Electrical Technology Grade 12 Eastern Cape Mock 2025 QP

NATIONAL SENIOR CERTIFICATE GRADE 12 SEPTEMBER 2025 ELECTRICAL TECHNOLOGY: POWER SYSTEMS MARKS: 200 TIME: 3 hours This question paper consists of 15 pages, including a 2-page formula sheet.

2 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) INSTRUCTIONS AND INFORMATION 1. This question paper consists of SEVEN questions. 2. Answer ALL the questions. 3. Sketches and diagrams must be large, neat and fully labelled. 4. Show ALL calculations and round off answer correctly to TWO decimal places. 5. Number the answers correctly according to the numbering system used in this question paper. 6. You may use a non-programmable calculator. 7 Calculations must include the following: 7.1 Formulae and manipulations where needed. 7.2 Correct replacement of values. 7.3 Correct answer and relevant units where applicable. 8. A formula sheet is attached at the end of this question paper. 9. Write neatly and legibly. Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 3 QUESTION 1: MULTIPLE-CHOICE QUESTIONS Various options are given as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.15) in the ANSWER BOOK, for example 1.16 D. 1.1 A burn must be treated by … A covering the burnt area with butter. B putting ice on the burn wound. C puncturing the blisters. D running cold water over the burnt area until the pain reduces. (1) 1.2 When the current lags the voltage in a RLC circuit: A VC > VL B VL < VC C VL > VC D R=Z (1) 1.3 The circuit will be more … in nature and the resulting impedance will have a lagging phase angle. A resistive B inductive C capacitive D resonance (1) 1.4 At what frequency will a coil of inductance 80 mH have a reactance of 302 Ω? A 50 Hz B 150 Hz C 60 Hz D 600 Hz (1) 1.5 Apparent power is expressed in the SI units of … A watts. B volt-amperes. C reactive volt-amperes. D amperes. (1) 1.6 The purpose of oil in a transformer is for … A insulating and cooling. B heating and insulating. C lubricating and insulating. D preventing rust and insulating. (1) Copyright reserved Please turn over

4 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) 1.7 The … method(s) can determine the total power and the power factor of a circuit. A two-wattmeter B three-wattmeter C one-wattmeter D All of the above-mentioned (1) 1.8 The main function of a transformer is to: A Change alternating current to direct current B Decrease the power C Step up and step down an AC voltage D Step and step down a DC voltage (1) 1.9 Main source of heat generation in transformers is … losses. A eddy current B friction C copper or I 2 R D hysteresis (1) 1.10 Electromagnetically operated switches used in starters are called … A overloads. B no-volt coils. C isolators. D contactors. (1) 1.11 Rated speed of an induction motor is the … A speed of rotation of the magnetic field. B speed when maximum load is connected. C difference between synchronous speed and rotor speed. D maximum speed that the motor is allowed to work properly. (1) 1.12 The simplest and cheapest of all starting methods and is usually used for squirrel-cage induction motors is the … starter. A direct-on-line B forward and reverse C sequence control with a timer D automatic star delta (1) 1.13 A sensor is … A a discrete switch or push button that can produce an electrical ON or OFF. B an electronic device used to detect light. C a device which converts a physical condition into an electrical signal that can be used by PLC. D an electro-mechanical device that translates a mechanical force into an (1) electrical signal. Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 5 1.14 An electro-mechanical device that translates a mechanical force into an electrical signal: A Level sensor B Proximity sensor C Strain gauge D Opto-coupler (1) 1.15 The ladder diagram below represents the … A ( ) B output A AND-gate B NAND gate C OR-gate D NOR gate (1) [15] Copyright reserved Please turn over

6 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY 2.1 State ONE chemical safety precaution observed during the manufacture of (1) printed circuit boards. 2.2 Explain the word danger with reference to the Occupational Health and Safety (1) Act, 1993 (Act 85 of 1993). 2.3 List TWO recommended ways to stop bleeding. (2) 2.4 Name TWO duties that every employer has to inform all employees and health (2) and safety representatives of. 2.5 Briefly explain the “let go” current during an electric shock. (2) 2.6 Explain how discipline is vital for a strong work ethic. (2) [10] Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 7 QUESTION 3: RLC CIRCUITS 3.1 Draw a detailed phasor diagram of a pure inductive circuit. (3) 3.2 State the reference quantity in a series connected circuit. (1) 3.3 Refer to FIGURE 3.3 below and answer the questions that follows. X - A C = 100 µF R = 29 Ω L = 0,15 H X- X- x Axi Axi i s s s VR VL VC X- X- X- IT X - A Axi AC Axi Axi x s s s i s VS=13 V/50 Hz FIGURE 3.3: SERIES RLC CIRCUIT Given: R = 29 Ω L = 0,15 H C = 100 µF f = 50 Hz VT = 13 V Calculate the: 3.3.1 Reactance of the inductor (3) 3.3.2 Reactance of the capacitance (3) 3.3.3 Circuit impedance (3) 3.3.4 Total circuit current (3) 3.4 Distinguish between the concepts reactance and impedance. (4) 3.5 Determine the resonant frequency of a series circuit consisting of an inductor of 0,5 H, a capacitor of 75 ɥF and a 100 Ω resistor. Given: 𝐿 = 0,5 H C = 100 ɥF R = 100 Ω (3) Copyright reserved Please turn over

