HARI JOGATHON

KV Matang akan mengadakan larian Jogathon pada hari Sabtu ini, 1/11/2014. Majlis tersebut akan bermula pada pukul 7.30 pagi. Semua pelajar di wajibkan hadir. Gerai jualan disediakan. Pengunjung luar dialu-alukan untuk memeriahkan lagi acara ini.

Maklumat kemasukan ke Kolej Vokasional tahun 2015

Tuan/Puan....Kemasukan murid ke Program Kolej Vokasional & Sekolah Menengah Teknik Ambilan Januari 2015..paparan dalam akhbar terpilih pada 2 November 2015 dan online pada 3 November 2015. Cadangan tarikh pendaftaran Program Kolej Vokasional pada 12 Januari 2015 & SMT pada 26 Januari 2015. Calon lepasan ting 3 thn 2014 boleh memohon melalui website www.moe.gov.my. Syarat2 umum & khusus bg setiap kursus akan kepilkan bersama surat makluman kpd KV/SMT dlm masa yg terdekat. Harap maklum

Pelajar ETE Batch 2014-2017

Semikonduktor

Semikonduktor ialah bahan yang boleh mengalirkan elektrik dan mempunyai sifat penebat dan pengalir. Semikonduktor juga boleh dipanggil sebagai separa pengalir.

Bahan yang selalu digunakan untuk membuat semikonduktor ialah silikon, germanium dan gallium arsenida. Kenapa semikonduktor penting dalam kehidupan kita? Ini kerana semikonduktor ialah penebat pada suhu yang sangat rendah namun pada suhu bilik ia boleh mengalirkan elektrik.

Bagaimana boleh menjadi penebat? Penebat tidak mempunyai kebolehan untuk mengalirkan elektron, elektron duduk diam saja. Jika lihat sifat silikon, silikon yang murni(Silikon 99%) pada suhu yang rendah semua elektron valans duduk diam dan bergabung sesama sendiri seperti penebat. Elektron valans ialah nilai elektron yang berada di orbit luaran.Gabungan ini dinamakan ikatan kovalen. Semua elektron tidak bebas bergerak oleh itu dia dinamakan penebat

Pelajar ETE Batch 2013-2016

TARIKH PEPERIKSAAN AKHIR TEORI DAN AMALI ETE SEM 2

PEPERIKSAAN AKHIR AMALI ETE 201

HARI SELASA, 28/10/2014
(PELAJAR DIMINTA BERSEDIA DENGAN ALAT LUKISAN MASING-MASING)


PEPERIKSAAN AKHIR AMALI ETE 202 DAN ETE 203

SESI PERTAMA
HARI SELASA, 28/10/2014

SESI KEDUA
HARI RABU, 29/10/2014


PEPERIKSAAN AKHIR TEORI- ETE 202 DAN ETE 203

HARI RABU, 5/11/2014

3 point and 4 point starter motor

A 3 point starter in simple words is a device that helps in the starting and running of ashunt wound DC motor or compound wound DC motor. Now the question is why these types of DC motors require the assistance of the starter in the first case. The only explanation to that is given by the presence of back emf E_b, which plays a critical role in governing the operation of the motor. The back emf, develops as the motor armature starts to rotate in presence of the magnetic field, by generating action and counters the supply voltage. This also essentially means, that the back emf at the starting is zero, and develops gradually as the motor gathers speed.

The general motor emf equation E = E_b + I_a.R_a,
at starting is modified to E = I_a.R_a as at starting E_b = 0.

Thus we can well understand from the above equation that the electric current will be dangerously high at starting (as armature resistance R_a is small) and hence its important that we make use of a device like the 3 point starter to limit the starting current to an allowable lower value.

Let us now look into the construction and working of three point starter to understand how the starting current is restricted to the desired value. For that let’s consider the diagram given below showing all essential parts of the three point starter.

Construction of 3 Point Starter

Construction wise a starter is a variable resistance, integrated into number of sections as shown in the figure beside. The contact points of these sections are called studs and are shown separately as OFF, 1, 2,3,4,5, RUN. Other than that there are 3 main points, referred to as 

1. 'L' Line terminal. (Connected to positive of supply.)

