T440(E)(N23)TNOVEMBER EXAMINATIONNATIONAL CERTIFICATEELECTRO-TECHNOLOGY N3(11040343)23 November (X-Paper)09:00–12:00This question paper consists of 6 pages, 1 diagram sheet anda formula sheet of 3 pages.

(11040343)-2-T440(E)(N23)TDEPARTMENT OF HIGHER EDUCATION AND TRAININGREPUBLIC OF SOUTH AFRICANATIONAL CERTIFICATEELECTRO-TECHNOLOGY N3TIME: 3 HOURSMARKS: 100INSTRUCTIONS AND INFORMATION1.Answer ALL the questions.2.Read ALL the questions carefully.3.Number the answers according to the numbering system used in this questionpaper.4.The correct information must be copied from the question paper andsubstituted for the correct symbol.5.Keep the subsections of questions together, for example QUESTION 1.1.1,1.2 and so forth. After the completion of each question rule off.6.Sketches and diagrams must be done in pencil and must be neat, reasonablylarge and fully labelled.7.The answers must be worked to THREE decimal places after a comma, forexample 3,142.8.Use the correct units for answers.9.Write neatly and legibly.

(11040343)-3-T440(E)(N23)TQUESTION 11.11.2Define the following terms as applicable in a DC machine:1.1.1Commutation(3)1.1.2Pole pitch(1)Draw a sketch of a DC machine and indicate the following:pole pitch, interpoles and directions of rotation for a motor and a generator.(6)[10]QUESTION 22.1Name TWO disadvantages of the commutation process.(2)2.2Briefly describe what a short compound motor is.(2)2.3State the function of commutation in: motor(1)2.3.2A generator(1)An 8 pole machine has a wave-wound armature with some conductors perslot. The flux per pole is 40 mWb and the EMF generated at 14 r/s is120V. Determine the total number of conductors in the armature.(4)[10]QUESTION 33.1Name TWO losses that torque has to overcome.(2)3.2Name TWO variables that the back EMF in a motor depends upon.(2)3.3The total torque exerted on an 8 pole motor is 980 Nm. The armature has 660conductors and carries a current of 400A.Determine the following:3.3.1The flux per pole when connected in the lap wound.3.3.2The flux per pole when connected in the wave wound.Copyright reserved(3)(3)[10]Please turn over

(11040343)-4-T440(E)(N23)TQUESTION 44.1.1Briefly explain the operation of a bi-metal type overload.(4)4.1.2How is time delay obtained in a bi-metal type overload?(1)4.2Study FIGURE 1 on the attached DIAGRAM SHEET and answer the followingquestions. Write only the answer next to the question number (4.2.1– 4.2.5) inthe ANSWER BOOK.4.2.1Name the type of fluid used in this device indicated by the arrow.(1)4.2.2Name the component indicated by the arrow.(1)4.2.3Name the component indicated by the arrow.(1)4.2.4Name the component indicated by the arrow.(1)4.2.5Name the component indicated by the arrow.(1)[10]QUESTION 55.1A resistor, inductor and capacitor are connected each in turn (that is not inseries or parallel) to a 210V, 60 Hz supply.Determine the current flows in each turn if the: value is 70 000 mΩ(1)5.1.2Capacitor value is 130 µF.(2)5.1.3Inductor value is 40 mH.(2)The components in QUESTION 5.1 are connected in series. Determine:5.2.1The circuit impedance5.2.2The total current flow through the circuitCopyright reserved(3)(2)[10]Please turn over

(11040343)-5-T440(E)(N23)TQUESTION 6An alternating quantity with a maximum value of 40A is represented by a sinusoidalwave and the following mid-ordinate values obtained over a half cycle: i 1 10 A ;i 2 20 A ; i 3 36 A ; i 4 38 A ; i 5 28 A ; i 6 14 A .Determine the following:6.1The virtual value of the quantity(4)6.2The average value of the quantity(3)6.3The form factor(1)6.4The crest factor(1)6.5The kind of wave form which is deduced from the values of the crest factorand form factor.(1)[10]QUESTION 7The inductor is connected in series with a 70W, 140V incandescent lamp so that it canoperate from a 200V, 60 Hz supply.Determine the following:7.1The circuit current flow(2)7.2The lamp resistance(2)7.3The circuit impedance(2)7.4The circuit inductance(4)[10]

