University of Jordan
Faculty of Engineering & Technology
Electrical Engineering Department
Power Lab. EE 489
Experiment # 3:
Current, Voltage & Power Relations
Across A Transmission Line
---------------------------------------------------------------------------------Objective :
To determine the A, B, C & D constants of a short and medium
length transmission lines and to investigate voltage, current and power
relations at both ends under no load and full load conditions with and
without shunt compensation.
Procedure :
P a r t (a) : Determination of A, B, C & D Constants of a Short
Length Transmission Line.
a . 1 - Open Circuit Test.
1 - Connect the circuit as shown in fig. 1.
2- Adjust the source voltage at 50V and take the readings of Vs, Is,W and
VR , and determine the phase shift between Vs and VR .
3-Repeat step (2) for source voltages of 75,100, 120V.
4- From each set of readings , calculate A and C constants and determine the
average values.
a . 2 - Short Circuit Test.
1-Connect the circuit as shown in fig. 2.
2- Increase the source voltage very slowly adjusting IR to 1A and take the
readings of VS, IS, W, IR and determine the phase shift between Vs and
IR(IS).
3- Repeat step (2) for IR = 2, 3 and 4 A respectively .
4- From each set of readings , calculate B and D constants and determine
the average values.
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Part (b) : Determination of A, B, C & D Constants of a Medium Length
Transmission Line.
b . 1 - Open Circuit Test.
1-Connect the circuit as shown in fig. 3.
2-Adjust the source voltage at 50V and take the readings of Vs, Is,
W,V R ,I c 1 , I c 2 and determine the phase shift between (Vs& VR )
,(Vs&Is). “use phasor diagrams where it is necessary”.
3- Repeat step (2) for source voltages of 75, 100, 120 V.
4- From each set of readings , calculate A and C constants and determine
their average values.
b . 2 - Short Circuit Test.
1- Connect the circuit as shown in Fig. 4.
2-increase the source voltage very slowly adjusting IR t o l A and take the
readings of Vs, IS; W, IR , I C1, I C2 and measure the phase shift between (Vs
& I s ), ( V S & I R ). “use phasor diagrams where it is necessary”
3- Repeat step (2) for IR = 2, 3 and 4 A respectively .
4-From each set of readings , calculate B and D constants and determine
the average values.
- Draw the equivalent circuit of this line .
-Verify the A, B, C, D constants using the relevent equations and the R, L,
C values deduced from measurments.
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Part (c) : Operation at No Load .
1 - Connect the circuit as shown in fig. 5 with switch S open.
2-Adjust Vs to 100 v ( L-N).
3- Take the readings of Vs, Is, and VR .
4- With XL adjusted to it's maximum value , close switch S .
5-Keep Vs constant and adjust XL till VR = V S =100v.
6- Take the reading of IL and calculate XL .
7-Comment on the value of IL .
8-From theory, calculate the combined A,B,C,D constants of the transmission
line connected in series with the inductor and comment on the result .
9- Draw the circle diagram of the uncompensated line and deduce from it the
amount of shunt compensation required at no load to make Vs = VR. How
does this value correlate with the measured value?.
Part (d) : Load Test.
1- Connect the circuit as shown in fig. 6.
2- Adjust I to 2A and adjust the P.F. to 0.8 lagging by adjusting individually I1
& I2 while keeping VR constant at 100v by continuous adjustment of Vs.
3- Take the readings of Vs, IR , PR , Is, VR , I1, I2, P.F. .
4- Draw the circle diagram and verify the measured results.
5- Determine from the circle diagram the amount of shunt compensation if Vs is
lowered to 100v ,and VR is required to remain constant at 100 v.
6- Ensure mat Xc is kept at it's maximum value ,and close switch S.
7- Increase Ic gradually to achieve Vs = VR = 100 v , measure Ic & repeat step
3.
8- Calculate the VAR injected by Xc and check this value with the value
determined in step 5.
9- Explain why ls increases after shunt compensation with reference to the
P.F. at the sending end.
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XL=3.75
Fig. 1 Short Transmission Line
Open Circuit Test
Fig. 2 Short Transmission Line
Short Circuit Test
Fig. 3 Medium Transmission Line
Open Circuit Test
Fig. 4 Medium Transmission Line
Short Circuit Test
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