2. 'A' Armature terminal. (Connected to the armature winding.)

3. 'F' Field terminal. (Connected to the field winding.)

And from there it gets the name 3 point starter

Now studying the construction of 3 point starter in further details reveals that, the point 'L' is connected to an electromagnet called overload release (OLR) as shown in the figure. The other end of 'OLR' is connected to the lower end of conducting lever of starter handle where a spring is also attached with it and the starter handle contains also a soft iron piece housed on it. This handle is free to move to the other side RUN against the force of the spring. This spring brings back the handle to its original OFF position under the influence of its own force. Another parallel path is derived from the stud '1', given to the another electromagnet called No Volt Coil (NVC) which is further connected to terminal 'F'. The starting resistance at starting is entirely in series with the armature. The OLR and NVC acts as the two protecting devices of the starter.

Working of Three Point Starter

Having studied its construction, let us now go into the working of the 3 point starter. To start with the handle is in the OFF position when the supply to the DC motor is switched on. Then handle is slowly moved against the spring force to make a contact with stud No. 1. At this point, field winding of the shunt or the compound motor gets supply through the parallel path provided to starting resistance, through No Voltage Coil. While entire starting resistance comes in series with the armature. The high starting armature current thus gets limited as the current equation at this stage becomes I_a = E/(R_a+R_st). As the handle is moved further, it goes on making contact with studs 2, 3, 4 etc., thus gradually cutting off the series resistance from the armature circuit as the motor gathers speed. Finally when the starter handle is in 'RUN' position, the entire starting resistance is eliminated and the motor runs with normal speed.
This is because back emf is developed consequently with speed to counter the supply voltage and reduce the armature current. So the external electrical resistance is not required anymore, and is removed for optimum operation. The handle is moved manually from OFF to the RUN position with development of speed. Now the obvious question is once the handle is taken to the RUN position how is it supposed to stay there, as long as motor is running ?

To find the answer to this question let us look into the working of No Voltage Coil.

Working of No Voltage Coil of 3 Point Starter

The supply to the field winding is derived through no voltage coil. So when field current flows, the NVC is magnetized. Now when the handle is in the 'RUN' position, soft iron piece connected to the handle and gets attracted by the magnetic force produced by NVC, because of flow of electric current through it. The NVC is designed in such a way that it holds the handle in 'RUN' position against the force of the spring as long as supply is given to the motor. Thus NVC holds the handle in the 'RUN' position and hence also called hold on coil.

Now when there is any kind of supply failure, the electric current flow through NVC is affected and it immediately looses its magnetic property and is unable to keep the soft iron piece on the handle, attracted. At this point under the action of the spring force, the handle comes back to OFF position, opening the circuit and thus switching off the motor. So due to the combination of NVC and the spring, the starter handle always comes back to OFF position whenever there is any supply problems. Thus it also acts as a protective device safeguarding the motor from any kind of abnormality.

Working Principle of Four Point Starter

The 4 point starter like in the case of a 3 point starter also acts as a protective device that helps in safeguarding the armature of the shunt or compound excited dc motoragainst the high starting current produced in the absence of back emf at starting.

The 4 point starter has a lot of constructional and functional similarity to a three point starter, but this special device has an additional point and a coil in its construction, which naturally brings about some difference in its functionality, though the basic operational characteristic remains the same.

Now to go into the details of operation of 4 point starter, lets have a look at its constructional diagram, and figure out its point of difference with a 3 point starter.

Construction and Operation of Four Point Starter

A 4 point starter as the name suggests has 4 main operational points, namely


1. 'L' Line terminal. (Connected to positive of supply.)

2. 'A' Armature terminal. (Connected to the armature winding.)

3. 'F' Field terminal. (Connected to the field winding.)


