1. 
A threephase generating system has an efficiency of around:

2. 
The windings of a threephase alternator are separated by:

3. 
Figure shows the stator winding arrangement of a 4 pole, three phase alternator:
The alternator has a 24slot stator and is wound with 24 coils in sets of:
A. 
4 coils per pole per phase 
B. 
3 coils per pole per phase 
C. 
2 coils per pole per phase 
D. 
1 coil per pole per phase 

4. 
One of advantages of a threephase system over a single phase system is that the power is more constant so that the torque of a rotating machine is more constant. The more constant torque results in:
A. 
much more vibration from the machine 
B. 
no vibration from the machine 
C. 
excessive load current from the machine 
D. 
much less vibration from the machine 

5. 
Figure shows the waveform for a threephase AC supply:
The displacement between the voltage is:

6. 
In a threephase system, where the three voltage sources are, connected to feed a threephase load, the phase sequence is important for rotating machinery, because the:
A. 
direction of current flow will increase 
B. 
direction of rotation will be affected 
C. 
machinery could draw excessive load current 
D. 
power factor will be leading instead of lagging 

7. 
One method of forming a threephase system is to connect the three similar ends of the windings together at one point. This type of connection is called a:

8. 
Look at the following diagram:
The threephase winding shown in figure have been connected in the:
B. 
double series configuration 
C. 
parallel configuration 

9. 
Look at the following diagram:
The threephase winding shown in figure has:

10. 
In a threephase starconnected system the line current equals:
A. 
Ö3 x the phase current 
C. 
1.732 x the phase current 

11. 
In a threephase starconnected system the line voltage equals:
B. 
the phase voltage / 1.732 
C. 
Ö3 x the phase voltage 

12. 
Figure shows one method of determining the line voltage of a threephase star connected system:
In the diagram, the line voltage phasor V_{AB} is equal to:

13. 
In a star connected threephase system, the line voltages:
A. 
lead the phase voltages by 30°E 
B. 
lag the phase voltages by 30°E 
C. 
lead the phase voltages by 60°E 
D. 
lag the phase voltages by 60°E 

14. 
Figure shows the phasor diagram method of determining the line voltage of a threephase star connected system:
In the diagram, the line voltage phasor V_{AB}:
A. 
lags the phase voltage V_{A} by 60°E 
B. 
leads the phase voltage V_{A} by 30°E 
C. 
leads the phase voltage V_{A} by 60°E 
D. 
lags the phase voltage V_{A} by 30°E 

15. 
Figure shows the phasor diagram of a threephase star connected system in which phase “C” phase has mistakenly been connected with the connections reversed:
The waveforms of the three phase voltages then have a displacement of 120º E between A and B, and:
A. 
90º E between A and C and also between C and B 
B. 
180º E between A and C and also between C and B 
C. 
60º E between A and C and also between C and B 
D. 
120º E between A and C and also between C and B 

16. 
One method of forming a threephase system is to connect the dissimilar similar ends of the windings together. This type of connection is called a:

17. 
Look at the following diagram:
The threephase winding shown in figure have been connected in the:
B. 
double series configuration 
C. 
parallel configuration 

18. 
In a threephase deltaconnected system the line current equals:
B. 
Ö3 x the phase current 
C. 
1.732 x the phase voltage 

19. 
In a threephase deltaconnected system the line voltage equals:
A. 
Ö3 x the phase voltage 
B. 
the phase voltage / 1.732 

20. 
Figure shows one a Delta connected 400 V threephase system in which one phase has been mistakenly connected with reversed connections:
In the diagram, the voltage between the open connections will be:

21. 
Figure shows a connection diagram for a threephase delta connected load:
The current in line 2, equals the:
A. 
phasor difference of phase currents I_{A} and I_{B} 
B. 
phasor sum of phase currents I_{A} and I_{B} 
C. 
arithmetic sum of phase currents I_{A} and I_{B} 
D. 
arithmetic difference of phase currents I_{A} and I_{B} 

22. 
Figure shows a phasor diagram for determining the line current in a threephase delta connected load:
In the diagram, the line current phasor I_{L2}:
A. 
leads the phase current I_{A} by 60°E 
B. 
leads the phase current I_{A} by 30°E 
C. 
lags the phase voltage V_{A} by 60°E 
D. 
lags the phase voltage V_{A} by 30°E 

23. 
Electrical power can be transmitted using low voltage and high currents. Higher currents result in:
A. 
lower transmission losses 
B. 
very efficient transmission 
C. 
higher voltage outputs 
D. 
higher transmission losses 

