VI Skim the text to fill in the gaps with correct prepositions.

1 Alternating current (ac) generators supply theelectrical energy ___ operating

aircraft avionicsequipment.

2 A generator is a machine that convertsmechanical energy ___ electrical energy

__electromagneticinduction.

3 Ac power systems result __ better design and use __equipment than older

electronic equipment powered __direct current (dc), which have inverters ___

ac powerand dynamotors __supplying higher voltage dc power.

4 These components are very heavy compared __ theirrelative power outputs.

5 The same ac-powered equipment obtainsvarious ac voltages and dc power __

using simpletransformers and transformer-rectifiers.

6 Thenumber __ magnetic poles and rotor revolutions perminute (rpm) determine

the voltage frequency __ thegenerator.

7 __ a fixed number __ poles, constant frequency requires constant rotor rpm.

8 An ac generator-rotating field has 12 poles ___adjacent poles of opposite

polarity.

9 Each pair __ polesproduces one cycle per revolution.

10 The output frequency __the generator varies __ direct proportion__ the engine

drive speed.

11 A generator operating at 6,000 rpm isoperating __ 100 revolutions per second

or __ 600 Hz.12 The 120-/208-volt, 400-Hz, three-phase ac powersystem has

many advantages ___ the 28-volt dcsystem.

13 The current required is a fraction of thatrequired __ the same power __ a 28-

volt dc system.14 This permits the use __ smaller aircraft wiring, saving

weight.

15 The ac generator and many __ the system’scontrol and protection components

are lighter.

16 Twelvekilowatts is the practical limit __the size __ an aircraftdc generator.

17 Aircraft now have ac generators __ratings __ __ 90 kilovolt-ampere (kVA).