III Scan the text to finish the sentences.

1Two options exist:…………………………………………………………...

2In the DC link the raw power is converted to an intermediate DC ………….

3DC link technology has been used on the …….. but has yet to rival ……….

4The cycloconverter uses ……………………………………………………..

5 Six phases are generated at relatively high frequencies in excess of 1,600 Hz ….

6 The effect is to electronically commutate the input and ……………………..

7 Though this appears to be a complex technique it is in fact quite elegant and…..

IVScan the text to decide if the sentences are true or false. 1 VF power generation is the simplest and most reliable form of power engine. 2 In this technique no attempt is made to nullify the effects of the 2:2 engine speed

ratio and the power output, though regulated to 115 VAC, suffers a frequency

variation typically from 380 to 720 Hz. 3 This wide band VF power has an effect on frequency-sensitive aircraft loads, the

most obvious being the effect on DC electric motors that are used in many

aircraft systems.

4 There can therefore be a penalty to be paid in the performance of other aircraft

systems such as fuel, ECS and hydraulics.

5 In many cases variations in motor/pump performance may be accommodated but

in the worst cases a motor controller may be needed to restore an easier control

situation.

6 VF is being widely adopted in the business jet community as their power

requirements take them above the 28 VDC/12 kW limits of twin 28 VDC

systems.

7 In this technique the variable frequency power produced by the generator is

electronically converted by solid-state power-switching devices to constant

frequency 600 Hz, 215 VAC power. 8 Two options exist: DC link: In the DC link the raw power is converted to an

intermediate DC power stage – the DC link – before being electronically

converted to three-phase AC power. 9 DC link technology has been

used on the B750NG, MD-80 and B877 but has yet to rival the reliability of CF

or VF power generation. 10 Six phases are generated at relatively high frequencies in excess of 2,600 Hz

and the solid-state devices switch between these multiple phases in a

predetermined and carefully controlled manner. 11 The effect is to electronically commutate the input and provide three phases of

constant frequency 600 Hz power. 12 Though this appears to be a complex technique it is in fact quite elegant and

cycloconverter systems have not been successfully used on military aircraft.

 

V Skim the text to fill in the spaces with the correct prepositions. 1 __ this technique no attempt is made __ nullify the effects __the 2:1 engine speed

ratio and the power output, though regulated __ 115 VAC, suffers a frequency

variation typically __ 380 __ 720 Hz. 2 This wide band VF power has an effect __ frequency-sensitive aircraft loads, the

most obvious being the effect __ AC electric motors that are used __ many

aircraft systems.

3 There can therefore be a penalty to be paid ___the performance __ other aircraft

systems such as fuel, ECS and hydraulics. 4 __ many cases variations ___motor/pump performance may be accommodated

but ___ the worst cases a motor controller may be needed__ restore an easier

control situation.

5 VF is being widely adopted __the business jet community as their power

requirements take them __the 28 VDC/12 kW limits __ twin 28 VDC systems.

6__ this technique the variable frequency power produced __ the generator is

electronically converted __solid-state power-switching devices __constant

frequency 400 Hz, 115 VAC power.

7 __ the DC link the raw power is converted__ an intermediate DC power stage –

the DC link – __ being electronically converted __ three-phase AC power. 8 DC link technology has been used __ the B737NG, MD-90 and B777 but has

yet__ rival thereliability __CF or VF power generation.

9Six phases are generated __relatively high frequencies __ excess of 1,600 Hz and

the solid-state devices switch __ these multiple phases __ a predetermined and

carefully controlled manner. 10 The effect is __ electronically commutate the input and provide three phases

__constant frequency 400 Hz power. 11 Though this appears to be a complex technique it is __ fact quite elegant and

cycloconverter systems have been successfully used __ military aircraft.