Electrical Technology Grade 12 Eastern Cape Mock 2023 Memo

NATIONAL SENIOR CERTIFICATE GRADE 12 SEPTEMBER 2023 ELECTRICAL TECHNOLOGY: POWER SYSTEMS MARKING GUIDELINE MARKS: 200 This marking guideline consists of 14 pages.

2 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) INSTRUCTIONS TO MARKERS 1. All calculations with multiple answers imply that any relevant, acceptable answer should be considered. 2. Calculations: 2.1 All calculations must show the formulae. 2.2 Substitution of values must be done correctly. 2.3 All answers MUST contain the correct unit to be considered. 2.4 Alternative methods must be considered, provided that the correct answer is obtained. 2.5 Where an incorrect answer could be carried over to the next step, the first answer will be deemed incorrect. However, should the incorrect answer be carried over correctly, the marker has to re-calculate the values, using the incorrect answer from the first calculation. If correctly used, the candidate should receive the full marks for subsequent calculations. 2.6 Markers should consider that learners answers may deviate slightly from the marking guideline depending on how and where in the calculation rounding off was used. 3. These marking guidelines are only a guide with model answers. 4. Alternative interpretations must be considered and marked on merit. However, this principle should be applied consistently throughout the marking session at ALL marking centres. Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 3 QUESTION 1: MULTIPLE-CHOICE QUESTIONS 1.1 B✓ (1) 1.2 A✓ (1) 1.3 C✓ (1) 1.4 C✓ (1) 1.5 A✓ (1) 1.6 B✓ (1) 1.7 C✓ (1) 1.8 D✓ (1) 1.9 C✓ (1) 1.10 B✓ (1) 1.11 D✓ (1) 1.12 A✓ (1) 1.13 D✓ (1) 1.14 B✓ (1) 1.15 C✓ (1) [15] Copyright reserved Please turn over

4 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY 2.1 • Integrity ✓ • Sense of responsibility ✓ • Emphasis on quality • Discipline • Sense of teamwork (Any 2 x 1) (2) 2.2 An event that causes grave or severe physical injury to a person, ✓ threatening their health and safety. ✓ (2) 2.3 • Avoid direct contact with any chemical ✓ • Always wear personal protective clothing • Always read and be aware of the warning symbols on containers (Any 1 x 1) (1) 2.4 An unsafe act is the wilful performance of a task or activity in a manner that may threaten the health and safety of everyone. ✓ A calculated risk is the probability that injury or damage may occur while using dangerous equipment. ✓ (2) 2.5 • To prevent oneself from being electrocuted. ✓ • To prevent injury (Any 1 x 1) (1) 2.6 This could damage the equipment and render the equipment unsafe ✓ and compromise the safety of the user. ✓ (2) [10] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 5 QUESTION 3: RLC CIRCUITS 3.1 It is the opposition offered to current flow by the reactive components of an inductor, ✓ when it is connected to an AC supply. ✓ (2) 3.2 VL I Y-Axis Y-Axis 0 90º 180º 270º 360º Y-Axis • Full cycles drawn correctly ✓ • Phase difference correct ✓ • Waveforms labelled correctly ✓ (3) 3.3 3.3.1 XC = 1 ✓ 2𝜋𝑓𝐶 1 = ✓ 2 × 𝜋 × 60 × 200 × 10-6 = 13,26 Ω ✓ (3) 3.3.2 I = V ✓ Z 110 = 101,65 ✓ = 1,08 A ✓ (3) 3.3.3 Z =√R2 + (XL − XC )2 ✓ R =√Z2 + (XL − XC )2 =√101,652 − (31,55 − 13,26)2 ✓ = 100 Ω ✓ (3) 3.3.4 𝑋𝐿 = 2𝜋𝑓𝐿 ✓ 𝐿 𝑋 𝐿 = 2𝜋𝑓 31,55 = 2 × 𝜋 × 60 ✓ = 0,084 𝐻 = 84 𝑚𝐻 ✓ (3) Copyright reserved Please turn over

