6. Power and Control

Electric Machines — Quiz

Test your understanding of electric machines with 5 practice questions.

Practice Questions

Question 1

In a 100 MVA, 13.8 kV/0.69 kV three‐phase transformer with a per‐unit leakage reactance of 0.10 on the high‐voltage side, what is the per‐phase actual reactance $X$ in ohms on the HV winding?

Question 2

For a synchronous generator with internal EMF $E=1.2$ pu, terminal voltage $V=1.0$ pu, and synchronous reactance $X_s=0.25$ pu, what load angle $\delta$ yields a real power output of 0.96 pu?

Question 3

If the supply voltage to a three‐phase induction motor is reduced by half, how does the starting torque $T_{st}$ change, assuming all other parameters constant?

Question 4

Which of the following best describes the difference in torque–speed characteristics between DC series and DC shunt motors, and which is preferable for variable‐speed drives?

Question 5

After synchronization, why does a synchronous motor draw mainly magnetizing current, and how does field excitation control its power factor?