Electrical Technology Digitals Memo 1 (English)

May-June 2019 — Grade 12 / Matric — Electrical Technology

Memo 2019 Grade 12 English

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🎯 200 marks 📄 12 pages 📝 82 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 incorrect answer

2.6Markers should consider that learner answers may deviate slightly from the guideline; depending on how and where in the calculation rounding off was used. These marking guidelines are only a guide with model answers. Alternative

Q1— Section header —

1.1An accident is an unplanned, uncontrolled event caused by unsafe acts and or unsafe conditions resulting in a personal injury, illness or the death of an employee. An accident means accident arising out of and in the course of an

1.2Move in an orderly manner. Follow the evacuation route as displayed in your workshop. Move to the designated assembly point in a calm and orderly manner. (2\

1.3To prevent oneself form being shocked, therefore precautions must be taken to isolate oneself when rendering assistance. To prevent injury.

1.4A third degree burn occurs when all layers of skin have been burnt, causing permanent skin damage affecting fat, muscle and even bone. A serious burn deserves 1 mark (2\

1.5A person who intentionally and recklessly interferes with equipment will cause damages and this will render equipment unsafe and compromise the safety of the user. (2\ [10]10

Q2— Section header —

2.1.1Capacitive reactance is the opposition to an alternating current by the reactive component of a capacitor in an ac circuit. (2\

2.1.2Inductive reactance is the opposition to an alternating current by the reactive component of a inductor in an ac circuit If only the formula is given by the learner = 1 mark If the formula is accompanied by the correct explanation = 2 marks.

2.2.116,59 (3\

2.2.2(3\

22.11(3\

2.3.13,67 (3\

2.3.22,33 3,67 (3\

2.3.3The phase angle is lagging because I is greater than I (2\

2.4.1At resonance frequency X = 50,27 (1\

2.4.23,17 3,17 1000 50,27 (3\

2.4.3The value of the current will be halved as the circuit resistance is inversely proportional to the applied voltage. The value of the current will be halved if the resistance is doubled = 1 mark (2\

2.5.1(3\

2.5.2resonance (3\

2.5.3196,94 49,24 (3\

2.5.4The voltage across X is During resonance current is at a maximum. As a result V would be higher due to the current being at a maximum. However because V the reactive voltage is zero and effectively this voltage increase does not affect the supply

Q3— Section header —

3.1The power factor meter is used to measure the power factor.

3.1The Kilowatt hour meter is used to measure the amount of electrical power consumed by the load over a certain period of time. (2\

3.2Generation Electricity is generated in power station . The power stations convert energy from its basic form (fossil fuel, natural gases, coal, nuclear fuel and water action\ into electrical energy. The basic fuel is used to make superheated steam to drive

3.3DIRECTION OF ROTATION (5\ 3 marks for phases 1 mark for degrees 1 mark for rotation

3.4Excessive curr ent will be drawn by the system. More losses will occur in the form of heat and the efficiency of the system will be reduced.

3.5.1Current in each phase 0,81 (3\

3.5.2Line current (3\

3.5.3Total power 921,65 500,65 (3\

3.6Single phase system applianc es are cheaper than three phase appliances Single phase voltage is lower than three phase and therefore safer (1\

Q4— Section header —

4.1Copper losses Iron losses Dielectric losses Stray losses Insufficient circulating air for cooling the transformer. Insufficient oil in which the transformer is immersed. Constant overloading. Internal fault

4.2When AC voltage is supplied to the primary windings, alternating current will flow in the windings. This current will produce alternating magnetic fluxes The produced magnetic fluxes

4.3.1It ensures that the: Device does not overheat ife expectancy is not reduced

4.3.2To ensure that the transformer is Isolated from the supply should internal fault arise Not damage as a result of short circuit

4.4.1Secondary line current 11,55 10000 (3\

4.4.2Transformer ratio 3460 3,46 6000 = 6,92 : 1

4.4.3Input power 9,70 0,97 11,55 Cos 9,70 0,97 10000

4.4.499,17% 9700 9700 loss (3\

4.5The kVA rating in the primary windings and the secondary windings of a transformer is identical.

