Electrical Technology Memo 1 (English)

Feb-March 2016 — Grade 12 / Matric — Electrical Technology

Memo 2016 Grade 12 English

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🎯 200 marks 📄 15 pages 📝 71 items found ∑ 1 math symbols 📚 3 topics

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2.1All calculations must show the formula

2.2Substitution of values must be done correctly

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

2.4Alternative methods must be consider ed, 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 r calculate the values, using the incorrect answer from the first

Q1— Section header —

1.1Unsafe conditions include: Inadequat e guards around machinery. No eye protection goggles in th e workshop and around the bench grinder. Loose and dangerous components on moving machinery. (1\

1.2An unsafe action is an action performed by a person/worker that could cause: njury to him/herself or his/her c olleagues e damage to tools and equipment ender a workplace unsafe ead to loss of income to the employer

1.3Protocol to follow when discovering a person experiencing electrical shock Do not touch the victim with bare hands until th e supply is turned off. Switch off the supply. Call a teacher or medical person for help.

1.4Productivi ty is an important work ethic to assist the growth of South Africa economy due to the following reasons: afe working procedures are more productive as less time is lost due to injuries and downtime related to accidents.

Q2— Section header —

2.1Kilo watt hour meter

2.2Two advantages of t hree phase systems over single phase systems are: an be operated in star or delta. Three phase systems can supply both three phase and single

2.3(5\ Note to markers: No additional marks are awarded for the manipulation of the formulae. Manipulatio n is shown to illustrate how the formula was derived.

2.4461.88 20000 (3\ 267.67 462.43 (3\

2.5.1(3\ +Vmax max or L 120 120 Showing amplitude Showing

0.8380 Cos

22.7912000 (3\ [20]20

Q3— Section header —

3.1By laminating and insulating the la minations of the core of the transformer. (1\

3.2Two similarities between single phase and three phase are: Both have the same functional operations Transformers are used to step down or step up the supply voltage Both can have either the closed core type or shell core type

3.3Two factors that may cause excessive heating in a transformer are: Insufficient ventilation Consta nt overloading Loose connections Ineffective tap changer contacts Impure

3.4Application of delta star connected transformer s in p ower distribution system s are: Single and three phase supply to

3.5The function of transformer is to step down or to step up (transform\ the voltage in a distribution network to the required value.

6.6PH PH

1.04230 30

1.0430

3.6.1(2\

3.6.2(2\

3.6.36600 Ph(p\ Ph(s\ Ph(s\ Ph(p\ (3\

3.6.4PH(p\ PH(s\ (3\ [20]20

Q4— Section header —

4.1Applications of three phase motors include: ump ift rane (1\

4.2Advantages of a three phase over single phase motors: For the same size frame a three phase motor delivers more power Three phase motors are self starting

4.3.1At start motors draw more than the motors rated current. This may lead to unnecessary tripping of the motor and the increased current at start causes wear on switch gear. (3\

4.3.2The motor is started in the star mode which reduces the voltage across each phase of the motor as in star V As the voltage across each phase is reduced, the current in each phase will also be reduced.

4.4The operation of three phase squirrel cage induction motor: Three phase supply is such that the peak voltage of each phase is reached at 120 ntervals. When a squirrel cage motor is connected across a three phase

4.5.1(5\ Coil 1:U1 U2 Coil 2: V1 Coil 3: W1 L1 , L2, L3 3 Phase specified N: Star is specified Not requested in the question

4.5.2The reading on the meter should be of high resistive value, more than between the windings showing sound /good insulation.

4.5.3A low resistance reading will indicate that there is electrical connection betwee n the winding and earth. This wil l indicate any electrical fault that may lead to an operator being shocked in the motor is

4.6pairs Pole (3\

4.7.1kVA

10.53(3\

4.7.2=100%

10.53Cos (3\

4.7.3(3\ [40]40

Q5— Section header —

5.1Factors influencing the capacitive reactance are Value of c apacitance requency of the supply

5.2Reactance is the opposition of the specific reactive component to the flow of current in AC circuits Impedance is the total opposition offered to the flow of current in an AC circuit which contains resistive and reactive components

5.3(4\

5.4(3\

5.5.1(3\

5.5.2(3\

5.5.3(3\ [20] Z R XC>XL XL>XC fr 1020

Q6— Section header —

6.1Advantages of a PLC over a hardwired systems are: Reduced space. PLCs are solid state devices and are compact and small compared to hard wire logic. Less maintenance PLCs have error diagnostic units making it easy to

6.2Output devices that can be used with a PLC are: Motor contactor indicator lamps relays switches (2\ PLC s could be programmed using the following methods: Ladder diagrams

6.6.1(6\

6.6.2(3\ Sequence starter with a time delay circuit Note to markers: The circuit cannot be tar delta s tarter as there is no lockout function included in the circuit.

Q7— Section header —

7.1Characteristics of ideal mps are: Open loop voltage gain A = infinite Input impedance = infinite Output impedance Z = zero

7.2The bandwidth is the range of frequencies within which an amplifier can amplify without distorting the output signal (retain linearity\ or losing gain. (3\

7.3Positive feedback is obtained when the output signal of an amplifier circuit is fed back to the input of the circuit. When the signal is fed back to the input, it is in phase with the input signal, thus added to the input signal.

7.4(6\

7.5.1(3\ Output put Amplification Cycles coincide/ same frequency Inversion Inverting inp Non

7.9(4\

7.10Positive feedback (1\

7.10Sine wave generator Tone Oscillator Buzzer dr iver

43.31(3\

7.11Timing circuit (1\ Trigger pulse 15

7.11.2TOTAAL: Vout if T=smaller Vin= Square wave 2 Marks Vout Alternative f T=larger Note: Higher order answers will show

Mathematical Content

trig

Topics Identified

CircuitsMachinesMaterials

Mark Allocation

Total200 marks

Sections10 + 20 + 20 + 40 + 20 + 40 = 150 marks

Paper information

SubjectElectrical Technology

Year2016

SessionFeb-March

TypeMemo

PaperPaper 1

LanguageEnglish

Pages15

Downloads3

Examination context

Decade2010s

Years ago10y

Season—

Start day—

Exam period—

Days since exam—

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