Electrical Technology Electronics Paper 1 (English)

November 2021 — Grade 12 / Matric — Electrical Technology

Past Paper 2021 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 7 pages 📝 81 items found ∑ 2 math symbols 📚 2 topics

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7.1Formulae and manipulations where needed

7.2Correct replacement of values

7.3Correct answer and relevant units where applicable 8. A formula sheet is attached at the end of this question paper. 9. Write neatly and legibly. Electrical Technology: Power Systems

Q1— Section header —

1.1Choose the correct example of an unsafe condition that is likely to cause damage to property or an injury: Running in the workshop Spilling liquid or oil without cleaning it up Faulty tools or equipment

1.2> X

1.3The phase angle of a predominantly leading. lagging. in phase.

1.4a range of frequencies. conductance dissipation factor resonant frequency

1.5The standard international phase seque nce for a three phase system is

1.6The phase angle between any two ph ases of a balanced three phase system is 150 degrees

1.7A measuring ins trument used to measure electrical energy is a wattmeter kWh meter

1.8step up transformer is used to increase the power. decrease

1.9In three phase transformers, the transfer of electrical energy from the primary winding to the secondary winding takes place by means of mutual induction

1.10Which ONE of the following relates to a mechanical inspection of a three phase motor? Insulation resistance test between the windings and earth

1.11switch on the motor. deactivate the control circuit and to isolate the power circuit when excessive current flows through the motor.

1.12The speed of rotation of the magnetic field in the stator windings is speed. rotor slip synchronous

1.13The chronological order of operation for the scan cycle of a PLC is scan inputs, update outputs, process inputs. pdate outputs,

1.14A semiconductor device that uses light to connect an electrical signal between two electrically isolated circuits opto

1.15The purpose of the rectifier stage of a variable speed drive is to convert AC to DC

2.1State TWO functions of a health and safety representative. (2\

2.2Give TWO examples of human rights in the workplace. (2\

2.3Differentiate between an unsafe act and an unsafe condition (2\

2.4Risk analysis can be divided into different categories. Name ONE category. (1\

2.5Define danger with reference to the Occupational Health and Safety Act, 1993 (Act 85 of 1993\ (2\

2.6Name ONE personal protective item you would use when etching a printed circuit board (PCB\ (1\ [10] Electrical Technology: Power Systems10

3.1Define capacitive reactance with reference to RLC circuits. (2\

3.2State the phase relationship between the current and voltage in a pure inductive AC circuit. (1\

3.3Refer to FIGURE 3.3 below and answer the questions that follow. FIGURE 3.3: RLC SERIES CIRCUIT Given:

3.3.1Calculate the inductance of the inductor. (3\

3.3.2Calculate the impedance of the circuit. (3\

3.3.3Calculate the power factor. (3\

3.3.4State THREE conditions that will occur if the power factor is at unity in a RLC series circuit. (3\ 120

3.4Refer to FIGURE 3.4 A and FIGURE 3.4 B below to answer the questions that follow. FIGURE 3.4 A: PARALLEL RESONANT CIRCUIT (Hz\

3.4.1Determine the resonant frequency in FIGURE 3.4 B. (1\

3.4.2Compare the values of the inductive reactance and capacitive reactance when the frequency increases from 200 Hz to 1 600 Hz. (2\

3.4.3Calculate the voltage drop across the inductor when the frequency is 600 Hz. (3\

3.4.4Calculate the value of the capacitor using the reactance value at 600 Hz. (3\ AC Electrical Technology: Power Systems

3.5Refer to FIGURE 3.5 below and answer the questions that follow. FIGURE 3.5: RLC SERIES CIRCUIT

3.5.1Calculate the total current flow through the circuit. (3\

3.5.2Calculate the voltage drop across the inductor. (3\

3.5.3Calculate the Q factor of the circuit. (3\

3.5.4Explain why the phase angle of the circuit in FIGURE 3.5 would be zero. (2\ [35] 2035

4.2.3Phase angle (3\ .2.4 Reactive power

4.3State TWO advantages of power factor correction to the consumer. (2\ Transformer Step up 11

4.4.3State how the meter reading could be brought closer to unity (1\ .5

4.5.3Explain why the two wattmeter method is preferred over the three wattmeter method (2\

5.3.2Secondary phase voltage (3\

5.3.3Transformer ratio (3\

5.3.4Apparent power (3\

5.3.5Efficiency if the copper losses are 1 kW and core losses are 500 W (3\

5.3.6Power factor (3\ [30]30

6.1.3State WO applications of squirrel cage induction motors.

6.1.4State TWO contributing factors that determine the speed of rotation in a three phase induction motor. (2\

6.2Refer to FIGURE 6.2 below and answer the questions that follow. FIGURE 6.2: THREE PHASE MOTOR CONNECTION

6.2.1Is this motor connected in star or in delta (1\

6.2.2State how the direction of rotation of this motor can be reversed (1\

6.2.3Name TWO important procedures to follow before testing the insulation resistance of the motor in FIGURE 6.2. (2\ End bell Stator windings Fan blades End bell Shaft

6.3A star connected three phase motor with four pole pairs per phase draws a line current of 6 A when connected to a 380 V/

6.3.1Synchronous speed (3\

6.3.2Percentage slip if the rotor speed is 700 r /min (3\

6.3.3Output power (3\

6.4Refer to FIGURE 6.4 below and answer the questions that follow. FIGURE 6.4: MANUAL SEQUENCE STARTER

6.4.1Name the component that prevents MC from automatically energising when the power is restored after a power failure. (1\

6.4.2State the function of MC (2\ MC

6.4.3Explain the purpose of wiring O and O in series

6.4.4Explain the operation of the circuit. (5\

6.4.5Explain how the circuit operation will be affected if contact MC is faulty and permanently closed. (2\ [35]35

7.1.3Name the component used to switch the load connected to a PLC. (1\

7.2Explain the term scan time with reference to the scan cycle of the PLC. (2\

7.3Explain the term software with reference to the PLC. (3\

7.4Refer to sensors as input devices of a PLC and nswer the questions that follow.

7.4.3Explain why the overload sensor in FIGURE 7.4.3 is connected to an analogue input on a PLC. (3\ Solder pads Insensitive direction Sensitive direction

7.5FIGURE 7.5 below shows a control circuit of a forward reverse starter. Draw the PLC ladder logic program that will execute the same function in a PLC system. FIGURE 7.5: CONTROL CIRCUIT

7.6FIGURE 7.6 below shows the different stages in a variable speed drive. Answer the questions that follow. FIGURE

7.6VARIABLE SPEED DRIVE STAGES

7.6.1Identify stage (1\

7.6.2Name a semiconductor component that could replace the switches used at (1\

7.6.3State TWO advantages of using variable speed drives. (2\

7.6.4Describe vector drives as a method of speed control. (3\

7.7Explain the process of regenerative braking in a VSD system when the momentum of a load starts to drive a motor. (3\

7.8Name the component used to dissipate the excessive energy during the process of regenerative braking. (1\ [40] TOTAL 20040

Mathematical Content

f(x)trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections15 + 10 + 35 + 30 + 35 + 40 = 165 marks

Paper information

SubjectElectrical Technology

Year2021

SessionNovember

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages19

Downloads10

Examination context

Decade2020s

Years ago5y

SeasonSpring (SH)

Start dayFriday

Exam periodNovember 2021

Days since exam1,813

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