Q4— Section header —

Q5— Section header —

5.1The speed of the rotating magnetic field the stator windings (2\

5.2.1To ensure: Earth continuity That t here is continuity between the ends of each coil. (2\

5.2.2To ensure that there is no electrical connection between: Each of the three coils ny of the three oils and earth. (2\

5.3When a three phase supply is connected to the stator winding, a rotating magnetic flux is produced This flux will cut the metal rod of the rotor, inducing an e.m.f in it which is responsible for the flow of current in the rotor.

5.4(N/C and MC (N/ (2\

5.4(N/O \ is connected in parallel with the start button so that when start button is pressed and released, current could flow in the circuit through thus keeping the starter on To latch

5.4When the start button is pressed, MC will be energised closing MC (N/O \ and MC (N/O will be energised opening the MC (N/C\ and the motor will run in

4.5100 955 100

5.5.1Synchronous speed The total of 18 poles = 6 poles per phase = 3 pole pairs per phase (p = 3\ rpm 1000 (4\

5.5.2Percentage slip 1000 1000 (3\ [30]30

Q6— Section header —

6.1Relays requires 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 take s much time to locate

6.2.1The function of the central processing unit is to execute the instructions as per the inputs and provide the outputs (2\

6.2.2The function of the modem is to isolate the processor against damage from random high current or voltage spike and pass information signal in and out of the processor (2\

6.3.1Supply lines to the PLC should be installed with either a fuse or a circuit breaker to prevent excessive over current (2\

6.3.2Wirings and connections should be checked before connecting the supply to the PLC to ensure that wiring is correctly connected, to prevent damage to the unit. (2\

6.4An ON delay timer contact would not operate until a pre set delay time has passed, after it has first been energised. An OFF delay timer contact will immediately operate

6.5.1An ON delay timer is applied in the control circuit to prevent the light from being switched on before

6.5.2When the start button is pressed, coil Y will be energised closing latching circuit Y contactor The timer will start

6.6.1An analogue input is represented by FIGURE 6.6 because it varies freely within a certain range (2\

6.6.2A digital input is represented by FIGURE 6.6 because it varies with definite steps which is digital in nature (2\

6.7.1Exclusive OR gate (1\

6.7.2(a\ (1\ (b\ (1\ (c\ (1\ (d\ (1\

6.8.1Light sensor is applied in: Cell phones The device uses the ambient light sensor to automatically control the brightness of the screen in situation where the intensity of light is high or low. To sense the light intensity level.

6.8.2Temperature sensor is applied Motor cars radiator: If the temperature of the water circulating in the engine exceed a preset value, the sensor will warn the driver by flicking the light on the dashboard

6.9Stop Start FWD MC FWD MC MC Start REV

6.10.1Diode bridge rectifier convert AC supply voltage voltage (2\

6.10.2Filtering circuit smooth the AC ripple to ensure a pure DC voltage on the DC rail. (2\

6.10.3The inverter inverts the DC voltage back to an AC voltage at variable frequency which will then control the speed of the motor as it depends on the frequency supplied by

6.11The is used in: Water pumping system Heating system Exhaust air system, dust extraction and fan system Variable air volume air conditioning system

6.12.1Regenerative braking methods may be used in: Lifts Cranes Electrical locomotive (2\

6.12.2Regenerative energy is energy recovered from the motor when it slows down by converting mechanical energy to electrical energy which can be either used immediately or stored until needed. [60] TOTAL:60

Mathematical Content

trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

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

Paper information

SubjectElectrical Technology

Year2019

SessionMay-June

TypeMemo

PaperPaper 1

LanguageEnglish

Pages12

Downloads6

Examination context

Decade2010s

Years ago7y

Season—

Start day—

Exam period—

Days since exam—

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