Perlindungan Sistem kuasa-Basic Protection Equipment - Bahagian 8

Understand fuse

-  Explain the function of fuse

A fuse is a short piece of metal inserted in the circuit, which melts when excessive current flows through it and thus breaks the circuit. Its combines the functions of sensing, comparing and interrupting the current into one.

- Terangkan fungsi fius


Fius adalah sekeping logam pendek dimasukkan ke dalam litar, yang mencair apabila arus berlebihan mengalir melaluinya dan dengan itu memutuskan litar. Ia menggabungkan fungsi (tiga dalam satu) iaitu.mengesan, membandingkan dan mengganggu arus. 

-  Discuss types of fuse

- Bincangkan jenis fius

a.         Re-wireable

this type of fuse consist of a tinned copper or tin-lead alloy fuse element (rewireable) which is directly screwed to the contact terminal of a semi-enclosed porcelain fuse carrier to plugged in to the socket fuse base.

a. Re-wireable

jenis fius ini terdiri daripada tembaga timah(tin) atau aloi timah utama  (rewireable) yang secara langsung diskru ke terminal contact pembawa fius seramik separa tertutup(semi-enclosed porcelain) untuk dipasang ke tapak soket fius.

b.         Cartridge

it is a totally enclosed type of fuse, whose fuse element is sealed by a tube which is filled with fireproof material. It has metal cap on both ends where the fuse element is welded or soldered.

b. Cartridge

ia adalah sejenis fius jenis yang tertutup, yang elemen fiusnya dimeteraikan oleh tiub yang dipenuhi dengan bahan tahan api. Ia mempunyai topi logam di kedua-dua hujung di mana unsur fius dikimpal atau dipateri.

c.         High Rapturing Capacity (HRC)

it consists of a pure silver fuse element totally enclosed in a ceramic tube which is filled with fireproof materials such as ‘silica’ and it is capable or interrupting a circuit under a heavy fault current at the shortest period of time.

c. Kapasiti Pengangkatan Tinggi (HRC)
ia terdiri daripada unsur fius perak tulen yang benar-benar tertutup dalam tiub seramik yang dipenuhi dengan bahan tahan api seperti 'silika' dan ia mampu atau mengganggu litar di dalam keadaan  arus 'fault' berat pada masa yang singkat.

- Explain the design and operation of fuses above

Terangkan reka bentuk dan operasi fius di atas

a.         Re-wireable

Rewireable fuse is used where low values of fault current are to be interrupted. It consists of (i) a base and (ii) a fuse carrier. The base is of porcelain and carries the fixed contacts to which the incoming and outgoing phase wires are connected. The fuse carrier is also of porcelain and holds the fuse elements (tinned copper wire) between its terminals. The fuse carrier can be inserted in or taken out of the base when desired.

a. Re-wireable
Fius gegelung digunakan di mana nilai rendah arus 'fault' akan terganggu. Ia terdiri daripada 
(i) tapak dan (ii) pembawa fius. Tapak adalah porselin dan membawa fixed contact yang mana wayar fasa masuk dan keluar terhubung. Pembawa fius juga porselin dan memegang elemen fius (dawai tembaga tin) di antara terminalnya. Pembawa fius boleh dimasukkan atau dikeluarkan dari tapak apabila dikehendaki.

When the fault occur, the fuse element is blown out and the circuit is interrupted. The fuse carrier is taken out and the blown out fuse element is replaced by the new one. The fuse carrier is then reinserted in the base to restore the supply.

Apabila kerosakan berlaku, elemen fius dibuang dan litar terganggu. Pembawa fius dikeluarkan dan elemen fius yang rosak diganti dengan yang baru. Pembawa fius itu kemudian dimasukkan semula ke pangkalan untuk memulihkan bekalan.

