Aircraft Electrical Power Generation & Distribution - Assignment Example

Aircraft Electrical Power Generation & Distribution Task one 1. Working of an aircraft 3 phase electrical generator An aircraft, just like other machines, utilize the concept of energy transformation for it to propel itself from one place to another through the air. It needs energy in the right form to do this. Energy, in an aircraft, is first converted from chemical form and through various processes before its conversion to the final state which is mechanical for the movement of the plane. For continuous supply of energy, alternator is necessary within a plane. This part of the essay will look into the explanation of the working of three phase alternator in an aircraft needed (Pallet 1987). Most of the planes use the three phase alternators. Three phase alternator, as the name suggests, consists of three single-phase windings that are spaced in such a manner that voltage induced in any of the phases undergoes displacement of 120 degrees from the other two alternators. The three phases of this type of alternator are independent, that is, they do not depend on the each other. Rather than having all the six leads coming out of the 3-phase alternator, the same leads from each of the phases are connected together and form a Y (wye) connection. This happens because when the neutrals are not there, the windings usually take the shape of letter Y, which in this case, is upside down or sideways. The neutral connection within a plane’s turbine engine is brought out to a terminal whenever a single phase load is applied to it. Also to note is that single phase voltage is always available from the three neutral phases. In a three phase Y connected alternator, like that in a plane, the total line voltage, or the total voltage passing across any two of the three leads represents the vector sum of the existing individual phase voltages needed (Pallet 1987). Due to the windings from only one of the path for the flow of current between the phases, the phase and line currents are equal. The whole system is equipped with circuit breakers that aid in the control and regulation of current to avoid destruction of certain elements due to excess heat by excess current. Voltage regulation in an alternator of an aircraft is controlled in a manner that its deficiency or excess is compensated appropriately. When the load on the generator is changed, the generator’s terminal voltage varies. The amount of this variation always depends on the design used in the generator. In this case, the voltage regulation of the plane’s alternator refers to the voltage change from full load to no load, and is expressed as the percentage of full-load volts, especially when the dc field current and the speed are held constant. That is, percentage voltage regulation = (EnL-Efl)/EfL This expression gives the percentage voltage regulation in an alternator of an aircraft. An alternating voltage is induced in the windings of the armature needed (Pallet 1987). This occurs when magnetic fields with alternating polarities pass across the windings. The voltage induced in the windings normally depend three major factors, the number of conductors generated in the series in each winding, alternator speed in rpm that the field cut through the winding. It also depends on the magnetic field strength. The three factors are used to ensure control of the voltage within the windings of the alternator. Task 2 Integrated drive generator, in aircrafts, has its simplest unit called, “Generator Control Unit” normally known as GCU. In aircrafts, paralleling of generators is automatically performed by respective GCU before the aircraft takes off. This is achieved through the comparison made between the line and offline rotational phase of the generator. After this, a signal is sent to the constant speed drive (CSD). This is basically IDG component transmission as it is made up of the generator and thee CSD. One of the CSD components is known as a governor, which is a set of flyweights that spins as they sit atop the generator’s sliding shaft. This has an effect of stabilizing the output rpm producing 400+/- 20 cycle operation needed (Pallet 1987). The generator’s shaft has slots which act to port or store oil pressure to either a decrease or an increase rpm port. The shaft is easily shifted by electrical solenoid input when in parallel mode. Since oil pressure is reduced, the positioning of the wobblers is affected. The component is a mechanical equivalence to any tilted swash plate that increases or decreases output rpm depending on the tilt angle. All generators function well when each is operating at the same frequency and the ABC rotation cycle of all of them are in match. There is also an ability that is built with an aim of creating slight variation electronically through subtraction or addition of inductance or capacitance values. Task 3 D.C. voltage is needed for the provision of controlling as well as lighting ac power equipments. This important voltage is provided by transformer rectifier, mostly referred to as TR. TR does not have any of its parts moving apart from the cooling fan needed (Pallet 1987). Therefore, there is no necessity of separate voltage when the ac voltage is maintained to a certain reasonable limit. The capability of D.C. current is high and mainly dependent on the available cooling system. Input ac voltage normally enters through three different pins and finally through a radio frequency filter. The frequency filter functions to reduce noise that causes interference to other components of avionics within the aircraft. Power connects with Y-Connected primary of the step down transformer needed (Pallet 1987). The output ac of the wye, which is delta-connected secondary, undergoes rectification by the first diode in the circuit through the second one. The output or rather the result of the rectification an interphase transformer, then through a network of filter that consists of a load and two capacitors. The interphase transformer is made of adjustable center tap that aids in balancing two delta transformers in order to reduce equal current. The existing filter network serves the role of reducing high frequency ripple voltage into a nearly straight line or lowest voltage possible. The fan motor, connected in parallel, to the primary transformer .is necessary for proper operation as well as provision of the only or mobile part of the transformer rectifier. The thermostat serves the role of detecting excessively and dangerous high temperatures. In conjunction with the external circuits, the thermostat performs another role of turning on warning lights when there is overheating, thus, disconnecting the input automatically. Task 4 Parasitic capacitance and resistance are always quite high in a long bus line. For instance, in the figure above, delay propagation from M1 to M6 is quite large. In order to improve energy consumption and timing of the long bus, partitioning of the bus is done into two major segments. The boundary between the first bus and the second one has a dual port driver whose function is relaying of data from a single bus to another, especially when the data transfer is needed (Pallet 1987). The split bus architecture, studied keenly, can be seen to utilize the same principle as that of monolithic-bus. Splitting bus architecture has certain advantages that make it a preference. For example, it has smaller parasitic load due to the reduced bus, thus reducing parasitic load of each bus segment. Its timing slack is also larger compared to other bus splitting. Task 5 Parallel buses, unlike the serial ones, consist of 8, 16, 32 or even 64 lines of data. The examples are PCI, ISA, EISA and VESA. They are much expensive in comparison to serial buses due to the higher throughput. The diagram below is an example of a parallel bus. In low voltage swing architecture, the signal that is transmitted to low voltage swing before its propagation along the bus. Conversion of the low voltage swing then takes place at the input’s receiving module. In this case, quantity of charge on the bus only changes by: Change in V x Bus Capacitance. Where V represents the bus’ voltage swing. There is also a reduction of the signal delay of the bus needed (Pallet 1987). References Pallet, E., (1987), Aircraft electrical systems, New York, NY, Longman Scientific & Technical. Read More