I Find the sentences with the words in the text. In small groups, discuss the meanings of the words and give the Kazakh or Russian equivalents.

II Make up four types of questions to the text.

 

Constant frequency/IDG generation

UNIT 2 VARIABLE FREQUЕNCY

AIM OF THE UNIT:- tounderstandvariable frequеncy

TASKS

1 Do your best to answer the brainstorming questions. 2 Read the text for general understanding.

3 Make up four types of 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 Do the given exercisesfor better remembering the topic. 7 Speak on the topic. Given schemes will help you to remember and understand

the topic.

8 Make up a project work on the topic.

Brainstorming questions

1 What is VF?

2 What is the function of VF?

Variable frequency (VF) power generation is the simplest and most reliable form of power generation. In this technique no attempt is made to nullify the effects of the 2:1 engine speed ratio and the power output, though regulated to 115 VAC, suffers a frequency variation typically from 380 to 720 Hz. This wide band VF power has an effect on frequency-sensitive aircraft loads, the most obvious being the effect on AC electric motors that are used in many aircraft systems. There can therefore be a penalty to be paid in the performance of other aircraft systems such as fuel, ECS and hydraulics. 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.

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.

In this technique the variable frequency power produced by the generator is electronically converted by solid-state power-switching devices to constant frequency 400 Hz, 115 VAC power. 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. DC link technology has been used on the B737NG, MD-90 and B777 but has yet to rival the reliability of CF or VF power generation.

The cycloconverteruses a different principle. Six phases are generated at relatively high frequencies in excess of 1,600 Hz and the solid-state devices switch between these multiple phases in a predetermined and carefully controlled manner. The effect is to electronically commutate the input and provide three phases of constant frequency 400 Hz power. Though this appears to be a complex technique it is in fact quite elegant and cycloconverter systems have been successfully used on military aircraft.

EXERCISES FOR BETTER REMEMBERING THE TOPIC