1: In a balanced star-connected three-phase load, the neutral current is zero because:
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The three phase currents are in phase
The neutral impedance is infinite
The phase currents have equal magnitudes and are displaced by 60 degrees
The phase currents have equal magnitudes and are displaced by 120 degrees
2: A single-phase and a balanced three-phase system supply identical active power at unity power factor. Which statement is correct?
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Both have pulsating total instantaneous power
Both deliver constant instantaneous power
Only the balanced three-phase system delivers constant instantaneous power
Only the single-phase system delivers constant instantaneous power
3: A balanced star-connected load draws 10 A at a line voltage of 400 V. If the same phase impedances are connected in delta across the same supply, the new line current is:
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17.32 A
10 A
30 A
5.77 A
4: In a balanced star-connected circuit with RYB sequence, V_RY = 200∠0° V. The corresponding R-phase voltage is:
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115.5∠30° V
115.5∠−30° V
115∠0° V
200∠−30° V
5: A balanced delta-connected load is supplied at constant line voltage. If each phase impedance is doubled, the line current becomes:
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Half the original value
Twice the original value
Unchanged
One-fourth of the original value
6: In a balanced three-phase system with RYB sequence, the phasor sum V_RY + V_YB + V_BR is:
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3V_L
V_L
Zero
√3 V_L
7: In the two-wattmeter method, one wattmeter reads zero while the other reads a positive value. For a balanced lagging load, the power factor is:
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0
0.5
1
0.866
8: In the two-wattmeter method, both wattmeters show equal positive readings for a balanced three-phase load. The power factor is:
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1
0.866
0
0.5
9: If the phase sequence changes from RYB to RBY while V_R remains the reference, the angle of V_RY changes from:
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+30° to −30°
+30° to +150°
−30° to +30°
−30° to −150°
10: According to Gauss's law for magnetism, the net magnetic flux through any closed surface is zero. What does this imply?