Assignment 4(Transformers)

                                                   

                                                            ASSIGNMENT-4

                                                      UNIT-3: Transformers

1.(A) Explain the working principle of 1-Ø (Single phase) Transformer and what happens If DC supply is given to transformer? Give the applications of transformer.

  (B) Derive the induced emf equation of transformer

  (C) The maximum flux density in the core of 250/3000V, 50Hz, single phase transformer is 1.2 web/m² .if the emf/turn is 8v determine the primary and secondary turns and the area of the core.

[Ans: 32, 375, 0.02m2]

     2.    (A) Explain the losses that occur in Transformers

     (B)Derive the maximum efficiency condition and expression for load KVA corresponding to Maximum efficiency

      (c).A 3000/300V 1-phase transformer gives 0.6A and 60W as ammeter and wattmeter reading, when supply is given to the low voltage winding, the high voltage winding is kept open. Find (i) power factor of no load current (ii) Magnetizing current (iii) Iron loss component

[Ans: 0.333 lagging, 0, 05656A, 0.02A]

    3.      (A) Draw the phasor diagram of Transformer under no load.(IDEAL T/F AND PRACTICAL T/F)

       (B) Draw the phasor diagram of transformer on load (consider resistance and leakage reactance)

        ( c ). A 250 KVA single phase transformer has iron loss of 1.8KW.The full load copper loss is 2000watts.caluculate (i) Efficiency at full load.  (ii) KVA supplied at maximum efficiency.(iii)Maximum efficiency at 0.8 lagging power factor.

[Ans:98.135%,237.1708KVA,98.137%]

    4.      (A) Define efficiency and regulation of a Transformer. Explain how will you pre - determine the efficiency and regulation with neat circuit diagrams.

                                        (OR)

          Explain OC and SC tests on single phase transformer to determine regulation and efficiency

 (B) Explain why the transformer is rated in KVA instead of KW.

  ( C) a 200/400V, 50 Hz 1-phase  transformer has the following test data.

OC Test (LV):200V, 0.7A, 70w on LV side.

SC Test (Hv); 15V, 10A, 80W on HV side.

Calculate the secondary voltage when delivering 5KW at 0.8 lag v1=200v.

     5.   (A) Explain the construction of transformer.  

          

        ( B) The required no load voltage ratio in a 150 KVA, 50Hz single phase transformer is 5000/250V.find the efficiency at half rated KVA, Unity power factor and also efficiency at full load 0.8 PF lagging if the full load copper losses are 1800watt, core losses are 1500W.

[Ans:97.46%,97.33%]