Question 1

**PART-A**

Accepted Answer

In a 3-phase delta connected system, the Line Voltage equals Phase Voltage, whereas the Line Current is √3 times the Phase Current.

Question 2

Q.2. Define Apparent power and Power factor.

Accepted Answer

Apparent power is the total power supplied to a circuit, measured in VA. Power factor is the ratio of true (active) power to this apparent power.

Question 3

Q.3. Why transformers are rated in kVA?

Accepted Answer

Transformers are rated in kVA instead of kW because their primary losses depend strictly on voltage and current, independent of the load's power factor.

Question 4

Q.4. Give the emf equation of a transformer and define each term.

Accepted Answer

The EMF equation of a transformer is E = 4.44 f Φm N, relating induced voltage to frequency, flux, and turns.

Question 5

Q.5. An 1100/400 V, 50 Hz single phase transformer has 100 turns on the secon…

Accepted Answer

Using the transformer turns ratio formula (V1/V2 = N1/N2), the number of turns on the primary winding is calculated to be 275.

Question 6

Q.6. Write down the expression of equivalent resistance for 'n'-number of res…

Accepted Answer

The reciprocal of the equivalent resistance for 'n' resistors in parallel is the sum of the reciprocals of the individual resistances.

Question 7

Q.7. Write the algorithm for Nodal Analysis.

Accepted Answer

Nodal analysis is a systematic application of Kirchhoff's Current Law (KCL) to determine the voltage at every node relative to a reference node.

Question 8

Q.8. Distinguish between induction motor and synchronous motor.

Accepted Answer

Induction motors operate asynchronously relying on induced rotor currents, whereas synchronous motors operate strictly at synchronous speed utilizing DC rotor excitation.

Question 9

Q.9. Draw the V-I characteristics of an ideal diode.

Accepted Answer

An ideal diode acts as a perfect conductor in forward bias and a perfect insulator in reverse bias.

Question 10

Q.10. Give some method available for measuring 3-phase power.

Accepted Answer

Common methods for measuring 3-phase power include the single-wattmeter, two-wattmeter, and three-wattmeter methods.

Question 11

**PART-B**

Accepted Answer

For the given sinusoidal voltage equation V = 230 sin(314t), the Frequency is 50 Hz, Maximum Value is 230 V, Average Value is 146.4 V, and RMS Value is 162.6 V.

Question 12

Q.2. State Thevenin's theorem and give a proof. Apply this theorem to calcula…

Accepted Answer

Thevenin's Theorem simplifies complex linear circuits into a single voltage source in series with a resistance to calculate load currents easily.

Question 13

Q.3. Determine the power factor of a RLC series circuit with R = 5 Ω, XL = 8 …

Accepted Answer

By calculating the total impedance of the RLC series circuit, the power factor is determined to be 0.78 lagging.

Question 14

Q.4. With a neat diagram explain the working of a PN junction diode in forwar…

Accepted Answer

A PN junction diode conducts current exponentially in forward bias due to barrier depletion and blocks current in reverse bias. Temperature heavily influences its characteristics.

Question 15

Q.5. List out the characteristics of DC motor.

Accepted Answer

DC motors are characterized by their Torque vs. Armature Current, Speed vs. Armature Current, and Speed vs. Torque relationships.

Question 16

Q.6. Derive an expression for conversion of a resistive network from star to …

Accepted Answer

A Star network can be transformed into an electrically equivalent Delta network where each Delta resistor equals the sum of two Star resistors plus their product over the third.

Question 17

Q.7. What is working of BJT? Draw its equivalent circuit.

Accepted Answer

A BJT works by injecting charge carriers from the emitter to the base, where a small base current controls a massive collector current flow.

Question 18

**PART-C**

Accepted Answer

A Synchronous Generator (Alternator) consists of a stationary stator armature and a rotating DC-excited rotor. It operates on Faraday's law to induce 3-phase AC power at a strict synchronous speed.

Question 19

Q.2. In a series circuit containing pure resistance and a pure inductance, th…

Accepted Answer

For the given Series RL Circuit, Impedance is 3 Ω, Resistance is 2.598 Ω, Inductance is 4.77 mH, Average Power is 32.47 W, and Power Factor is 0.866 lagging.

Question 20

Q.3. What is a SCR? Sketch V-I characteristics of Thyristor. Label the variou…

Accepted Answer

A Silicon Controlled Rectifier (SCR) is a robust, four-layer semiconductor power switch capable of handling high voltages and currents, operating in three distinct distinct modes.

Question 21

Q.4. Explain Superposition theorem. Use the superposition theorem to find 'I'…

Accepted Answer

Superposition theorem dictates that in a linear network with multiple power sources, the total current in any branch is the algebraic sum of the currents produced by each source acting independently.

Question 22

Q.5. Write short notes on the following: (i) ELCB (ii) SFU

Accepted Answer

ELCBs detect life-threatening earth leakages to prevent electric shocks, while SFUs combine heavy-duty switching with fuses for robust short-circuit protection.

Basic Electrical Engineering