Electrical Technology Power Systems Paper 1 (English)

May-June 2025 — Grade 12 / Matric — Electrical Technology

Past Paper 2025 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 21 pages 📝 85 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 A formula sheet is attached at the end of this question paper. Write neatly and legibly. 2025

Q1— Section header —

1.1ritical incident is an event where learner is injured without requiring first aid pain is caused due to a soldering iron burn. a learner

1.2

1.3

1.4

1.5The instrument that indicates the ratio of the real power the load to the apparent power from the supply is a/an ammeter energy meter power factor meter wattmeter

1.6What effect does power factor correction have on the efficiency of three phase electrical systems? It decreases the efficiency by increasing losses. It has no effect on the efficiency. It improves the efficiency by increasing the voltage.

1.7

1.8In a transformer, the factor that contributes to the continu degradation of its insulation is low input supply voltage. many windings around the core. insufficient magnetic field. insufficient ventilation.

1.9The contribute the highest percentage of the most common internal faults of three phase transformers. core windings bushing terminals

1.10

1.11A/An is essential in a forward reverse motor starter to enable the motor to reverse its direction of rotation circuit breaker overload relay second contactor second stop button (1\

1.12

1.13In a PLC refer all the physical parts and components to form the device. hardware software firmware ladder

1.14

1.15

Q2— Section header —

2.1Define health and safety equipment (2\

2.2State TWO unsafe acts regarding safety equipment that are forbidden in an electrical technology workshop (2\

2.3State the purpose of the Occupational Health and Safety Act, 1993 (Act 85 of 1993\

2.4Explain why it is important for employers to inform employees about health and safety at the workplace. (2\

2.5Briefly explain why discipline is considered an important work ethic with reference to the electrical technology workshop. (2\ [10]10

Q3— Section header —

3.1Explain the term reactance with reference to a pure inductive circuit. (2\

3.2Refer to the circuit in FIGURE 3.2 below and answer the questions that follow. FIGURE 3.2: RLC SERIES CIRCUIT Given: = 120 V = 74,28 V = 164,22 V = 60 Hz Calculate the:

3.2.1Capacitive reactance (3\

3.2.2Total current (3\

3.2.3Voltage across the inductor (3\

3.2Capacit e value that will cause resonance (3\ Redraw and complete the phasor diagram in FIGURE 3. below. When labelling, use the relevant calculated values from the calculations above. = 164,22 V = 74,28 V

Q4— Section header —

4.2In hronological order, name the TWO stages after eneration in the South African National Power Grid. (2\

4.3Explain how the voltage value of the power generated changes from the ower station u p to when it is used in domestic households in South Africa.

4.4kW delta connected inductive load is powered from a three phase supply with a

4.4.1Apparent power (3\

4.4.2Phase angle (3\

4.4.3Reactive power (3\

4.4.4Line current after the power factor was improved to 0,95 (3\

4.5Prove by means of a calculation

Q4— Section header —

4.6Explain why the addition of capacitors in parallel with the load (power factor correction\ reduces the current drawn from the supply. (3\ 10

5.5Refer to FIGURE 5.5 below and answer the questions that follow Primary Secondary FIGURE 5.5: SINGLE PHASE TRANSFORMERS

5.5.1Name the configuration in which the three single phase transformers are connected in FIGURE 5.5 above. (1\

5.5.2State whether the primary or secondary windings are thicker if the transformer in FIGURE 5.5 above is a step down transformer. Motivate why. (2\

5.5.3Explain why the windings in the three single phase transformers must be connected in the correct phasing sequence on both primary and secondary sides. (2\

5.6Explain the term step with reference to transformers. (2\ 13

5.7FIGURE 5.7 below shows a line diagram of the protection devices typically used in a substation for the transformer to operate safely. Answer the questions that follow. 11 kV Buch REF DOC 3,3 kV

5.7.1Name the protection device abbreviated DOC (1\

5.7.2State the purpose of a Buchholz relay. (1\

5.7.3Explain how the BEF (Balanced Earth Fault relay protects the transformer. (2\ [30] DOC Directional vercurrent Isolator30

6.1FIGURE

6.1below shows an exploded view of a three phase motor. Answer the questions that follow. FIGURE 6.1: EXPLODED VIEW OF A THREE PHASE MOTOR

6.1.1Name (3\

6.1.2Explain the purpose of the fan blades on the rotor.

6.1.3State TWO mechanical inspections that must be carried out on an electric motor regularly (2\

6.1.4FIGURE 6.1.4 below shows the terminal box and table with readings from three electrical tests carried out

6.2A three phase delta connected motor has a total of 18 poles and is connected to a 400 V/50 Hz supply. The input power to the motor is 12 kW with a lagging power factor of 0,9. The total losses on the motor is 500 W.

6.2.1Synchronous speed of the motor (3\

6.2.2Rotor speed if there is 5% slip (3\

6.2.3Efficiency of the motor (3\

6.2.4Output power of the motor (3\

6.2.5Line current drawn by the motor (3\ 16

6.3FIGURE 6.3 below shows the control circuit of an automatic star delta motor starter with a timer. The timer is set to 3 seconds. Answer the questions that follow STOP

6.3.1State whether timer is an ON delay or an OFF delay timer. (1\

6.3.2Name the function of contacts N/C and N/C (1\

6.3.3State which contactor is responsible for connecting the motor in star. Motivate your answer. (2\

6.3.4Explain the operation of the circuit from 3 seconds after the start button has been pressed. (4\ [35] 1735

7.1Name ONE advantage of soft wired systems as used on PLCs.

7.2Explain the term put scan with reference to the programmed scan cycle of a PLC. (2\

7.3Explain why a PLC system is safer than a hardwired system when a fault condition occurs. (2\

7.4Describe the following with reference to PLCs:

7.4.1Central processing unit (2\

7.4.2Soft wired systems (2\

7.4.3PLC software (2\

7.5Differentiate between an analogue signal and a digital signal (2\

7.6With reference to sensors:

7.6.1Explain the term sensor (2\

7.6.2Name TWO types of sensors other than a proximity sensor. (2\

7.6.3State TWO uses of a proximity sensor. (2\ 18

7.7Refer to FIGURE 7.7 (A\ below edraw and complete the PLC ladder logic diagram in FIGURE 7.

7.8.1DC capacitors (1\

7.8.2Braking resistor (2\ Refer to FIGURE 7. below nswer the questions that follow. Three phase supply

7.9: BLOCK DIAGRAM OF VSD Label block (1\ Name the main component used in the filter circuit. (1\ Describe the operation of the inverter. (5\ State TWO advantages of using VSDs

Mathematical Content

f(x)trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

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

Paper information

SubjectElectrical Technology

Year2025

SessionMay-June

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages21

Downloads14

Examination context

Decade2020s

Years ago1y

Season—

Start day—

Exam period—

Days since exam—

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