Electrical Technology Digitals Memo 1 (English)

November 2020 — Grade 12 / Matric — Electrical Technology

Memo 2020 Grade 12 English

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🎯 200 marks 📄 16 pages 📝 86 items found ∑ 1 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 the

Q1— Section header —

1.1Any article or part thereof which is manufactured, provided or installed in the interest of the health or safety of any person. (2\

1.2Your right to fair labour practices. Your right to work reasonable hours. Your right to belong to a trade union. Your right to earn a living wage. Your right not to be discriminated against. (1\

1.3If a person dies. A major incident. An ncident where the health and safety of any person has been/was endangered. (2\

1.4To dismiss an employee without due process. To reduce the rate of remuneration without due process Alter the terms of conditions of his/her employment to terms of conditions that is less favourable to him/herself.

1.5In an emergency it can be pushed and it would immediately cut all electric power to all the equipment, stopping them thus making the workshop safe. (2\

Q2— Section header —

2.1.1If V lags V by 35 (2\

2.1.2The voltages represent RC circuit because, is always in phase with I

2.2.1(3\ OR

2.2.2(3\

2.2.3The voltage is lagging, because the capacitive reactance is greater than the inductive reactance (V is greater than V (2\

2.2.4NOTE: 5 marks , 1 mark for each correct label of which V , V and

2.3.1Phasor diagram of a parallel RLC circuit at resonance. (2\

2.3.2The voltage drop across the components in a parallel circuit is the same, hence the voltage is used as the reference. (1\ OR The applied voltage is common across all components.

2.3.3In a parallel resonant circuit impedance is at maximum, and the total current is at minimum. (2\ OR The relationship between impedance and current in a parallel RLC circuit is inversely proportional.

2.4.1(3\

2.4.2(3\ OR If candidates calculate X or Xc they can use the following formulae:

2.4.3(2\

2.4.4(3\ OR For resonance. Calculating X first and then since X = X

2.5.1(1\

2.5.2Reading the values from the graph where f = 30000 Hz and = 35000 Hz the following can be deduced: (3\ NOTE:

2.5.3Deducing the indicated bandwidth of Q from the graph as 35 kHz 30 kHz the candidate will be able to calculate as follows: OR (3\

Q3— Section header —

3.1.1Reactive power is the power in an AC circuit when the current is out of phase with the voltage as a result of the capacitive an /or the inductive load

3.1.2Efficiency is the percentage ratio of the output power to the input power. (2\ NOTE : If only the formula is explained or written only 1 mark will be awarded

3.2(3\

3.3.1The load will draw more current from the supply Large cables may be needed to carry the current Maintenance cost will increase. More heat will be generated in the cables. (4\

3.3.2By adding power factor correction capacitors in parallel with a load. Use synchronous motors in shunt (parallel\ with the load Make use of phase advancers. Variable speed drives Soft starters (3\

3.4Kilo watt our meter/Energy meter (1\

3.5.1(3\

3.5.2(5\ When candidates substitute Vph correctly as 380 V without calculating it , two additional marks should be awarded to the 3 mark calculation.

3.5.3(3\

3.6(3\

3.7A wattmeter is used to measure the input power/output power in an AC system. Any acceptable application that uses a wattmeter to indicate power usage. (1\ [30]30

Q4— Section header —

4.1A step up transformer steps up alternating voltage from low voltage to high voltage A step up transformer compensates for losses in a transmission system. (2\

4.2Overloading Lack of entilation Insufficient oil (3\

4.3Oil Natural, Air Forced. Oil Natural, Air Natural. Oil Forced, Air Forced. Oil Forced, Water Forced.

4.4emperature rises nsulation failure hort circuit Gas forming due to oil breakdown

4.5If the load is increased, the secondary current will increase resulting in an increase in the primary current. This increase is due to the increased magnetic force that results due to higher current flow.

