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Education

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Three Phase AC circuits

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30 questions

30 questions

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1. Multiple Choice
2 minutes
1 pt
Calculate the line voltage and Line current in this balanced Y-Y system:
Eline = 1.38 KV
Iline = 0.5312
Eline = 13.8 KV
Iline = 5.312 A
Eline = 7.967 KV
Iline = 5.312 A
Eline = 7.967 KV
Iline = 0.5312
2. Multiple Choice
2 minutes
1 pt
Calculate phase voltage and phase current in this balanced Y-Y system:
Ephase(source) = 7.967 kV
Iphase(source) = 5.312 KA
Ephase(source) = 7.967 V
Iphase(source) = 5.312 A
Ephase(source) = 7.967 kV
Iphase(source) = 5.312 A
Ephase(source) = 7.967 V
Iphase(source) = 5.312 A
3. Multiple Choice
2 minutes
1 pt
Calculate the total power consumed in this balanced Y-Y system:
1.2696 kW
126.96 W
12.696 kW
126.96 kW
4. Multiple Choice
30 seconds
1 pt
In a three-phase system, the voltages are separated by
45⁰
90⁰
120⁰
180⁰
5. Multiple Choice
30 seconds
1 pt
In a three-phase system, when the loads are perfectly balanced, the neutral current is
zero
one-third of maximum
two-thirds of maximum
at maximum
6. Multiple Choice
45 seconds
1 pt
In a -connected source driving a -connected load, the
load voltage and line voltage are one-third the source voltage for a given phase
load voltage and line voltage are two-thirds the source voltage for a given phase
load voltage and line voltage cancel for a given phase
load voltage, line voltage, and source phase voltage are all equal for a given phase
7. Multiple Choice
45 seconds
1 pt
Three ideal inductors are connected in star. The combination is supplied from a balanced three phase ac supply. The power consumed by the circuit will be
infinite
$\sqrt{3}\times VL\times IL\times\cos\theta$
zero
$3\times Vph\times Iph\times\cos\theta$
8. Multiple Choice
45 seconds
1 pt
Three ideal inductors are connected in star. The combination is supplied from a balanced three phase ac supply. The power factor of the circuit will be...
1
0.5
0.866
0
9. Multiple Choice
45 seconds
1 pt
Three practical inductors are connected in delta. The combination is supplied from a balanced three phase ac supply. The power factor of the circuit will be...
1
0
$\infty>pf>0$
$0<pf<1$
10. Multiple Choice
45 seconds
1 pt
Three pure resisrors are connected in delta. The combination is supplied from a balanced three phase ac supply. The power factor of the circuit will be...
1
0
$\infty>pf>0$
$0<pf<1$
11. Multiple Choice
1 minute
1 pt
A three phase AC circuit is connected with 2 watt-meters to measure the three phase power consumed. It is observed that one of the watt-meter is "kicked back" while taking the reading. What will be the circuit power factor?
0
0.5
$0.5>pf>0$
1>pf>0.5
12. Multiple Choice
1 minute
1 pt
A three phase AC circuit is connected with 2 watt-meters to measure the three phase power consumed. It is observed that both the watt-meters are giving positive reading while measuring the power. What will be the circuit power factor?
0
0.5
$0.5>pf>0$
1>pf>0.5
13. Multiple Choice
1 minute
1 pt
A three phase AC circuit is connected with 2 watt-meters to measure the three phase power consumed. It is observed that both the watt-meters are giving equal and opposite reading. What will be the circuit power factor?
0
0.5
$0.5>pf>0$
1>pf>0.5
14. Multiple Choice
1 minute
1 pt
A three phase AC circuit is connected with 2 watt-meters to measure the three phase power consumed. It is observed that both the watt-meters are giving equal and positive readings. What will be the circuit power factor?
0
1
$0.5>pf>0$
1>pf>0.5
15. Multiple Choice
45 seconds
1 pt
A single watt-meter is connected in one of the phase in a three phase balanced star connected load system. Can we measure the three phase power?
