PAST EXAM PAPER & MEMO N3 ABOUT THE QUESTION PAPERS:

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1 EKURHULENI TECH COLLEGE. No. 3 Mogale Square, Krugersdorp. Website: www. ekurhulenitech.co.za info@ekurhulenitech.co.za TEL: CELL: / PAST EXAM PAPER & MEMO N3 ABOUT THE QUESTION PAPERS: THANK YOU FOR DOWNLOADING THE PAST EXAM PAPER AND ITS MEMO, WE HOPE IT WILL BE OF HELP TO YOU. SHOULD YOU NEED MORE QUESTION PAPERS AND THEIR MEMOS PLEASE SEND US AN TO INFO@EKURHULENITECH.CO.ZA AND WE WILL SEND YOU A FULL DOWNLOAD VERSION OF THESE. HOWEVER PLEASE NOTE THAT THESE ARE SOLD FOR A SMALL AMOUNT OF R300 PER DOWNLOAD PER SUBJECT. ABOUT REGISTERING WITH OUR COLLEGE CONSIDER REGISTERING WITH OUR COLLEGE AND WE HAVE THE FOLLOWING TYPES OF LEARNING: ONLINE OR CORRESPONDENCE LEARNING. THIS IS THE MOST PREFARED ONE BY THOUSANDS PART-TIME CLASSES DURING SATURDAYS IF NEAR OUR OFFICES IN KRUGERSDORP FULL-TIME CLASSES IF NEAR OUR CLASSES IN KRUGERSDORP ABOUT EXTRA TEXTBOOKS IF LOOKING FOR TEXBOOKS FOR CERTAIN SUBJECTS I N1-N6 ENGINEERING STUDIES PLEASE SEND US AN ON INFO@EKURHULENITECH.CO.ZA ABOUT VIDEO MATERIAL WE HAVE VIDEO MATERIAL FOR EXTRA UNDERSTANDING ON CERTAIN ENGINEERING FOR A FEE. REQUEST A QUOTE. SEND US AN ON INFO@EKURHULENITECH.CO.ZA Website: info@ekurhulenitech.co.za

2 T460(E)(A5)T APRIL EXAMINATION NATIONAL CERTIFICATE ( ) 5 April 016 (X-Paper) 09:00 1:00 This question paper consists of 9 pages and 1 formula sheet.

3 ( ) -- T460(E)(A5)T DEPARTMENT OF HIGHER EDUCATION AND TRAINING REPUBLIC OF SOUTH AFRICA NATIONAL CERTIFICATE TIME: 3 HOURS MARKS: 100 INSTRUCTIONS AND INFORMATION Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. Where applicable, answers must be in accordance with the SABS (SANS) Code of Practice SANS :003 for the Wiring of Premises. Sketches must be neat, labelled and large enough to show the required detail. Answers must be given to TWO decimal places. Write neatly and legibly.

4 ( ) -3- T460(E)(A5)T QUESTION 1: DOMESTIC APPLIANCES 1.1 A stove using 40 A must be installed in a new house. Explain the procedure of installing a stove, type of materials used and placement of parts. Start from the distribution board to the stove's screw connectors. (4) 1. Explain how you would test each circuit (plate number 1 and oven) of the above stove for continuity with the aid of an ohm-meter. (3) 1.3 Draw the single phase sub-circuit that adheres to wiring code regulations that would supply the stove with power. (3) QUESTION : PROTECTION.1 Name the conductors in a single-phase domestic installation that the earthleakage relay disconnect when the earth-leakage protection is activated. (). State what value of 0 V AC current is it considered dangerous to humans ().3 FIGURE.1 shows a Balanced Core Earth Leakage Relay. Explain the operating principle of a core balance earth-leakage relay. FIGURE.1: BALANCED CORE EARTH LEAKAGE RELAY (6)

