# Model Paper DEEE III SEM ||DC Machines EE- 302||

## BOARD DIPLOMA EXAMINATIONS, (C-14)

### DEEE-THIRD SEMISTER EXAMINATIONSMODEL PAPEREE-302  D.C. MACHINESTime: 3Hours Total marks: 80

###### PART-A

NOTE: Answer all questions.                                                             3X 10=30

Each question carries three marks.

1. State the Fleming’s right hand rule?

2. Define (a) Pole pitch (b) Back pitch (c) Front pitch?

3. Draw the power flow diagram of d.c generator?

4. State the causes of sparking at brush of d.c generator?

5. List the advantages of parallel operation of d.c generator?

6. A 4 pole 500V, shunt motor has 720 wave wound armature conductors. The full load armature current is 60A, and the flux/pole is 0.03Wb.The armature resistance is 0.2ohm and the contact drop is 1V/Brush, Calculate the full load speed of the motor?

1. State the different losses in D.C motors?

2. State the factors that affect the speed of a D.C motor?

3. Draw the connection diagram for speed control of d.c.series motor

4. What are the disadvantages of Swinburne’s Test.

PART-B                                                5 X 10=50
Instructions: 1) Answer any five questions.
2) Each answer carries ten marks.

1. Explain the construction of a dc generator with neat sketch?

2. . Classify the D.C generators based on excitation along with voltage and current equations, showing diagrammatically?

1. A100kw, 400V, 6pole dc shunt generator has a lap wound armature with 36 slots and 28 Conductors per slot. The shunt field resistance is 100 ohms. The brush is given a lead of 12°. Calculate the Demagnetising and cross magnetising AT/Pole?

1. Explain O.C.C, Internal and external characteristics of D.C Shunt generator?

2. (i) Classify DC motors in to different types with figures of each. Also write voltage and Current  equation?

(ii) Derive an equation for armature torque in dc motors?

1. (i) Derive the condition for maximum efficiency of D.C motor?

(ii) A 220V, dc shunt motor takes 5A at no load when running at 700r.p.m. the field Resistance is 200ohms.aThe resistance of armature is stand still gave a drop of 5V Across armature terminals when 10Amps wave passed through it. Calculate (i) speed on load (ii) torque in N.M (iii) Efficiency.

1. Draw the schematic diagram of a 3-point starter and explain the working with protective devices?

1. A 250V 15KW Shunt motor has a maximum efficiency of 88% and a speed of 750 r.p.m when delivering 75% of its rated output. The resistance of its shunt field is 100ohms.Calculate the efficiency when the motor draws a current of 78Amp from mains?