(11040343)-6-T440(E)(N23)TQUESTION 88.1State THREE advantages of a three-phase distribution system.(3)8.2A three-phase delta connected motor draws a current of 9A from a 380Vsupply at a power factor of 0,85 lagging.Determine the following:8.2.1The apparent input power in kVA(2)8.2.2The actual input power in kW(3)8.2.3The phase current of the motor windings(2)[10]QUESTION 99.19.2State FOUR similar components which are found in both a moving-iron anddynamo-meter instrument.(4)A galvanometer has a resistance of 120 Ω and gives a full-scale deflectionwhen 6 mA passes through.Show how the instrument can be used as follows:9.2.1A voltmeter capable of measuring between 0 and 6V.9.2.2An ammeter to measure up to 2A.(3)(3)[10]QUESTION 1010.110.210.3Indicate the valence number of the following as applicable in an atom:10.1.1N-type material(2)10.1.2P-type material(2)Which electronic component is used for smoothing out the wave in a rectifiercircuit?State FIVE uses of a silicon-controlled rectifier in electronic circuits.(5)[10]TOTAL:Copyright reserved(1)100Please turn over

(11040343)T440(E)(N23)TDIAGRAM SHEET4. 1Copyright reserved

(11040343)-1-T440(E)(N23)TELECTRO-TECHNOLOGY N3FORMULA SHEETAny applicable formula may also be used1. E V - I a Ra2. E V I a Ra3. E 2pФZN60c4. N VKF5. T 0,318 I a ZpFC6. Efficiency VI2VI I a Ra I sV C 100%27. Efficiency VI - ( I a Ra I sV C ) 100%VI8. Efficiency 2pN (W - S )r 100%60VI9. Efficiency I1 100%I1 I 210. E Blv11. e E m Sin2цft12. i I m Sin2цft13. e ave / gem or i ave / gem 0,637 E m or I m14. e rms / wgk or i rms / wgk 0,707 E m or I m15. E ave / gem e1 e2 e3 e4 . enn

(11040343)-2-Or I ave / gem i1 i2 i3 . inn22222i1 i2 i3 . innE rms / wgk17. Form factor E ave / gem18. Crest factor 19. I 2e1 e2 e3 . enn16. E rms / wgk Or I rms / wgk EmE rms / wgki VXL21. X C 2цfC;i VXC2R2 X L ; Z 23. Tan q XL;R24. V R I x R;25. Z oror22I RMS / WGKi AVE / GEMImI rms / wgkVR20. X L 2цfL;22. Z T440(E)(N23)T2R2 X C ;Tan θ I VZXCRV L I XL; VC I XCR 2 ( X L - X C ) 2 ; Z R 2 ( X C - X L ) 226. Tan θ XL - XC;R27. P V x I; P I 2 R ;Tan θ P XC - XLRV2R28. P VICosθ29. Cos θ R;ZCopyright reservedCos θ W or kWVA or kVAPlease turn over

(11040343)-3-30. I active ICosq ;I reactive ISinq31. P VI Cos θQ VI Sin θ32. f r 12p LC222233. I I R I L ; Tan θ 34. I I R I C ; Tan θ 35. I I R (I L - I C ) 2 ;36. I I R (I C - I L ) 2 ;ILIRICIR2Tan θ I L - ICIR2Tan θ IC - I LIR37. Cos θ IRI38. V L V p ; I L 3I p39. V L 3V p ;40. W 41.IL Ip3VL I L Cosq hV1 N 1 I 2 V2 N 2 I 142. kVA 3V L I L1 00043. V shunt Vmeter ;44. I T I m I s45. I t VtRtCopyright reservedI s R s I m RmT440(E)(N23)T