INSTRUCTION: This section consists of FOUR (4) structured questions. Answer ALL questions.

Transcription

1 SECTION B: 60 MARKS BAHAGIAN B: 60 MARKAH INSTRUCTION: This section consists of FOUR (4) structured questions. Answer ALL questions. ARAHAN: Bahagian ini mengandungi EMPAT(4) soalan berstruktur. Jawab SEMUA soalan. QUESTION 1 SOALAN 1 C1 (a) List THREE (3) types of losses in DC generator. Senaraikan TIGA (3) jenis kehilangan pada penjana AT. (b) A 20 kw compound generator works on full load with a terminal voltage of 250 V. The armature, series and shunt windings have resistances of 0.05 Ω, Ω and 100 Ω respectively. Calculate the total emf generated in the armature when the machine is connected short shunt. Satu penjana majmuk 20 kw bekerja pada keadaan beban penuh dengan voltan terminal sebanyak 250 V. Rintangan belitan angker, siri dan pirau bernilai 0.05 Ω, Ω dan 100 Ω masing-masing. Kirakan jumlah dge terjana dalam angker bila mesin ini disambungkan secara belitan pirau pendek. [5 marks] [5 markah] 6 SULIT

2 (c) A direct current short compound generator 240 V has armature windings resistance, series resistance and shunt field windings of 0.1 Ω, 0.2 Ω and 150 Ω for each of them. The current for armature, series and shunt winding is A, A and 1.71 A respectively. This generator supplies 20 kw at 80% efficiency, calculate the total emf generated and it copper loss. Sebuah penjana AT majmuk pirau pendek 240 V mempunyai rintangan belitan angker, rintangan siri dan belitan medan pirau sebanyak 0.1 Ω, 0.2 Ω dan 150 Ω setiap satu. Arus angker, siri dan pirau adalah A, A and 1.71 A masing-masing. Penjana meletakkan sebanyak 20 kw pada 80% kecekapan, kirakan jumlah dge terjana dan jumlah kehilangan tembaga. [7 marks] [7 markah] QUESTION 2 SOALAN 2 C1 (a) Draw and label the schematic diagram for long compound DC motor. Lukis dan labelkan gambarajah skematik bagi Motor AT pirau panjang. (b) A 4-pole, 500 V shunt DC motor has 720 conductors connected via wavewinding on its armature. The armature current is 60 A, flux per pole is 0.03 Wb and armature resistance including brush contact is 0.02 Ω. Calculate the speed of the motor. Sebuah motor AT jenis pirau, 4 kutub, 500 V serta mempunyai pengalir sebanyak 720 yang disambungkan secara belitan gelombang. Sekiranya arus angker adalah 60 A, fluks per kutub adalah 0.03 Wb dan rintangan angker termasuk berus adalah 0.02 Ω. Kirakan kelajuan motor. [5 marks] [5 markah] 7 SULIT

3 (c) A series connected DC motor has an armature resistance of 0.5 Ω and field winding resistance of 1.5 Ω. In driving a certain load at 1200 prpm, the current drawn by the motor is 20 A from a voltage source of VT = 220 V. The rotational loss is 150 W. Calculate the output power. Sebuah motor AT sambungan sesiri mempunyai rintangan angker sebanyak 0.5 dan rintangan lilitan medan sebanyak 1.5 Ω. Semasa mempunyai beban pada kelajuan 1200 ppm, arus sebanyak 20 A dimasukan ke dalam motor daripada punca bekalan VT =220 V. Kehilangan kuasa putaran ialah 150 W. Kirakan kuasakeluaran motor. [7 marks] [7 markah] QUESTION 3 SOALAN 3 (a) List THREE (3) conditions that must be met prior to paralleling/synchronizing AC generators. Senaraikan TIGA (3) syarat yang mesti dipatuhi semasa hendak selarikan panjana AU. (b) An Alternative Current (AC) generator, 8 pole, 50 Hz, generated emf 1000 V between line in star connection. The stator has 320 conductor inside the armature windings with full pitched distributed winding. The distribution factor (Kd) is assumed as Calculate the flux and line current. Penjana arus ulangalik (AU) 8 kutub,50hz menjana dge 1000V antara talian sambungan bintang. Stator mempunyai 320 pengalir angker dengan belitan dalam pitch penuh. Andaikan faktor jarak (Kd) Kira nilai flux dan arus talian. 8 SULIT

