MODEL PAPER

 

Attempt any four parts;

 

1. Voltage across resistance, inductance and capacitance connected in series are 3v,4v,and 5v.if supply voltage has 50 hz frequency what is the magnitude of supply voltage. Find the resonant frequency of the series RLC ckt.

 

2. Explain Selectivity of series RLC resonance circuit. prove that selectivity is reciprocal of quality of circuit.

 

3. Show that in RLC series circuit the resonant frequency is W0 =square root of W1 W2, where W!andW2 are the lower and upper half power frequencies .

 

4. In series RLC circuit ,the voltage across LandC at resonance may exceed even the supply voltage .discuss?

 

5. The shape of resonance curve depends on Q of the coil. why?

 

6. At resonance the current is maximum in series circuit and minimum in parallel?

 

Attempt any three parts;

 

1. Derive  expression  for converting Delta network to a star equivalent network?

 

 

2. State maximum power transfer theorem .for Which type of circuits is it generally applied ?

 

3. Draw and explain load characteristics of DC generator ?

 

4. Why single phase induction motor is not self  starting?

 

5. Why starter is need for three phase induction motor?

 

Attempt any two parts;

 

1. A 12-pole ,3-phase alternator is coupled to a engine running at 500 rpm.it supplied a three induction motor having a full load speed of 1440 rpm .find the percentage slip ,frequency of rotor current and number of poles of motor?

 

 

  2.(a) Explain the principle of electo-mechanical energy conversion in motor and generator?

 

 

(b)   Draw magnetization  characteristics of DC shunt generator?

 

 

3. Explain principle of three phase synchronous motor ? why is starting torque not produced in this motor?

 

Attempt any Two parts ;

 

1.   Explain the methods   to measure power in thre phase circuits . In two wattmeter method  power measured was 30kw at 0.7 pf lagging .find reading of each wattmeter?

 

 

2. Explain the following for single phase transformer :

 

(a)    phasor diagram for inductive load .

(b)    Equivalent circuit

(c)    Voltage regulation

 

 

3.   Rotor of three phase induction motor cannot run at synchronous speed ,explain .A three phase slip ring ,4- pole induction motor has rotor frequency 2hz while connected to 400v,3-phase ,50hz supply .determine slip and rotor speed?

 

 

Attempt any two parts ;

 

1. Define voltage regulation of a transformer. Determine the condition for zero power factor load . give expression for  efficiency of transformer and condition for maximum efficiency?

 

 

2. Explain:  (a)  synchronous motor always runs at synchronous speed.

(b)      field winding of synchronous generators is placed on rotor.

 

 

3.  Derive the relation ship for line and phase voltages and currents for delta connected 3-phase balanced system.