BASIC AC THEORY EXAM

1. A simple generator consists of a conductor loop turning in a magnetic field, cutting across the magnetic lines of force.

2. The sine wave output is the result of one side of the generator loop cutting lines of force.

3. Effective value of AC equals effective value of DC.

4. Phase angle is used to compare two wave forms.

5. As the generator coil rotates 180°, the output voltage goes through one complete cycle.

6. Effective voltage is equal to                          times the peak voltage.

7. Average voltage is equal to                          times the peak voltage.

8. Opposition to the flow of alternating current caused by inductance is called Inductive Reactance.

9. Current lags voltage in a purely inductive circuit by a 90° phase angle.

10. Which device below operates on the principals of inductance?

11. Opposition to the flow of alternating current caused by inductance is called capacitive reactance.

12. Current leads voltage by 90 degrees in a purely capacitive circuit.

13. Impedance is the total opposition to current flow in an AC circuit.

14. Impedance is equal to total resistance.

15. R-C-L series circuit at resonance is when net reactance is zero and circuit current output is determined by the series resistance of the circuit.

16. R-C-L parallel circuit at resonance is when net reactance is maximum and circuit current output is at minimum.

17. In AC circuits, current and voltage are normally in phase and, as a result, not all the power produced by the generator can be used to accomplish work.

18. While direct current has one form of power, alternating current has three different forms of power that are related in a unique relationship.

19. True power  is the power delivered to an electrical circuit.

20. Apparent power is the power consumed by the resistive loads in an electrical circuit.

21. Reactive power is the power consumed in an AC circuit because of the expansion and

collapse of magnetic and electrostatic fields.

22. Reactive power is not useful power because it is stored in the circuit itself.

23. The total power delivered by the source is the apparent power.

24. Power factor is the ratio between true power and apparent power.

25. In a three phase system each phase is                       out of phase with each other.

26. Unbalanced three-phase circuits are indicated by abnormally high currents in one or more of the phases.

27. Slip rings are electrical connections that are used to transfer power to and from the rotor of an AC generator.

28. Efficiency of an AC generator can be calculated by dividing the output by the input and multiplying by 100.

29. The frequency of the generated voltage in an AC generator can be calculated by multiplying the number of               by the speed of the generator and dividing by a factor of 120.

30. The advantage of the delta-connected AC generator is that if one phase becomes damaged or open, the remaining two phases can still deliver three-phase power at a reduced capacity of 57.7%.

31. The advantage of a wye-connected AC generator is that each phase only has to carry 57.7% of line voltage and, therefore, can be used for high voltage generation.

32. The purpose of a voltage regulator is to maintain the output current of a generator at a desired value.

33. It is virtually impossible for the rotor of an AC induction motor to turn at the same speed as the rotating magnetic field.

34. Slip is the percentage difference between the speed of the rotor and the speed of the rotating magnetic field.

35. Synchronous motors are used to accommodate large loads and to improve the power factor of transformers in large industrial complexes.