5 ( ) -4- T460(E)(A5)T QUESTION 3: ILLUMINATION 3.1 Indicate whether the following statements are TRUE or FALSE. Choose the answer and write only 'true' or 'false' next to the question number ( ) in the ANSWER BOOK A fluorescent tube emits light because of a continuous electric arc in the tube Gasses used in discharge lamps have a positive temperature coefficient of resistance and the current needs to be limited as the temperature increases Phosphor powder is used in lamps because it has a long afterglow Rotating machinery give a stroboscopic effect under incandescent lamps When compared with discharge lamps, tungsten halogen lamps emit bright light but consume a higher amount of energy. (5 x 1) (5) 3. Draw a labelled circuit diagram of a fluorescent lamp that is started with the aid of a glow starter. (You will lose marks if the components are not labelled.) (5) QUESTION 4: ALTERNATING CURRENT THEORY 4.1 FIGURE 4.1 shows a sine wave. NOTE: The angle is in degrees. e = 310 sin( t ) Volts FIGURE 4.1: SINE WAVE Calculate the waveform's effective value. (3) 4.1. Redraw the waveform indicating the RMS, peak and Average Values on the waveform correctly. (3)

6 ( ) -5- T460(E)(A5)T 4. Draw a phasor diagram that will represent a balanced three phase voltage supply. Indicate on the diagram the following: Correct order of Phases if the reference point is at 0 Correct Direction of Rotation Correct phase angle between phases Current in each phase lagging the voltage Exact scale is not required. (4) QUESTION 5: SERIES RLC CIRCUITS 5.1 FIGURE 5.1 shows an RLC Circuit. Answer the following questions. R=5Ω L=0.1 H Xc=7,65 Ω 0V 50Hz FIGURE 5.1: RLC CIRCUIT Calculate the inductive reactance (3) 5.1. Calculate the circuit impedance. (3) Sketch a fully labelled phasor diagram. (4) QUESTION 6: THREE-PHASE AC SYSTEMS 6.1 Calculate the power in balanced 3-phase delta connected system with the following information: Line Voltage = 40 Volt Line Current = 3A Φ=9 Load = inductive (3) 6. Calculate the line voltage between two phases in a star connected system if the phase voltage between one fase and neutral is 0 V. (3) 6.3 Figure 6.1 shows a block diagram representing the losses in a 3-phase motor. Calculate the output power of the motor from the given information.

7 ( ) -6- T460(E)(A5)T Losses in a motor Input V L =380 Volt I L =4.A Δ Connected QUESTION 7: TRANSFORMERS Cosθ=0.8 ŋ=90% efficient FIGURE 6.1: LOSSES IN A MOTOR Output (4) 7.1 The circuit in FIGURE 7.1 below consists of three single-phase transformers connected together. This circuit is connected to a three-phase 380 V supply. The primaries are labelled with capital letters. A 1 B 3 C 550:1 FIGURE 7.1: 3-PHASE TRANSFORMER Identify the configuration in which the transformer is connected from primary to secondary. () 7.1. State whether this is a step up / step down transformer. (1) Identify the Neutral connector/s on the transformer (1) 4 7. Calculate the output line voltage of a delta/delta step up transformer if the transformer has a turns ratio of 1:10 and an input line voltage of 380 Volts. (3) 7.3 A current of A at a power factor of 0,8 is drawn from the 380 V supply when a transformer is connected to a balanced three-phase load. Calculate the total power consumed. (3)

8 ( ) -7- T460(E)(A5)T QUESTION 8: DC MACHINES 8.1 Name the functions of the following components of a DC motor circuit: A variable resistor placed in series with the armature of a shunt motor 8.1. A no-volt release coil An overload relay (3 x 1) (3) 8. Name any TWO types of field-coil connections used in DC motors. () 8.3 Name any TWO methods to reduce armature reaction with reference to DC motors. () 8.4 Explain how you would do a field volt-drop test on a four-pole DC motor. (3)

9 ( ) -8- T460(E)(A5)T QUESTION 9: AC MACHINES 9.1 Explain why the running winding of a split-phase motor has a lower resistance and lower inductive reactance than the starting winding () 9. Draw a circuit diagram of a split-phase motor that has one capacitor which is permanently connected during operation. (3) 9.3 State the code of practice on motor circuits regarding the starter circuit of a large DC motor and loss of supply. (1) 9.4 Explain how the slip-ring motor in FIGURE 9.1 below is started and how it reaches full speed. FIGURE 9.1: SLIPRING MOTOR STARTER (4)

10 ( ) -9- T460(E)(A5)T QUESTION 10: MEASURING INSTRUMENTS AND ELECTRONICS 10.1 Explain how you would increase the range of the following instruments: A DC ammeter (1) A DC voltmeter (1) An AC wattmeter (3) 10. Define each of the following terms: Electron current flow 10.. Semi-conductor Positive ions P-type doping Pentavalent atom (5 x 1) (5) TOTAL: 100

