A 220 V series motor is taking a current of 40 amperes. The resistance of armature is 0.5 Ω and resistance of series field is 0.25 Ω.

Calculate (i) Voltage at the brushes (ii) Back emf (iii) Power wasted in armature (iv) Power wasted in field.

## Problem

## Question

A 220 V series motor is taking a current of 40 amperes. The resistance of armature is 0.5 Ω and resistance of series field is 0.25 Ω.

Calculate (i) Voltage at the brushes (ii) Back emf (iii) Power wasted in armature (iv) Power wasted in field.

## Topic

## DC Motor Problems

- The field current in shunt DC machine is 2 A and the line current is 20 A at 200 V. Calculate the (i) Generated EMF when working as generator (ii) Torque in N-m when running at 1500 rpm as motor. Take the armature resistance as 0.5 Ω.
- A shunt DC machine connected to 250 V supply, has an armature resistance of 0.02 Ω and the field resistance of 100 Ω. Find the ratio of the speed of the machine as a generator to the speed as a motor, the line current in each case being 80 A.
- A shunt generator delivers 50 KW at 250 V and runs at 400 rpm. The armature and field resistances are 0.02 Ω and 50 Ω respectively. Calculate the speed of the machine running as a shunt motor and taking 50 KW input at 250 V. Allow 1 V per brush for contact drop.
- A 4-pole DC shunt motor takes 22 A from 220 V supply. The armature and field resistances are 0.5 Ω and 100 Ω respectively. The armature is lap connected with 300 conductors. If the flux per pole 20 mwb, Calculate the speed and gross torque.
- A 200 V lap wound DC shunt motor has 800 conductors on its armature. The resistance of the armature winding is 0.5 Ω and that of field winding is 200 Ω. The motor takes a current of 21 A, the flux per pole is 30 mwb. Find the speed and torque developed in the motor.
- A 220 V series motor is taking a current of 40 amperes. The resistance of armature is 0.5 Ω and resistance of series field is 0.25 Ω. Calculate (i) Voltage at the brushes (ii) Back emf (iii) Power wasted in armature (iv) Power wasted in field.
- A 6-pole lap connected DC series motor with 864 conductors, takes a current of 110 A at 480 V. The armature resistance and field resistance are 0.18 Ω and 0.02 Ω respectively. The flux per pole is 50 mwb. Calculate (i) The speed (ii) The gross torque.
- A 4-pole 230 V DC series wave connected armature with 1254 conductors with flux per pole of 22 mwb, takes 50 A for motoring. The armature and series field coil resistances are 0.3Ω and 0.2Ω respectively. Calculate the speed and torque developed.
- A 4-pole motor is fed at 440 V and takes an armature current of 50 A. The resistance of the armature circuit is 0.28 Ω. The armature winding is wave connected with 888 conductors and useful flux per pole is 0.023 wb. Calculate the back EMF and speed.
- A 4-pole DC shunt motor takes 22 A from 220 V supply. The armature and field resistances are 0.5Ω and 100 Ω respectively. The armature is lap connected with 300 conductors. If the flux per pole is 20 mwb, calculate (i) Speed (ii) Torque