## UNIT-I

DC CIRCUITS

TWO MARKS QUESTIONS:

1. Define ohms law

2. Define Kirchhoff’s current law

3. Define Kirchhoff’s voltage law

4. State the the superposition theorem with example

5. Define votage and current

6. Define active and passive element with example

7. Define unilateral and bilateral element with example

8. Define voltage division rule with example

9. Define current division rule with example

10. Define voltage and current transformation techniques

ESSAY TYPE QUESTIONS (10M)

1. In the network shown below, find the current delivered by the battery.

2. Explain star to delta transformation (both) with formula.

3. Find the voltage across ‘A’ and ‘B’ in the below circuit

4. Obtain Norton’s equivalent circuit to the left of terminals a-b .Use the result to find current ‘i’.

5. Explain the Superposition theorem limitation.

6. State and explain Thevenin’s theorem.

7. State and explain Norton’s theorem.

8. State and prove Maximum power transfer theorem.

9. State and Prove Kirchhoff’s laws.

10. Explain the rms value, form factor and peak factor of alternating voltages.

## UNIT-II

Ac circuits

TWO MARKS QUESTIONS:

1. Define peak value and rms value?

2. Define real power and what their units?

3. Define power factor

4. Define reactive power and apparent power along with units?

5. Define resonance

6. Define resonant frequency

7. Define the expression for R-L circuit

8. Define the expression for R-L-C circuit

9. Define the expression for R-C circuit

10. What are the relations b/n phase and line voltages and currents in star connection?

ESSAY TYPE QUESTIONS:

1. Derive an expression for RL circuit?

2. Derive an expression for RC circuit?

3. Derive an expression for RLC circuit?

4. Derive an expression for series resonance?

5. Derive an expression for parallel resonance?

6. A 4 ohm resistance connected in series to a 10 mH inductance across a 100v, 50 HZ supply. Find

a) Impedance

b) Current

c) Drop across resistance and inductance

d) Power factor

e) Phase angle b/n v and I

f) Total power supplied

7. a non-inductive resistor of 8 ohm is connected in series with an inductive load across a 100V, 50 HZ A.C.supply.The voltage across resistor is 64 v and that across inductive load is 48V.Calculate

1. Impedance of the circuit.

2. Power factor of the circuit.

3. Power absorbed by the load

5. Power factor of the load

8.A coil of resistance 40 ohm and inductance 0.75 H forms part of series circuit for which the resonant frequency is 55 HZ. If the supply is 250V, 50 Hz, find

a. Line current

b. power factor of the total circuit and coil

C.voltage across the coil

9. A circuit of (6+i8) ohms is connected in parallel with another circuit of (6+i8) ohms. This is connected across a 220v, 50 Hz supply. Find i) total current ii) total power drawn by the circuit and also draw vector diagram

10. Explain the three-phase balanced circuits, along with voltage and current relations in star and delta connections

Unit-III

Transformers

1. What is all day efficiency?

2. What are the applications of auto transformers?

3. Why transformer rating is expressed in KVA?

4. Does transformer draw any current when secondary is open? Why?

5. Define voltage regulation of a transformer.

6. Write down the condition for maximum efficiency of a transformer. 7. Classify the transformer according to the construction.

8. What are the advantages of three phase transformer?

9. Write own the emf equation of a transformer

10. What are the limitations of a auto transformer?

ESSAY TYPE QUESTIONS:

1. a) Explain the working principle of operation of single-phase transformer.

b) Explain why transformer rating will be given in KVA but not in KW.

2. a) Derive the emf equation of a single-phase transformer.

b) A transformer with an output voltage of 4000V is supplied at 220V. If the secondary has2000 turns, calculate the no. of primary turns.

3. Explain the constructional details and types of single-phase transformers.

4. Draw the equivalent circuit parameters of a single-phase transformer.

5. a) Define efficiency and voltage regulation of a transformer. Show how the power factor affects both of them.

b) Draw the phasor diagram for R and L load.

6. a) Explain the various losses and derive the condition for maximum efficiency of a transformer.

b) The efficiency at unity power factor of 6600/384 V, 100 KVA, and 50 Hz single-phase transformer is 98% both at full-load and at half full-load. The power factor on no load is 0.2 and the full-load regulation at a lagging power factor of 0.8 is 4%. Draw the equivalent circuit referred to LV side and insert all the values.

