The correct answer is: C. increase armature current but decrease power factor.
When a load is applied to a synchronous motor, the motor draws more current from the power supply. This increased current causes the motor’s magnetic field to become stronger, which in turn causes the motor to turn faster. The faster the motor turns, the greater the load it can carry.
However, the increased current also causes the motor’s power factor to decrease. This is because the motor’s inductive reactance causes it to draw a current that is out of phase with the voltage. This out-of-phase current causes the motor to waste power, which is reflected in a lower power factor.
In summary, when a load is applied to a synchronous motor, the motor’s armature current increases and its power factor decreases.
Here is a more detailed explanation of each option:
- Option A: decrease both armature current and power factor. This is not the correct answer because the armature current increases when a load is applied to a synchronous motor.
- Option B: decrease armature current but increase power factor. This is not the correct answer because the armature current increases when a load is applied to a synchronous motor.
- Option C: increase armature current but decrease power factor. This is the correct answer because the armature current increases when a load is applied to a synchronous motor, and the power factor decreases when a load is applied to a synchronous motor.
- Option D: increase both its armature current and power factor. This is not the correct answer because the power factor decreases when a load is applied to a synchronous motor.