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FACULTY OF ENGINEERING
LAB SHEET
EET2026
POWER TRANSMISSION AND DISTRIBUTION
TRIMESTER 2
PTD1- Performance of Transmission Line under Different Loading Conditions
PTD2- Parameters which affect Real and Reactive Power Flow
*Note: On-the-spot evaluation may be carried out during or at the end of the experiment.
Students are advised to read through this lab sheet before doing experiment. Your
performance, teamwork effort, and learning attitude will count towards the marks.
EET 2026 Transmission and Distribution
Instruction
1. Before coming to the laboratory, read the lab sheet carefully and understand the
procedure of performing the experiments.
2. Do not switch-on the power supply unless permitted by the lab supervisor.
3. Do not make or break any connection with the power supply on.
4. Handle the equipments with care.
5. Do the necessary calculation, draw the graphs and submit the report within the specified time of the
lab session.
Experiment # 1
Performance of Transmission Line under Different
Loading Conditions
Objectives



To calculate the voltage regulation of the given transmission line under resistive,
inductive and capacitive loading conditions.
To analyze the reason for the voltage drop across the transmission line when the sendingend and receiving-end voltages have the same magnitude.
To investigate the effectiveness of the shunt capacitors to improve the power transfer
capability of the line.
Introduction
A short transmission line is modeled by a single reactance as shown in Fig. 1. A good
understanding of the behaviour of most of the transmission lines can be obtained by the short
line model. It is this model which will be used in this experiment.
Depending upon the loading condition the phase angle difference between the sending-end
and receiving-end voltages and the voltage drop along the line will vary. These effects can be
easily understood from the phasor diagram shown in Fig. 1. It may also be observed that a
significant voltage drop will exist across the line even when the sending -end voltage, E1 and
the receiving-end voltage, E2 are equal in magnitude.
(a)
(b)
I
E1
XL
E1
IX L
E2
E2
I
Fig. 1 (a) Transmission line (b) Phasor diagram
We have studied that the voltage drop along the transmission line and the receiving-end
voltage vary widely for inductive loads. In order to regulate the voltage at the receiving-end
of the line in some way so as to keep it at as constant as possible we should adopt some type
of compensation. One method commonly used is to connect shunt capacitors at the end of the
line. These capacitors produce a significant voltage rise thus compensating for the voltage
drop. Static capacitors are switched in and out in a practical system and their value is adjusted
depending on the loads. For purely inductive loads, the capacitor should deliver reactive
power equal to that consumed by the inductive load. For resistive loads, the reactive power,
which the capacitor must supply to regulate the voltage, is not easy to calculate. In this
experiment, we shall determine the reactive power (the value of capacitor) by trial and error,
adjusting the capacitors until the receiving-end voltage is approximately equal to the sendingend voltage. For loads, which draw both real and reactive power, the same trial and error
method is adopted.
Note that for a short transmission line having a line reactance of X /phase and resistance
neglected. The following formulas will be useful.
Sending-end voltage (L-L) = E11; Receiving end voltage (L-L) = E22
Three-phase sending-end power = Three-phase receiving end Power
E E Sin (1   2 )
= P1 = P2 = 1 2
X
2
E
E E Cos(1   2 )
Three-phase sending-end reactive power = Q1 = 1 - 1 2
X
X
2
E E Cos(1   2 ) E 2
Three-phase receiving-end reactive power = Q2 = 1 2
X
X
Apparent power at sending end = S1 
Apparent power at receiving end = S 2
P  Q ;
 P  Q ;
2
1
2
1
2
2
2
2
Equipment required
Three-phase transmission line (8329)
Resistive load (8311)
Inductive load (8321)
Capacitive load (8331)
AC voltmeter (8426)
Phase meter (8451)
Three-phase wattmeter/varmeter (8446)
Power supply (8821)
Connection leads (9128)
Procedure
1. Set the impedance of the transmission line to 200  and connect the meters as shown in
Fig. 2. The circuit should be connected to the three-phase variable supply. Note that
watt/var meters and phase meter need 24V AC supply provided in the power supply unit.
Connect all the loads in star. Verify your connections with the lab supervisor before
switching on the power supply.
0-500V
E2
0-500V
E1
4
1
5
2
3
6
P1
1
5
2
3
6
8821
0-415V
Q1
4
8446
8329
4
P2
Q2
5
6
8446
3-phase
Yconnected
LOAD
8311
8321
8331
Fig. 2 Connection diagram for steps 2, 3 and 4
2. Adjust the sending-end voltage E1 to 300 V and keep it constant for the reminder part of
the experiment. Use a three-phase resistive load and increase the load in steps making
sure that the loads are balanced. Take readings of sending end and receiving end voltages
and powers, E1, Q1, P1, E2, Q2, and P2. Record your results in Table 1.
3. Switch off the power supply and connect a three-phase balanced inductive load in parallel
with the balanced resistive load. Don’t remove any other connections shown in Fig.2.
Increase the load in steps making sure that the loads are balanced. Take readings of
sending end and receiving end voltages and powers, E1, Q1, P1, E2, Q2, and P2. Record
your results in Table 2.
4. Switch off the power supply, remove the inductive load and connect a three-phase
balanced capacitive load in parallel with the balanced resistive load. Take readings of
sending end and receiving end voltages and powers,E1, Q1, P1, E2, Q2, and P2 for different
loadings. Record your results in Table 3.
5. Draw three graphs of receiving end voltage, E2 (obtained from steps 2, 3, and 4) on the
same graph paper as a function of the receiving-end power P2 and discuss your results.
6. Switch off the power supply and connect a phase meter to measure the phase angle
difference between E1 and E2 and a voltmeter to measure the voltage across the
transmission line as shown in Fig. 3. Note that the load consists of resistances in parallel
with capacitances. Now for each resistive load, adjust the capacitive load so that the load
voltage E2 is as close as possible to 300 V. Take readings of XC, E1, P1, Q1, E2, P2, Q2, and
the phase angle for different loadings. Record your results in Table 4.
7. Draw the graphs of E2 and the phase angle difference between E1 and E2 as a function of
P2 from the results in Table 4. Note that the addition of static capacitors has yielded a
much more constant voltage, and further more, the power P2 which can be delivered has
increased. On this curve, indicate the phase angle between E2 and E1 as well as the
reactive power Q2 used for individual resistive load settings.
8. In this part of the experiment, we shall observe a significant voltage drop along the
transmission line even when the voltages E1 and E2 are equal in magnitude. This voltage
drop is due to the phase angle difference between the two voltages. Switch off the supply
and insert an ammeter in series with the transmission line as shown in Fig. 3 to measure
the line current without removing any other connection. Using the circuit shown in Fig. 3,
set the load resistance per phase at 686  and E1 = 300 V, adjust the capacitive reactance
until the load voltage is as close as possible to 300 V. Measure and record E1, Q1, P1, E2,
Q2, P2, E3, the line current I and the phase angle.
8451
0-500V
1
2
3
4
E2
0-500V
E1
686
8329
4
1
5
6
2
3
4
1
5
6
2
3
4
686
P1
Q1
P2
Q2
5
6
A
8821
686
8446
0-415V
8446
E3
3-phase
8311
8331
0-250V
Fig.3 Connection diagram for Steps 6 – 8
9. Using the results of step 8, draw the phasor diagram of per phase values of E 1 and E2 to
scale and draw E3. From the diagram compute E3 and compare it with the measured
value. Also compute the real power, reactive power and apparent power consumed by the
line. From the apparent power compute the line current and compare it with the measured
value.
Observations
Table 1: Results of procedure step 2
R


