Electrical Technology Digital Electronics Memo 1 (English)

May-June 2024 — Grade 12 / Matric — Electrical Technology

Memo 2024 Grade 12 English

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🎯 200 marks 📄 5 pages 📝 88 items found ∑ 2 math symbols 📚 2 topics

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2.1All calculations must show the formulae.

2.2Substitution of values must be done correctly.

2.3All answers MUST contain the correct unit to be considered.

2.4Alternative methods must be considered, provided that the correct answer is obtained.

2.5Where 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

Q1— Section header —

1.1(1\

1.2(1\

1.3(1\

1.4(1\

1.5(1\

1.6(1\

1.7(1\

1.8(1\

1.9(1\

1.10(1\

1.11(1\

1.12(1\

1.13(1\

1.14(1\

1.15(1\ [15] Ele ctrical Te ch nolog y: Power Systems15

2.1Failure to use safety equipment. Tampering or misusing safety equipment. Wilfully or recklessly operating machinery that threatens the health of the user. (2\

2.2Furnishing false information to the inspector. Failure to comply with any performance or safety requirements made by the inspector. Obstructing the inspector in the performance of his/her duties. (2\

2.3Manufacturers who design and manufacture articles for the use at work must ensure that the product is safe to use and the information and processes for the use of the artefact manufactured is clear and would assist with safe

2.4It is an event that is not expected that would not require calling for outside emergency assistance. (2\

2.5It can cause the heart muscle to contract so strongly leading to heart failure. [10] Ele10

3.1Reactance is the opposition offered to the flow of alternating current by an inductor or capacitor in an AC circuit. Reactance is the ratio of voltage to current in an alternating circuit when voltage and current are not in phase.

3.2.1The circuit is predominantly capacitive because V is greater than (2\

3.2.2(3\

3.2.3(3\

3.2.4NOTE: If I is indicated in the place of V , a mark will be awarded. If the phase angle is correctly indicated in the place of (V

3.2.5The supply current (I \and the voltage across the resistance (V are always in phase

3.3.1(3\

3.3.2(3\

3.3.3(3\

3.3.4At resonance X =X , Therefore (4\

3.4.1A decrease in resistance increases the Q factor. (1\

3.4.2(3\

3.4.3(3\ [35] Ele ctrical Te ch nolog y: Power Systems35

4.1.122 kV (1\

4.1.2Phase 1 Red Phase 2 Yellow Phase 3 Blue NOTE:

4.1.3The National grid is a network of over 25 000 km of high voltage power lines to various bulk users. OR The national grid is a network of power stations, high voltage power lines

4.1.4The transmission of electricity is done at such high voltages to decrease the current flowing in the transmission lines and in the process reducing the copper losses. (2\

4.1.5An industrial consumer make use of three phase systems which require a three phase voltage

4.2A three phase system is more economical. A three phase system can be connected in st ar or delta. A three

4.3.1(3\

4.3.2(3\ Ele ctrical Te ch nolog y: Power Systems DBE/May/June 2024

4.3.3(3\

4.4.1At a central substation. Built into power consuming equipment. Spread out over a distribution system. (1\

4.4.2Reduced phase angle. Reduced reactive power. Reduced apparent power. (1\

4.4.3The phase angle and apparent power decreased after power factor correction. With the load and the supply voltage remaining the same, the current drawn from the supply decrease because of the improved power factor.

4.5Wattmeters are used with electrical devices to measure their power. Energy meters are used to measure electrical energy consumed over a period of time for billing or monitoring purposes.

4.6(3\ [35] Ele ctrical Te ch nolog y: Power Systems35

5.1.1Core type three phase transformer. (1\

5.1.2A shell type transformer is less prone to magnetic stray loss than a core type transformer. NOTE: Double magnetic circuit is captured in the comparison between

5.1.3Star delta configuration (2\

5.1.4When an alternating voltage is applied to the primary windings, an alternating flux is set up in the core which links with the secondary windings, inducing an e.m.f of the same frequency When the load is connected to the secondary winding, a current

5.2.1An increase in the load will increase the secondary current resulting in more primary current drawn from the supply (2\

5.2.2It provides electrical insulation between the windings and the case. It also helps to provide cooling and prevents the formation of moisture on the windings. (1\

5.2.3Hysteresis losses Eddy current losses (2\

5.2.4Air Natural: transformers are cooled by natural air flowing across the transformer windings Air Forced: transformers are cooled by air being forced

5.2.5Single phase transformer: Conductor size is bigger than for a three phase transformer. A three

6.1Rotor Cooling Fan Shaft (2\

6.2.1

6.2.2When a three phase supply is connected to the stator, each coil pair is connected to a different phase of the three phase supply. This causes current to flow in each coil at an angle of 120

6.2Because induction motors have no brushes on slip rings that cause sparks. (1\

6.3.1(3\

6.3.2(3\

6.4.1(3\

6.4.2(3\ Ele ctrical Te ch nolog y: Power Systems 12 DBE/May/June 2024

6.4.3(3\

6.4.4(3\

6.5.1Manual sequence starter. NOTE : Two DOL starters (1\

6.5.2MC is a contactor that energises and de energises motor 1 in the main (power\ circuit whenever the start or stop button is pressed. (2\

6.5.3Each motor is protected by its own overload relay independently. (1\

6.5.4If motor 2 is overloaded and switched off by the overload, motor 1 will continue operating and feeding material onto conveyor 2. his will cause a pile up of material on conveyor 2.

6.5.5By connecting a N O contact of MC in the place of the temporary connection MC will only be able to energise after MC

7.1It is easy to trace a circuit along its wires using a multi meter. It is easier to fault find as one could easily follow the wiring. Easier to install, maintain and fault find. All sensors, contacts and alarms are physically connected to a central panel via

7.2.1(3\

7.2.2= 1 = 0

7.3.1Light sensor. Level sensor. Overload sensor. Temperature sensor. (3\

7.3.2A computing device (microprocessors, computers, and logic units\can only interpret digital signals when process ing the input. n analogue

7.4The concept of latching makes it possible for circuit to be triggered 'on' and remain 'on' regardless of whether the activating trigger has been removed. (3\

7.5.1T is a timer that creates a time delay in the operation of the circuit to energise MC a preset time after MC (2\

7.5.2MC must be energised. The timer must have timed through after being energised.

7.5.3The ON lapsed when the timer is energised. An OFF acts immediately operate when the timer is energised

7.6AC 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

7.7At start up the torque is at 200%. When the speed increases to the breakdown speed, the torque will increase. Thereafter torque will decrease as the motor speed increases further. The motor is accelerated from start to a region above the breakdown speed

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

Year2024

SessionMay-June

TypeMemo

PaperPaper 1

LanguageEnglish

Pages15

Downloads4

Examination context

Decade2020s

Years ago2y

Season—

Start day—

Exam period—

Days since exam—

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File size382 KB

Pages15

Archived on11 October 2026

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