11 ( ) -10- T460(E)(A5)T FORMULA SHEET V I T Z I ACTIVE I REACTIVE I T I X L πf L 1 X C πfc Z R Cos T (X Sin L R Cos 1 Z VR ITR VXL ITXL V I X XC V T V P I R S VI C 3-phase P 3 V I S X C R (VXL VXC) L L 3 V L I L Cos ) V V p s N N ω f p s I I s p f.60 N p n nr s n The next five formulae are true for voltage i Im Sin ( t) Irms 0,707 I m I 0,637 ave I m i1 i...in Irms n i1 i.. in Iave n RMSfactor value Form AVE - value MAX - value Crest factor RMS- value SERIES R R R T 1... R n DELTA V L V PH / F I L 3I PH / F STAR V L 3V PH / I L I PH / F F PARALLEL 1 1 R R T 1 1 R... 1 R n

12 MARKING GUIDELINE -1- T...(E)(A )T MARKING GUIDELINE NATIONAL CERTIFICATE APRIL EXAMINATION 5 APRIL 016 This marking guideline consists of 8 pages.

13 MARKING GUIDELINE -- T460(E)(A5)T NOTE: There is not only one answer or one method (approach) of answering the questions. This memorandum gives only one answer or one possible method (approach). Examiners must analyse the student's solution to determine if the question has been answered and therefore must not adhere strictly to this memorandum. QUESTION 1: DOMESTIC APPLIANCES mm conduit installed from D.B to stove. Isolator box not more than 0,5 m from stove. Flexible conduit between wall and stove. 6 mm L, N and E conductors from D.B to stove. (4 x 1) (4) 1. Make sure the disconnector is off. Place meter on ohms scale and measure between live and neutral. Switch the stove plate or the oven on. Ohms value should be low. (Any 3 x 1) (3) 1.3 Distribution Board Stove Live Neutral Earth MCB for Stoveü Liveü Neutral Earth Stove Disconnectorü (3) QUESTION : PROTECTION.1 Live üand neutral. ü (). Approximately 0 ma ü and higher. ü ().3 When the live and neutral wire current is the same,ü the magnetic fields cancel each other since the current flows in opposite directions.ü No EMF will be induced in the secondary.ü If an earth fault occurs, the live will carry more current than the neutralü and at 0 maü the resultant field will be strong enough to activate the relay.ü (6)

MARKING GUIDELINE -3- T460(E)(A5)T QUESTION 3: ILLUMINATION 3.1 3.1.1 3.1. 3.1.3 3.1.4 3.1.5 3.

Filamentsü Glow Starter ü RF Capacitor ü (5) QUESTION 4: ALTERNATING CURRENT THEORY 4.1 4.1.1 (3) 4.

14 MARKING GUIDELINE -3- T460(E)(A5)T QUESTION 3: ILLUMINATION False False True False True (5 x 1) (5) Chokeü PF Correcting Capacitor ü Flourescent Tube Filamentsü Glow Starter ü RF Capacitor ü (5) QUESTION 4: ALTERNATING CURRENT THEORY (3) 4.1. V (Maximum) ü V (RMS) = V (Maximum) X 0,707 ü V (Average) = V (Maximum) X 0,637 ü Over ½ cycle (3)

15 MARKING GUIDELINE -4- T460(E)(A5)T 4. L 3 ü 10 I I 3 10 ü 10 I 1 ü L 1 ü 0 L (4)

16 MARKING GUIDELINE -5- T460(E)(A5)T QUESTION 5: SERIES RLC CIRCUITS X L =.π.f.l ü X L =.π.50.0,1 ü X L = 31,4 Ωü (3) 5.1. ü ü ü (3) V XL V X =V XL -V XC V X =6,5ü Vzü Θ=0.8 Laggingü I Z V R ü V XC Note to Marker Must show lagging p.f OR X L X C ] Vz leads I Z Φ = angle between V Z and V R (4)

