Problem 103-3    Source:  Problem prepared by the website author.

A DC motor in the shunt configuration, fed by a line voltage of 380  V, has a armature current of 125  A. Considering the field resistance equal to 110  Ω and the resistance of armature equal to 0,2  Ω, determine:

a) The current in the field winding.

b) The current in the supply line.

c) The voltage generated by the armature.

d) Power absorbed from the supply line.

Solution of the Problem 103-3   

Item a

The shunt configuration of a DC motor is characterized by the circuit shown in Figure 103-03.1.

Note that the field winding is connected in parallel with the supply line, V_T = 380  V. Then, applying Ohm's law, we can easily determine the field current, because:

Item b

From Figure 103-03.1 we conclude that the equation below is valid, that is:

Item c

To find the value of E_A, we will use the eq. 103-06, reproduced below:

Substituting the variables for their numerical values ​​and performing the calculation, we obtain:

Item d

To find the power that the machine absorbs from the supply line, just use the power equation, that is: