Terima kasih kerana mengunjungi blog ini. Komentar kalian amat dialu-alukan. Sebarang komentar dengan menggunakan "Anonymous" tidak lagi akan dilayan. Bersama bertanggungjawab memajukan dan mengangkat martabat Industri Kekompetenan.

Penulisan di dalam blog ini cuma pandangan penulis sahaja. Ia tidak menggambarkan pandangan atau pendirian atau mewakili mana-mana pertubuhan atau syarikat atau Institusi yang penulis sedang atau pernah sertai.

Dari Meja Penulis,
Mohd Razib Bin Ramili

Saturday, April 17, 2010

Perbezaan antara Pemutus Litar Vacuum dan SF6

Artikel dibawah, adalah di dalam Bahasa Inggeris dan sebarang perbincangan atau pertanyaan amatlah dialukan.

Table 1. Characteristics of the SF6 and vacuum current interrupting technologies.


SF6 Circuit Breakers Vacuum Circuit Breakers
Criteria Puffer Circuit Breaker Self-pressuring circuit-breaker Contact material-Chrome-Copper
Operating energy requirements Operating Energy requirements are high, because the mechanism must supply the energy needed to compress the gas. Operating Energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over short distances. The mechanism does not have to provide the energy to create the gas flow Operating energy requirements are low, because the mechanism must move only relatively small masses at moderate speed, over very short distances.
Arc Energy Because of the high conductivity of the arc in the SF6 gas, the arc energy is low. (arc voltage is between 150 and 200V.) Because of the very low voltage across the metal vapour arc, energy is very low. (Arc voltage is between 50 and 100V.)
Contact Erosion Due to the low energy the contact erosion is small. Due to the very low arc energy, the rapid movement of the arc root over the contact and to the fact that most of the metal vapour re-condenses on the contact, contact erosion is extremely small.
Arc extinguishing media The gaseous medium SF6 possesses excellent dielectric and arc quenching properties. After arc extinction, the dissociated gas molecules recombine almost completely to reform SF6. This means that practically no loss/consumption of the quenching medium occurs. The gas pressure can be very simply and permanently supervised. This function is not needed where the interrupters are sealed for life. No additional extinguishing medium is required. A vacuum at a pressure of 10-7 bar or less is an almost ideal extinguishing medium. The interrupters are ‘sealed for life’ so that supervision of the vacuum is not required.
Switching behavior in relation to current chopping The pressure build-up and therefore the flow of gas is independent of the value of the current. Large or small currents are cooled with the same intensity. Only small values of high frequency, transient currents, if any, will be interrupted. The de-ionization of the contact gap proceeds very rapidly, due to the electro-negative characteristic of the SF6 gas and the arc products. The pressure build-up and therefore the flow of gas is dependent upon the value of the current to be interrupted. Large currents are cooled intensely, small currents gently. High frequency transient currents will not, in general, be interrupted. The de-ionization of the contact gap proceeds very rapidly due to the electro-negative characteristic of the SF6 gas and the products. No flow of an ‘extinguishing’ medium needed to extinguish the vacuum arc. An extremely rapid de-ionization of the contact gap, ensures the interruption of all currents whether large or small. High frequency transient currents can be interrupted. The value of the chopped current is determined by the type of contact material used. The presence of chrome in the contact alloy with vacuum also.
No. of short-circuit operation 10—50 10—50 30—100
No. full load operation 5000—10000 5000—10000 10000—20000
No. of mechanical operation 5000—20000 5000—20000 10000—30000

Comparison of the SF6 And Vacuum Technologies

The most important characteristics of the SF6 gas and vacuum-circuit breakers, i.e., of SF6 gas and vacuum as arc-extinguishing media are summarized in Table-1.

In the case of the SF6 circuit-breaker, interrupters which have reached the limiting number of operations can be overhauled and restored to ‘as new’ condition. However, practical experience has shown that under normal service conditions the SF6 interrupter never requires servicing throughout its lifetime. For this reason, some manufacturers no longer provide facilities for the user to overhaul the circuit-breaker, but have adopted a ‘sealed for life’ design as for the vacuum-circuit breaker.

