SMART MINDS

A DC shunt motor runs at 1000 rpm at no load on 200 V. A resistance of 4.5 ohms is added to the armature whose resistance is 0.5 ohms and motor load current is 10 A. the speed will be :

• 500 rpm      

• 1000 rpm            

• 750 rpm          

• 250 rpm

The speed of the DC shunt motor increases as the armature torque increases.

• true

• false

Dummy coils in generators are provided :

• to reduce eddy current losses  

• to enhance flux

• mechanical balancing

• none of the above

In a DC generator, armature reaction pole tip.

• weakens the flux at the trailing

• weakens the flux at the leading

• strengthens the flux at the leading          

• none of the above

Lap winding is suitable for ....... current...... voltage DC generators:

• high, low

• low, high

• low, low

• High,high

A step down transformer has a turns ratio of 4:1. The resistance of the HV winding is 8 ohms and that of the LV winding is 1 ohm. The total resistance of the transformer when referred to HV side is

• 20 ohms

• 24 ohms

• 28  ohms

• 30 ohms

If a transformer rated at 400 volts, 50 Hz is supplied with 200 volts, 25 Hz, the magnetizing current :

• gets doubled 

• becomes half  

• remains same 

• increases abnormally

In a transformer the tapings are generally provided on :

• primary side

• secondary side

• low voltage side

• high voltage side

Buchholz relay is used to

• identify faults       

• rectify the fault

• trip-off connections when fault exists    

• clears the fault

In a low voltage distribution system, the following transformer connection is preferred

• Delta/ Delta         

• Delta/ Star

• Star / Star

• Delta/Star with neutral