5.1 Historical Fuse is the most com

5.1 Historical
Fuse is the most common and widely used protective device in electrical circuits. Though ‘fuseless’ concept had been catchingon for quite some time, still quite a lot of low-voltage distribution circuits are protected with fuses. Further fuses from a major backup protection in medium-voltege and high-voltage distribution to 11 kV, where switches and contactors with limited short-circuit capacities are used.
In 1881, Edison patented his ‘lead safety wire’, which was officially recognized as the first fuse. However,it was also said that swan actually used this device in late 1880 in the lighting circuits of lord Armstrong’s house. He used stripsof tin-foil jammed between brass blocks by plugs of woods. The application of the fuse in those days was not to protect the wires and system against short circuit,but to protect the lights which cost 25 shilling a time ( a fortune in those days ).
Later, as electrical distribution systems grew, it was found that after short circuits, certain conductors failed. This was due to the copper conductors, not being accurately drawn out ( extruded ) to a constant diameter throughout the cable length; faults always occurring at the smallest cross-sectional area.
Fuses were often considered as casual devices until not so long ago. The open tin-foil ( rewireable ) sometimes came in for a lot of abuse. If it blew constantly, then the new fuse was just increased until it stayed in permanently. Sometimes hairpins were used. Greater precision only became possible with the introduction of the Cartridge fuse.

5.2 Rewireable type
As the name indicates the fuse can be replace or ‘rewired’ once it fails. Fusible wire used to be contained in an asbestos tube to prevent splashing of volatile metal.
Disadvantages
1. Open to abuse due to incorrect of replacement elements hence affording incorrect protection.
2. Deterioration of element as it is open to the atmosphere.







Motor circuit
Strarting current surge normally lasts for 20 s. Squirrel cage induction motors :
• Direct-on-line takes about 7 times full-load current.
• 75% tap auto-transformer takes about 4 times full-load current .
• 60% tap auto-transformer takes about 2.5 times full-load current.
• Star/delta starting takes about 2.5 times full-load current.

5.8.2 Overload protection
Recommend 2:1 ratio to give satisfactory discrimination.
5.9 special type
5.9.1 Striker pin
This type is most commonly used on medium-and low-voltage circuits. When the fuse blows, a strike pin protrudes out of one end of the cartridge. This is used to hit a tripping mechanism on a three-phase switch-fuse unit, so tripping all three phase. This prevents single phasing on three-phase motors.
Note : On switch-fuse LV distribution gear, it is a good policy to have an isolator on the incoming side of the fuse to facilitate changing.
5.9.2 Drop-out type
Used mainly on rulal distribution systems. drops out when fuse blows, isolating the circuits and giving line patrolman easy indication of fault location.
5.10 General
The fuse acts as both fault detector and interrupter. It is satisfactory and adequate for both of these fungtions in many application. Its main virtue is speed. However, as a protective device it does have a number of limitations, the more important of which are as follows :
• It can only detect faults that are associated with excess current.
• Its operating characteristic (i.e current/time relationship) cannot be adjustedor set.
• It requires replacement after each operation.
• It can be used only at low and medium voltages.
Because of these limitations, fuses are normally used only on relatively unimportant, small power, low-and/or medium-voltage circuits (see figure 5.4).
5.10.1 Series overcurrent AC trip coils
These are based on the principle of working of fuses where the coils are connected to carry the normal current and operated as noted below :
• A coil ( instead of a fuse ) is connected into the primary circuit and magnetism is used to lift a plunger to trip a circuit breaker.
• Refinement on this arrangement is the daspot, which gives a time/current characteristic like a fuse.

