A dc, separately excited motor has the following data:
Rated field voltage = 300 V
Field constant (K?) = 3 Vs
Armature resistance = 2 ?
Field resistance = 150 ?
The motor is used to drive an assembly line consisting of a conveyor belt moving
horizontally. The load on the belt varies depending on the amount of goods being
moved. The load torque seen by the motor varies from a maximum of 24 Nm to a
minimum of 3 Nm. At all loading conditions, the speed of the motor must be
maintained constant and equal to 200 rpm.
a. To achieve the required operation, the armature voltage of the motor is adjusted
by a single-phase, full-wave, ac/dc converter. The input to the converter is 240 V
(rms). Calculate the range of the triggering angle (minimum and maximum)
required to maintain the motor speed at the specified value at all loading
conditions. Assume that the armature current is always continuous.
b. Another method to achieve the desired operation is to adjust the field voltage.
In this case, the armature voltage can be kept constant at some value. Calculate
the range of the field voltage (minimum and maximum). Hints: Assume that the
maximum value of the field voltage is equal to its rated value (i.e., 300 V). Also
assume that the field constant (K?) is linearly proportional to the field voltage.
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