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Probably the most commonly found machinę is the totally-enclosed, fan-cooled motor (TEFC). The motor winding is totally enclosed in the metor housing which is usuaily ribbed on the outside. A fan is mounted on the shaft external to the housing and 20 is protected by a shield. This fan blows air over the casing removing heatfromthe motor. In largersizes,there is also a fan inside the casing blowing airoverthe windingstransferring heatto the casing.

Where motors are required to operate in explosive situations, the 25 motor must be of flame-proof construction. This means that it must be enclosed in such a manner that any explosion which may occur within the motor must be contained within the motor. Often it is easier to prevent explosive gases entering the motor. Ventilated motors are used which draw air from an uncontaminated area. This 30 is pumped into the motor which keeps its internal pressure above that of its surroundings.

Fig. 1 illustrates a variety of protected motors.

Source: Adapted from D.W. Tyler, Elactrical Applications, 3

Z 4 Computer Aided Design (CAD)

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Equallons:

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Scalę conuertina

fl-FI*d

f2-F2*d

f3-F3*d

f4“F4*d

fS-FS»d

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Forces resulllng from the diagram:

Beam Forces Bearlng Forces FI is 2I640.29:FB Is 6375.000 Ib F2 is 26439.95:FB Is 6375.000 Ib F3 is 22I85.65:FU is 5999.999 Ib F4is 15250.000 Ib F5 is l8843.74(Cable Forces)

F6 is 3000.000 :Fc is 3000.000 Ib

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Fig. 1

Task 1

1

2

3

Study the example of Computer Aided Design in Fig. 1. Answer these ąuestions about the diagram.

What structure does it show?

Apart from the design, what other information does the drawing provide? What do you think the top row of words are for - File, Edit. Constrain, etc.?

Listening

Task 2    You are going to listen to an interview with a designer of car engines. He

describes some of the advantages of CAD over traditional approaches to design - for example. drawing and modelling. Before you listen, list any advantages you think CAD has over these traditional approaches.

Task 3 o Study the following extract from the tapescript of the interview. It covers the intcrvicwcr's first ąuestion and answer. Fili in the gaps before you listen. One word is missing from each gap. Then listen to this part of the interview to check your answers.

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