Faculty of Engineering– Zagazig University
Electrical Power & Machines Eng. Program
جامعة الزقازيق – كلية الهندسة – برنامج هندسة القوى واآلالت الكهربية
Electrical Power and Machines Testing (1)b
EPE 323b – Reg. 2021
3rd year, 2nd Term
(2024_2025)
Experiment No. : (3)
Title
Determination The Parameters of Transmission
Line Model Simulator
Student name : …………………………….…….………
Sec : …………………………….…….………
Coordinator : Dr. Mohamed Tayseer
Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
EXPERIMENT
3
Determination the Parameters of Transmission
Line Model Simulator
3.1 Object:
The objectives of this experiment are to:
Understand the classification of transmission line parameters
experimentally using a model simulator that imitates practical
transmission system.
Determine the line model simulator parameters based on open
circuit and short circuit tests with a comprehensive familiarity
for the deduced parameters from each test.
Refer the measured parameters of the line model simulator to
their actual values in the practical model based on the data –
sheet of the chosen line simulator model.
3.2 Preliminary Questions (Attempt all questions)
A. Explain the skin effect and its cause
B. Does the value of R and X change if the supply frequency is
different than the rated value? Explain.
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
3.3 Experimental Setup
3.3.1 General Overview on Transmission Line Parameters
Transmission line parameters are major factors that affect the
operation of power systems, for example voltage profile, power flow,
system losses and system stability depend on these parameters. An
electric transmission line has four parameters which affects its ability
to fulfill its function as a part of a power system: resistance,
inductance, capacitance, and conductance.
The resistance of transmission-line conductors is the most cause of
power loss in a transmission line. The effective resistance is equal to
the DC resistance if the distribution of the current
through the conductor is uniform. As the frequency of alternating
current increases, the non-uniformity of the distribution becomes
pronounced. This phenomenon is called skin effect, in a circular
conductor the current density usually increases from the interior
toward the surface.
The inductance of a transmission line is calculated as flux linkage per
ampere. If the permeability is constant, sinusoidal current produces a
sinusiodally – varying flux in phase with the current. Flux lines are
not only external to the conductors, but also inside them. The
changing lines of flux inside the conductors also contribute to the
induced voltage of the circuit and therefore to the inductance.
Capacitance of a transmission line is the result of the potential
difference between the conductors. An alternating voltage impressed
on a transmission line causes the charge on the conductors at any
point to increase and decrease with the increase and decrease of the
instantaneous value of the voltage between conductors at the point.
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
The current caused by the alternate charging and discharging of a
line due to alternating voltage is called the charging current of the
line. Earth affects the capacitance of a transmission line because its
presence alters the electric field of the line, so that the electric field of
the charged conductors is forced to conform to the presence of the
earth’s surface
Conductance exists between conductors or between conductors and
ground. Conductance accounts for leakage current at the insulators of
the overhead lines. Since leakage at insulators of overhead lines is
negligible, the conductance of an overhead line is usually neglected.
3.3.2 Simulation Model of Transmission Line
The Lab model is a simulation system that mimics a practical electric
overhead power transmission line of the following features:
Length: 136 km
Operating Voltage: 77 kV – Three Phase
Current: 100 A
Power: 13.4 MVA
The concluded ranges of referring the measured parameters of the
line simulator model to the practical model can be expressed as:
Voltage scale: =
Current scale: =
Power scale : =
Impedance ⁄ : ( )=
The line capacity has been concentrated with one half of the total
capacity at each end of the line. On a power transmission line, there
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
is capacity between the conductors and also between the conductors
and earth as shown in Fig.1.
The capacitances form a delta connection which can be delta –
star transformed. If capacitances are equal, which is very often
the case in practice; the derived star can be combined with the earth
capacitances ( ) to form a resultant mutual capacitance .
𝑪𝒎
𝑪𝒎 𝑪𝒎
𝑪𝒋 𝑪𝒋 𝑪𝒋
Fig. 1. Classification of Transmission Line Capacitances
3.3.3 Short Circuit Test
The impedance of the line is determined with short circuit test, in
which we short circuited one side of line model and feed the other side
with a low voltage so; the resultant current is equal to rated current.