4.6Delta star Star delta Star star Delta delta Step

4.7Over current relay Balance earth fault relay Restricted earth fault relay Standby earth fault relay Bucholtz relay Fuse

4.8(3\ CORE TYPE THREE PHASE TRANSFORMER CONSTRUCTION Coil Flux Core

4.9Ensure the supply is switched off before wiring the transformer Never touch any electrical wires or terminals on an energised transformer with bare hands Wear safety gear (PPE\ Be careful of the secondary terminals of

4.10.1(5\ OR If the learner calculated the input power by using the given line current, the following answer will be accepted.

4.10.2(3\ 50 219,39 11000 TR

4.10.3(3\ OR = 303,86 A [30]30

Q5— Section header —

5.1Check that the bolts securing the motor to the frame are tight. Check that the end plates are fastened properly. Check the bearings for smooth rotation. Check the movement of the shaft. Check for cracks

5.2It is cheaper and more robust It has slightly high efficiency and power factor These motors are explosion proof, since the risk of sparking is eliminated by the absence of slip rings and brushes. Reduced maintenance due to absence of brushes.

5.3.1Sequence motor starter without a timer NOTE: This cannot be a forward / reverse motor due to no lock out.

5.3.2(a\ The function of the stop button is to disconnect the supply from the control circuit and stops both motors. (2

5.3.3When the start button 1 is pressed the current flows through the stop button and O/L MC (Motor 1\ill energise and will close

5.4.1(3\

5.4.2(3\ NOTE: If the candidate calculated 5% of the synchronous speed 0,05 x 500 = 25 rpm the following can apply: S = ns nr Nr = Ns slip(revolutions\

5.5.1(3\

5.5.2(3\ OR [30] rpm 500 50 6030

Q6— Section header —

6.1.1Hardware refers to all the physical parts (e.g. CPU\ of the device that can be seen and touched. (2\

6.1.2Software refers to machine/graphical language (e.g. windows, software programmes\ that is installed on a computer or written into the PLC that instruct it to interact with its input and output hardware.

6.1.3An pto coupler is a semiconductor device that uses light (e.g. Light Emitting Diode\to transmit a signal between two circuits that are

6.2Input module Output module Power supply Central processing unit (Microprocessor\ (3\

6.3Supply lines to the PLC should be installed with either a fuse or a circuit breaker. (protection\ Correct wiring and connections should be checked before connecting the supply to the PLC. Ensure that wiring is of adequate size to carry the required current.

6.4.1NOTE: One mark for the inputs One mark for the logic function (2\ NOTE: See examination instruction

6.4.2(a\ (b\ (c\ 1 (d\ (4\

6.5The inductive proximity sensor is applied in: Counting of metal objects Positioning of metal objects Detect the presence of metal objects and whether they are ferrous or

6.6.1An ON delay timer contact Edge triggered wiping relay (Siemens\ (1\

6.6.2When the push button (I is pressed, the Timer will be energised. The normally closed contact of the Timer will open (TD\ The output (Q\ will be at low state. (OFF\

6.7The circuit will not latch when the start button is released.

6.8.1The Red Lamp will be ON The Green

6.8.2The function of the MC (contactor coil\is to close and open the contacts the moment it is energised. (i.e. MC/NO and MC/NO will close and MC/NC

6.8.3OR (9\ FIGURE 6.8: LADDER LOGIC DIAGRAM STOP Red Lamp START

6.9When a three phase AC is applied to the input unit, the diode bridge rectifying circuit convert AC to DC The DC waveform contains

6.10Synchronous motor with a permanent magnet stator. Synchronous motor with

6.11.1Pulse has shorter on time and Pulse

6.11.2he greater the width of the pulses the higher the average voltage (2\

6.12The installation of the syste should be done

6.13.1Braking Unit (1\

6.13.2Braking resistor (1\

6.14When the load goes down, the motor hold back the downwards acceleration, thus Creating excess energy through induction This energy will be fed back

Mathematical Content

trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections10 + 40 + 30 + 30 + 30 + 60 = 200 marks

Paper information

SubjectElectrical Technology

Year2020

SessionNovember

TypeMemo

PaperPaper 1

LanguageEnglish

Pages16

Downloads9

Examination context

Decade2020s

Years ago6y

SeasonSpring (SH)

Start dayThursday

Exam periodNovember 2020

Days since exam2,178

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Archived on11 October 2026

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