Electrical Technology Power Systems Memo 1 (English)

May-June 2023 — Grade 12 / Matric — Electrical Technology

Memo 2023 Grade 12 English

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🎯 200 marks 📄 5 pages 📝 93 items found 📚 3 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 nolog15

Q2— Section header —

2.1The purpose of the act is to provide good health and safety to all people at work especially when using machinery and for protection against the hazards arising out of activities of other people. To establish an advisory council

2.2An unsafe act may lead to an accident injuring an employee, this reduces the number of skilled personnel in the workplace therefore reducing the rate of productivity. (2\

2.3Actions that will have serious consequences when they occur, but there is a low chance of these risks happening (2\

2.4Apply direct pressure to the wound using a cloth or gauze. Apply continual pressure to a pressure point to stop all circulation to that part of the body. (2\

2.5Not to be in direct contact with blood due to the risk of HIV infection. (1\ [10] Ele ctrical Te ch nolog10

3.1When the voltage and current waveforms start at the same time, have the same frequency resulting in a zero phase angle. OR When any waveforms of electrical quantities start at the same time, reach their peak at the same time, pass through zero at the

3.2(3\

3.3Radio tuning circuits Television tuning circuits (2\

3.4.1Impedance versus frequency. (1\

3.4.2Current versus frequency. (1\

3.5.1(3\ Ele ctrical Te ch

3.5.2(3\ OR

3.5.3Lagging. (Reason The voltage across the inductor is greater than the voltage across the capacitor (1\

3.6.1At resonance X = X 6 mH (3\

3.6.2(3\ Ele ctrical Te ch nolog Power Systems

3.6.3(3\

3.6.4The value of the current will be doubled. (1\

3.7.1(3\

3.7.2(3\ OR

3.7.3The circuit is inductive because the inductive current is greater than the capacitive current. (2\ [35] Ele ctrical Te ch35

4.1.1(a\ Step up transformer (1\ (b\ Step down transformer

4.1.2Household 220 V 240 V Industrial 380 V 415 V (2\

4.1.3The secondary windings of the transformer at \ are connected in star to create a neutral point

4.1.4Transformer at \is a step up transformer that increases the voltage across the lines and in turn reduces the current through

4.1.5(4\

4.2.1(3\

4.2.2(3\

4.2.3In star I =I PH (4\

4.2.4(3\

4.2.5(3\ NOTE: VAR will also be accepted as a correct unit.

4.2.6The power factor is lagging. (1\

4.2.7The power factor of the system can be improved by connecting power factor correcting capacitors in parallel with the load. Phase advancers can be used. (2\

4.2.8An improved power factor will draw less current generate less heat, resulting in thinner supply cables etc. and the p ower factor will be closer to one (unity\ (2\

4.2.9Reduced monthly electricity bill. Equipment lasts longer because less heat is generated. Less maintenance of equipment. (2\ [35] Ele ctrical35

5.1Mutual induction

5.2Th AC supply voltage connected to the primary winding creates alternating current to flow in the primary winding

5.3Size Frequency Turns ratio Voltage rating Power rating Efficiency (3\

5.4Delta delta transformers are mainly used in industries where high power transfer is essential. (2\

5.5.1Single phase transformers (1\

5.5.2Three phase transformers (1\

5.5.3Single phase transformers (1\

5.6.1Dry type transformers Oil immersed transformers (2\

5.6.2Air Natural Air forced Oil Natural, Air Natural (ONAN\ Oil Natural, Air Forced (ONAF\ Oil Forced, Air Forced (OFAF\ Oil Forced, Water Forced (OFWF\ (2\

5.6.3Buchholtz relay (1\ Ele ctrical Te ch nolog

5.7.1(3\

5.7.2(3\

5.7.3(3\

5.7.4In transformers (primary\ = S (secondary\ OR (4\ [30] Ele30

6.1Shaft Rotor conductor bars End ring Steel laminations Cooling fins (3\

6.2.1Synchronous speed (1\

6.2.2Rotor slip is the difference between the synchronous speed and rotor speed. (2\

6.2.3At point the rotor speed is equal to the synchronous speed, therefore there is no relative movement between the stator magnetic field and the rotor conductors resulting in zero torque being developed.

6.3.1(3\

6.3.2(3\

6.4.1(3\

6.4.2(3\ Ele ctrical Te ch nolog Power Systems

6.4.3(3\

6.4.4(3\

6.5.1MC N/C MC N/C (2\

6.5.2A normally closed contact will allow current to flow in the circuit MC will de energise

6.5.3While MC is energised its MC N/C contact in series with MC is

6.5.4When MC N/O is faulty and permanently open, MC will only energise when START is pressed. As soon as START

7.1Relays require regular maintenance and repair. Uses much more energy. It requires a lot of space to be wired. It has lower response time. When a single relay develops faults in a panel, it takes much time to locate

7.2Soft wired systems are cheaper when modifications to the system is done Instead of buying new devices, the program is simply altered. (2\

7.3.1After pressing the ON button he function of the ON delay timer is to prevent the l

7.3.2When the ON button is pressed (ON contact closes\ , coil Y will be energised closing contact Y.

7.4.1Relay a change in conditions in the same circuit or in one or more commonly used in lower power circuits Contactor an electric circuit commonly used

7.4.2The moment an OFF delay timer is de energised

7.5.1Detection and positioning of objects Measuring rotating speed Counting objects on a conveyer Detecting direction (2\

7.5.2Inductive Capacitive Ultrasonic Photoelectric (2\ Ele ctrical Te ch

7.6.1NOTE: Alternatively, the candidate could use closed symbols in the place of the open stop symbol and both overload symbols. Stop and overload symbols must be in the same normal state. (8\ 7. .2 The motors may have different rated current values,

Topics Identified

CircuitsMachinesConstruction

Mark Allocation

Total200 marks

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

Paper information

SubjectElectrical Technology

Year2023

SessionMay-June

TypeMemo

PaperPaper 1

LanguageEnglish

Pages15

Downloads8

Examination context

Decade2020s

Years ago3y

Season—

Start day—

Exam period—

Days since exam—

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