BE-II - Baral



Electrical Engineering I

Tutorial 4

1. A circuit consists of resistance R, and capacitive reactance of 60Ω connected in series. Determine the value of R for which p.f. of the circuit is 0.8.

2. A circuit consisting of a variable resistor in series with a capacitance of 80µF is connected across 120V, 50 Hz supply. Calculate the value of resistance so that the power absorbed is 100W.

3. A pure inductive coil is connected with a 10Ω resistor to a 50 Hz ac supply. The voltage across the resistor, and inductor were found to be 30 and 40 V respectively. Find the value of inductive reactance of coil and the supply voltage.

4. An alternating voltage of (160+j120) V is applied to a circuit, and the current in the circuit is given by (6+j8). Find :

a. The values of elements of the circuit;

b. The power factor

c. Power consumed

5. An alternating voltage of (80+j60) V is applied to a circuit , and the current in the circuit is given by (-4+j10).Find

a. The impedance of the circuit

b. Power consumed

c. Phase angle

d. Apparent power.

6. An inductive coil when connected across a 200V, 50 Hz supply, draws a current of 6.25 A, and a power of 1000W.Another coil, connected across the same power supply draws a current of 10.75 A and power of 1155W. Find the current drawn and the active power, when connected in series across the same supply.

7. A 100Ω resistor is connected in series with a choke coil. When a 220 V, 50 Hz, supply is applied, the voltage across the resistor and choke coil are 200V and 300V respectively. Find the power consumed by choke coil.

8. A voltage of 200V is applied to a series circuit consisting of a resistor, an inductor and a capacitor. The respective voltages across the components are 170V, 150V and 100V and the current is 4A. Determine the power factor of the circuit.

9. Find the active and reactive component of current taken by a series circuit consisting of a coil of inductance 0.1H, and resistance 8Ω and a capacitor of 120µF, connected to a 220V, 50Hz supply.

10. A coil of resistance 20Ω and inductance 100mH is connected in series with a capacitance of 40µF across 100V, 50Hz supply. Calculate

a. Magnitude of current

b. Power factor

c. Voltage across each elements

11. A current of 10A flows in a series circuit consisting of R = 10Ω, L = 0.1H and C = 100µF .Find the power and impedance if frequency of supply is 50Hz.

12. A series circuit consisting of R = 100Ω, L = 0.12H and C = 1µF is fed from a 100V, 50Hz supply. Find the current, active power, impedance rms values of voltage across resistance, inductance and capacitance.

13. A coil of resistance 5Ω and inductance 10mH is connected in series with a condenser of 100µF across a 230V, 50Hz supply. Find

a. Total power consumed

b. Power factor

c. Resonance frequency

d. Current at resonance

14. A series RLC circuit has L = 50µH, C = 2µF and R = 50Ω. Calculate

a. Q-factor of circuit

b. The new value of C required for resonance at same frequency, if the inductance is doubled and

c. New Q-factor.

15. An inductive circuit of resistance 2Ω and inductance 0.01H s connected to a 250V, 50Hz supply. What value of capacitance to be placed in parallel with inductive circuit will produce resonance? Also find the current taken from supply at resonance.

16. Two circuits, having the same numerical ohmic impedance are joined in parallel. The power factor of one circuit is 0.8 and the other 0.6, both lagging. Calculate the power factor of combination.

17. A resistor of 10Ω and an inductance of 0.02H are connected in series across a 50Hz supply. What value of resistance and inductance are connected in parallel will have resultant impedance and p.f. as series arrangement? Find the current in each case when voltage is 200V.

18. Two circuits having impedances (12+j15) Ω and (8-j4) Ω are connected in parallel. If the potential difference across impedances is (230+j0)V, calculate

a. Total current and branch currents

b. Total power and power of each branch

c. Total power factor and power factor of each branch

19. Two circuits A and B are connected in parallel across a 200V, 50Hz mains. Circuit A consists of a resistance of 10Ω and an inductor of 0.12H connected in series. Circuit B consists of a resistance of 20Ω and a capacitor of 40µF connected in series. Calculate

a. current in each branch

b. total current

c. power factor.

20. An inductance of 0.5H and 90Ω resistance is connected in parallel with a 20µF capacitor. Find

a. Total rms current

b. P.f. of circuit

c. Total power taken from source.

A voltage of 230V, 50 Hz is supplied across the circuit.

21. Two circuits having impedances (14+j5) Ω and (18+j10) Ω are connected in parallel. If the potential difference across impedances is (220+j0)V, 50 Hz supply. Calculate

a. Total current and p.f.

b. The capacitance which when connected in parallel with original circuit will make resultant p.f. unity.

22. Impedance (150-j157) Ω and (100-j110) Ω are connected in parallel across 200v, 50Hz supply. Find

a. branch currents and total current

b. total power

23. Two circuits A and B are connected in parallel across a 220V, 50Hz mains. Circuit A consists of a resistance of 7Ω and an inductor of 0.0125H connected in series. Circuit B consists of a resistance of 8Ω and a capacitor of 1000µF connected in series. Calculate

a. current in each branch

b. total current

24. A circuit consists of the following in parallel : a resistor of 5800Ω, an inductance of 2H and a capacitor of 10µF.

In this circuit, a 200V, 50Hz supply is applied. Calculate

a. Total current drawn from supply

b. Complex power

c. Active power

d. reactive power

25. Each phase of a star-connected load consists of a resistance of 100Ω in parallel with a capacitance of 32µF. Calculate the line current, power absorbed, total kVA, and the power factor, when connected to a 415V, 50Hz, 3-phase supply.

26. A balanced 3-phase, star-connected load of 100kW takes a leading current of 80A, when connected across1100V, 50Hz supply. Find resistance impedance and capacitance of the load per phase. Also calculate the p.f. of the load.

27. When the balanced impedance are connected to a delta across a 3-phase, 500V, 50Hz supply, the line current drawn from supply 20A at p.f. of 0.3 lagging. Calculate the resistance and inductance per phase.

28. A star connected 50Hz source supplies W watts to a balanced load of (3+j4)Ω. Find the power supplied from source when the same load is connected to delta.

29. A balanced delta-connected load consumes 2 kW of power, when connected to 40V, 50Hz 3-phase supply, and draws a current of 2A at a lagging p.f., when connected to 230 V, 3-phase supply. Determine

a. Resistance and inductance per phase

b. Load p.f.

c. Power consumed, when load connection changed to star and supply voltage 400V.

30. Two watt meters connected to measure the input to a balanced 3-phase circuit indicate 2500W and -500W respectively. Find the total power supplied and p.f. of the circuit.

31. Two watt meters connected to measure the input to balanced 3-phase circuit indicate 2500W rand 500W respectively. Find the p.f. of circuit:

a. When both readings are positive

b. When latter reading is obtained after reversing the connections to current coil

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