Quiz 2(DC Motor)

The torque available at the shaft of a DC motor is less than the torque developed in the armature because of………losses.

• copper

• mechanical

• iron

• rotational

The armature resistance of a 110 V DC motor is 0.5 ohm. What will be its armature current if the back emf is 100 V.

• 20 A

• 200 A

• 220 A

• 60 A

With the increase in load, the speed of a DC shunt motor

• reduces slightly

• increases slightly

• remains constant

• increases proportionately

When a 220 V DC shunt motor draws an armature current of 10 A, it develops a torque of 50 Nm. What will be the torque developed when armature current reduces to 20 A.

• 54 N-m

• 108 N-m

• 81 N-m

• None of the above

A four-pole DC shunt motor draws a current of 36 A when connected to 230 V mains and delivering 10 hp. If armature and field circuit resistances are 0.1 ohm and 300 ohms respectively, find the Eb. (2 decimals)

(a)  

A 6-pole, 250 V series motor is wave-connected. There are 240 slots and each slot has four conductors. The flux per pole in 1.75 × 10^–2 Wb when the motor is taking 80 A. The field resistance is 0.05 ohm the armature resistance is 0.1 ohm. Calculate speed.(2 decimals)

(a)  

A 250 V shunt motor takes 4A at no-load and resistance of armature is 0.4 ohm and that of shunt field is 125 ohm, calculate output is kW.(2 decimals)

(a)  

A 220 V DC series motor takes 50 A. Armature resistance 0.1 ohm, series field resistance 0·08 ohm. If the iron and friction losses are equal to copper losses at this load, find the poer output in kW.(1 decimal)

(a)  

A 220 V DC series motor takes 50 A. Armature resistance 0.1 ohm, series field resistance 0·08 ohm. If the iron and friction losses are equal to copper losses at this load, find the percent efficiency.(2 decimals)

(a)  

Usually, the normal value of the armature resistance of a DC motor is

• 100 ohms

• 0.5 ohm

• 10 ohms

• 50 ohms