Electrical Power Engineering

Questions: 1.Why power transmission lines are three-phases rather than 1, 2, or 5?2.What are the important parameters for designing cables? What are the standard tests used in the cable companies?3.Explain what the skin effect is and how we can reduce it? 4.Explain the mutual coupling and explain why in artificial transmission line experiments for no-load test the receiving end voltage in single- phase configuration had lower voltage than the sending end voltage? 5.What is surge impedance and how surge impedance loading (SIL) is utilized for efficient power transfer? Answers: 1. The generation of power in three phases and its delivery is very much efficient when compared to two phase which as result much more efficient then the phase1. Likewise as the number of phases increases it will result in increased of efficiency as well. This is the reason when 3 phase compared with 4 Phase, 4 Phase is more efficient but in comparison with 5 phase, 4 phase is less efficient and so on. The delivery of power with 3 phase is around 150 percent much more in comparison to single phase (Grigsby, 2012). So three phase is the correct choice because reaching the higher efficiency then increased as it is, do not rationalize the complexity that is increased by using extra phases. Three phases is usually used because it can generate the rotating magnetic field easily which is simply carried out by spatial arrangement of the coils which is energized in contact with each phase. 2. The important parameters that are considered while designing cables are as follows: Cables require transition joints which consist of different insulationLevel of voltage has to be considered a sit is required by insulationElectrical stress control varies with the various level of voltagesNumber of phases also differs as the 3 phase and 1 phase consists on various number of cores. Hence cable design differs (McDonald et al., 2012).The interface dielectric strength is differed by interface pressure and surface smoothnessBy applying high pressure and the exact smoothness the interface dielectric strength can be achieved in a better wayMaterial should be chosen in such a way that it is easy for installation along with reliability and safetyManufacturing of joint and its installation should be cost effectiveCable ampacity is affected by the thermal performanceControl measure on the electrical stress has to be maintainedThe cable should be environmentally friendlyMechanical strength for cables should be quite supportive to prevent damageThe following are some standard te sts used in cable companies as follows:DC voltage withstand with dielectricVLF voltage withstand with dielectricFrequency of powerInsulation resistance of DCPower factor testDischarge of offline partial test 3. The skin effect occurring in transmission lines can be described as the phenomenon arising because of the distribution of current unequally in the conductor over the whole cross section which is being used for the power transmission of long distance. By making some modifications in the line calculations, it can be reduced. For reducing this skin effect the conductor should be made of Cu and hollowness should be of 80 Hz (McDonald, 2012). Though it is completely not possible to reduce the skin effect but the specially made and insulated conductors that are woven in various patterns can be used as a special application (Okress, 2013). 4. Mutual coupling can be described as the phenomenon where the energy that is absorbed by one of the receiver of the antenna when the other antenna nearby is in operating mode. Mutual coupling is considered objectionable because the energy which is supposed to be radiated is being absorbed by the other antenna (Okress, 2013). Ferranti effect is noticed to occur when the distributed capacitance of the line itself is drawing the current which is considered to be more when compared with the current that is associated with the receiving end of the line load (Grigsby, 2012). The charging current of capacitor is leading to the drop of voltage along the transmission system of the inductor line when it is in the sending end voltages phase. The drop in voltage is kept on increasing till the time it moves to the load end of the line. Hence the voltage at receiving end is larger than the voltage that the applied one. 5. The transmission line surge impedance can be defined as the ration of the voltage amplitudes and the current propagating from a single wave which is along the line. It is explained as the wave that is travelling in one of the direction while the reflections are absent in the other direction (McDonald, 2012). It is considered to be the natural power of the transmission line. For the efficient transfer of the power using the surge impedance load the value of the receiving end voltage should be increased so the power that is transmitted along the long transmission line can also be increased. By using many transmission lines simultaneously it can even be increased. But it is expensive. So for increasing the SIL, Vr is always increased or the Zc is always decreased. References Grigsby, L.L. ed., 2012.Power system stability and control(Vol. 5). CRC press. McDonald, J.R., McArthur, S., Burt, G. and Zielinski, J. eds., 2012.Intelligent knowledge based systems in electrical power engineering. Springer Science Business Media. McDonald, J.D. ed., 2012.Electric power substations engineering. CRC press. Okress, E.C. ed., 2013.Microwave power engineering: Applications. Academic Press.