BEE FREE BEE Bachelor of Electrical Engineering Power Systems and Machines Questions and Answers 2

Question 1

What is the primary purpose of a buck-boost transformer in a power distribution system?

Accepted Answer

To regulate voltage levels within a narrow range

Answer

To convert AC to DC power

Answer

To isolate two circuits galvanically

Answer

To increase the power factor of the system

Question 2

In a three-phase synchronous generator, what happens when the field excitation is increased beyond the value needed for unity power factor?

Accepted Answer

The generator supplies reactive power to the grid

Answer

The generator operates at leading power factor

Answer

The generator operates at lagging power factor

Answer

The generator absorbs reactive power from the grid

Question 3

Which type of DC motor is best suited for electric traction applications requiring high starting torque?

Accepted Answer

DC series motor

Answer

DC shunt motor

Answer

DC compound motor

Answer

Permanent magnet DC motor

Question 4

What is the swing equation used for in power system stability analysis?

Accepted Answer

Determining the rotor angle dynamics of a synchronous machine after a disturbance

Answer

Calculating the steady-state power flow in transmission lines

Answer

Finding the short-circuit current during a fault

Answer

Estimating transmission line losses under varying loads

Question 5

In a per-unit system, if a transformer has a per-unit impedance of 0.05 on its own base, what does this indicate about its voltage regulation?

Accepted Answer

Approximately 5% voltage drop at full load under unity power factor

Answer

The transformer can handle 5% overload

Answer

The transformer efficiency is 95%

Answer

The short-circuit current is 5% of rated current

Question 6

What is the main advantage of using HVDC transmission over HVAC for long-distance bulk power transfer?

Accepted Answer

Lower transmission losses and no reactive power compensation needed

Answer

Higher voltage levels can be achieved more easily

Answer

Standard transformers can be used at both ends

Answer

Protection systems are simpler and less expensive