24. 
In economic terms, the higher the voltage used for power transmission systems, the:
A. 
lower the cost of installing and maintaining the transmission lines 
B. 
higher the cost of installing and maintaining the transmission lines 
C. 
higher the cost of the current along the transmission lines 
D. 
lower the cost of installing underground transmission lines 

25. 
Look at the following diagram:
Transmission system voltages are far higher than the voltages required by the average consumer, therefore the voltage is:
A. 
stepped up to a suitable value using transformers 
B. 
stepped down to a suitable value using transformers 
C. 
kept the same right through to the customer’s circuits 
D. 
converted to DC for the customer’s machines 

26. 
The distribution system shown in figure is a:
A. 
switched wiring electrical reticulation system 
B. 
subtransmission electrical receiving system 
C. 
single wire earth return distribution system 
D. 
sixteenkilovolt wiring earthed resister system 

27. 
Figure shows a 4wire distribution system with the star point of the phase windings connected to earth:
One advantage of this system is that:
A. 
only one voltage is available to the consumer 
B. 
the neutral conductor is not used by the consumer 
C. 
the active conductors are connected to the earth 
D. 
two voltages are available to the consumer 

28. 
For a balanced load, the current in a neutral conductor of a threephase, fourwire system is equal to:
B. 
the current in any phase 
C. 
the arithmetic sum of the phase currents 
D. 
the phasor difference of any two line currents 

29. 
For any type of load, the current in a neutral conductor of any threephase, fourwire system is equal to:
A. 
the phaser difference of the line currents 
B. 
minus the phasor sum of the line currents 
C. 
minus the arithmetic sum of the line currents 
D. 
the arithmetic difference of the line currents 

30. 
The currents in the lines of a threephase fourwire system are:
A phase—8 amperes at unity power factor
B phase—10 amperes at 0.866 leading power factor
C phase—10 amperes at 0.866 lagging power factor.
In this case the current flowing in the neutral conductor will be approximately:

31. 
Figure shows the readings obtained when checking the voltages of a faulty 230/400 V threephase fourwire system:
The most likely cause of the fault will be a:
A. 
faulty threephase alternator 
B. 
faulty threephase poletop transformer 
C. 
high resistance load on one phase 
D. 
broken neutral conductor 

32. 
The power consumed by a threephase load can be determined using the formula:

33. 
A threephase 400 V motor draws 10 A at 0.8 lagging power factor. The power is consumed by this motor will be approximately:

34. 
Figure shows the one wattmeter method of measuring threephase power on a threephase fourwire system:
One advantage of this method is that:
A. 
only one reading is needed 
B. 
it is suitable for fluctuating loads 
C. 
only one wattmeter is required 
D. 
a neutral connection is not required 

35. 
Figure shows the twowattmeter method of measuring power in a threephase threewire system:
One advantage of using this method is that:
A. 
a neutral conductor is available for the meters 
B. 
the meters only need to measure the phase voltages 
C. 
threeterminal wattmeters can be used 
D. 
the power factor can be obtained for balanced loads 

36. 
The power consumed by a threephase motor has been measured using the twowattmeter method. At full load, the two wattmeters gave readings of 6 kW and 3 kW. At this load, the power factor of the motor will be:

37. 
Figure shows the threewattmeter method of measuring threephase power in a threephase fourwire system:
To find the total power, the following calculation must be made using the readings: P_{TOTAL} =
C. 
W_{1} – W_{2}. / W_{1} + W_{3} 

38. 
Figure shows the threewattmeter method of measuring threephase power in a threephase fourwire system.
This method is suitable for:
C. 
balanced and unbalanced loads 
D. 
measuring the power factor with balanced loads 

39. 
One advantage of using threephase digital wattmeters is as well as the power, they can show the value of such things as:
A. 
the current in each phase 
B. 
the VAR value for each phase 
C. 
frequency and total harmonic distortion 
D. 
all of the given answers 

40. 
In power stations operating under normal conditions, the values of voltage and current are generally too high and unwieldy to be used directly with portable instruments. To avoid these highenergy circuits when measuring voltage, current and power, in these cases:
A. 
potential transformers and current transformers must be used 
B. 
only high voltage ammeter and voltmeters must be used 
C. 
digital voltmeters can be used with a high voltage extension arm 
D. 
275 kV ammeters and voltmeters must be used for 11 kV circuits 