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
P2
W
Q2
Var
Table 2 Results of procedure step 3
R


4800
2400
1600
1200
960
800
686
Xl


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
P2
W
Q2
var
P2
W
Q2
var
Table 3 Results of procedure step 4
R


4800
2400
1600
1200
960
800
686
Xc


4800
2400
1600
1200
960
800
686
E1
V
P1
W
Q1
var
E2
V
Table 4 Results of procedure step 6
R


4800
2400
1600
1200
960
800
686
Xc

E1
V
P1
W
Q1
var
E2
V
P2
W
Q2
var
Angle
degree
Results of procedure step 8
E1=
E2=
P1=
P2 =
Q1=
Q2=
E3=
Phase angle =
Sample calculation
Line current, I =
This sample calculation is to help you to answer Exercise 3.
Let
E1 = 350 V
E2 = 350 V
E3 = 165 V
P1 = 600 W
P2 = 510 W
Q1 = 170 var
Q2 = -280 var
Phase angle = 48o and Line current, I = 0.95
E1 per phase = 350/3 = 202 V
E2 per phase = 350/3 = 202 V
E3 = 165 V
P1 per phase = 600/3 = 200 W
P2 per phase = 510/3 = 170 W
Q1 per phase = 170/3 = 56.7 var
Q2 per phase = -280/3 = 93.3 var
The phasor diagram of voltages to scale is shown in Fig.4.
E1
-48o
E3=165
E2
Fig. 4 Phasor diagram
From the figure E3 = 165 V which is the same as the measured value. [The voltage E3 may
also be calculated using the formula, E3 = 2*E1*sin(24o)]
Real power consumed = 200 –170 = 30 W
Reactive power consumed = 56.7 –(-93.3) = 150 var
Apparent power in the line = 1502  302  153 VA
Current through the line = 153/165 = 0.93 A
The difference between the calculated value and the measured value is 0.02 A.
Exercise
1. Discuss your results based on the graphs you have drawn in steps 5 and 7. From the
graphs plotted calculate the voltage regulations for load powers of 60W, 70W and 80W
respectively under different loading conditions (resistive, resistive-inductive and
resistive-capacitive) and compare the results.
2. Discuss your results obtained in step 9.
3. A three-phase transmission line has reactance of 100  per phase. The sending-end
voltage is 100 kV and the receiving-end voltage is also regulated to be 100 kV by placing
a bank of static capacitors in parallel with the receiving-end load of 50 MW. Calculate
(a) the reactive power supplied by the capacitor bank
(b) the reactive power supplied by the sending-end side
(c) the voltage drop in the line per phase
(d) the phase angle between the sending-end and receiving-end voltages and
(e) the apparent power supplied by the sending-end side.
4. If the 50 MW load in Exercise 3 is suddenly disconnected evaluate the receiving-end
voltage which would appear across the capacitor bank. What precaution, if any, must be
taken?
5. Tell why it is not possible to raise the receiving-end voltage by static capacitors if the
transmission line is purely resistive.
6. State briefly what you have learned from this experiment.