Electrical Technology Power Systems Paper 1 (English)

November 2018 — Grade 12 / Matric — Electrical Technology

Past Paper 2018 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 13 pages 📝 79 items found ∑ 1 math symbols 📚 2 topics

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Q1— Section header —

1.1Define the term major incident with reference to the Occupational Health and Safety Act, 1993 (Act 85 of 1993\. (2\

1.2State TWO general duties of manufacturers with regard to a product that will be used at the workplace. (2\

1.3Explain why horseplay is unsafe act in the workshop. (2\

1.4State TWO procedures to protect yourself when helping a person who is being shocked by electricity. (2\

1.5Define the term qualitative risk analysis (2\ [10]10

Q2— Section header —

2.1Define the term impedance with reference to RLC circuits. (2\

2.2Illustrate the phase relationship between current and voltage by drawing the waveforms of the following circuits on the ANSWER SHEET

2.2.1Pure capacitive circuit (2\

2.2.2Pure inductive circuit (2\

2.3FIGURE 2.3 below shows a reactance of the questions that follow. FIGURE 2.3: RLC SERIES CIRCUIT Given:

2.3.1Capacitance of the capacitor (3\

2.3.2Inductance of the inductor (3\

2.3.3Impedance of the circuit (3\

2.3.4Total current through the circuit (3\

2.3.5

2.4Explain how the value of the inductive reactance will be affected if the supply frequency is doubled (2\

2.5Define the term resonant frequency (2\

2.6Refer to FIGURE 2.6 and answer the questions that follow. 100 FIGURE 2.6: RLC PHASOR DIAGRAM

2.6.1Calculate the following: (a\ Inductive reactance (3\ (b\ Capacitive reactance (3\ (c\ Reactive current

2.6.2State whether the phase angle is lagging or leading. (1\

2.7Describe how a low resistance value affects the bandwidth of an LC tuned circuit. (2\ [40]40

Q3— Section header —

3.1State the of the angle between the phases of a balanced hree

3.2Define the following terms

3.2.1Apparent power (2\

3.2.2(2\

3.3State THREE advantages the supplier when the power factor improve (3\

3.4With reference to three phase power generation

3.4State THREE disadvantages of single phase AC generation (3\ Explain the advantage of connecting a three phase alternator in star

3.5Explain how copper losses are reduced in overhead transmission lines

3.6phase system supplies a star connected inductive load. The input power to the load is 18 kW with a lagging power

3.6Phase voltage (3\ Line current to the load (3\ Apparent power (3\ The two

Q4— Section header —

4.1Name THREE losses that occur in transformers.

4.2State TWO applications of a delta star transformer.

4.3State TWO functions the oil used in transformer (2\

4.4Describe the operation of transformer.

4.5Explain why transformers have a better efficiency in comparison to other machines. (3\

4.6State the purpose of the Buchhol relay in transformers. (2\

4.7A three phase transformer with 1 500 primary turns is connected in delta star to a supply voltage of 2,2 primary

4.7.1Secondary phase voltage (3\

4.7Transformation ratio (3\

4.7Number of secondary turns (3\

4.8A three phase transformer with a turns ratio of 30 1 is connected in delta star Answer the question that follow

4.8Determine whether the transformer is step down or step tran former

4.8Describe why the transformer can be used for distributing electrical power to domestic and industrial load (3\ [30]30

Q5— Section header —

5.1TABLE below shows the name plate of a three phase induction motor Answer

5.1State the amount of current the motor will draw from the supply at

5.1Explain why the motor is suitable for use in South Africa (2\

5.1State what the kW the name plate indicates

5.1Determine the total number of poles

5.1Calculate the efficiency of the motor at full load if the total loss is 1,2 kW Explain the purpose of no volt protection with reference to motor control circuits. Explain how the direction of rotation

5.4State TWO mechanical inspections that must be carried out on an induction motor before commissioning. (2\

5.5Refer to the control circuit diagram in FIGURE 5.5 and answer the following questions. MC STOP MC MC MC MC FWD

5.5CONTROL CIRCUIT dentify the control circuit in FIGURE

5.5(1\

5.5State ONE application of the control circuit

5.5State the purpose of the overload relay. (2\

5.5Describe the operation of the control circuit [30]30

Q6— Section header —

6.1State THREE disadvantages of hard wiring

6.2Name the THREE steps that PLC has to undergo to complete one programmed scan cycle. (3\

6.3Explain the term scan time with reference to the scan cycle of PLC. (2\

6.4Refer to FIGURE 6.4 below and answer the questions that follow FIGURE 6.4 : NAND gate Draw the ladder logic diagram (3\ Draw the truth table for the NAND gate.

6.5Describe how PLC achieves its function. (3\

6.6With reference to analogue and digital inputs

6.6.1Give HREE examples of analogue input devices

6.6Explain why an analogue input may be converted to a digital input (4\

6.7Describe how PLC use a relay to drive motor.

6.8State the purpose of the timer function (2\

6.9Explain the latching concept with reference to retaining circuits (3\ 10

6.1Name HREE types of motors used with variable speed drive

6.1Explain voltage frequency control with re

6.1Explain the purpose of the braking resistor with reference to regenerative braking. (2\

6.1Explain (2\ [60] TOTAL60

Q2— Section header —

Mathematical Content

trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections10 + 40 + 30 + 30 + 30 + 60 = 200 marks

Paper information

SubjectElectrical Technology

Year2018

SessionNovember

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages13

Downloads10

Examination context

Decade2010s

Years ago8y

SeasonSpring (SH)

Start dayMonday

Exam periodNovember 2018

Days since exam2,909

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