Electrical Technology Digital Paper 1 (English)

November 2024 — Grade 12 / Matric — Electrical Technology

Past Paper 2024 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 2 pages 📝 89 items found ∑ 1 math symbols 📚 2 topics

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7.3Formulae and manipulations where needed Correct replacement of values Correct answer and relevant units where applicable 8. 9. A formula sheet is attached at the end of this question paper. Write neatly and legibly.

Q1— Section header —

1.1A disastrous event, resulting from the use of plant and machinery, or from activities at a workplace, is minor incident. major incident. accident.

1.2The impedance in a RLC series circuit, is minimum when the inductive reactance equals the capacitive reactance. inductive reactance is greater than the capacitive reactance. capacitive reactance is greater than the inductive reactance.

1.3In a pure capacitive circuit that is connected to an AC supply voltage leads the current by 90

1.4The quality factor of a to the bandwidth. inversely proportional

1.5between the supply inductor or capacitor and performs no real work.

1.6he purpose of the neutral conductor in a three phase AC syste m is t

1.7easure the energy. measure the voltage difference between phases

1.8configuration is used extensively as step down transformers in distribution systems where a four wire system is required.

1.9If there is an earth fault one of the phases of a three phase transformer, the difference

1.10When a three phase induction motor is connected to a three phase AC supply, a rotating magnetic field is

1.11In a three phase forward reverse motor of each contactor prevent the forward and reverse contactors from being energised at the same time.

1.12In an automatic sequence starter control circuit, the start button of motor 2 is e the contactor of the second motor after a pre determined time

1.13A ladder logic diagram in PLC software is executed from

1.14A device that is used to provide a delay in the operation of a PLC s program is known as

1.15During the process of regenerative braking, a braking resistor is connected in de

Q2— Section header —

2.1Define the term workplace with reference to the Occupational Health and Safety Act, 1993 (Act 85 of 1993\. (2\

2.2Name TWO human rights in the workplace. (2\

2.3Explain why poor ventilation is an unsafe condition in a workshop. (2\

2.4State TWO types of victimisation by an employer that are forbidden. (2\

2.5Explain why a person should not interfere with equipment in the workshop that is provided for safety. (2\ [10] Electrical Technology: Power Systems DBE/November 2024 NSC10

Q3— Section header —

3.1Explain the following terms with reference to RLC circuits

3.1.1Inductive r eactance (2\

3.1.2Bandwidth (2\

3.2FIGURE 3.2 below shows a RLC series circuit with a variable frequency supply . Answer the questions that follow. FIGURE 3.2: RLC SERIES CIRCUIT Given:

3.2.1State whether the circuit represented in FIGURE 3.2 has a leading or a lagging power factor.

3.2Calculate the current through the inductor. (3\

3.2Calculate the value of the inductor. (3\

3.2Calculate the value of resistor R if the impedance (3\ = 150 2,5 V/50 Hz

3.2Complete the phasor diagram in FIGURE 3.2. below in your ANSWER BOOK

3.2After decreasing the frequency, the current increased slightly. Explain why this happened. (3\

3.3FIGURE 3.3 below shows an RLC parallel circuit and its impedance vs frequency response curve. A nswer the questions that follow. FIGURE 3.3: RLC PARALLEL CIRCUIT AND FREQUENCY RESPONSE CURVE

3.3.1Calculate the current th ough the resistor. (3\

3.3.2Calculate the capacitive reactance. (3\

3.3.3Determine the total current. Give a reason for your answer. (2\

3.3.4Calculate the Q factor of the circuit (3\

3.3.5Calculate the bandwidth of the circuit (3\ [35] Electrical Technology: Power Systems DBE/November 2024 NSC Confidential Copyright reserved35

Q4— Section header —

4.1State TWO advantages of three phase systems. (2\

4.2efer to electricity generation at power stations in South Africa and answer the following questions 4.

4.2.2Name TWO energy sources other than coal used for electricity generation in South Africa. (2\

4.2.3Explain the transmission process with reference to voltages in the ational rid. (3\

4.3FIGURE 4.3 below shows the coil connection in a balanced three phase generator. Answer the questions that follow. FIGURE

4.3: THREE PHASE GENERATOR

4.3.1Identify the con figuration of the coils in FIGURE 4.3 above (1\

4.3.2Draw the voltage waveforms of a three phase AC generator. (4\

4.5FIGURE

4.5below shows how a three phase supply is connected to a three phase load.