In this test, three measurements must be obtained as follows:
Short Circuit Voltage:
Short Circuit Current:
Short Circuit Power:
These measurements can be obtained using the following apparatus:
Transmission line simulator model 220 V, 5 A.
AC power supply 50 Hz, , 5 A.
Wattmeter
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
Ammeter
Voltmeter
Connection leads.
From the previous measured values, the line resistance and inductive
reactance can be calculated as follows:
3.3.4 Open Circuit Test
From the no load test we can calculate the capacitance per unit
length of the real line.
In this test, two measurements must be obtained as follows:
Open Circuit Voltage:
Open Circuit Current:
These measurements can be obtained using the following apparatus:
Transmission line simulator model 220 V, 5 A.
AC power supply 50 Hz, , 5 A.
Ammeter
Voltmeter
Connection leads.
From the previous measured values, the equivalent shunt capacitive
reactance can be calculated as follows:
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
3.4 Connection, Procedures and Instrumentations
3.4.1 Required Instrumentations
The following instrumentations should be available:
1. Variable AC power supply (Control Panel Unit)
2. Line Model Simulator
3. Multi – range DC Voltmeter / Ammeter / Wattmeter
4. Leads with different sizes
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
3.4.2 Connection Diagram and Procedures for performing the
Short circuit test
1. Be sure that the variable three phase output switch is open and
the variac is fully turned in counter clock wise direction.
2. Build the following circuit
3. Switch on three phase voltage and increase the voltage slowly until
the current in the R phase, I, is equal to the rated current 5 A.
4. Fill the Table 3.1 and calculate the required values.
Table 3.1
Measured and Required Values to Be Calculated
Line Model Actual Model
Phase
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
5. Calculate the mean values of three readings of three phase and fill
the Table 3.2
Table 3.2
Mean Values of Line model and actual model parameters
Line Model Actual Model
3.4.3 Connection Diagram and Procedures for performing the
Open circuit test
1. Be sure that the variable three phase output switch is open and
the variac is fully turned in counter clock wise direction.
2. Build the following circuit
3. Switch on three phase voltage and adjust the voltage to 220 V.
4. Fill the Table 3.3 and calculate the required values.
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
Table 3.3
Measured and Required Values to Be Calculated
5.
Line Model Actual Model
Phase
5. Calculate the mean values of three readings of three phase and
fill the Table 3.4
Table 3.4
Mean Values of Line model and actual model parameters
Line Model Actual Model
3.5 Estimation (Use Draft Lines for Calculating Parameters)
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
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3.6 Post – Experimental Questions (Attempt all questions)
A. Draw the equivalent model of the true line indicating the
value of each parameter.
B. Draw equivalent circuit of a transmission line for short circuit
test. Why effect of charging currents is neglected in this case?
C. Draw equivalent circuit of a transmission line for open circuit
test. Why effect of series impedance is neglected in this case?
D. Choose the Answer:
o Shunt reactors are installed in the transmission system to
[a] Increase the maximum power transfer
[b] Compensate for the voltage rise
[c] Redistribute the power flow across the line
[d] Both a and c
o Series capacitors are installed in the transmission system to
[a] Increase the maximum power transfer
[b] Compensate for the voltage rise
[c] Redistribute the power flow across the line
[d] Both a and c
o In the short circuit test on a transmission line the shunt
capacitance can be neglected because:
[a] Line current is small
[b] Operating voltage is low
[c] There no reactive power consumed by the line
[d] The losses can be neglected
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Electrical Power and Machines Testing (1)b EPE323b Experiment no.3
o In the open circuit test on a transmission line series
impedance can be neglected because:
[a] Line current is low
[b] Operating voltage is the rated
[c] There no reactive power developed by the line
[d] Active power losses is high
o Reactive power losses are ……….. active power losses in a
full loaded transmission line
[a] equal to
[b] Greater than
[c] Lower than
o The ratio between X to R of an overhead transmission line is
[a] equal to one
[b] Greater than one
[c] Less than one
3.7 Conclusions and Discussions
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