The document is a study guide containing questions and problems related to electrical engineering topics like single-phase and three-phase AC circuits. Some key points covered include: - The advantages of three-phase systems over single-phase, such as using less material for the same power output. - Calculating values like impedance, current, power, and power factor in RLC circuits connected to AC power sources. - Analyzing phasor diagrams for series RLC circuits. - Determining line and phase voltages and currents in wye-delta and delta-wye connected three-phase systems.

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BANGLADESH UNIVERSITY OF TEXTILES
TEJGAON, DHAKA-1208
B.Sc. in Textile Engineering
Electrical and Electronic Engineering
EEE-4
 Single Phase AC circuit
 Three Phase Circuit
Date: 26/02/2017

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Question
1.4) What are the advantages of 3-Φ system compared to 1- Φ system? List the possible connection of three
phase system. Show that the algebraic summation of phase voltages of three phase system will be zero.
Draw the phasor diagram relationship between the line voltage and phase voltages of the 3-Φ system.
2.4) Why the delta connected load is more desirable than the wye connected load? Why Y-connected source is
more preferable?
3.4) Prove that the three phase system uses only 75% of the material used in the equivalent single phase
system.
4.4) Show that the instantaneous power supplied by the balanced three phase system is constant. How the
balanced three phase power can be measured by two wattmeter method?
5.4) Why a textile engineer should study electrical and electronic engineering? Or Write down the
significance of electrical engineering and its applications in textile fields.

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Problem
6.4) The potential difference measured across a coil is 4.5 V, when it carries a direct current of 9 A. The
same coil when carries an alternating current of 9 A at 25 Hz, the potential difference is 24 V. Find the
current, the power and the power factor when it is supplied by 50 V, 50Hz supply.
Solution:
7.4) Two impedances consist of (resistance of 15 ohms and series-connected inductance of 0.04 H) and
(resistance of 10 ohms, inductance of 0.1 H and a capacitance of 100 μF, all in series) are connectd in
series and are connected to a 230 V, 50 Hz a.c. source. Find : (i) Current drawn, (ii) Voltage across each
impedance, (iii) Individual and total power factor. Draw the phasor diagram.
Solution:

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8.4) A tungsten filament bulb rated at 500-W, 100-V is to be connected to series with a capacitance across
200V, 50Hz supply. Calculate : (a) the value of capacitor such that the voltage and power consumed by
the bulb are according to the rating of the bulb. (b) the power factor of the current drawn from the
supply. (c) draw the phasor diagram of the circuit.
Solution:
9.4) A pure resistance of 50 ohms is in series with a pure capacitance of 100 microfarads. The series
combination is connected across 100-V, 50-Hz supply. Find (a) the impedance (b) current (c) power
factor (d) phase angle (e) voltage across resistor (f) voltage across capacitor. Draw the vector diagram.
Solution:

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10.4) A 240-V, 50-Hz series R-C circuit takes an r.m.s. current of 20 A. The maximum value of the current
occurs 1/900 second before the maximum value of the voltage. Calculate (i) the power factor (ii) average
power (iii) the parameters of the circuit.
Solution:
11.4) A resistance of 20 Ω, an inductance of 0.2 H and a capacitance of 100 μF are connected in series
across 220-V, 50-Hz mains. Determine the following (a) impedance (b) current (c) voltage across R, L
and C (d) power in watts and VA (e) p.f. and angle of lag.
Solution:
12.4) A resistance of 20ohm, inductance of 0.2H and capacitance of 150μF are connected in series and are
fed by a 230V, 50Hz supply. Find XL, XC, Z, Y, p.f., active power and reactive power.
Solution:

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13.4) A two-element series circuit consumes 700W and has a p.f.=0.707 leading. If applied voltage is
v=141.1sin (314t+30°
), find the circuit constants.
Solution:
14.4) A voltage e(t)=100sin314t is applied to series circuit consisting of 10ohm resistance, 0.0318henry
inductance and a capacitor of 63.6μF. Calculate (i) expression for i(t) (ii) phase angle between voltage
and current (iii) power factor (iv) active power consumed.
Solution:
15.4) A resistance R, an inductance L=0.01H and a capacitance C are connected in series. When a voltage
v=400cos(300t−10°
) volts is applied to the series combination, the current flowing is 10√2cos( 3000 t-55°
)
amperes. Find R and C.
Solution:

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16.4) Determine the phase sequence of the set of voltages
van = 200 Cos(ωt + 10◦
)
vbn = 200 Cos(ωt − 230◦
)
vcn = 200 Cos(ωt − 110◦
)
Solution:
17.4) Given that Vbn=110∠30◦
, find Van and Vcn, assuming a positive (abc) sequence.
Solution:

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18.4) Calculate the line currents in the three-wire Y-Y system of Fig. 12.13.
Fig.12.13
Solution:
Fig.12.12

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19.4) A balanced abc-sequence Y-connected source with Van= 100∠100
V is connected to a Δ-connected
balanced load (8+j4)Ω per phase. Calculate the phase and line currents.
Solution:
This can be solved in two ways.

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20.4) One line voltage of a balanced Y-connected source is VAB =120∠-20◦
V. If the source is connected to a
Δ-connected load of 20∠40◦
Ω, find the phase and line currents. Assume the abc sequence.
Solution: