This document contains 5 practice problems and their solutions related to analyzing electrical circuits with 3-phase power supplies. The problems involve calculating line currents, neutral currents, displacement voltages, power, power factor, and wattmeter readings for various star- and delta-connected resistive loads.

1. ELE101/102 Dept of E&E,MIT Manipal 1
Tutorial
1. A 400V, 3phase supply feeds an unbalanced four-wire star
connected load. The branch impedances of the load are ZC =
6∠00
Ω; ZB = 6∠300
Ω and ZA = 5∠450
Ω. Find the line
currents and the neutral current. Assume CBA system.
Ans:
IC = 38.5∠0°A
IB = 38.5∠-150°A;
IA =46.2∠-285°A
IN = 30.6∠56°A

2. ELE101/102 Dept of E&E,MIT Manipal 2
Tutorial
Ans:
104.8∠-120.35V
IR = 28.41∠-69°A
IY = 29.85∠136.54°A
IB =13∠27.60°A
2. A 400V, 3phase supply feeds an unbalanced three wire star
connected load. The branch impedances of the load are ZR =
(4+j8) Ω; ZY = (3+j4) Ω and ZB = (15+j20) Ω. Find the neutral
displacement voltage. Also find the line currents using (i)
Neutral displacement method. (ii) Mesh current analysis.
Assume RYB phase sequence.

3. ELE101/102 Dept of E&E,MIT Manipal 3
3. Three similar loads 20∠-450
Ω are connected in delta across a
balanced, 3 phase, 400 V ac supply. Determine (i) the line
currents (ii) active power (iii) apparent power (iv) power factor and
(v) the readings of the 2 wattmeters connected to measure the 3
phase power.
Tutorial
Ans:
34.64∠15°A, 34.64∠-105°A,34.64∠-225°A
16.97KW
24KW
0.707
3586 W and 13384 W

4. ELE101/102 Dept of E&E,MIT Manipal 4
4. Two wattmeters are connected to measure the power in a 3
phase circuit read 5 KW and 1 KW, the reading of second
wattmeter being obtained after reversing the potential coil of the
wattmeter. Calculate the power and power factor.
Ans:
4000 W
0.36
Tutorial

5. ELE101/102 Dept of E&E,MIT Manipal 5
5. Three loads ZR = 10∠00
Ω; ZY = 15∠-300
Ω and ZB = 20∠450
are
connected in star across a balanced, 3 phase, 400 V, RYB
supply. Determine the readings of the 2 wattmeters connected to
measure the 3 phase power, if the current coils of the wattmeters
are inserted in the lines R and Y.
Tutorial
Ans:
WR = 2907.2 W
WY = 7489.5 W

6. ELE101/102 Dept of E&E,MIT Manipal 5
5. Three loads ZR = 10∠00
Ω; ZY = 15∠-300
Ω and ZB = 20∠450
are
connected in star across a balanced, 3 phase, 400 V, RYB
supply. Determine the readings of the 2 wattmeters connected to
measure the 3 phase power, if the current coils of the wattmeters
are inserted in the lines R and Y.
Tutorial
Ans:
WR = 2907.2 W
WY = 7489.5 W