Problems on AC and DC distribution

1. DC and AC Distribution
1. A 2 wire dc distributor AB is 300m long. It is fed from point A. the various loads and their
positions are given below:
At point Distance from point A in metres Concentrated load in Amp.
C 40 30
D 100 40
E 150 100
F 250 50
If the maximum permissible voltage drop is not to exceed 10V, find the cross-sectional area of the
distributor. Take ρ = 1.78x10-8Ωm.
[ 1.164cm2 ]
2. Two tram cars (A & B) 2 km away from a sub- station return 40A and 20 A respectively to the
rails. The sub- station voltage is 600V dc. The resistance of trolley wire is 0.25Ω/km and that of
track is 0.03Ω/km. calculate the voltage across each tram car. [Va = 566.4V, Vb = 544V].
3. The load distribution on a 2 wire dc distributor is shown in the figure below:
The cross-sectional area of each conductor is 0.27cm2. the end A is supplied at 250V. Resistivity
of the wire is 1.78µΩcm. calculate (i) the current in each section of the conductor (ii) the 2 core
resistance of each section (iii) the voltage at each tapping point. [20A,35A,47A; 0.099,
0.132,0.066Ω; 245.35, 240.73,239.41V]
4. A 2 wire dc distributor AB is fed from both ends. At feeding point A, the voltage is maintained as
at 230V and at B 235V. the total length of the distributor is 200m and loads are tapped of as
under:
25A at 50m from A : 50A at 75m from A : 30A at 100m from A : 40A at 150m from A

2. The resistance per km of one conductor is 0.3Ω. Calculate :
(i) currents in various section of the distributor
(ii) minimum voltage and the point at which it occurs
[ 33.34A, 8.34A, 41.66A, 71.66A, 111.66A ; 228.875V]
5. A 2 wire dc distributor AB, 600m long is loaded as under:
Distance from 150 300 350 450
A(m)
Loads in Amp 100 200 250 300
The feeding point A is maintained at 440V and that at B at 430V. if each conductor has a
resistance of 0.01 Ω per 100m, calculate:
(1)The currents supplied from A to B, (2) the power dissipated in the distributor
[437.5A, 412.5A,; 14.705KW]
6. An electric train runs between 2 sub-stations 6 km apart maintained at voltages 600V and 590V
respectively and draws a constant current of 300A while in motion. The track resistance of go
and return path is 0.04 Ω/km. calculate :
(i) The point along the track where minimum potential occurs
(ii) The current supplied by the two sub-stations when the train is at the point of minimum
potential [3.425km, 170.45A, 129.55A]
7. A 2 wire dc ring distributor is 300m long and is fed at 240V at point A. At point B, 150m from A,
a load of 120A is taken and at C, 100m in the opposite direction, a load of 80A is taken. If the
resistance per 100m of single conductor is 0.03 Ω, find
(i)current in each section of distributor
(ii)voltage at point B and C [86.67A, 33.33A, 113.33A; 232.2V, 233.2V]
8. A 2 wire dc distributor ABCDEA in the form of a ring main is fed at point A at 220 V and is loaded
as under:
10A at B ; 20A at C; 30A at D and 10A at E
The resistances of various sections (go and return) are: AB = 0.1 Ω; BC = 0.05 Ω; CD = 0.01 Ω ; DE
= 0.025 Ω ; EA = 0.075 Ω. Determine:
(i)the point of minimum potential

3. (ii)current in each section of the distributor
[C is at minimum potential, ; 29.04A, 19.04A, 0.96A, 30.96A, 40.96A]
9. A dc ring main distributor ABCDEA is fed from point A from a 250V supply and the
resistances(including both lead and return) of various sections are as follows: AB = 0.02 Ω; BC =
0.018 Ω ; CD = 0.025 Ω ; DA = 0.02 Ω. The main supplies loads of 150A at B; 300A at C and 250A
at D. determine the voltage at each load point.
If the points A and C are linked through an interconnector of resistance 0.02 Ω, determine the
new voltage at each load point.
[243.265V,239.904V, 242.735V; 245.93V, 244.97V, 245.1V]
10. A single phase distributor 2km long supplies a load of 120A at 0.8p.f. lagging at its far end and a
load of 80A at 0.9p.f. lagging at its mid-point. Both power factors arereferred to the voltage at
the far end. The resistance and reactance per km (go and return) are 0.05 Ω and 0.1 Ω
respectively. If the voltage at the far end is maintained at 230V, calculate :
(i) Voltage at the sending end
(ii) Phase angle between voltages at the two ends.
[261.67V ; 3.82°]
11. A single phase AC distributor 1 km long has resistance and reactance per conductor of 0.1 Ω and
0.15 Ω respectively. At the far end, the voltage VB = 200V and the current is 100A at a p.f. of 0.8
lagging. At the mid-point M of the distributor, a current of 100A is tapped at a pf of 0.6 lagging
with reference to the voltage VM at the mid-point. Calculate:
(i)Voltage at mid-point
(ii)Sending end voltage VA
(iii)Phase angle between VA and VB [217.1V, 252.32V, 3.07°]