer 

        (B) Y-Δ sign 

        (C) Δ-Δ sign

        (D) Y-Y sign

         Answer: (B)
'
         227- In the parallel operation of a transformers , which statement is false 

 (A) Transformer transformation ratio is same 

        (B) Transformer voltage rating is same 

 (C) Transformers kVA ratings equal 

        (D) None of above 

         Answer: (C)

         228- A step up transformer increases 

 (A) current 

        (B) power 

  (C) frequency 

        (D) Voltage 

         Answer: ()

          229- Open circuit test is done on transformer to determine 

 (A) Efficiency 

        (B) CU loss

 (C) Core loss

        (D) None of above 

         Answer: (D)


          230- When a 400 Hz transformer is operated at 50 Hz , its KVA rating is

  (A) reduced to 1/4

        (B) reduced to 1/8

        (C) reduced to 1/2

        (D) reduced to 1/16

         Answer: (B)








           











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