Like in the case of the 3 point starter, and in addition to it there is

4. A 4th point N. (Connected to the No Voltage Coil)

The remarkable difference in case of a 4 point starter is that the No Voltage Coil is connected independently across the supply through the fourth terminal called 'N' in addition to the 'L', 'F' and 'A'. As a direct consequence of that, any change in the field supply electric currentdoes not bring about any difference in the performance of the NVC. Thus it must be ensured that no voltage coil always produce a force which is strong enough to hold the handle in its 'RUN' position, against force of the spring, under all the operational conditions. Such a electric current is adjusted through No Voltage Coil with the help of fixed resistance R connected in series with the NVC using fourth point 'N' as shown in the figure above.

Apart from this above mentioned fact, the 4 point and 3 point starters are similar in all other ways like possessing is a variable resistance, integrated into number of sections as shown in the figure above. The contact points of these sections are called studs and are shown separately as OFF, 1, 2, 3, 4, 5, RUN, over which the handle is free to be maneuvered manually to regulate the starting current with gathering speed.

Now to understand its way of operating lets have a closer look at the diagram given above. Considering that supply is given and the handle is taken stud No.1, then the circuit is complete and line current that starts flowing through the starter. In this situation we can see that theelectric current will be divided into 3 parts, flowing through 3 different points.

i) 1 part flows through the starting resistance (R₁+ R₂+ R₃…..) and then to the armature.

ii) A 2^nd part flowing through the field winding F. 

iii) And a 3^rd part flowing through the no voltage coil in series with the protective resistance R.

So the point to be noted here is that with this particular arrangement any change in the shunt field circuit does not bring about any change in the no voltage coil as the two circuits are independent of each other. This essentially means that the electromagnet pull subjected upon the soft iron bar of the handle by the no voltage coil at all points of time should be high enough to keep the handle at its RUN position, or rather prevent the spring force from restoring the handle at its original OFF position, irrespective of how the field rheostat is adjusted.

This marks the operational difference between a 4 point starter and a 3 point starter. As otherwise both are almost similar and are used for limiting the starting current to a shunt wound DC motor or compound wound DC motor, and thus act as a protective device.

Keselamatan Elektrik

Keselamatan Elektrik

Jangan gunakan plag atau soket yang pecah dan rosak

Jangan membuat sambungan yang banyak daripada satu punca

Jangan cuba menyentuh wayar hidup yang tidak bertebat

Jangan cuba menmengantikan dawai fius dengan sebarang dawai atau logam

Jangan menggunakan kabel yang pecah atau terlalu lama

Hendaklah utamakan KESELAMATAN DIRI, KESELAMATAN MAKMAL/BENGKEL dan KESELAMATAN PERALATAN. Pamirkan slogan UTAMAKAN KESELAMATAN agar selalu dapat mengingatkan guru-guru dan pelajar-pelajar sepanjang berada dan melakukan aktiviti di makmal/bengkel.

AMALKAN BUDAYA KERJA SELAMAT

Pakai Peralatan Perlindungan Diri Sebelum Memulakan Kerja.

Pekerja Dikehendaki Memakai Topi Keselamatan Dan Berkasut, Jika Didapati Ada Pekerja Yang Tidak Mematuhi Peraturan Ini Denda Akan Dikenakan RM 10.00(Potong Bayaran Sub-Kont)

Patuhi Tanda Amaran Dan Tanda Keselamatan Di Tapak Bina.

Periksa Dahulu Jentera/Mesin Sebelum Memulakan Kerja.

Pastikan Alat Pengangkat Sempurna Sebelum Digunakan.

Pastikan Tiada Orang Di Bawah Semasa Membuang Bahan/Sampah.

Amalkan Sistem Pembuangan Sampah Yang Sihat.

Membuka “FORMWORK” Dengan Keadaan Penyeliaan.

Pelantar Perlindungan Di Tepi Pintu Masuk Ke Dalam Bangunan Dalam Pembinaan.

Berhati-Hati Ketika Menggunakan Bahan Kimia.

Pasang Penghadang Kawasan Pembinaan Bagi Menjamin Keselamatan Awam.

