Electrical Technology English

November 2008 — Grade 12 / Matric — Electrical Technology

Past Paper 2008 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 11 pages 📝 71 items found ∑ 1 math symbols 📚 3 topics

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Q1— Section header —

1.1Technology is developed by people for people. At the very foundation of this action are entrepreneurs. Entrepreneurs are the people who can identify possibilities and who are willing to take financial risks in order to establish

1.2People use technologies and systems to meet their needs and desires. The use of technology has positive and negative impacts on society and the environment. Discuss briefly how the use of technologies can impact

1.2.1Land (2\

1.2.2Water (2\

1.2.3Air (2\ [10]10

Q2— Section header —

2.1On reaching old age, some elderly people find it very difficult, and often frightening, to climb up and down stairs. Common possible solutions might be to live downstairs, to make renovations to the house, or maybe to move into

2.2During the year you were required to complete a practical assessment task (PAT\ocess you were required to complete a number of steps. These steps included the following: 1. Critical evaluation of a scenario and the identification of a problem

Q3— Section header —

3.1State ONE unsafe act that could take place in an electrical technology workshop. (1\

3.2State ONE unsafe condition that could exist in an electrical technology workshop. (1\

3.3State FOUR steps that must be ad hered to, in order of priority, when discovering a person who has become a victim of an electrical shock in a workshop. (4\

3.4Describe TWO good housekeeping rules that will ensure that the electrical technology workshop is a safe place to work in. (4\ [10]10

Q4— Section header —

4.1Name ONE method that can be used to improve the cost effectiveness of an induction motor operating with a poor lagging power factor. (1\

4.2Draw a neatly labelled phasor diagram of a balanced three-phase system. (4\

4.3A three-phase star-connected induction motor draws a current of 8 A when connected to a 415 V/50 Hz supply. If the motor has a power factor of 0,85 determine the following:

4.3.1The current in each phase of the motor winding (2\

4.3.2The voltage across each phase (3\ [10]10

Q5— Section header —

5.1

5.2

5.2.1The current flow through each branch (9\

5.2.2The total current flow through the circuit (3\

5.3

5.430

Q6— Section header —

6.1The circuit diagram shown in FIGURE 6.1 makes use of an SCR to control the brightness of a lamp. The circuit is connected to 240 V/50 Hz mains supply. Explain the basic principle of the operation of the circuit.

6.2How is a TRIAC switched ? (5\

6.3How is a TRIAC switched ? (2\

6.4State THREE advantages that a TRIAC has over that of a SCR. (3\ SCR R1R2 D C Rload 240 V/50 Hz

6.5Draw and label the following symbols:

6.5.1TRIAC (3\

6.5.2DIAC (2\ [25]25

Q7— Section header —

7.1Name FOUR characteristics of an ideal operational amplifier. (4\

7.2The circuit shown in FIGURE 7.1 must switch between a gain of 10 and 90. Calculate the values of R and R that must be used. x 10 x 90 F2 1k

7.3

7.4Determine the output voltage (V out \he voltage comparator shown in FIGURE 7.3 with the following input:

7.4.1= 6 V and V = 5 V (1\

7.4.2= 5 V and V = 5 V (1\

7.4.3

7.5

Q8— Section header —

8.1There are various methods of connecting the primary and the secondary windings of three-phase transformers. State TWO methods. (2\

8.2A transformer used to supply a farm gets very hot, which is unacceptable and has to be switched off in order to cool down.

8.2.1State TWO causes of overheating in transformers. (2\

8.2.2Explain how overheating in transformers can be prevented. State TWO methods. (2\

8.3A 24 kVA transformer supplies power to a football stadium that is being erected for the 2010 FIFA Soccer World Cup. The transformer supplies the stadium with an output line voltage of 415 V when it is connected in delta-star.

8.3.1The phase voltage supplied to the stadium (3\

8.3.2The maximum line current that can be drawn from the supply (the primary current\ (3\

8.3.3The maximum power that can be delivered at full load if the power factor is lagging at 0,85 (3\ [15]15

Q9— Section header —

9.1Consider the following scenario and solve the problem stated using LOGIC: A manufacturing plant uses two tanks to store a liquid chemical. Each tank has a sensor that detects when the liquid chemical level drops

9.2A network of cascade inverters is shown in FIGURE 9.1. If a HIGH (logic 1\ is applied to point A, determine the logic levels at the points labelled B through to F. A B C D E

9.3

9.4Apply De Morgan's theorem to the following Boolean expression: ____________ Z = ABC + DEF (4\

9.5Give the Boolean expression of the ladder diagram shown in FIGURE 9.3. a c d Q1 (S\

9.6

9.7State FIVE advantages of programma ble logic controllers (PLCs\ (5\ ENABLE

Q10— Section header —

10.1Answer the following questions with reference to star-delta starters.

10.1.1Why are star-delta starters us ed to start three-phase motors? (2\

10.1.2Briefly explain the star-delta starting process . (6\

10.2What action does a forward-reverse three-phase starter need to change the direction of a three-phase motor? (2\

10.3Explain the term normally-open contacts , with reference to motor starters. (2\

10.4Explain the function of an overload unit in a motor starter. (3\

10.5Electrical motors have internal losses. Name and describe ONE of the losses. (3\

10.6Explain the basic principle of operation of a three-phase squirrel-cage induction motor. (7\

10.7Before a motor is started, after it has been installed, basic mechanical and electrical inspections should take place. Name TWO basic mechanical and THREE basic electrical inspections that must take place before the

Mathematical Content

trig

Topics Identified

CircuitsMachinesConstruction

Mark Allocation

Total200 marks

Sections10 + 10 + 10 + 10 + 30 + 25 + 25 + 15 + 35 + 30 = 200 marks

Paper information

SubjectElectrical Technology

Year2008

SessionNovember

TypePast Paper

PaperSee title

LanguageEnglish

Pages12

Downloads5

Examination context

Decade2000s

Years ago18y

SeasonSpring (SH)

Start dayWednesday

Exam periodNovember 2008

Days since exam6,564

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