**BE (I Year )**

** Examination Nov-Dec 2006-07**

**Unit-I**

Q1(a) Explain Kirchhoffs lows applied to electric circuit: Use Nodi analysis to determine the value of current “I” in the give circuit.

(b) Find the unknown current in ammeter by reducting the electric circuit.

(c) Give comparison between magnetic and electric circuit . steelring has mean diameter of 20 cm a cross section of: cm 2 and a radial air gap 0.8 mm cut across it. When a current of 1 amp through a coil of 1000 turns wound of the ring core, it produces an air gap flux of 1 milli we Neglecting leakage flux and fringing , calculate

(i) The total reluctance of the magnetic circuit.

(ii) The relative permeability of steel.

**Unit-II**

Q2 (a) A two element series Circuit is connected across an A C source *e* = 200 √2 sin+20°) volt. The current in the circuit then is found to be i = 10√2cos(314/-25°)amp. Determine parameters of the circuit.

(b) Three identical coils connected in delta across 400 V 50 F three phase supply take a line current of 17.32 amp at power factor of 0.6 lag.

Determine :

(i) Resistance inductance of each winding

(ii) If the chokes are reconnected in star against the supply what will be the KVA taken from supply.

(c) Deduce a condition for resonance in the given circuit. If* R = 5Ohm ,L=* 0.05 H and capacitor C is 0.1* uF* calculate

(i)Resonant frequency

(ii)Dynamic impendence and

(iii)Q factor

**Unit-III**

Q3 (a) Derive an expression for induces voltage in a single phase transformer at no load. Draw the phasor diagram under this condition.

(b) A transformer has its maximum efficiency of 0.98 at 15 k at unity power factor during the day it is loaded as under.

(i) 12 Hours 2 kW at pf 0.5

(ii)06 Hours 12 kW at pf 0.8

(iii)06 Hours 18 kW at pf 0.9

(c) Give the procedure to perform no load test and short circuit test on single phase transformer. Deduce the squivalent circuit on LV side from following test result , c n 5 KVA. 220/442 V single phase transformer :

No load test 220 – v 110 W 2amp – LV side

Short circuit test – 40V200W 11.4 amp – HV side

**Unit-IV**

Q4 (a) Derive an expression for the torque developed by DC motor Give the torque speed characteristics for dc series and dc shunt motors.

(b)The armature of a 6 pole DC generator has a wave containing 650 conductor.

Calculate the generated emf when the flux per pole is 0.055 wb and speed is 300 rpm. Calculate the speed at which the armature must be driven to generate an elf of 550 V if the flu x is reduced to 0.05 web.

(c) Derive an expression for the torques of three phase induction motor plot the torques slip characteristics of motor and show the position of maximum torque.

**Unit-V**

Q5 (a)What are the essential requirement of indicating type instruments ? Explain each of them

(b) A moving coil instrument has a resistance of 10 Ohm and gives full scale deflection when carrying a current of 50 m amp. Show howls can be adopted to measure voltage up to 750 V and currents up to 100 A.

(c) Describe the constructional details; Operation and expression of de fleeting torque for dynamotor type wattmeter