7. a) Define regulation of transformer and also derive the condition for zero voltage regulation.

b) At 400V and 50 Hz the core loss of a transformer was found to be 2400W when the transformer is supplied at 200V, and 25 Hz, core loss is 800W. Calculate the hysteresis and eddy current losses at 400V 50Hz.

8. The maximum efficiency of 50 KVA transformer is 97.4% and occurs at 90% of the full-load. Calculate the efficiency of transformer at

(i). Full-load 0.8 power factor lagging

(ii). Half full-load 0.9 power factor.

9. Explain the working principle of auto-transformer with a neat diagram and mention its applications?

10. Explain the Three-phase transformer connections with a neat diagram?

UNIT-IV

SINGLE PHASE INDUCTION MOTORS

1. Define the principle of single phase induction motor

2. Write the emf equation of single phase induction motor

3. Define autotransformer

4. What are the applications of the autotransformers?

5. Draw the phasor diagram of single phase induction motor

6. Define split phase & capacitor motor?

7. Why is the power factor of a single-phase induction motor is low?

8. What is the centrifugal starting switch in a single phase induction motor?

9. What are the essentials to prefer single phase induction motor?

10. A single phase induction motor has an output torque of 0.25 nm and a speed of 100 rad/sec. If the input current is 0.6 a at 230v and 0.6 lagging pf find

i) Output power

ii) Efficiency

ESSAY TYPE QUESTIONS:

1. Explain the construction of induction motor?

2. Explain the working of induction motor with a neat diagram?

3. Explain the equivalent circuit of induction motor?

4. Explain the no-load and blocked rotor test of induction motor with necessary equations?

5. Explain starting methods of induction motors?

6. How the speed control induction motor can be done? Explain?

7. Prove the resultant magnetic field is equal to 1.5m?

8. Explain the torque speed characteristics of single phase induction motor with a neat diagram?

9. Explain split-phase & capacitor type induction motors

10. Explain repulsion& shaded pole induction motors with a neat diagram?

UNIT-V

THREE PHASE INDUCTION MOTORS

Two marks questions

1. What are the types of three phase induction motor?

2. What is the principle of operation of three Phase Induction Motor?

3. What is slip & Percentage Slip?

4. List out the differences between Squirrel Cage & Slip Ring Induction Motors?

5. What are the Speed controls Methods of 3phase Induction Motor?

6. What are the types of starters?

7. Draw the torque speed characteristics of 3-phase induction motor?

8. Write the torque equation for 3-phase induction motor?

9. What are the losses in induction motor?

10. What are different parts of a 3 phase induction motor?

Essay questions:

1. Explain how rotating magnetic field produced in 3-phase induction motor.

2. a) Derive torque equation of 3-phase induction motor under running condition.

b) Derive condition for maximum torque under running condition

3. a)The stator of a 3-phase,4 pole induction motor is connected to a 50 HZ supply. The rotor runs 5M at 1455 r.p.m at full load. Determine

i) Synchronous speed

ii) Slip at full Load speed

b) Derive condition for maximum torque under running condition.

4. a) Explain the constructional details of 3phase induction motor.

b) If three phase induction motor with 6-poles runs at 970 r.p.m when connected to a 50HZ supply

Calculate i) percentage slip

ii) Frequency of rotor currents

5. a) Explain the torque slip characteristics of 3-phase induction motor.

b) A 3-phase induction motor is wound for 4 poles and is supplied from 50 Hz system.

Calculate: (i) the synchronous speed.

(ii) The speed of the motor when slip is 4% and

(iii) The rotor current frequency when the motor runs at 600 r.p.m.

6. Explain the difference between slip ring and squirrel cage induction motor.

7.    a) Explain the principle of operation of 3-phase induction motor

b) A 3-phase 50HZ, 4 pole induction motor has a slip of 4% calculate

a) Speed of the motor

b) Frequency of rotor emf

8. a) Derive the expression for the rotor e.m.f and rotor current of an induction motor

b) A 5 h.p,230V,50 HZ induction motor has a rated full load speed of 950 r.p.m.The induced voltage per phase of rotor at stand still is 100V.calculate,i)number of poles and % full load speed ii)rotor induced voltage and its frequency at full load.

9. a) Explain why the rotor of 3-phase induction motor can never attain synchronous speed

b) Explain the terms slip, slip speed, rotor frequency, rotor emf

10. Explain the equivalent circuit of three phase induction motor with a neat diagram?