Yes
No
May be
Yes but with modifications in the circuit
16. Multiple Choice
1 minute
1 pt
Three similar coils are connected in delta across a three phase AC supply. The watt-meter readings are 12KW & 7KW . Calculate the power input
5KW
19KW
12KW
7KW
17. Multiple Choice
1 minute
1 pt
Three similar coils are connected in delta across a three phase AC supply. The watt-meter readings are 12KW & 7KW . Calculate the phase angle
4.5 degree lagging
4.5 degree leading
24.5 deg lagging
24.5 deg leading
18. Multiple Choice
1 minute
1 pt
Three similar coils are connected in delta across a three phase AC supply. The watt-meter readings are 12KW & 7KW . Calculate the power factor
unity power factor
zero power factor
0.91 lagging
0.91 leading
19. Multiple Choice
3 minutes
1 pt
three impedances (10+j 8) ohms are connected in star across a 400 V 3 phase supply. Determine the line and phase current
18 A and 18 A respectively
10.39 A and 18 A respectively
18 A and 10.39 A respectively
31.17 A and 18 A respectively
20. Multiple Choice
3 minutes
1 pt
three impedances (10+j 8) ohms are connected in star across a 400 V 3 phase supply. Determine the total power consumed?
3248.66 W
9746 W
5626.94 W
16,880 W
21. Multiple Choice
3 minutes
1 pt
three impedances (10+j 8) ohms are connected in star across a 400 V 3 phase supply. Determine the reading of the two wattmeters to measure three phase power.
7119 W & 2627 W
7119 KW & 2627 KW
7119 KW & 2627 KW
7119 W & 9762 W
22. Multiple Choice
3 minutes
1 pt
3 phase load consisting of three equal impedances connected in delta across a 400 V 3-phase ac supply. The line current drawn is 10A at 0.7 lagging. Determine the total reactive power.
49.47 KVAR
4.947 KVAR
4.850 KVAR
48.5 KVAR
23. Multiple Choice
5 minutes
1 pt
3 phase load consisting of three equal impedances connected in delta across a 400 V 3-phase ac supply. The line current drawn is 10A at 0.7 lagging. What would be the phase current if the loads were connected in star?
10 A
3.33 A
5.77A
17.32 A
24. Multiple Choice
5 minutes
1 pt
3 phase load consisting of three equal impedances connected in delta across a 400 V 3-phase ac supply. The line current drawn is 10A at 0.7 lagging. What would be the total active power if the loads were to be connected in star?
48.5 KW
4.85 KW
16.17 KW
1.617 KW
25. Multiple Choice
2 minutes
1 pt
The voltage VAB=50 $\angle$ 30 $\degree$ volts. The voltage VBA = ?
$50\angle-180\degree$
$50\angle-150\degree$
$50\angle-30\degree$
$50\angle-210\degree$
26. Multiple Choice
45 seconds
1 pt
when the two wattmeters used to measure a three phase power, give equal reading then the phase angle of the circuit is.
0 degree
30 degree
60 degree
90 degree
27. Multiple Choice
5 minutes
1 pt
A balanced three phase load consists of three coils, each of 4 ohm resistance and 0.02H inductance. Determine the total active power when the coils are connected in star. The supply is a 415 V, 50 Hz, 3-phase ac.
12.41 W
37.23 W
37.23 KW
12.41 KW
28. Multiple Choice
5 minutes
1 pt
A balanced three phase load consists of three coils, each of 4 ohm resistance and 0.02H inductance. Determine the total active power when the coils are connected in delta. The supply is a 415 V, 50 Hz, 3-phase ac.
12.41 W
37.23 W
37.23 KW
12.41 KW
29. Multiple Choice
15 minutes
1 pt
calculate the current flowing into each terminal and in each phase of the winding of a 3 phase delta connected motor developing an output of 250 hp at 2300 V between the terminals at a p.f. of 0.75 & an efficiency of 85 %
42.4 A & 24.48 A
42.4 A & 73.44 A
73.44 A & 42.4 A
24.48 A & 42.4 A
30. Multiple Choice
45 seconds
1 pt
For a balanced 3 phase AC system, what should be angle separation between the phases.
180 deg
90 deg
120 deg
0 deg
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