Hasil (Bahasa Indonesia) 1:

5.1 Sejarah Sekering adalah yang paling umum dan banyak digunakan perangkat pelindung di sirkuit listrik. Meskipun konsep 'fuseless' telah catchingon untuk beberapa waktu, masih cukup banyak distribusi rendah tegangan sirkuit dilindungi dengan sekering. Lebih lanjut sekering dari perlindungan cadangan utama dalam distribusi media-voltege dan tegangan tinggi 11 kV, mana switch dan kontaktor dengan limited hubungan arus pendek kapasitas yang digunakan. Pada tahun 1881, Edison dipatenkan nya 'memimpin keselamatan kawat', yang secara resmi diakui sebagai sekering pertama. Namun, juga dikatakan angsa itu benar-benar menggunakan perangkat ini di akhir 1880 di sirkuit pencahayaan rumah Tuhan Armstrong. Dia menggunakan stripsof-timah macet antara blok kuningan oleh colokan Woods. Penerapan sekring pada zaman itu tidak untuk melindungi kabel dan sistem terhadap korsleting, tapi untuk melindungi lampu yang biaya 25 shilling waktu (keberuntungan dalam hari-hari). Kemudian, sebagai sistem distribusi listrik tumbuh, ditemukan bahwa setelah sirkuit pendek, konduktor tertentu gagal. Ini adalah karena konduktor tembaga, tidak akurat ditarik (diekstrusi) memiliki diameter konstan seluruh panjang kabel; kesalahan yang selalu terjadi di daerah penampang terkecil. Sekering sering dianggap sebagai perangkat santai sampai tidak begitu lama. Buka-Timah (rewireable) kadang-kadang datang untuk banyak penyalahgunaan. Jika itu meledak terus-menerus, kemudian sekering baru hanya meningkat sampai itu tinggal di secara permanen. Kadang-kadang jepit rambut yang digunakan. Lebih presisi hanya menjadi mungkin dengan pengenalan sekering Cartridge.5.2 Rewireable type As the name indicates the fuse can be replace or ‘rewired’ once it fails. Fusible wire used to be contained in an asbestos tube to prevent splashing of volatile metal. Disadvantages1. Open to abuse due to incorrect of replacement elements hence affording incorrect protection.2. Deterioration of element as it is open to the atmosphere. Motor circuit Strarting current surge normally lasts for 20 s. Squirrel cage induction motors :• Direct-on-line takes about 7 times full-load current.• 75% tap auto-transformer takes about 4 times full-load current .• 60% tap auto-transformer takes about 2.5 times full-load current.• Star/delta starting takes about 2.5 times full-load current.5.8.2 Overload protection Recommend 2:1 ratio to give satisfactory discrimination.5.9 special type5.9.1 Striker pinThis type is most commonly used on medium-and low-voltage circuits. When the fuse blows, a strike pin protrudes out of one end of the cartridge. This is used to hit a tripping mechanism on a three-phase switch-fuse unit, so tripping all three phase. This prevents single phasing on three-phase motors.Note : On switch-fuse LV distribution gear, it is a good policy to have an isolator on the incoming side of the fuse to facilitate changing.5.9.2 Drop-out type Used mainly on rulal distribution systems. drops out when fuse blows, isolating the circuits and giving line patrolman easy indication of fault location.5.10 General The fuse acts as both fault detector and interrupter. It is satisfactory and adequate for both of these fungtions in many application. Its main virtue is speed. However, as a protective device it does have a number of limitations, the more important of which are as follows :• It can only detect faults that are associated with excess current.• Its operating characteristic (i.e current/time relationship) cannot be adjustedor set.• It requires replacement after each operation.• It can be used only at low and medium voltages.Because of these limitations, fuses are normally used only on relatively unimportant, small power, low-and/or medium-voltage circuits (see figure 5.4).5.10.1 Series overcurrent AC trip coils These are based on the principle of working of fuses where the coils are connected to carry the normal current and operated as noted below :• A coil ( instead of a fuse ) is connected into the primary circuit and magnetism is used to lift a plunger to trip a circuit breaker.• Refinement on this arrangement is the daspot, which gives a time/current characteristic like a fuse.