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Pharos University EE-272

Pharos University EE-272. Electrical Power Engineering 1 “Electrical Engineering Dep ” Prepared By: Dr. Sahar Abd El Moneim Moussa. Electric Performance of overhead transmission lines. Electrical Performance of OHTL.

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Pharos University EE-272

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  1. Pharos UniversityEE-272 Electrical Power Engineering 1 “Electrical Engineering Dep” Prepared By: Dr. SaharAbd El MoneimMoussa Dr. SaharAbd El MoneimMoussa

  2. Electric Performance ofoverhead transmission lines Dr. SaharAbd El MoneimMoussa

  3. Electrical Performance of OHTL • Electrical performance of transmission line can be quantitavely measured and governed by the following concepts : • Percentage Line voltage regulation (%VR). • Percentage transmission line efficiency (% tr). • Steady-state power limit of the transmission line (PRE,max). • Surge Impedance Loading of the transmission line (SIL). Dr. Sahar Abd El Moneim Moussa

  4. 1- Percentage Line voltage regulation (%VR): = x100 2- Percentage transmission line efficiency (% tr). x100% Dr. Sahar Abd El Moneim Moussa

  5. 3- Surge Impedance Loading of the transmission line (SIL). • The surge impedance loading or SIL of a transmission line is the MW loading of a transmission line at which a natural reactive power balance occurs. • A transmission line's surge impedance loading or SIL is simply the MW loading (at a unity power factor) at which the line's Mvar usage is equal to the line's Mvarproduction, as follows; Dr. Sahar Abd El Moneim Moussa

  6. i- The amount of Mvar produced is dependent on the transmission line's capacitive reactance (XC) and the voltage (kV) at which the line is energizedis; Dr. Sahar Abd El Moneim Moussa

  7. ii- Transmission lines also utilize reactive power to support their magnetic fields.  The magnetic field strength is dependent on the magnitude of the current flow in the line and the line's natural inductive reactance (XL). The amount of Mvar used by a transmission line is a function of the current flow and inductive reactance is: Dr. Sahar Abd El Moneim Moussa

  8. = • A natural reactive power balance occurs at which the line's Mvar usage is equal to the line's Mvar production, as follows; • The term is the surge impedance Impedance Surge Impedance Dr. Sahar Abd El Moneim Moussa

  9. The theoretical significance of the surge impedance is that if a purely resistive load that is equal to the surge impedance were connected to the end of a transmission line with no resistance, a voltage surge introduced to the sending end of the line would be absorbed completely at the receiving end.  The voltage at the receiving end would have the same magnitude as the sending end. • Substituting with in the voltage equation we get; Dr. Sahar Abd El Moneim Moussa

  10. Conclusion: • The SIL of a transmission line is defined as the power transmitted by the line to a unity power factor load; whose load impedance equals ZC. • In a loss-less line under SIL the voltage and current at any point along the line are constant in magnitude and are equal to their receiving-end values. • Since has no reactive component, there is no reactive power in the line. Dr. Sahar Abd El Moneim Moussa

  11. The surge impedance loading or SIL (in MW) is equal to the voltage squared (in kV) divided by the surge impedance (in ohms).  In equation form:   • The Reactive power equals ZERO Dr. Sahar Abd El Moneim Moussa

  12. Line Voltage Profile Under Different Loading Conditions Dr. Sahar Abd El Moneim Moussa

  13. 4- Steady-state power limit of the transmission line (PRE,max). • It determines the maximum power that can be transmitted through the line, taking into account all limiting conditions, such as reliability, corona losses, and the heating of conductors and contacts. • The complex power SR delivered to the receiving end is SR=VR IR* Dr. Sahar Abd El Moneim Moussa

  14. From the previous equation we get real power for a lossless line delivered to the load is Where; :is the angle between the sending end voltage & the receiving end voltage. : Wavelength, is the distance required to change the phase of the voltage or the current 2 radians or 360 Dr. Sahar Abd El Moneim Moussa

  15. The maximum power that can be delivered to the load when =90 • The theoretical maximum power that can be transmitted under steady-stable operation condition occurs for an angle of 90o . • To assure an adequate margin of stability, the practical operating power angle is usually limited to 35o~30o Dr. Sahar Abd El Moneim Moussa

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