## BOARD DIPLOMA EXAMINATIONS, (C-14)

### DEEE-THIRD SEMISTER EXAMINATIONS

MODEL PAPER

EE-302 D.C. MACHINES

Time: 3Hours Total marks: 80

** PART-A**

**NOTE: Answer all questions. 3X 10=30**

**Each question carries three marks.**

- State the Fleming’s right hand rule?
- Define (a) Pole pitch (b) Back pitch (c) Front pitch?
- Draw the power flow diagram of d.c generator?
- State the causes of sparking at brush of d.c generator?
- List the advantages of parallel operation of d.c generator?
- 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?

- State the different losses in D.C motors?
- State the factors that affect the speed of a D.C motor?
- Draw the connection diagram for speed control of d.c.series motor
- 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.**

- Explain the construction of a dc generator with neat sketch?
- . Classify the D.C generators based on excitation along with voltage and current equations, showing diagrammatically?

- 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?

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

- (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.

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

- 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?