6 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) 1 3.4 fr = 2π√LC ✓ 1 = ✓ 2 × π ×√50 × 10−3 × 60 × 10−6 = 91,89 Hz ✓ (3) 3.5 3.5.1 V IC = X ✓ C 100 = 11,83 ✓ = 8,45 A ✓ (3) 3.5.2 IT = √IR 2 + (IC − IL )2 ✓ = √9,092 + (8,45 − 4,54)2 ✓ = 9,9 A ✓ (3) I 3.5.3 cosθ = IR ✓ T 9,09 = 9,9 ✓ = 0,918 ✓ (3) 3.5.4 Leading, ✓ because Ic is larger than IL . ✓ (2) 3.6 Selectivity is a measure of how well a resonant circuit responds to a range of frequencies ✓ and separates other frequencies. ✓ (2) 3.7 • The value of the series resistor ✓ • The LC ratio ✓ (2) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 7 QUESTION 4: THREE-PHASE AC GENERATION 4.1 4.1.1 B✓ (1) 4.1.2 C✓ (1) 4.1.3 A✓ (1) 4.2 • Installation costs are high ✓ • Not available everywhere ✓ • Not suitable for most residential applications • Appliances are expensive (Any 2 x 1) (2) 4.3 Direction of VBN rotation Z- A xi s120º 120º VRN xi s Z-Axis 120º Z- A VYN • 120º ✓ • Direction of rotation ✓ • Phasors drawn correctly ✓ • Labelling of phasors ✓ (4) 4.4 • Static capacitors ✓ • Synchronous motors ✓ • Phase advances ✓ (3) 4.5 4.5.1 VL = VPH ✓ = 415 V ✓ (2) 4.5.2 IPH = VPH ✓ RPH 415 = 45 ✓ = 9,22 A ✓ IL = √3IPH ✓ = √3 × 415 ✓ = 15,97 A ✓ (6) 4.5.3 P = √3VL IL cosθ ✓ = √3 × 415 ∂15,97 × 0,86 ✓ = 9 872,16 W = 9,87 kW ✓ (3) Copyright reserved Please turn over

8 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) 4.5.4 P ƞ = Poutput × 100% input 9 872,16 = 12 000 × 100 ✓ = 82,27% ✓ (3) 4.5.5 cos θ = 0,86 ✓ θ = cos-1 (0,86) ✓ = 30,68° ✓ (3) 4.6 PTOT = W1 + W2 + W3 ✓ = 2 000 + 1 780 + 3 500 ✓ = 7 280 W = 7,28 kW ✓ (3) 4.7 • Connect the current coils to two of the phases. ✓ • Connect the positive terminals of the voltage coils to the same two phases. ✓ • Connect both of the negative terminals to the third phase. ✓ (3) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 9 QUESTION 5: THREE-PHASE TRANSFORMERS 5.1 • Eddy current losses ✓ • Hysteresis losses ✓ (2 x 1) (2) 5.2 The excessive temperatures may cause serious problems ✓ like insulation failure. ✓ (2) 5.3 5.3.1 False ✓ (1) 5.3.2 True ✓ (1) 5.3.3 True ✓ (1) 5.4 • Cools the windings ✓ • Improves the insulation (Any 1 x 1) (1) 5.5 5.5.1 Heavy industries, where a high-power transfer is essential. ✓ Large low voltage systems that carry large currents. (Any 1 x 1) (1) 5.5.2 VLP = VPP ✓ = 11 kV ✓ VLS = VPP ✓ = 380 V ✓ (4) 5.5.3 P = √3VLS ILS cosθ ✓ P ILS = √3VLS cosθ 20 000 = ✓ √3 × 380 × 0,88 = 34,53 A ✓ (3) 5.5.4 IPS = ILS ✓ √3 34,53 = ✓ √3 = 19,94 A ✓ (3) 5.5.5 𝑃 = 𝑆 cos 𝜃 ✓ 𝑃 𝑆 = cos 𝜃 20 000 = 0,88 ✓ = 22 727,27 VA = 22 73 kVA ✓ (3) Copyright reserved Please turn over

