UNIT 6TYPES OF AC GENERATORS

AIMS OF THE UNIT:- to identify typesof generators

- to characterize generators

- to understand the function of the three phase ac

generator

- to understand the grammar point `Preposition `

TASKS

1 Do your best to answer the brainstorming questions. 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 Do the given exercisesfor better remembering the tеxt.7 Study grammar point ‘Preposition` do the tasks.

8 Speak on the topic. Given schemes will help you to remember and understand the

topic. 9 Get more information about the topic. Do some research, create slideshow or a

project work and present them.

Brainstorming questions

 

 

1 How generators are categorized?

2 Can you give common characteristics of generators?

 

Aircraft ac generators range in size from thetachometer instrument generator up to the 90,000volt-ampere generators. Generators are categorized as either brush-type or brushless. Regardless of weight,shape, or rating, practically all of these generators havethe following common characteristics:

The stator (stationary armature winding) provides the ac output.

The ac generator field (rotor) is a rotating magnetic field with fixed polarity.

Regulating the rpm of the rotating magnetic field controls the voltage frequency.

Controlling the strength of the magnetic field regulates the voltage.

A three-phase generator isactually three separate power sources enclosed in onehousing. To produce the required120-/208-volt output, external connections form a wye. Each output winding produces 120 voltsas measured from n to a, b, or c (phase voltage). Whenmeasuring two separate phase voltages together (linevoltage), such as a to b, a to c, or b to c, the voltage is1.73 times the single-phase voltage, or 208 volts.The line voltage found in a three-phase,WYE-connected system is the vector sum of the voltagesgenerated by two separate phase windings. Because a120-degree phase difference exists between thevoltages, they reach their peak amplitudes at differenttimes. They add vectorically and not directly.In the four-wire, grounded-neutral, WYE-connectedsystem, the neutral wire attaches to the frame of theaircraft (ground). The three-phase wires run to buses,which supply power to various loads. A bus is a primarypower distribution point that is connected to the mainpower source. The connections for loads requiring 120volts are between one of the buses and the aircraftframe. The load connections requiring 208 volts arebetween two of the buses (phases).