Electrical Technology Memo 1 (English)

May-June 2018 — Grade 12 / Matric — Electrical Technology

Memo 2018 Grade 12 English

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📄 14 pages 📝 85 items found ∑ 1 math symbols 📚 2 topics

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2.1All calculations must show the formula/e

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 same answer is obtained

2.5Where an erroneous 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

Q1— Section header —

1.1The type of work done in an electrical technology workshop requires the correct intensity of light because good vis ibility is crucial in performing work, e.g. soldering work, panel wiring, measuring electrical quantities and

1.2Dangerous practices are processes or activities that have some form of inherent risk or hazard when performed and may lead to serious injuries or even death. (2\

1.3Be calm. Assess the situation Call the emergency services Report the injuries to appropriate authority Administer first aid and CPR (2\

1.4Workers infected with HIV tend to be absent from work regularly due to illness because of their weakened immune system and this impacts negatively on productivity. (2\

1.5It is ethically correct to report a person who is working under the influence of medication that may lead to drowsiness because the person may place himself/herself and other persons in danger while operating

Q2— Section header —

2.1Single phase generate less power It can supply power to single phase load only Single phase is more expensive to generate power (2\

2.2Three coils are placed at 120 relative to each other. When these coils are rotated anti clockwise they cut the magnetic field lines which induce the emfs of the same frequency and magnitude in these coils.

2.3.113,75 (3\ SC

Q3— Section header —

3.1.1Core type transformer Shell type transformer (2\

3.1.2The iron core of transformers is laminated to reduce circulating eddy current in the core which generate ses in the form of heat

3.2When an alternating voltage is connected to the primary windings, a magnetising current will flow, and an alternating magnetic field is set up in the core. This alternating magnetic field links with the secondary windings,

3.3Same voltage and urns Ratio (both primary and secondary voltage rating is same\ Same KVA ratings Same requency rating Same p olarity Similar impedance

3.4It improves the insulation qualities of the windings It cool down the temperature rise due to heat generated in the transformer during its circulation process. (1\

3.5.1381,05 (3\

3.5.2454,55 381,05 300000 454,55 (5\

3.5.320

Q4— Section header —

4.1.1It ho use s the bearings that hold the rotor axis (1\

4.1.2The purpose of the cooling fins is to dissipate generated heat to the outside of the motor (1\

4.1.3It houses the end wires of the three coils and earth (1\ It is used to connect the supply to the m

4.2High starting torque Can be connected in star or delta Wide range of application Higher efficiency They are self starting (3\

4.3.1Synchronous speed of the motor. RPM (3\

4.3.2Rotor speed of the motor. RPM 1440 0,04 1500 (3\

4.4.17,108 (3\

4.4.2The supply current will be less for the same output power. (2\

4.5.1The start button normally is open and spring loaded, when it is pressed and released, the main contact (MC \ will energise, closing MC (N/O\ and current will flow through it which will enable the circuit to operate

4.5.2The two motors are running, because the MC (N/O\ MC (N/O\ and T (N/O\ are closed. (3\

4.5.3The overload relays are connected to each motor so that each motor can be disconnected from the supply the moment the current in that motor exceed the value that the overload is specifically designed for

4.5.4When the start button is pressed, the MC will be energised, closing MC (N/O \ and MC (N/O \ and Motor 1 will run. Timer contact (T\ will also be energised and after pre

4.5.5Conveyer belt (1\

4.6Check the: shaft bearings for smooth movement motor housing for cracks end plate s for

4.7The motor cannot be used because there is continuity between winding U due to damaged insulation of the two windings which will result in short circuit and further burning of wires

4.8The function of the zero volt coil is to switch off the supply to the circuit in the event of power failure. and when the power is restored, the system will remain off until it is re started. (2\

Q5— Section header —

5.1Frequency Inductance Capacitance (3\

5.2.1The power factor is lagging (1\

5.2.20,62 32,02 Cos therefore (60 Cos (5\

5.2.3The Q factor will be halved because the Q factor is inversely proportional to the resistance of the circuit . The doubling of the inductance and capacitance as a ratio will have no effect on the Q factor.

5.3At resonance, the impedance of the circuit is at a minimum and hence the current is at a maximum. When there is a change in frequency from resonance, the impedance will increase causing the current to decrease.

5.4.158,705 0,0147 (0,5 (3\

5.4.2[20] SC20

Q6— Section header —

6.1.1(1\

6.1.2(1\

6.2elay logic (1\

6.3Laptop Handheld device Desktop computer PLC interface (1\

6.4High power SCRs or Triacs Solid state relays (1\

6.5A series of instructions written in ladder logic/function block or instruction list that is used to control the operation of a PLC. (2\

6.6Function block diagram nstruction list (2\

6.7.1A timer is a function in PLC programs that waits for a predetermined time before executing a certain programmed function. (2\

6.7.2Markers are registers in the memory used to store information until needed by the program. Markers are also use to retain information from the end one rung to the beginning of the next rung of program.

6.8It would reduce the complexity of the ladder program and the reaction and execution time would be quicker with a smaller program. (2\

6.9(6\ 10 SC

6.10(6\

6.11(8\

6.12Stop Start MC MC (5\ 11

Q7— Section header —

7.1.1

7.1.2The bandwidth refers to the range of frequencies that the op amp can operate without distortion (linearly\ (2\

7.2.1OUT REF (4\

7.2.2reshold detector Voltage level detector (1\

7.3Oscillator circuits (1\

7.4(2\

7.5.1Summing amplifier circuit (1\

7.5.2Audio mixer Temperature measurement (1\

7.5.3VRVRVRVRVfout9,022,022,025,02332211 (3\ All values in kilo ohm 12 SC

7.6.1By replacing the feedback capacitor with feedback resistor (2\

7.6.2(4\

7.7.1Audio oscillators Electronic organs (1\

7.7.243,805 8000 6RC (3\ 13

7.7.3

7.8Upper trigger level Lower trigger level Input signal .. (4\

7.9HzfmHLLLbutLCfrr27,1098 (3\ 14 SC

7.10therefor (5\

7.11Input pulses Output (5\

7.12.1used as a buffer (1\

7.12.250

Mathematical Content

trig

Topics Identified

CircuitsMachines

Mark Allocation

Sections10 + 20 + 40 + 20 + 50 = 140 marks

Paper information

SubjectElectrical Technology

Year2018

SessionMay-June

TypeMemo

PaperPaper 1

LanguageEnglish

Pages14

Downloads3

Examination context

Decade2010s

Years ago8y

Season—

Start day—

Exam period—

Days since exam—

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