Electrical Technology Paper 1 (English)

November 2015 — Grade 12 / Matric — Electrical Technology

Past Paper 2015 Grade 12 English

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🎯 200 marks ⏱️ 3h 📄 3 pages 📝 92 items found ∑ 1 math symbols 📚 2 topics

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Q1— Section header —

1.1State ONE unsafe act that may lead to an accident in n electrical technology workshop. (1\

1.2Define the term dangerous practices with reference to workshop practice

1.3Name TWO unsafe conditions that may exist in n electrical work shop

1.4Explain the term human rights in the workplace with reference to the protection of a worker. (2\

1.5Explain why risk manageme nt is important for ensuring safety in a workshop. (3 [10]10

Q2— Section header —

2.1Describe the term active power (2\

2.2Draw a neat ly labelled phasor diagram of the voltages generated by a three phase AC system. Indicate

2.3A three phase star connected motor has an output p ower of 50

2.3.1Line current (3\

2.3.2Apparent power (3\

2.4State TWO advantages of power factor correction in AC systems. (2\

2.5State the function of a wattmeter. (2\

2.6Two wattmeters that are used to measure the input power are connected to a balanced thr ee phase circuit and

Q3— Section header —

3.1Name ONE protection device used in transforme rs. (1\

3.2State ONE negative impact of losses in transformers. (1\

3.3Name THREE methods of cooling transformers. (3\

3.4Describe the effect on the primary current of a transformer if the load is increased. (3\

3.5The delta star connected transformer in FIGURE 3.1 supplies a factory with 60 kW. The current lags the voltage by 36,87 . The primary line voltage

3.5.1Secondary line current (3\

3.5.2Primary line current 3\

3.5.3Apparent power (3\

3.5.4Reactive power (3\ [20]20

Q4— Section header —

4.1Name TWO parts of a three phase squirrel cage induction motor. (2\

4.2State TWO advantages of a three phase mo tor when compared to

4.3Describe why it is important to carry out electrical inspections on a motor after installation and before energi ing. (2\

4.4Refer to the circuit diagram in FIGURE 4.1 FIGURE 4.1 CONTROL CIRCUIT OF FO WARD

4.4.1Describe how the contact O/L protects the motor (3\

4.4.2Describe how interlocking is used in the starter (5\

4.5Describe the unction of a star delta starter. (3\

4.6Describe the function of a no volt coil in a motor starter. (3\

4.7State how the direction of rotation of a three phase motor may be reversed. (2\

4.8The name plate on a three phase motor prov ides important information about the motor. List THREE types of information it provides. (3\ Hold in MC

4.9A three phase motor is connected to a 380 V/50 Hz supply. The motor has six pole pairs

4.9.1Synchronous speed (3\

4.9.2Rotor speed (3\

4.10A three phase delta connected motor is connected to a 380 V/50 Hz supply. The motor develops 29

4.10.1Input p ower (3\

4.10Input line current (3\

4.11Explain what will happen to the curr ent drawn by a motor if the power factor of the motor is improved. (3\ [40] Electrical Technology DBE/November 2015 NSC40

Q5— Section header —

5.1

5.2Describe why the current in a RLC series circuit is at maximum at resonant frequency. (4\

5.3Refer to the circuit diagram in FIGURE 5. and answer the questions that follow FIGURE 5.1: PARALLEL RLC CIRCUIT Given

5.3.1 Calculate the total current in the circuit (3\

5.3.2 Calculate the inductive reactance of the coil (3\ .3.3 Describe what will happen to the current through the coil if the frequency of the supply is increased

5.4Define the term factor with reference to a parallel circuit (4\ [20]20

Q6— Section header —

6.1Study FIGURE 6.1 which shows a typical PLC scan cycle and nswer the questions that follow

6.1.1Name TWO input devices that may be connected in Step 1. (2\

6.1.2List THREE programming la nguages that may instruct the PLC in Step 2. (3\

6.1.3Describe how EACH step in FIGURE 6.1 is used to run a PLC program (6\

6.1.4Explain why heavy current devices cannot be connected directly to the output of a PLC t hat uses transistor output (3\

6.1.5Describe how the problem in QUESTION

6.1.4is solved in industrial applications (3\

6.2Describe why relay control systems (hard wired systems\ are replaced by PLC control systems. (2\

6.3Refer to the following Boolean equation to answer the questions that follow

6.3.1Draw Karnaugh map and show the grouping (9\

6.3.2Write down the simplified expression that can be extracted from the Karnaugh map (3\ STEP 1 Input STEP 2

6.4Refer to the circuit in FIGURE 6.2. FIGURE 6.2 CONTROL CIRCUIT OF SEQUENCE STARTER

6.4.1MC switches on a lamp and MC closes a contactor that energises a fan Draw the PLC

6.4.2State what programming function must be included in the ladder diagram to automate the starting of the fan (MC (1\ [40]40

Q7— Section header —

7.1List THREE characteristics of an ideal operational amplifier ( op amp (3\

7.2Describe the term bandwidth in relation to op amps. (3\

7.3Give TWO reasons why negative feedback is used in op amp circuit s. (2\

7.4Describe the term positive feedback (3\

7.5Describe the term stability in relation to op amps. Hold in MC

7.6Study FIGURE 7.1 and a nswer the questions that follow. FIGURE

7.1OP AM CIRCUIT

7.6.1Identify the op amp circuit in FIGURE 7.1 (1\

7.6.2Draw the input and output waveform on the same axis and

7.6.3Calculate the voltage gain if the feedback resistor has a value of (3\

7.6.4Calculate the output voltage if an input signal of 1 V is applied to the op amp (3\

7.7Study FIGURE 7.2 and answer the questions that follow. FIGURE

7.2INVERTING SCHMID T TRIGGER

7.7.1State TWO applications of the op amp circuit in FIGURE 7.2 (2\ in

7.7.2Red raw the input waveform shown in FIGURE 7.3 and directly below it draw the output waveform FIGURE 7.3: INPUT WAVEFORM TO AN INVERTING SCHMIDT TRIGGER (6\

7.8

7.9Study FIGURE 7.5 and answ er the questions that follow. FIGURE 7. OP AMP CIRCUIT

7.9.1Identify the op amp circuit in FIGURE 7. (1\

7.9.2State ONE practical application of this type of op amp (1\

7.9.3Calculate the time the multivibrator will remain in the set state after it has received a trigger pulse

7.9.4Redraw the input waveform shown in FIGURE 7.6 and directly be low it draw the output waveform. Show the time calculated in QUESTION

7.9.3on the output waveform. FIGURE 7.6: INPUT TRIGGER PULSE FOR FIGURE 7.5 (5\ Trigger pulse Output waveform en-GB0 V en-GBV ut

7.10Study FIGURE 7.7 and answer the questions that follow. FIGURE 7.7: BI STABLE MULTI VIBRATOR

7.10.1State ONE application of a bi stabl e multi vibrator (1\

7.10.2If the input trigger pulse is negative, describe what value the output would move to (2\

7.11Describe the function of the dual DC supply in op amp circuits. (3\ [50] TOTAL: 200 out50

Mathematical Content

trig

Topics Identified

CircuitsMachines

Mark Allocation

Total200 marks

Sections10 + 20 + 20 + 40 + 20 + 40 + 50 = 200 marks

Paper information

SubjectElectrical Technology

Year2015

SessionNovember

TypePast Paper

PaperPaper 1

LanguageEnglish

Pages15

Downloads3

Examination context

Decade2010s

Years ago11y

SeasonSpring (SH)

Start dayThursday

Exam periodNovember 2015

Days since exam4,006

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