Kunci Cangkuk Dan Ikat Dengan Sempurna Sebelum Mengangkat Barang Dengan Menggunakan Kren Atau Backhoe.

Jangan Menumpang Dalam “BUCKET BACKHOE”.

Jangan Bekerja Dalam Lubang Bawah Tanah Tanpa Penyaliaan.

Pastikan Laluan Kerja Tiada Halangan.

Tanggalkan/Bengkokkan Paku Dengan Segera.

Jangan Longgokkan Bahan Binaan Di Tepian Tempat Tinggi.

Dapatkan Kebenaran Sebelum Membuat Kerja Elektrik.

Laporkan Segera Kemalangan Yang Berlaku.

Bersih Dan Simpan Dengan Sempurna Sekitar Tempat Kerja.

Jauhi Dari Jentera Bergerak.

Awasi Pergerakan Jentera Pengangkut Dan EXCAVETOR,Berhati-Hati Dengan Kabel Atas.

Pasang Perancah Dengan Sempurna.

 

LANGKAH KESELAMATAN SEMASA KERJA

LANGKAH KESELAMATAN SEMASA KERJA

Bahaya elektrik tidak boleh dianggap ringan. Oleh kerana aliran arusnya tidak nampak, bahaya ini sukar dikesan. Jika tersilap ia boleh mencacatkan anggota, menyebabkan renjatan, lumpuh, kebakaran, letupan, kematian dan sebagainya. Gejala ini hanya boleh diatasi jika semua peraturan keselamatan dipatuhi. Peraturan keselamatan ini bertujuan untuk melindungi pekerja, pengguna, alat-alat dan bangunan dari bahaya yang disebabkan oleh elektrik.Peraturan ini diambil berdasarkan peraturan IEE (Institution Of Electrical Engineers) dan Jabatan Bekalan Elektrik & Gas yang dikemaskini dari masa ke semasa.

Berikut adalah antara langkah keselamatan terpenting yang perlu dipatuhi :

1. Lantai tempat bekerja mestilah bersih daripada minyak, air atau gris. Semua bahan ini boleh menyebabkan pekerja tergelincir semasa mereka bekerja ditempat tersebut.

2. Peralatan yang digunakan mestilah berada dalam keadaan baik dan sempurna.
Jika tidak, sila beritahu pegawai yang bertugas.
Peralatan harus disimpan ditempat yang betul dan selamat supaya mudah dicari bila diperlukan, lebih-lebih lagi di waktu kecemasan.
Pastikan semua peralatan diletakkan ditempatnya yng asal selepas digunakan.

3. Pakai pakaian yang bersesuaian, tidak terlalu sempit atau terlalu longgar. Kasut bertapak tebal dan berjahit disekelilingnya lebih digalakkan semasa membuat kerja-kerja pendawaian.

4. Seseorang tidak dibenarkan bergurau atau bermain peralatan yang tajam atau panas dengan kawan semasa melakukan kerja dibengkel.

5. Pastikan pembumian disetiap pemasangan berkesan. Elakkan dari berkarat.

6. Pastikan pengalir (dawai) yang digunakan memenuhi saiz dan penebatan yang sesuai.

7. Penambahan litar mesti dielakkan kecuali mendapat kebenaran dari pegawai.

8. Jangan menceraikan bahan-bahan elektrik yang digunakan dalam ujikaji tanpa pengetahuan pegawai bertugas.

9. Sebelum sesuatu ujikaji diuji dengan bekalan elektrik, dapatkan bantuan dari pegawai yang bertugas untuk memeriksa litar dan penyambungannya.

10. Selepas bekerja atau selepas menggunakan mesin elektrik, pastikan suisnya dimatikan.

11. Sekiranya berlaku sebarang kemalangan, pegawai yang bertugas harus diberitahu dengan serta-merta.

12. Semua bekalan elektrik harus dimatikan selepas kerja atau semasa hendak meninggalkan makmal.

13. Sebelum memasangkan plug pada soket, pastikan suis pada soket dimatikan terlebih dahulu.