10 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) 5.5.6 Transformer ratio = VPP ∶ VPS ✓ = 11 000 ∶ 380 ✓ = 28,95 ∶ 1 ✓ (3) 5.5.7 ƞ =𝑃 𝑃𝐿𝑂𝐴𝐷 × 100% ✓ 𝐿𝑂𝐴𝐷 + 𝑙𝑜𝑠𝑠𝑒𝑠 𝑃𝐿𝑂𝐴𝐷 × 100 𝐿𝑜𝑠𝑠𝑒𝑠 = − 𝑃𝐿𝑂𝐴𝐷 88 20 000 × 100 = − 20 000 ✓ 88 = 2 727,27 W = 2,73 kW ✓ (3) 5.6 This will decrease the secondary current, ✓ resulting in a decrease in the primary current due to the decrease of the magnetic force. ✓ (2) [30] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 11 QUESTION 6: THREE-PHASE MOTORS AND STARTERS 6.1 The rotor consists of copper or aluminium conducting rods, ✓ mounted slightly skew, ✓ and connected to the two end rings. ✓ (3) 6.2 The slope of the torque is approximately proportional to the slip. ✓ (1) 6.3 6.3.1 Ns = p ✓ 60.f s N .p f = 60 3 600×2 = ✓ 60 = 120 Hz ✓ (3) 6.3.2 % slip = 𝑁𝑠 −𝑁𝑟 × 100 ✓ 𝑁𝑠 3 600 − 3 400 = × 100 ✓ 3 600 = 5,56% ✓ (3) 6.4 6.4.1 𝑃𝐼𝑁𝑃𝑈𝑇 = √3VL IL cosθ ✓ 𝑃 𝑉𝐿 = √3𝐼𝐿 cos 𝜃 10 000 = ✓ √3 ×18,99 × 0,8 = 380,04 V ✓ (3) 6.4.2 𝑃𝑂𝑈𝑇𝑃𝑈𝑇 = √3𝑉𝐿 𝐼𝐿 cos 𝜃 ƞ ✓ 90 = √3 × 380,04 × 18,99 × 0,8 × 100 ✓ = 9 000,1 W = 9 kW ✓ (3) 6.4.3 Q = √3VL IL sin 𝜃 ✓ = √3 × 380,04 × 18,99 × sin 36,87 ✓ = 7 500,1 𝑉𝐴𝑟 = 7,5 𝑉𝐴𝑟 ✓ (3) 6.5 • Insulation resistance test ✓ • Continuity test ✓ • Check for loose connections • Bearing test (Any 2 x 1) (2) 6.6 A normally closed contact of the forward contactor is connected in series with the coil of the reverse contactor ✓ and a normally closed contact of the reverse contactor is connected in series with the coil of the forward contactor. ✓ (2) Copyright reserved Please turn over

12 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) 6.7 6.7.1 Automatic star delta ✓ (1) 6.7.2 A – stop button ✓ B – start button ✓ MC N C – O1 ✓ (3) 1 6.7.3 The N/C timer keeps the star contactor energized, until the preset time is reached then it opens. ✓ After the preset time the N/O contact closes and the delta contactor is energised. ✓ (2) 6.7.4 Overload setting = 125% × rated current ✓ = 1,25 × 8 ✓ = 10 A ✓ (3) 6.7.5 The motor would still run, in star for the preset time. ✓ After the preset time the current will flow to the delta coil but it will not energise, ✓ and the motor will stop. ✓ (3) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2023) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 13 QUESTION 7: PROGRAMMABLE LOGIC CONTROLLERS 7.1 A PLC is an industrial computer, ✓ that is programmed to perform a number of routine tasks, ✓ in a strict order at exactly the right time. ✓ (3) 7.2 Modems are circuits the PLC uses to connect its CPU to the input sensing devices ✓ as well as the output load devices. ✓ (2) 7.3 7.3.1 NOR gate ✓ (1) 7.3.2 A B Output 1 mark for each correctly labelled symbol. Symbols only = 1 mark only (3) 7.3.3 a – 1 ✓ b–0✓ c–0✓ d–0✓ (4) 7.4 • Measure tank levels ✓ • High/low level alarms ✓ • Irrigation control • Monitoring of rivers and dams • Remote monitoring of chemical, petrol, and diesel manufacturing (Any 2 x 1) (2) 7.5 • AC induction motors speed depends on the frequency of the supply. ✓ • A variable speed control receives the frequency, and its circuitry increases or decreases the output frequency to the motor. ✓ • This varying of the frequency then increases or decreases the motor speed. ✓ (3) 7.6 7.6.1 Diode bridge rectifier converts an AC voltage ✓ to a DC voltage. ✓ (2) 7.6.2 Filter smooths the AC ripple ✓ to ensure a pure DC voltage on the DC rail. ✓ (2) 7.6.3 The inverter inverts the DC voltage ✓ back to an AC voltage, at a variable frequency, ✓ that controls the motor speed. ✓ (3) Copyright reserved Please turn over

14 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2023) 7.7 7.7.1 Lamp 1 comes on once the motor is energised ✓ to indicate that it is running. ✓ (2) 7.7.2 The overload protects the motor, ✓ by switching the supply off to the motor when excessive currents flow. ✓ (2) 7.7.3 If lamp 2 was fused, there would no indication ✓ that the motor was not energised. ✓ (2) 7.7.4 stop ✓ start ✓ O/L ✓ motor ✓ Lamp 1 ✓ ✓ N/O1 ✓ N/O2 M M Lamp 2 ✓ ✓ N/C M (9) [40] TOTAL: 200 Copyright reserved Please turn over