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%]

  

ASSIGNMENT-3-Alternating quantities

ASSIGNMENT-3(Alternating quantities)

Assignment -2 (UNIT-1.b Network analysis )

                        Assignment -2  (UNIT-1.b  Network analysis )

              

                                                       

                                                            

BEE unit 1 (a ) assignment

                                                      BEE

                  

Note: write the below guidelines in the first page of the Assignment note book

Guidelines for writing assignment:

1. Read the entire unit thoroughly before writing the assignment

2. Don’t copy the assignment from the others.

3. Write the assignment in separate note book (do not write in papers, do not write in class work)

4. During the evaluation of the assignment questions will be asked from the corresponding unit.

5. Strictly instructed to submit the assignment on or before scheduled time. Assignments will not be accepted after schedule time.

6. during the evolution of the assignment approach towards the concept, practical understanding of the concept, documentation skills, presentation skills, problem solving skills are checked. Assignment will be evaluated for 10 marks.

                ASSIGNMENT-1 (unit-1(a): Introduction to electrical engineering)

NOTE:  Submit the assignment on or before 09-09-2013

1. (a) write about electrical engineering concepts that you come across in your daily life(not more than two pages)

   (b) A copper wire is stretched so that its length is increased by 0.1%. What is the percentage change in its resistance? 

 (Ans: 0.2%)

2. (a) Explain the characteristics of resistor, inductor, capacitor.

    (b) A length of wire has a resistance of 4.5 ohms. Find the resistance of another wire of the same material three times long and twice the cross-sectional area (ans: 6.75 ohm)

     (c) Explain about self inductance and mutual inductance.

3. (a) State and explain ohm’s law and discuss where it fails.

   (b) An electric radiator is required to dissipate 1KW when connected to a 230V supply. If the coils of the radiator are of wire 0.5mm in diameter having resistivity of 60µΩ-cm, caluculate the necessary length of the wire

(Ans: 1730.2cm)

4. (a) Explain Laws of resistance  (or)  explain the different factors on which the resistance is dependent

   (b) Three resistances of 5 ohms, 10 ohms and 15 ohms are connected in parallel. If the current in 10 ohms resistance is 3 A, What is the current in other resistors and total current? Also determine the voltage applied to the circuit

(Ans: 6A, 2A, 11A, 30V)

5. (a)  state and explain Kirchhoff’s laws.

    (b ) Two coils connected in parallel across 100v Dc supply, takes 10A current from the supply. Power dissipated in one coil is 600W.find

(a)  What is the resistance of the coil (ans: 16.667ohm)

(b)  What is the current flowing through that coil(ans:6A)

(c)  What is the current in the other coil(4A)

(d)  What is the resistance of the other coil(25ohm)

  

6. (a) write a short notes on

    (1) Conductors (2) insulators (3) semiconductors

     (b) What is the voltage across X and Y in the circuit shown in below figure.