4.5.1State ONE method other than capacitors used for power factor correction.

4.5.2Red raw FIGURE 4.5 above and show how a three phase power factor correcting capacitor bank will be connected to this system (3\

4.5.3State the preferred wattmeter method that would be used to measure the total power of the load. Motivate your answer. (2\ [35] SUPPLY35

Q5— Section header —

5.1Explain the function of transformers with reference to voltage and current. (2\ 5. Briefly describe the principle on which a transformer operates (2\

5.3.2Explain the purpose of the laminated iron core in a transformer. (2\

5.3.3Compare the construction of a three phase transformer with reference to core type and

5.3.4Describe how hysteresis losses occur in t he iron core of a transformer (3\ Windings Core Electrical Technology: Power Systems

Q6— Section header —

6.1State TWO typical applications (uses\ of three phase induction motor in

6.2FIGURE 6.2 below shows the terminal box of a three phase induction motor and an insulation resistance tester indicating a reading of 100 questions that follow. FIGURE 6.2: TERMINAL BOX

6.2.1State why this motor is NOT safe for use. (1\

6.2.2Explain the danger of the fault in FIGURE 6.2 above when the motor is powered. (1

6.2.3Redraw the terminals of the coils in your ANSWER BOOK and indicate how you would place the connecting plates/bars to connect this motor in delta (3\

6.3A three phase induction motor with six poles is connected to a 400 V/50 Hz supply. The motor experience s a slip of 6% at full load.

6.3.1Pole pairs per phase

6.3.2Synchronous speed (3\

6.3Rotor speed

6.4FIGURE 6.4 below shows the control circuit of an automatic star delta motor starter with contactor T set to 5 seconds. Answer the questions that follow. FIGURE 6.4: AUTOMATIC STAR DELTA CONTROL CIRCUIT

6.4.1State the function of MC N/O.

6.4.2Explain the function of contactor T. (2\

6.4.3Explain why it is safe to assume that MC will be the contactor connecting the motor coils in star in the main circuit. (2\

6.4.4Describe the operation of the circuit 5 seconds after the start button is pressed. (3\ Stop Start

6.5The name plate o a three phase induction motor indicates that it is able to power a 30 kW mechanical load when connected to a 400 V supply. The

6.5.1Efficiency (3\

6.5.2Line current (3\

6.5.3Reactive power (5\ [35] Electrical Technology: Power Systems 18 DBE/November 2024 NSC Confidential Copyright reserved35

Q7— Section header —

7.1Refer to the programmed scan cycle of a PLC and answer the questions that follow.

7.1.2State the TWO steps, other than the process scan of a programmed scan cycle. Explain the process scan

7.2Refer to FIGURE 7.2 below of the symbol of a logic gate and answer the questions that follow. FIGURE 7.2: LOGIC GATE

7.2.2Identify the logic gate in FIGURE 7.2 above. Draw the ladder logic of this logic gate. (1\ (3\

7.2.3Complete the truth table in FIGURE 7.2.3 below by writing down only the state of the output in the ANSWER BOOK. OUTPUT (W\

7.3Refer to inputs on a PLC and answer the questions that follow.

7.3.3Name TWO categories of input devices. Name TWO applications (uses\ of a level sensor Differentiate between the application of an

7.4FIGURE 7.4 below shows the relay diagram of a forward reverse motor starter Redraw and complete the PLC ladder logic diagram in FIGURE 7.4.1 that will execute the same function in a PLC system

7.5FIGURE 7.5 below shows a variable frequency drive (VFD\ circuit. Study the circuit and answer the questions that follow FIGURE 7.5: VARIABLE FREQUENCY DRIVE (VFD\ CIRCUIT

7.5.4Label blocks and State TWO types of motors used with a VSD.

Mathematical Content

f(x)

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections15 + 10 + 35 + 35 + 30 + 35 + 40 = 200 marks

Paper information

SubjectElectrical Technology

Year2024

SessionNovember

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages22

Downloads7

Examination context

Decade2020s

Years ago2y

SeasonSpring (SH)

Start dayTuesday

Exam periodNovember 2024

Days since exam720

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