ET201: THREE PHASE SYSTEMS (ANSWER FOR DISCUSSION EXPERIMENT 4)

(ii)       Current

Figure 1.1.4 (b) shows the current in star connection. The value of line current (I_R, I_Y , I_B ) and phase current (I_r , I_y , I_b) are the same.

     

Line current,      I_L:  I_R , I_Y , I_B

Phase current, I_PH :  I_r , I_y , I_b


So, current element in star connection:

              I_L = I_PH


Neutral current (I_N) is the sum of the three current i.e. I_R, I_Y, and I_{B ;} having same magnitude but 120^o difference in phase. Therefore mathematically, the sum of these vectors will make neutral current I_N equals zero.

       I_N = I_R + I_Y + I_B = 0 

ET201: THREE PHASE SYSTEMS (PART 4)

a)                  Three phase emf generation

Let us consider Red (R) phase taken as reference and the coil rotates clockwise as indicated in Figure 1.1.2 (c) to (e), the induced voltage (emf) waveform for R (e_R), Y(e_Y)  and B(e_B)  can be derived separately. Figure 1.1.2 (f) shows the combination of the RYB waveform; therefore it is called the three phase waveform.

Figure 1.1.2. Emf waveform; (c) R phase  (d) Y phase (e) B phase (f) Three phase

ET201: THREE PHASE SYSTEMS (PART 3)

1.1.2        Generation of three phase voltages (emf).

In a single phase AC system, alternating voltage may be generated by rotating a coil in magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends, in each case, upon the number of turns in the coil. Consider a case of a single phase alternator with one armature winding only. If the number of armature windings is increased, then it becomes polyphase alternator and it produces as many independent voltage waves as the number of windings or phases. These windings are displaced from one another by equal angles, the values of these angles being determined by the number of phases or windings. In fact, the word “polyphase” means poly(many) and phase(winding or circuit).

A three phase alternator, as the name shows, has three independent armature windings which are 120 electrical degrees apart. Hence, the voltages induced in the three windings are 120⁰ apart in time phase. In Figure 1.1.2(a) is shown a two pole, stationary-armature, rotating-field type three phase alternator. It has three armature coils RR’, YY’ and BB’ displaced 120⁰ apart from one another. Figure 1.1.2(b) is shown a pole, stationary-magnet, rotating coils type.

Figure 1.1.2. (a) Rotating-field, stationary coils   (b)Rotating- coils, stationary field

ET201: THREE PHASE SYSTEMS (PART 2)

1.1.1    Three phase system advantages

There are several reasons why three phase system is superior to single phase system for transmission and distribution of electricity;

a)   In a balanced three phase system, the conductors need be only about 75% the size of conductors for a single phase two-wire system of the same power (KVA) rating. This helps to reduce the cost because less copper (or aluminium) is needed.

b)    The power delivered by a single-phase system pulsates and falls to zero three times during each cycle. The power delivered by a three-phase circuit pulsates also, but it never falls to zero

Figure 1.1.1. Three phase power never falls to zero

a)     The horsepower rating of three phase motors and the KVA (kilo-volt-amp) rating of three phase transformers is about 150% greater than for single-phase motors or transformers with a similar frame size.

b)   The efficiency and power factor of three phase motors much better than single phase motors for the same power transferred.

c)   Three phase motors have the ability to “self-start”; caused by the phase difference between three phase coils, but not in single phase motors.

d)  Three phase transformers are lighter, more efficient and cheaper compared to single phase transformer for the same size.

e)     When connected in parallel, single phase generator present difficulties which do not occur with three phase generators.

h)  The instantaneous three phase power flow is constant.  This is advantageous for both the end user and the generator, which does not have to supply a pulsating torque.

ET201: THREE PHASE SYSTEMS (PART 1)

1.0    Introduction

Three Phase Systems

Most domestic supplies are single-phase alternating current (AC). As you are aware, to transmit power with single phase AC, we need two wires (live wire, L and neutral wire, N). However, you would have seen that distribution lines usually have 4 wires. This is because distribution is done using three phase and the 4^th wire is the neutral. (4-wire supplies are normally used to distribute domestic supplies since they can provide an earthed neutral. 3-wire systems are commonly used for transmission of high voltage supplies between substations because money is saved by not providing a neutral wire).

Therefore, most of the electrical power generated and transmitted in the world today is three phase. Industrial supplies are three phase, whilst domestic supplies receive only one of the phases. 

Three phase system contains three AC voltages. The three phases usually designated R, Y, B corresponding to Red (R), yellow (Y) and Blue (B), which are phase displaced from one another. We can obtained single phase from three phase system by connecting any phase (R or Y or B) and neural (N) to form R-N, Y-N or B-N single-phase system. The single phase load of domestic supplies is shared out across the three phases by supplying different groups of users with different phase voltages.

Three phase supply voltages and load systems have two basic configurations, the star (wye) connection and the delta connection.

Figure 1.0 shows the three phase RYB system with star and delta connections and also single phase systems obtained from the three phase system as discussed earlier.

ET201: ELECTRICAL CIRCUITS (TRANSFORMER)

Transformers

A transformer is a device for stepping-up, or stepping-down, the voltage of an alternating electric signal. Without efficient transformers, the transmission and distribution of AC electric power over long distances would be impossible. There are two circuits. Namely, the primary circuit, and the secondary circuit. There is no direct electrical connection between the two circuits, but each circuit contains a coil which links it inductively to the other circuit. In real transformers, the two coils are wound onto the same iron core. The purpose of the iron core is to channel the magnetic flux generated by the current flowing around the primary coil, so that as much of it as possible also links the secondary coil. The common magnetic flux linking the two coils is conventionally denoted in circuit diagrams by a number of parallel straight lines drawn between the coils.