17 MARKING GUIDELINE -6- T460(E)(A5)T QUESTION 6: THREE-PHASE AC SYSTEMS 6.1 ü ü (3) 6. V L =.xv ph ü = x 0ü = 381 Vü (3) 6.3 P in = V L I L cos Ф x ŋü =.380 X 4, X 0,8 X 0.9ü = Watt ü η = 90% = 0.9ü If candidate can show 90% efficiency = 0.9 as a factor of 1 = fourth mark is awarded. (4) QUESTION 7: TRANSFORMERS Deltaü: Starü connected transformer Note: Order must be correct () 7. Step down transformerü. 550:1 indicates 550 turns for every 1 turn on the secondary (1) 7.3 Neutral = 4ü (1) 7.4 V a1a = V A1A T.Rü = 380 1/10ü =3 800 Vü (3) 7.5 P = x V L x I L cosøü = x 380 x x 0,8 ü = 5,77 A ü (3)

18 MARKING GUIDELINE -7- T460(E)(A5)T QUESTION 8: DC MACHINES For speed control 8.1. To disconnect the motor when the supply voltage is too low To trip when the motor draws too much current (3 x 1) (3) 8. Shunt Series Combination of series and parallel (Any x 1) () 8.3 Brush shifting Interpoles Compensating windings, add a series field. (Any x 1) () 8.4 Connect the 4 windings in series to a low voltage supply. Use a voltmeter to measure the voltage across each winding. The readings should be the same across all the poles. (3 x 1) (3) QUESTION 9: AC MACHINES 9.1 The running winding has less turnsü in the coils than the starter winding, but it is of a thicker wire, thus having less inductance and less resistanceü, ergo less reactance. () 9. Note to marker: Must show Centrifugal switch in series with starter capacitor and labelled. Run Cap must be permanently connected in circuit and labelled. Main Winding / run Winding in parallel with supply (3)

19 MARKING GUIDELINE -8- T460(E)(A5)T 9.3 The starting arm must move back to the OFF position during loss of supply. (1) 9.4 The motor will only start up if the resistors are in circuit and the brushes are on (short-circuit rings open). As the motor gains speed the resistors are gradually removed from the circuit. Once removed, the slip rings are short-circuited. (4) QUESTION 10: MEASURING INSTRUMENTS AND ELECTRONICS Insert a shunt resistor (parallel to meter) into the circuit. (1) Insert a resistor in series with the meter. (1) Use instrument transformers. The secondary of a current transformer supplies the current coil of the meter and the secondary of a potential transformer supplies the voltage coil of the meter (3) Flow of electrons in the external circuit (not in the battery) from negative pole to positive pole Material with special properties and electrical resistance between a conductor and an insulator Atoms with fewer electrons than protons An impurity added to Si or Ge that has only 3 valence electrons An atom that has 5 valence electrons (electrons available for bonding). (5 x 1) (5) TOTAL: 100

20 EKURHULENI TECH COLLEGE. No. 3 Mogale Square, Krugersdorp. Website: www. ekurhulenitech.co.za info@ekurhulenitech.co.za TEL: CELL: / REGISTERING WITH OUR COLLEGE CONSIDER REGISTERING WITH OUR COLLEGE AND WE HAVE THE FOLLOWING TYPES OF LEARNING: ONLINE OR CORRESPONDENCE LEARNING. THIS IS THE MOST PREFARED ONE BY THOUSANDS PART-TIME CLASSES DURING SATURDAYS IF NEAR OUR OFFICES IN KRUGERSDORP FULL-TIME CLASSES IF NEAR OUR CLASSES IN KRUGERSDORP ABOUT EXTRA TEXTBOOKS IF LOOKING FOR TEXBOOKS FOR CERTAIN SUBJECTS I N1-N6 ENGINEERING STUDIES PLEASE SEND US AN ON INFO@EKURHULENITECH.CO.ZA ABOUT VIDEO MATERIAL WE HAVE VIDEO MATERIAL FOR EXTRA UNDERSTANDING ON CERTAIN ENGINEERING FOR A FEE. REQUEST A QUOTE. SEND US AN ON INFO@EKURHULENITECH.CO.ZA Website: info@ekurhulenitech.co.za

PAST EXAM PAPER & MEMO N3 ABOUT THE QUESTION PAPERS:

PAST EXAM PAPER & MEMO N3 ABOUT THE QUESTION PAPERS: EKURHULENI TECH COLLEGE. No. 3 Mogale Square, Krugersdorp. Website: www. ekurhulenitech.co.za Email: info@ekurhulenitech.co.za TEL: 011 040 7343 CELL: 073 770 3028/060 715 4529 PAST EXAM PAPER & MEMO N3