In a three-phase system, when the loads are perfectly balanced, the neutral current is

A)
Zero
B)
At maximum
C)
One-third of maximum
D)
Two-thirds of maximum

Correct Answer : Option (A) :   Zero

Recently Updated in Three-Phase Systems in Power Applications Questions
In a three phase, delta connection
A)
Line current is equal to phase current
B)
Line voltage and line current is zero
C)
Line voltage is equal to phase voltage
D)
None of the above

Correct Answer :   Line voltage is equal to phase voltage

Explanation : A delta connected AC circuit is achieved by connecting the start end of a winding to the finish end of another winding such that all three windings form a mesh. Since each end of the windings forms the line connection, voltage across each winding is equal to the potential difference between the corresponding lines taken from that winding. Hence the phase voltage is equal to the line voltage.

For a three-phase delta connected load, fed from a star connected network, the power transferred to the load is_
A)
3 KW
B)
4.7 KW
C)
5 KW
D)
7KW

Correct Answer :   4.7 KW

Explaination :

For a balanced three phase, three wire system with input power of 10kW, at 0.9 power factor, the readings on both wattmeter are ________ respectively
A)
7kW, 3kW
B)
5000W, 5000W
C)
6350W, 3650W
D)
7600W, 1200W

Correct Answer :   6350W, 3650W

Explanation :

Let reading of one Wattmeter = W1

Reading of second Wattmeter = W2

Input Power, P = W1+W2 = √3VLILcosφ = 10000………………1

Power Factor, cosφ = 0.9

Phase angle, φ = 25.8 degrees

Therefore, W1 = VLILcos(30-φ) = 0.99VLIL = 6350W

W2 = VLILcos(30+φ) = 0.56VLIL = 3650W

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