4 (c) A 3 phase star connected AC generator is rated 1000 kva, 11 kv. The effective resistance and synchronous reactance per phase are 1.5 Ohm and 30 Ohm respectively. If the generator runs at unity power factor, calculate: i. Full load current ii. EMF generated Sebuah penjana AU 3 fasa, berkadar 1000 kva, 11 kv bersambungan bintang. Nilai rintangan efektif dan regangan segerak sefasa ialah masing-masing 1.5 Ohm dan 30 Ohm. Jika penjana beroperasi pada faktor kuasa uniti, kira: i. Arus beban penuh ii. DGE terjana QUESTION 4 SOALAN 4 (a) Identify THREE (3) types of single phase motors. Senaraikan TIGA ( 3) jenis motor satu fasa. (b) A synchronous motor is not a self-starting and there are various methods to start. Briefly interpret THREE (3) of the methods. Motor segerak tidak boleh berputar dengan sendiri dan motor ini memerlukan beberapa kaedah untuk memulakannya. Taksirkan secara ringkas TIGA (3) kaedah tersebut. 9 SULIT

5 (c) A three-phase induction motor has four poles and given supply of 50 Hz. Calculate: i. The synchronous speed ii. The speed of the rotor when the slip is 4% iii. The slip when the rotation speed is 1400 rpm iv. The rotor frequency when the speed of the rotor is 600 rpm v. The rotor frequency during starting Sebuah motor aruhan tiga fasa mempunyai 4 kutub dan diberikan bekalan 50 Hz Kirakan: i. Kelajuan segerak ii. Kelajuan rotor jika gelinciran sebanyak 4% iii. Nilai gelincir sekiranya kelajuan putaran adalah 1400 psm iv. Frekuensi putaran jika diberi kelajuan rotor adalah 600 psm v. Nilai frekuensi pemutar ketika motor baru bermula 10 SULIT

6 SECTION C: 30 MARKS BAHAGIAN C: 30 MARKAH INSTRUCTIONS: This section consists of TWO (2) essay questions. Answer ALL questions. ARAHAN: Bahagian ini mengandungi DUA (2) soalan esei. Jawab SEMUA soalan. QUESTION 1 SOALAN 1 A series DC machine of 4 poles 250 V motor has 469 armature conductors wave windings. The number of flux per pole is 22mWb and total of losses, wind and friction is 810 W. Armature resistance and serial field respectively is 0.19 ohm and 0.14 ohm. When the motor usage current is as much as 50 A, sketch the motor circuit and calculate: i. Armature torque ii. Rotation speed iii. Output torque and iv. Efficiency Motor siri AT mempunyai 4 kutub 250 V mempunyai 469 pengalir angker jenis belitan gelombang. Bilangan fluk per kutub adalah 22 mwb dan jumlah kehilangan, kehilangan angin dan geseran sebanyak 810 W. Rintangan angker dan medan siri masing-masing adalah 0.19 ohm dan 0.14 ohm. Bila motor menggunakan arus sebanyak 50 A, lakarkan litar motor ini dan kirakan: i. Dayakilas angker ii. Kelajuan putaran iii. Dayakilas keluaran dan iv. Kecekapan [15 marks] [15 markah] 11 SULIT

7 QUESTION 2 SOALAN 2 A 3-phase induction motor, 8 pole, is connected to 3 phase supply, 415 V, 50 Hz. At full load conditions, the efficiency is 85% at 0.8 lagging power factor and slip (s) is 3%. Calculate: - i. The rotational speed of the rotor ii. The frequency of the rotor iii. Shaft torque v. Phase current and line current if delta-connected at stator Sebuah motor aruhan 3 fasa, 8 kutub, disambungkan kepada bekalan 3 fasa, 415 V, 50 Hz. Pada keadaan beban penuh, kecekapannya adalah 85 % pada faktor kuasa 0.8 mengekor dan gelincir(s) adalah 3 %. Kirakan: i. Kelajuan putaran pemutar ii. Frekuensi pemutar iii. Daya kilas aci v. Arus fasa dan arus talian jika pemegun bersambungan delta [15 marks] [15 markah] SOALAN TAMAT 12 SULIT