8 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) 3.6 A three-branch parallel RLC circuit has the following in each branch; a resistor with a value of 10 Ω, an inductor with a reactance of 28,23 Ω and a capacitor with a reactance of 42,44 Ω. The circuit is connected to a 100 V/25 Hz supply. Given: R = 10 Ω 𝑋𝐿 = 28,23 Ω 𝑋𝐶 = 42,44 Ω V = 100 V f = 25 Hz Calculate the: 3.6.1 Current through each branch (9) 3.6.2 Total current drawn from the supply (3) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 9 QUESTION 4: THREE-PHASE AC GENERATION 4.1 List THREE advantages of three-phase systems. (3) 4.2 Draw a fully labelled phasor diagram of the voltages generated by a star connection, showing the direction of rotation, the phase angles and relative magnitudes of the phasors. (5) 4.3 Define the following terms: 4.3.1 Transmission (1) 4.3.2 Substation equipment (1) 4.3.3 National grid (1) 4.4 Name the type of induction that occurs in transformers. (1) 4.5 List TWO advantages of power factor correction for the supplier. (2) 4.6 A three-phase delta connected load is supplied by a 250 kVA generator with a phase voltage of 240 volts. The power factor of the load is 0,8 lagging. Given: S = 250 kVA V = 240 V Cosθ = 0,8 lagging Calculate the: 4.6.1 Line voltage (2) 4.6.2 Line current (3) 4.6.3 Phase current (3) 4.6.4 Active power (3) 4.6.5 Phase angle (3) 4.7 Two wattmeters are connected to a balanced three-phase system. Wattmeter R gives a reading of 3 kW and wattmeter B gives a reading of 8,5 kW. Calculate the power factor. Given: WRED = 3 kW WBLUE = 8,5 kW (5) 4.8 Name the meter used to measure power. (1) 4.9 State ONE advantage of the three wattmeter method. (1) [35] Copyright reserved Please turn over

10 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) QUESTION 5: THREE-PHASE TRANSFORMERS 5.1 State ONE application of each of the following transformers: 5.1.1 Delta-delta transformer (1) 5.1.2 Star-delta transformer (1) 5.2 Name THREE factors that contribute to excessive heating in three-phase transformers. (3) 5.3 A delta-star connected transformer shown in FIGURE 5.3 below supplies a factory with 85 kW of electrical power. The current is lagging the voltage with a phase angle of 36,87º. The total loss in the transformer is 12,5 kW. The primary line voltage is13,8 kilo-volts and the secondary line voltage is 450 V. FIGURE 5.3 Calculate the: 5.3.1 Secondary line current (3) 5.3.2 Apparent power (3) 5.3.3 Reactive power (3) 5.3.4 Efficiency of the system (3) 5.4 Write down THREE methods employed when cooling oil immersed transformers. (3) 5.5 Name TWO types of transformer constructions available. (2) 5.6 List TWO requirements that must be satisfied for three single-phase transformers to operate as a three-phase transformer. (2) 5.7 State TWO safety aspects that should be adhered to when doing simulations with transformers. (2) 5.8 State TWO external conditions which could cause faults to develop in a transformer. (2) 5.9 Explain what effect an increase in the load will have on the primary current of a transformer. (2) [30] Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 11 QUESTION 6: THREE-PHASE MOTORS AND STARTERS 6.1 Name any THREE parts of a three-phase squirrel-cage induction motor. (3) 6.2 State the main function of a starter in a three-phase motor. (1) 6.3 The stator of a three-phase induction motor driving a conveyor belt has 8 polepairs and the supply frequency is 50Hz. Given: p = 8 f = 50 Hz Calculate the synchronous speed of the motor. (3) 6.4 The rotor speed of a squirrel-cage induction motor is 3 420 rpm while the synchronous speed is 3 600 rpm. Determine the slip in rpm. Given: nr = 3 420 ns = 3 600 (3) 6.5 Briefly describe the principle of operation of a squirrel-cage induction motor. (6) 6.6 Mention TWO mechanical inspections that should be performed on a motor after installation and before commissioning. (2) 6.7 Describe the term full load speed of an induction motor. (1) 6.8 List TWO examples of the information shown on the nameplate of a motor. (2) 6.9 Name TWO reasons for having a skewed rotor. (2) Copyright reserved Please turn over

