Three-Phase Systems in Power Applications — Engineering Board Exam Practice Questions

25 free engineering board exam reviewer questions on Three-Phase Systems in Power Applications (AC Circuits), each with the correct answer and a worked solution.

  1. A balanced three-phase resistive load is connected in delta. One of the three line wires opens. Compared with the original total power…
  2. In a balanced three-phase system with abc (positive) phase sequence, VAN=120 0° V. Find the line voltage VBC=VBN-VCN in polar form.
  3. The same three equal resistors are connected first in wye and then in delta across the same three-phase line. The total power absorbed in…
  4. A balanced delta load has Z =60+j45, in each phase and is supplied from a 400 V line. Replace the delta with its equivalent wye and find…
  5. A three-phase, four-wire wye system with a 120 V phase voltage (VAN=120 0°, VBN=120 -120°, VCN=120 120°) feeds the unbalanced resistive…
  6. The balanced load shown has Z=30+j40, in each phase and is wye-connected to a 400 V line. If the same three impedances are reconnected in…
  7. A three-phase generator is rated 1500 kVA at 4160 V (line-to-line). What is its rated line current?
  8. Three 10, resistors are connected in delta across a 240 V three-phase line. What is the line current?
  9. A balanced three-phase load of 100 kW operates at 0.8 power factor lagging. How many kvar of capacitors are needed to raise the power…
  10. In the two-wattmeter method on a balanced three-phase load, the wattmeters read 5 kW and 3 kW. What is the load power factor?
  11. The 30 kW, 0.8 power factor lagging three-phase load above is supplied from a 480 V line. Find its total reactive power.
  12. A balanced three-phase load takes 30 kW at 0.8 power factor lagging from a 480 V line. Find the line current.
  13. A balanced delta-connected load, with Z=6+j8, in each phase, is supplied from a three-phase line of 400 V (line-to-line, rms). Find the…
  14. A balanced delta-connected load, with Z=24+j18, in each phase, is supplied from a three-phase line of 208 V (line-to-line, rms). Find the…
  15. A balanced delta-connected load, with Z=12+j9, in each phase, is supplied from a three-phase line of 208 V (line-to-line, rms). Find the…
  16. A balanced wye-connected load, with Z=15+j20, in each phase, is supplied from a three-phase line of 480 V (line-to-line, rms). Find the…
  17. A balanced wye-connected load, with Z=16+j12, in each phase, is supplied from a three-phase line of 400 V (line-to-line, rms). Find the…
  18. A balanced wye-connected load, with Z=15+j20, in each phase, is supplied from a three-phase line of 208 V (line-to-line, rms). Find the…
  19. In a balanced three-phase, four-wire wye system the current in the neutral conductor is
  20. A balanced three-phase load draws 10 A from a 400 V line at a power factor of 0.8. What total real power does it absorb?
  21. A wye-connected three-phase source has a line-to-line voltage of 480 V. What is its phase voltage?
  22. The three voltages of a balanced three-phase supply are displaced from each other by
  23. In a balanced delta-connected load, the relationship between the line current IL and the phase current Iph is
  24. In a balanced wye-connected system, the relationship between the line voltage VL and the phase voltage Vph is
  25. The balanced wye-connected load shown is supplied from a three-phase line of 240 V (line-to-line, rms). What is the voltage across each…