JNTU
JNTU B.Tech II ELECTRICAL SYSTEMS Previous Question Paper (March - 2022 - R13)
Answer any five questions
All questions carry equal marks
Main
Obtain the necessary equations for converting a delta network into an equivalent star network.
Answer
To convert a delta (Δ) network with resistors Rab, Rbc, and Rca into an equivalent star (Y) network with resistors Ra, Rb, and Rc, we equate the resistances between any two terminals. The transformation equations are derived by setting the resistance between two nodes in the delta configuration equal to the series sum of the corresponding arms in the star configuration.
Each star resistor is the product of the two adjacent delta resistors divided by the sum of all three delta resistors.
For the circuit as shown in figure 1, Calculate the current in the various branches and the power delivered and consumed? (All resistances are in ohms).
Answer
Since the circuit diagram (Figure 1) is not provided in the prompt, the general procedure to solve for branch currents and power is as follows:
- Identify all nodes and loops in the circuit.
- Apply Kirchhoff's Current Law (KCL) at each node or Kirchhoff's Voltage Law (KVL) to each independent loop to establish a system of linear equations.
- Solve the resulting system of equations to determine the current flowing through each branch.
- Calculate the power consumed by each resistor using the formula P = I2R.
- Calculate the total power delivered by the sources using P = VI, where V is the source voltage and I is the current leaving the positive terminal.
- Verify that the total power delivered by the sources equals the total power consumed by all resistors in the circuit.
State the maximum power transfer theorem. Show that the maximum power transfer if RL = Rth and explain its importance.
Answer
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Using superposition theorem, find the current passing through the 5 Ω resistor, as shown in figure 2.
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What is power factor? Discuss the practical importance of power factor.
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A capacitor having a capacitance of 10 µF is connected in series with a non-inductive resistance of 120 Ω across 100 V, 50 Hz. Calculate the power, current and the phase difference between current and voltage.
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A series RL circuit is supplied by DC voltage. Find the expression for i(t) when the switch is closed at t = 0.
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A balanced delta connection with load impedance of (2 + j3) ohms per phase is connected to a balanced three-phase 440 V supply. Find active, reactive, and apparent powers if phase current is 10 A.
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Derive the emf equation of a single-phase transformer.
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The transformation ratio in single phase 50 Hz transformer is 6600/600V. If the maximum value of flux in the core is to be about 0.05 Wb, determine the number of turns in each winding.
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Explain how the short circuit test on a transformer is to be conducted. What information do you get from the short circuit test data?
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A 30 kVA, 200/120V, 50 Hz transformer has a high voltage winding resistance of 0.1 ohm and a leakage reactance of 0.22 ohm. The low voltage winding resistance is 0.035 ohm and the leakage reactance is 0.012 ohm. Find the equivalent winding resistance, reactance and impedance referred to the low voltage side.
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Explain the principle of operation of DC generator.
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A 220V, DC shunt motor runs at 700 r.p.m when the armature current is 50 A. Calculate the speed if the torque is doubled. The armature resistance of the motor is 0.15Ω.
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Discuss the principle of operation of 3-Phase induction motor.
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Explain Measurement of power in three phase system using two-watt meter method.
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