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Cara-cara Memilih Tajuk Projek Elektronik yang sesuai

Bagaimana mencari tajuk projek yang sesuai

Biasanya tajuk ini banyak dibincangkan oleh pelajar-pelajar IPT yang ingin menentukan tajuk projek akhir mereka. Biasanya pada waktu ini para pelajar menghadapi masalah menentukan tajuk yang sesuai dan diterima oleh penyelia projek mereka. Disini saya meletakkan beberapa kaedah yang saya anggap ia dapat membantu pelajar.

1. Senaraikan Tajuk

Di sini saya mencadangkan supaya anda menyenaraikan tajuk-tajuk yang terlintas di fikiran anda pada sehelai kertas.
a. Senaraikan sekurang-kurangnya 10 tajuk.
b. Pastikan tajuk-tajuk yang anda senaraikan itu adalah berkaitan dengan kursus yang anda ceburi dalam  institusi anda. Sebagai contoh, sekiranya kursus yang anda ambil adalah dalam bidang kejuruteraan komputer, cuba anda cari projek yang melibatkan pengaturcaraan dan juga peranti elektronik.
c. Pastikan tajuk yang anda pilih itu tidak terlalu rumit.
d. Pastikan tajuk yang anda pilih itu menggambarkan skop yang tidak terlalu besar.
e. Selepas perkara-perkara di atas sudah dibuat, buat short list pada senarai yang telah dibuat.

2. Tentukan Objektif anda

Untuk pengetahuan anda setiap tugasan yang ingin dilaksanakan, terlebih dahulu kita harus menentukan sasaran kita untuk dicapai. Sekiranya sasaran ini tidak diletakkan pada peringkat awal, maka sebenarnya kita tidak mempunyai satu TITIK akhir. Dengan itu penentuan objektif itu adalah sangat penting. Ciri-ciri objektif yang baik adalah seperti berikut:

a. Menentukan Objektif Terhadap Projek
    i. halatuju projek
b. Menentukan Obejktif Terhadap Diri Anda
    i. apa yang anda ingin capai untuk diri sendiri (Kebaikan untuk masa hadapan diri)
c. Menentukan Objektif tempat projek ini akan diaplikasi sendiri.
    i. menentukan sasaran tempat projek ini digunakan dan menentukan kebaikan kepada lokasi dan persekitaran projek anda digunakan.

Sebenarnya bilangan objektif itu adalah menentukan jumlah kerja yang anda perlu selesaikan.


3. Menyediakan kerta kerja

Kertas Kerja merupakan satu dokumentasi cadangan projek. Dan cadangan saya kepada anda sebelum berjumpa dengan penyelia sama ada yang anda pilih sendiri atau penyelia yang memilih anda, pastikan sebelum anda berjumpa dengan penyelia anda sudah menyediakan sekurang-kurangnya 2 atau 3 kertas kerja dengan tajuk yang berlainan. Ini bertujuan penyelia yang menyelia projek anda dapat melihat secara keseluruhan halatuju projek anda dan juga akan menjimatkan masa anda mencari tajuk yang akan dipilih. Antara isi kandungan yang perlu ada dalam kertas kerja ini adalah seperti berikut:

a. Tajuk Projek
b. Objektif Projek
c. Skop projek
d. Research and Methodology
e. Abstrak
d. Pengenalan secara ringkas kepada projek

4. Berjumpa dengan penyelia

Sebelum anda berjumpa dengan penyelia anda, pastikan anda sudah mendapatkan banyak maklumat tentang projek yang ingin laksanakan. Dan pastikan anda mentetahui sumber maklumat tentang peranti-peranti yang diperlukan. Keran ini adalah menjadi sebahagian daripada perkara yang amat penting dalam menentukan halatuju projek anda.

Jangan sekali-kali berjumpa dengan penyelia anda dengan tangan kosong, atau secara langsung meminta cadangan projek daripada penyelia anda.

Tajuk Projek Elektronik

Disini saya sertakan beberapa contoh tajuk projek elektronik yang biasa dipilih oleh pelajar
1. line follower robots
2. Mesin Pembasuh Tangan Automatik
3. Sistem Penggera Rumah
4. Home Security System Using Microcontroller
5. Door Lock using Microcontroller
6. Sistem Keselamatan menggunakan RFID
7. Sistem pengesan banjir
8. Robot Line Tracker
9. Sistem Keselamatan Komputer
10. Sistem Bekalan Kuasa Mudah Alih (DC to AC).
11. Smart Card Reader
12. Multiple Input/Output Box: Kawalan Tandas Automatik
13. Conveyor (PLC)
14. Robot Arm
15. PC Controlled Parallel Port
16. Sistem Pengasingan Kotak dan Motor Berpenghantar (PLC)
17. Automatic Dryer Packer and Process
18. Score Board Electronic
19. Sistem Pempembersih tangan Automatik menggunakan PLC Omron CPM2A-40
20. Automatic Room Light by Counter Control
21. Mini Golf Training Score Board
22. Bar Code reader
23. RFID Reader
24. Robot Kawalan Jauh
25. Kawalan Seven Segment untuk lampu isyarat
26. Gas Detector 3 in 1
27. PLC controlled fire fighting system (kss)
28. Projek Sistem Akuarium sistematik29. Floor Cleaning Machine
30. Peojek Sistem siraman automatik
32. Projek Noise Detector with "SILENR" LED display.