Choose the correct answer of the following:
At resonance frequency the impedance of series circuit is Z XL

(ii) Z =Xc

(iii) Z R

(iv) Z 0 A reciprocal network consists of unilateral elements only

(ii) bilateral elements only

(iii) any type of network

(iv) None of the above
Resistance of armature winding in a DC machine is approximately in the range of
one ohm

(ii) 50 ohms

(iii) 1 k.ohms
100 ohms
No-load current of a transformer is of the rated current.
5
10

(iii) 20
50 A 3-phase induction motor normally operates equal to slip
10% slip

(iii) 50% slip
100% slip
In a 3-phase synchronous generator,voltage regulation is negative when the connected load is
pure resistive
inductive

(iii) capacitive
no load Speed of rotor of a synchronous motor is
same as synchronous speed

(ii) less than synchronous speed

(iii) above synchronous speed

(iv) None of the above
State true or false for the following statements: Ideal independent voltage source has zero internal resistance.
Using principle of superposition, power calculation is possible in DC networks.
DC series motor never operates at no-load.
Core of a transformer is made of copper.
Speed of rotor in an induction motor is synchronous speed.
Synchronization of alternators is done by three dark lamps method.

(g) Over-excited synchronous motor operates as leading power factor load.

2.(a) State and explain Thevenin's theorem.
Find the current I using superposition theorem. <img src='./qimages/11534-2b.jpg'> Discuss various methods used for speed control of a DC series motor.
A 6-pole wave-wound DC generator has 2 parallel paths In armature, each path contains 1000 conductors. If the armature rotates at 500 rpm and flux per pole is 0·05 Wb, calculate the emf induced in the armature.

4.(a) Draw the equivalent circuit of a transformer. Also draw the simplified equivalent circuit by referred total resistance and reactance of two windings in any one winding.
A 100 kVA transformer has 2 kW iron loss and 10 kW full load copper loss. Calculate the load at which the efficiency of the transformer is maximum. Also calculate the maximum efficiency.

5.(a) Draw a circuit diagram of a star delta starter used to start a 3-phase induction motor and explain its working.
A 3-phase induction motor has the following data:

Power input to the stator 20 kW

Stator losses 1 kW

Mechanical losses 1·5 kW

Slip 5%

Calculate the output of the motor and its efficiency.

6.(a) Write the need of parallel operation of alternators. Explain any one method used for synchronization of two alternators.
Explain the requirement and working of a synchronous condenser.

7. Write short notes on any two of the following:
3-point starter of DC motor Auto-transformer and its applications Starting of synchronous motor Merits of three-phase system