DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING
EE18B ELECTRICAL ENGINEERING TECHNOLOGY
TUTORIAL SHEET
The current through an inductor with inductance L = 10 - 3 henry is given as:
1.
iL (t) = 0.1 sin 10 6 t.
Find the voltage VL (t) across this inductor.
2. Given two circuits (see figure) in parallel, one branch consisting of a
resistance of 15 ohms and the other of an inductive reactance of 10 ohms.
When the impressed voltage is 110, find the
(a)
Current through the ohmic resistance.
(b)
Current through the inductive reactance.
(c)
Line current.
(d)
Power factor.
(e)
Angle of lag of the line current.
Resistance and inductance in parallel
3. A series circuit consists of a 30-microfarad capacitance and a resistance of
50 ohms connected across a 110-volt, 60-hertz supply.
Calculate the
(a)
Impedance of the circuit.
(b)
Current in the circuit.
(c)
Voltage drop across the resistance.
(d)
Voltage drop across the capacitance.
(e)
Angle between the voltage and the current.
(f)
Power loss.
(g)
Power factor of the circuit.
4.
(i)
Figure (a) shows a circuit containing a resistance of 20 ohms, an
inductance of 0.10 henry, and a 100-ìf capacitor all connected in
series, the applied voltage is 240 volts at 60 cycles. It is desired to
find
(a)
the circuit impedance;
(b)
the current flow;
(c)
the voltage across each part;
(d)
the power factor;
(e)
the voltage-amperes; and
(f)
the power.
(ii)
Find the total impedance of two coils and a capacitor in series. Coil
1 has a resistance of 15 ohms and an inductive reactance of 35
ohms. Coil 2 has a resistance of 20 ohms and an inductive reactance
of 45 ohms. The capacitor has a capacitive reactance of 60 ohms and
has negligible resistance.
5. A voltage of 104 + j60 volts is applied to a circuit consisting of 2 parallel
branches. One branch contains 6 ohms resistance, 10 ohms inductive reactance,
and 5 ohms capacitive reactance. The second branch contains 8 ohms resistance
and 3 ohms capacitive reactance. Using phasors, determine the branch currents,
the line current, the equivalent impedance, the power input to each branch, and
the total power input.
6. Find the Thevenin equivalent circuit for the network shown in fig. 6.
55.8   17.4 °
Ans.
7. Obtain the Thevenin equivalent for the bridge circuit shown in fig. 7.
8. Compute the full -load coil currents for both delta and wye connected,
three -phase alternators with a rating of 25 kva at 480 volts.
Ans. 30.1A ; 17.35A
9. A three -phase, three -wire, 100 volt, ABC system supplies a balanced
delta -connected load with impedances of 20 45 ° ohms. Determine the
line currents and draw the phasor diagram.
Ans. IAB = 5.0 75 °
10. Three identical impedances of 12 30 °ohms in a delta connection and
three identical impedances of 5 45 °ohms in a wye connection are on the
same three -phase, three -wire, 208 volt, ABC system. Find the line
currents and the total power.
Ans. 53.6   36.6 °
15.5kW