Consider the operation of a dc shunt motor that is affected by the following changes in its operating conditions. Explain the corresponding approximate changes in the armature current and speed of the machine for each change in operating conditions.
(a) The field current is doubled, with the armature terminal voltage and the load torque remaining the same.
(b) The armature terminal voltage is halved, with the field current and load torque remaining the same. (c) The field current and the armature terminal voltage are halved, with the horsepower output remaining the same.
(d) The armature terminal voltage is halved, with the field current and horsepower output remaining the same.
(e) The armature terminal voltage is halved and the load torque varies as the square of the speed, with the field current remaining the same.