The operating mechanisms of all types of circuit-breakers require servicing, some more frequently than others depending mainly on the amount of energy they have to provide. For the vacuum-circuit breaker the service interval lies between 10,000 and 20,000 operations. For the SF6 designs the value varies between 5,000 and 20,000 whereby, the lower value applies to the puffer circuit-breaker for whose operation, the mechanism must deliver much more energy.

The actual maintenance requirements of the circuit-breaker depend upon its service duty, i.e. on the number of operations over a given period of time and the value of current interrupted. Based on the number of operations given in the previous section, it is obvious that SF6 and vacuum circuit-breakers used in public supply and /or industrial distribution systems will, under normal circumstances, never reach the limits of their summated breaking current value. Therefore, the need for the repair or replacement of an interrupter will be a rare exception and in this sense these circuit-breakers can be considered maintenance-free. Service or maintenance requirements are therefore restricted to routine cleaning of external surfaces and the checking and lubrication of the mechanism, including the trip-linkages and auxiliary switches. In applications which require a very high number of circuit-breaker operations e.g. for arc furnace duty or frequently over the SF6 design, due to its higher summated-breaking current capability. In such cases it is to be recommended that the estimation of circuit-breaker maintenance costs be given some consideration and that these be included in the evaluation along with the initial, capital costs.

Bacaan penuh di http://www.csanyigroup.com/comparison-between-vacuum-and-sf6-circuit-breaker
Selamat Membaca!

Sunday, April 4, 2010

Toyol: Penipuan Di Dewan Peperiksaan Kekompetenan

Maaf kerana terlalu lama menyepi. Blog ini belum mati kerana ajalnya belum tiba. Maka, teruskanlah berkongsi idea dan pandangan melalui chat box ataupun melalui akaun Facebook (Orang Kompeten Elektrik).

Toyol...nama yang sering diperkatakan apabila tibanya hari peperiksaan. Tidak terkecuali peperiksaan kekompetenan. Ramai yang bergantung pada nya dan ada juga yang merasakan bahawa mereka akan gagal apabila toyol tidak dibawa bersama. Kecelakaan seumpama menjelma apabila toyol yang diharapkan tidak mampu memberi jawapan yang dipinta Suruhanjaya Tenaga.

Yang terbaru, calon-calon orang kompeten menaip toyol mereka diatas kepingan kertas A4 dan menampalkannya di dalam buku akta 447. Teman saya amat bangga apabila saya tidak perasan tentang penipuan yang beliau lakukan. Memang real. Sekali imbas, memang tak perasan.

Tidak sedarkah mereka bahawa ia adalah suatu perkara yang mungkin akan menyukarkan calon-calon orang kompeten dimasa akan datang seandainya Buku Akta tidak lagi dibenarkan dibawa masuk ke dalam Dewan?

Saya pernah melalui peperiksaan PW1 pada tahun 1998 dan ketika itu peperiksaan kompeten dibawah Jabatan Bekalan Elektrik dan Gas (JBE&G). Buku akta 447 tidak boleh dibawa kedalam Dewan dan ia amat menyukarkan kami untuk menjawab soalan-soalan berkaitan akta. Malah, kami juga sukar untuk menjawab soalan pengiraan kerana tidak dapat merujuk Jadual Faktor Kepelbagaian yang sedia tercetak di muka belakang buku Akta tersebut.

Toyol dalam poket, toyol dalam tandas dan toyol dalam telefon bimbit adalah beberapa modus operandi penipuan didalam peperiksaan kompeten. Mungkin sudah tiba masanya ST menjadi tegas.

Namun, ST juga perlu bertegas bagi memantau peperiksaan di Institut-institut kemahiran kerana di sana juga berlaku kes-kes peniruan sebegini. Percayalah, pemantauan di Institut Kemahiran amatlah lemah.

Bukankah kita dambakan orang kompeten yang berkualiti? Atau sekurang-kurangnya lulus kerana usaha mereka yang gigih dan bukannya kerana toyol mereka yang lengkap?

Fikir-fikirkanlah.