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Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) PDF Download

Q1: For a two-phase network, the phase voltages Vp and Vq are to be expressed in terms of sequence voltages Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)

The possible option(s) for matrix S is/are      (2024)
(a) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)

(b) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
(c) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
(d) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Ans: (a, d)

Q2: In the circuit shown below, a three-phase star-connected unbalanced load is connected to a balanced three-phase supply of 100√3 with phase sequence  ABC. The star connected load has ZA = 10Ω and Z= 20∠60°. The value of ZC in Ω, for which the voltage difference across the nodes n and  n′ is zero, is       (2022)
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)(a) 20∠−30°
(b) 20∠30°
(c) 20∠−60°
(d) 20∠60 °
Ans:
(c)
Sol: Given: n & n' are at same potential, therefore,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Q3: A three-phase balanced voltage is applied to the load shown. The phase sequence is RYB. The ratio Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) is ____________.        (2021)
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)(a) 1
(b) 2
(c) 3
(d) 4
Ans:
(a)
Sol: Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)and Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)

Q4: In the given network Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) The phasor current i (in Ampere) is      (SET-2  (2015))
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)(a)173.260 173.2 ∠ −60°
(b) 173.2 ∠ 120°
(c) 100.060100.0  ∠ −60°
(d) 100.0120100.0 ∠ 120
Ans:
(a)
Sol: ′i′ is taken as input,  
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Apply KCL at node
Node voltage is 100 ∠ 120
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Q5: The line A to neutral voltage is 10 ∠ 15°V for a balanced three phase star connected load with phase sequence ABC . The voltage of line B with respect to line C is given by       (SET-3 (2014))
(a) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)

(b) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
(c) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
(d) Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Ans: (c)
Sol: Given,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)As the system is balanced and phase sequence is ABC, therefore,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)∴ voltage of line w.r.t. line C is
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Q6: A two-phase load draws the following phase currents : Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) These currents are balanced if ϕ1 is equal to.       (2012)
(a) -ϕ2
(b) ϕ2
(c) (𝜋/2𝜙2)(π/2−ϕ2)
(d) (π/2+ϕ2)
Ans:
(d)
Sol: In two phase, current are balanced if phase difference is 90.
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Phase difference is 90,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)
Q7:  For the three-phase circuit shown in the figure, the ratio of the currents I:  I: IB is given by      (2005)
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)(a) 1:1: √3
(b) 1:1:2
(c) 1:1:0
(d) 1:1:√3/2
Ans:
(a)
Sol: Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Assuming phase sequence to be RYB
Taking VRY as the reference,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)Using KCL,
Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE)

The document Previous Year Questions- Three-Phase Circuits | Network Theory (Electric Circuits) - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Network Theory (Electric Circuits).
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FAQs on Previous Year Questions- Three-Phase Circuits - Network Theory (Electric Circuits) - Electrical Engineering (EE)

1. What are the advantages of using three-phase circuits over single-phase circuits?
Ans. Three-phase circuits offer higher power efficiency, smoother power delivery, and reduced power loss compared to single-phase circuits. They also allow for smaller wire sizes and less voltage drop over long distances.
2. How do you calculate the total power in a three-phase circuit?
Ans. The total power in a three-phase circuit can be calculated by adding up the individual powers of each phase. This can be done using the formula: Total power = √3 x Voltage x Current x Power Factor.
3. What is the importance of balancing the load in a three-phase circuit?
Ans. Balancing the load in a three-phase circuit is crucial to ensure even distribution of power among all three phases. Imbalanced loads can lead to overheating of equipment, voltage fluctuations, and inefficiency in the system.
4. How does a neutral wire function in a three-phase circuit?
Ans. The neutral wire in a three-phase circuit acts as a return path for unbalanced currents flowing through the system. It helps maintain a stable voltage across all three phases and prevents overloading of any single phase.
5. What are common types of three-phase connections used in industrial applications?
Ans. Common types of three-phase connections include delta connection, star (wye) connection, and open delta connection. Each configuration has its own advantages and is chosen based on the specific requirements of the application.
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