1.0 INTRODUCTION

Power transmission lines are designed to transmit large values of power between even far points. Generally power plants are created where an energy source is available. Then these plants will serve all users located in industrial areas.

The operating voltage is choosing according to minimize joule effect losses. It can immediately by realized that sources will be reduced when current it reduced, but when huge volumes of power have to be sent, energy will be exclusively transmitted with high voltages. All that will lead to consider also the accessories that are step up transformers at the origin and the respective step down transformers at the destination of the lines.

The parameter of capacitance is directly proportional the length of the transformer line, its concentrated into an equivalent total of capacitance only for easier study. Actually the parameter of a transmission line (capacitance and resistance in this particular case) are distributed crossing to line resistor the capacitance current will produce power losses occurring even when the transmission line is in no load condition.

2.0 EXPERIMENT OBJECTIVES

Measurement of the voltage increase and charging power in lines of different lengths in no load operation. Different performance characteristics of overhead transmission line and cable.

3.0 METHODOLOGY

1. The circuit is assembled as shown in figure 5.2. The secondary side voltage of the three-phase transformer is set to UN -10% using the bridging plugs.3. The connection of the bridging plugs made for this experiment means that the shortest possible transmission line length, 144km, has been selected.4. The voltage between the two outer conductors at the beginning and end of the line is measured, as well as the reactive power consumed by one of the phases.5. The line length is changed to 216km by reconnecting the bridging plugs as shown in figure 6 and the measurement is repeated.6. The line length is changed to 360km by reconnecting the bridging plugs as shown in figure 7 and the measurement is repeated.7. To demonstrate the concept of operating capacitance, the circuit in figure 8 is assembled.8. The voltage at the three-phase transformer is set to the value UN -10%, all bridging plug is removed, and the capacitances is connected to the transmission line model.9. The voltage between the two outer conductors at the beginning and end of each line is measured, as well as the reactive power consumed by a phase.10. The difference between the performance of a cable and the performance of an overhead transmission line in no-load operation is demonstrated by the connection shown in figure 9.11. The operating capacitance of the transmission line model is doubled by connecting the two (artificial) line capacitances. The voltage increase effect at the line end is thus amplified.12. The voltage between two outer conductors at the beginning and end of each line is measured as well the reactive power consumed by a phase.

4.0 RESULTS

LINE LENGTH (KM)U1 / VU2/ VRATIO U2 / U1QC / Var

1443803901.0330

2163804001.0540

3603854201.0980

Table 1: The characteristics of a transmission lines in no-load.

CONDITIONSU1 / VU2/ VRATIO U2 / U1QC / Var

OPERATING CAPACITANCE3804201.1140

INCREASED OPERATING CAPACITANCE

390

470

1.21

170

Table 2: The characteristics of transmission line model with operating capacitance and increased operating capacitance.

5.0 DISCUSSION

The secondary-side voltage of the three-phase transformer is set to UN -10%, using the bridging plugs. The connection of the bridging plugs is made for the shortest possible transmission line length 144km. The voltage between the two outer conductors at the beginning and end of the line is measured. The charging reactive power QC is measured. The ratio of U2 to U1 is calculated. This step is repeated for transmission line length 216km and 360km. The result is shown in table 1.

Based on the result in table1, the Q/Var against 1/% graph and U2/U1 against 1/% is plotted. From the graph1, the charging reactive power is increasing exponentially with the line length. From the graph2, the ratio U2/U1 is increasing with the line length. The transmission line required active power in no-load operation because of the increase in the charging reactive power QC will cause increasing in active power.

The circuit is connected as shown in figure 8 to demonstrate the concept of operating capacitance. The voltage at the three-phase transformer is set to the value UN-10%, all bridging plugs are removed and the capacitances are connected to the transmission line model. Compare the result with that for the transmission line model at a length of 100%, transmission line model at length at 100% will be slightly affected due to the capacitive coupling that produced by the equivalent capacitance.

The transmission line is connected as shown in figure 9 to figure out the difference between the performance of a cable and the performance of an overhead transmission line in no-load operation. Compare the result with those for a line length of 100% but without additional capacitances, the reactive power become increase due to the double operating capacitance of the transmission line model.

6.0 CONCLUSION

The objectives of this experiment were achieved. The measurement of the voltage increases and the charging power in lines of different length in no-load operation. Besides that, the length line shows that the different performance characteristics of overhead line and cable which is the charging reactive power is increasing exponentially with the line length and it will cause increasing in active power.

7.0 REFERENCE

1. http://en.wikipedia.org/wiki/Transmission_line2. http://www.electrical4u.com/performance-of-transmission-line/3. http://www.skm-eleksys.com/2011/02/transmission-line-model-short-and.html

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