12 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) 6.10 Refer to FIGURE 6.10 below and answer the questions that follow. L1 O/L Stop MC1 button N/02 Start button MC1 N/C N/O N/O1 timer timer N/C N/C Δ Υ MC1 Timer Υ Δ N FIGURE 6.10: AUTOMATIC STAR DELTA CONTROL CIRCUIT 6.10.1 Identify the interlocking contacts in the circuit. (2) 6.10.2 Explain the purpose of the following contacts: (a) MC1N/O1 (2) (b) MC1N/O2 (2) 6.10.3 Describe the operation of the star-delta control circuit. (6) [35] Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 13 QUESTION 7: PROGRAMMABLE LOGIC CONTROLLERS (PLCs) 7.1 Define an opto-isolator. (3) 7.2 When referring to a PLC explain what is meant by the following input categories: 7.2.1 Discrete (2) 7.2.2 Analogue (2) 7.3 Explain the term sensor as a device connected to the input of a PLC. (2) 7.4 Draw the block diagram of a typical PWM VFD speed control system. (7) 7.5 Refer to FIGURE 7.5 below and answer the question that follows. L1 Stop Keep open N/O2 MC1 N/O1 N/O Timer Start motor 1 MC1 Hold in O/L1 O/L2 Motor Motor Timer MC2 MC1 N FIGURE 7.5 7.5.1 Identify the circuit shown in FIGURE 7.5. (1) 7.5.2 Draw the ladder logic diagram that will execute the same function in a PLC system. (10) 7.5.3 State the function of the timer in the circuit. (2) 7.6 State THREE points that should be considered in the application of VSDs. (3) 7.7 Discuss the start-up and run profiles of adjustable speed drives. (4) 7.8 State TWO applications of regenerative braking. (2) 7.9 Name TWO types of synchronous AC motors used with VSDs. (2) [40] TOTAL: 200 Copyright reserved Please turn over

14 ELECTRICAL TECHNOLOGY: POWER SYSTEMS (EC/SEPTEMBER 2025) FORMULA SHEET RLC-CIRCUITS THREE-PHASE AC GENERATION 1 STAR XL = 2πfL and XC = 2πfC 1 V VL = √3 × VPH and VPH = IPH × ZPH fr = and I = 2π√LC R IL = IPH 𝑃 = 𝑉𝐼 cos 𝜃 DELTA SERIES VL = VPH and VPH = IPH × ZPH IT = IR = IL = IC IL = √3 × IPH Z = √R2 + (X L − XC )2 POWER VL = I × XL and VC = I × XC S = √3VL IL VT = IZ and 𝑉𝑇 = √𝑉𝑅 2 + (𝑉𝐿 − 𝑉𝐶 )2 Q = √3VL IL sin θ P = √3VL IL cos θ R VR cos θ = and cos θ = Z VT P = S cos θ XL XC VL VC 1 L P Q= = = = = √ cos θ = Z Z VS VS R C S PARALLEL 𝑜𝑢𝑡𝑝𝑢𝑡 ƞ= × 100% 𝑖𝑛𝑝𝑢𝑡 VS = VR = VL = VC TWO-WATTMETER METHOD VR IR = PT = W1 + W2 R VL VC W1 −W2 IL = and IC = tanθ = √3 ( ) XL XC W1 +W2 THREE-WATTMETER METHOD IT = √IR 2 + (IL − IC )2 PT = W1 + W2 + W3 V Z= IT I cos θ = R IT XL XC VL VC 1 L Q= = = = = √ Z Z VS VS R C Copyright reserved Please turn over

(EC/SEPTEMBER 2025) ELECTRICAL TECHNOLOGY: POWER SYSTEMS 15 FORMULA SHEET THREE-PHASE THREE-PHASE MOTORS AND TRANSFORMERS STARTERS STAR STAR VL = √3 × VPH and IL = IPH VL = √3 × VPH and IL = IPH DELTA DELTA VL = VPH and IL = √3 × IPH VL = VPH and IL = √3 × IPH POWER POWER 𝑆 = √3𝑉𝐿 𝐼𝐿 𝑆 = √3𝑉𝐿 𝐼𝐿 𝑄 = √3𝑉𝐿 𝐼𝐿 𝑠𝑖𝑛 𝜃 𝑄 = √3𝑉𝐿 𝐼𝐿 𝑠𝑖𝑛 𝜃 𝑃 = √3𝑉𝐿 𝐼𝐿 𝑐𝑜𝑠 𝜃 𝑃 = √3𝑉𝐿 𝐼𝐿 𝑐𝑜𝑠 𝜃 𝑃 = 𝑆 𝑐𝑜𝑠 𝜃 𝑃 = 𝑆 𝑐𝑜𝑠 𝜃 𝑃 𝑐𝑜𝑠 𝜃 = 𝑃 𝑆 𝑐𝑜𝑠 𝜃 = 𝑆 𝑃 ƞ = 𝑜𝑢𝑡𝑝𝑢𝑡 × 100% 𝑃𝑖𝑛𝑝𝑢𝑡 𝑃𝑜𝑢𝑡𝑝𝑢𝑡 ŋ= × 100% 𝑃𝑜𝑢𝑡𝑝𝑢𝑡 +𝑙𝑜𝑠𝑠𝑒𝑠 MOTOR SPEED VPHP NP I 60×f T. Ratio = = = PHS ns = VPHS NS IPHP p ns −nr %Slip = × 100% ns 𝑆 = N S − NR Overload setting = 125% × rated current Copyright reserved Please turn over