Figure 12: Rewireable fuse

b.         Cartridge

This is similar in general construction to the low voltage cartridge type except that special design features are incorporated. Some designs employ fuse elements wound in the form of a helix so as to avoid corona effects at higher voltages. On some designs, there are two fuse elements in parallel; one of low resistance (silver wire) and the other of high resistance (tungsten wire). Under normal load condition, the low resistance elements is blown out and the high resistance elements reduces the short circuit current and finally breaks the circuit.

b. Cartridge

Ini adalah sama dalam pembinaan umum untuk jenis kartrij voltan rendah kecuali ciri reka bentuk khas yang diperbadankan. Sesetengah reka bentuk menggunakan elemen fius dibelit dalam bentuk helix untuk mengelakkan kesan korona pada voltan yang lebih tinggi. Pada beberapa reka bentuk, terdapat dua elemen fius selari; salah satu rintangan rendah (dawai perak) dan rintangan yang tinggi (wayar tungsten). Di bawah keadaan beban normal, elemen rintangan yang rendah ditiup dan unsur rintangan yang tinggi mengurangkan arus litar pintas dan akhirnya memutuskan litar.

Figure 13: Cartridge Fuse

c.         High Rapturing Capacity (HRC)

The primary objection of low and uncertain breaking capacity of semi-enclosed rewireable fuses is overcome in HRC cartridge fuse. It consists of a heat resisting ceramic body having metal end-caps to which is welded silver current-carrying element. The space within the body surrounding the element is completely packed with a filling powder. The filling material may be chalk, plaster of paris, quartz or marble dust an arc quenching and cooling medium.

c. Kapasiti Pengangkatan Tinggi (HRC)

Bantahan utama kapasiti pecah yang rendah dan tidak menentu bagi fius rewireable separuh tertutup akan diatasi dalam fius kartrij HRC. Ia terdiri daripada badan seramik yang menahan haba yang mempunyai logam penutup akhir yang dikimpal (silver current-carrying element.) Ruang di dalam badan yang mengelilingi elemen itu penuh dengan serbuk pengisian. Bahan pengisian boleh jadi kapur, plaster paris, kuarza atau habuk marmar dengan medium quenching and cooling arka.

Figure 9: HRC catridge fuse

Relate the right formula in solving selection of fuses

Using the guideline that the fuse is rated at 125% of the normal operating current.

Power (Watts) = Current (Amps) x Voltage (Volts)

Therefore: Current = Power/Voltage

Therefore: Fuse rating = (Power/Voltage) x 125%

OR, put another way:

Fuse rating = (Power/Voltage) x 1.25

OR, put another way:

Fuse rating = (watts/volts) x 1.25

·    Note the power of the appliance – usually in the appliance manual,

·    Note the voltage (240 volts in the Malaysia).

·    Use the next highest fuse rating after the calculation.

• Say the calculated fuse rating is 2.2679 amps, use a 3 amp fuse.
• Say the calculated fuse rating is 4.9431 amps, use a 5 amp fuse.
• Say the calculated fuse rating is 8.9032 amps, use a 13 amp fuse.
• Say the calculated fuse rating is 10.6421 amps, use a 13 amp fuse.

Fuse Rating Calculations

The assumption in this calculation is that their only 3 fuse ratings, 3 amps, 5 amps and 13 amps.

Say the power is 500 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (500/240) x 1.25

Fuse rating = (2.083333333) x 1.25

Fuse rating = 2.604166667 amps

Next fuse up is a 3 amp fuse, use a 3 amp fuse.

Say the power is 200 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (200/240) x 1.25

Fuse rating = (0.83333333) x 1.25

Fuse rating = 1.04166667 amps

Next fuse up is a 3 amp fuse, use a 3 amp fuse.

Say the power is 1500 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (1500/240) x 1.25

Fuse rating = (6.25) x 1.25

Fuse rating = 7.8136 amps

Next fuse up is a 13 amp fuse, use a 13 amp fuse.

Say the power is 900 watts.

Fuse rating = (watts/volts) x 1.25

Fuse rating = (900/240) x 1.25

Fuse rating = (3.755) x 1.25

Fuse rating = 4.6875 amps

Next fuse up is a 5 amp fuse, use a 5 amp fuse.