External power supply schematic pack
External ground power from a battery
External ground power 3-pin connector External ground power 3-pin connector schematic UNIT 11 DC POWER GENERATION
AIM OF THE UNIT:- to understand dc power generation
TASKS 1 Do your best to answer the brainstorming question. 2 Read the text for general understanding. 3 Make up questions to the text. 4 Find the sentences with the new words in the text. Give the Kazakh or Russian equivalents of the words. 5 Write sentences with the new vocabulary. 6 Make up exercises as in the UNIT 2 (Master`s degree students individual work withthe teacher) page 210 (exercises for better remembering the topic). 7 Speak on the topic. Given schemes will help you to remember and understand the topic. 8 Find more information about the topic and make up a project work on the topic.
DC systems use generators to develop a DC voltage to supply aircraft system loads; usually the voltage is 28 VDC but there are 270 VDC systems in being which will be described later in the chapter. The generator is controlled- the technical term is regulated – to supply 28 VDC at all times to the aircraft loads such that any tendencies for the voltage to vary or fluctuate are overcome. DC generators are self-exciting, in that they contain rotating electromagnets that generate the electrical power. The conversion to DC power is achieved by using a device called a commutator which enables the output voltage, which would appear as a simple sine wave output, to be effectively half-wave rectified and smoothed to present a steady DC voltage with a ripple imposed. In aircraft applications the generators are typically shunt-wound in which the high resistance field coils are connected in parallel with the armature. The natural load characteristic of the shunt-wound generator is for the voltage to ‘droop’ with the increasing load current, whereas the desired characteristic is to control the output at a constant voltage – nominally 28 VDC. For this purpose a voltage regulator is used which modifies the field current to ensure that terminal voltage is maintained while the aircraft engine speed and generator loads vary.
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