Fichas
Electrical System
Fichas del conjunto (40)
- 1Tasks of Electrical System- Control of movable parts (transform electrical energy in mechanical energ.)
- Heating through Joule effect (anti-icing de-incing)
- Internal and external lighting
- Suppley of electric energy to avionics and on-board instrumentation - 2Functions of Electrical system- Generation (AC- DC)
- Outputvoltage/ current control
- Power transfer
- Use - 3Why standardized values have been set in power generation?Because although, tension and frequency can be optimized for each user, it is economically inconvenient
- 4Standardized Conditions in aircrafts? Power Generation- DC: Tension [V]: 28
- AC: Tension [V]: 115/120 ;
Frequency [Hz] : Variable or 400
(for structural integrity 400) - 5Problems with high voltage- Isolation (thicker sheath)
- Weight of high voltage DC accumulators - 6VDC for more electric aircraft configuration270 VDC with conversion to 115 VAC and 28 VDC
- 7Why is DC absolutely necessay onboard?Because it can be stored in accumulators capacities, chemical batteries)
- 8Which components require AC?Avionics
- 9Maximum current and power transfer with 28 VDC?Current: 400 A
Power transfer 11.2 kW - 10DC, AC ot Both?It is required both, the solution is to generate one type of power (primary) and then convert it when required to the other form (secondary)
- 11When is DC primary and the other way around- DC primary for small transport aircrafts
- AC primary for turbofan airlines and military
- A mixed of AC and DC generation is adopted in some cases ATR 42 - 12Simplest DC generatorDynamo
- 13How does the DC generator works?A conductor armature or wire loop, rotates in a magnetic field inducing an EMF in the wire. Wire is connected to the external circuit via sliding brush contacts. A commutator is used to switch the contacts every 180º resulting in a sinus modulus current. Many armatures: steady tension
- 14How is the magnetic field produced in the DC generator?By an electromagnet whose current can be modulated in intensity to regulate the output voltage to a constant value, even when the rotating speed is variable
- 15what does it mean that the DC generator is reversible? What is the limit of the generatorIt can act as a DC motor: by giving an electric current input, a torque is generated on the shaft.
The degradation of the conteacts due to brush sparkling is its main limit - 16How are AC generators called?Alternators
- 17Difference between AC and DC generatorsAC does not require commutation to rectify the current and the output AC voltage is obtained in the stator coils
- 18How is the magnetic field generated in the AC generator?By either flowing a DC current through the rotor via an exciter or by using a permanent magnet rotor. The stator typically presents 3 different windings at 120º phase: an output AC is then generated in these stator coils with 120º phase separation
- 19On what does the output frequency depend in the AC generator?On the frequency of the engine
- 20On what does the output voltage depend in the AC generator?Number of coils, magnetic field intensity and rotational speed
- 21Advantages of AC over DC- AC can be transmitted over long distances more readily and economically since AC voltages can be increased or decreased by transformers.
- Space and weight saving (AC devices as motors are smaller and simpler) - 22Advantages of AC over DC (bis)- Most AC motors don't require brushes: less maintenance
- Most airplanes have special equipment that required 400 cycle AC current - 23Two AC frequency control- IDG: Integrated drive generator
- VSCF: variable speed constant frequency - 24Explain IDGIs an alternator coupled with a CSD. This system is able to generate a constant rotating speed in a wide range of input frequencies (3000-9000 rpm)
- 25CSDConstant Speed Driver. It is a hydro-mechanical devide composed by a differential gearbox, an hydraulic pump with variable displacement coupled with a motor
- 26Explain VSCF converter- DC link: the raw power is converted to an intermediate DC power stage (DC link) before being electronically converted to 3-phase AC power.
- Cycloconverter: synthetize lowe frequency AC by high-freq. AC through recombination of the phases - 27AC to DC conversionObtained by TRUs, which comprise transformer windings together with three-phases full wave rectification and smoothing to provide the 115 VAC/ 28 VDC conversion
- 28DC to AC conversionObtained by solid-state inverters or using DC motors connected to AC alternators
- 29Tasks of energy power storage- Provide start-up energy (APU or small engines)
- Emergency supply in case of failures
- Dump voltage fluctuations - 30Battery performance indicators- Capacity (Ampere-Hours): indicates the amount of charge the battery can deliver. Typically for 20h discarge time.
- Storage density (Wh/Kg): the energy specific weight of the battery - 31What is a cell?A device that transforms chemical energy into electrical energy (redox). It contains an electrolyte (salt, acid or alkaline solution), an anode and a cathode (made of diff metals). A batery is made of cells connected in parallel
- 32Most common batteries- Lead acid
- Nickel Cadmium - 33Lead Acid battery2.1 V cell with two electrodes made of lead dioxide (Pb=2) abd sponge lead (Pb) and the electrolyte made of water solution of sulphuric acid (H2SO4)
- 34Ni-Cd battery1.2 V cell with two electrodesmade of cadmium (Cd) and nickel oxyhydroxide (NIOOH) and the electrolyte made of a water solution of potassium hydroxide (KOH)
- 35Advantages and Disvantages of Ni-Cd batteryThey are more efficient at high discharge rates, have more stable voltage at discharge, largerlifetime and storage density. On the other side, they are affected by the memory effect and are more expensive
- 36Motors: application on board- Actuation for the control of movable parts
- Activation of hydraulic and pneumatic valves
- Engine Start-up
- Operation of hydraulic pumps, gyroscopes, fans ... - 37DC motorsDC motors are constructively as a DC generator, with the difference that the current is applied in input on the rotor coil, and the Lorentz force produces a torque if the coil is immersed in a magnetic field. The speed of rotation can be modulated by tunning the intensity of magnetic field or input current
- 38DC motor applicationsEmployed for variable speed functions: actuation, valve activation, engine start-up
- 39AC motorThey can be seen as a reverser alternator
- 40Motor common in aircraftsInduction motor. The stator same as AC synchronous motor; rotor laminated sylinder with copper bars inserted in slots of the cylinder surface and connected, then creating a sort of cage included in the cylinder. Stator magnetic field induces electric current in rotor cage. Interaction between current and magnetic field causes the rotor to turn
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- Sistemas Fichas sobre Electrical System, creado por Ana Castilla el 15/06/2020.
- Creado por
- Ana Castilla
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