Perlindungan Sistem kuasa-Basic Protection Equipment - Bahagian 9

Apply high voltage circuit breaker

-  Identify types of high voltage circuit breakers

a. air blast circuit breaker

Air blast circuit breaker used compressed air or gas as the arc interrupting medium. In the air blast, circuit breaker compressed air is stored in a tank and released through a nozzle to produce a high-velocity jet; this is used to extinguish the arc. Air blast circuit breakers are used for indoor services in the medium high voltage field and medium rupturing capacity.

a. pemutus litar  letusan udara

Pemutus litar letusan udara menggunakan udara atau gas termampat sebagai medium yang mengganggu arka. Dalam letusan udara, pemutus litar udara termampat disimpan dalam tangki dan dilepaskan melalui muncung untuk menghasilkan jet halaju tinggi; ini digunakan untuk memadamkan arka. Pemutus litar udara digunakan untuk perkhidmatan dalaman dalam medan voltan tinggi sederhana dan kapasiti pecah sederhana.

The contacts are opened in a flow of air-blast established by the opening of blast valve. The air-blast cools the arc and sweeps away the arcing products to the atmosphere. This rapidly increases the dielectric strength of the medium between contacts and prevents from re-establishing the arc. Consequently, the arc is extinguished and flow of current is interrupted.

Contact dibuka dengan aliran letupan udara yang dihasil kan oleh pembukaan injap letupan. Letupan udara menyejukkan arka dan menyapu produk arcing ke atmosfera. Ini dengan cepat meningkatkan kekuatan dielektrik medium antara contact dan pencegahan daripada membina semula arka. Akibatnya, arka dipadamkan dan aliran arus terganggu.

Types of Air Blast Circuit Breaker

All air blast circuit breakers follow the principle of separating their contacts in a flow of arc established by the opening of a blast valve. The arc which is drawn is usually rapidly positioned centrally through a nozzle where it is kept to a fixed length and is subjected to the maximum range by the air flow. The air blast circuit breakers according to the type of flow of blast of compressed around the contacts are of three types namely axial, radial and cross blast.


Depending upon the direction of air-blast in relation to the arc, air-blast circuit breakers are classified into:

a)    Axial-blast type in which the air-blast is directed along the path as shown in Figure 13 (i) 

Figure 13: Types of Air-Blast Circuits Breakers

b)    Cross-blast type in which the air-blast is directed at right angles to the arc path as shown in Figure 13 (ii)

c)    Radial-blast type in which the air-blast is directed radially as shown in Figure 13 (iii)

i)     Axial-blast air circuit breaker

Figure 14 shows the essential component of a typical axial-blast air circuit breaker. The fixed and moving contacts are held in the closed position by spring pressure under normal conditions. The air reservoirs are connected to the arcing chamber through an air valve. This valve remains closed under normal conditions but open automatically by the tripping impulse when a fault occurs on the system.

Rajah 14 menunjukkan komponen penting bagi pemutus litar udara paksi-letusan tipikal. Contact tetap dan bergerak dipegang dalam kedudukan tertutup oleh tekanan spring di bawah keadaan normal. Takungan udara disambungkan ke ruang pembongkaran melalui injap udara. Injap ini tetap ditutup di bawah keadaan normal tetapi dibuka secara automatik oleh dorongan tersendiri apabila berlaku kerosakan pada sistem.

Figure 14: Axial-blast air circuit breaker

When a fault occurs, the tripping impulse causes opening of the air valve which connects the circuit breakers reservoirs to the arcing chamber. The high pressure air entering the arcing chamber pushes away the moving contact against spring pressure. The moving contact is separated and an arc is struck. At the same time, high pressure air blast flows along the arc and takes away the ionized gasses along with it. Consequently, the arc is extinguished and current flow is interrupted.

Apabila berlaku kerosakan, impuls 'tripping' yang menyebabkan injap udara membuka saluran yang menghubungkan takungan pemutus litar ke arcing chamber. Udara tekanan tinggi yang memasuki arcing chamber menolak contact bergerak terhadap tekanan spring. Contact bergerak dipisahkan dan arka di'struck'. Pada masa yang sama, letusan udara tekanan tinggi mengalir sepanjang arka dan menghilangkan gas terion dengannya. Akibatnya, arka dipadamkan dan aliran arus terganggu.

It may be noted that in such circuit breakers, the contact separation required for separation is generally small. Such a small gap may constitute inadequate clearance for the normal service voltage. Therefore, as isolating switch is incorporated as a part of this type of circuit breakers. This switch opens immediately after faults interruption to provide the necessary clearance for insulations.

Perlu diperhatikan bahawa dalam pemutus litar tersebut, pemisahan contact yang diperlukan untuk pemisahan pada umumnya kecil. Jurang kecil itu mungkin merupakan pelepasan(clearance) yang tidak mencukupi untuk voltan perkhidmatan biasa (normal service voltage). Oleh itu, sebagai mengasingkan suis dimasukkan sebagai sebahagian daripada pemutus litar jenis ini. Suis ini dibuka dengan serta-merta selepas gangguan 'fault' untuk menyediakan pelepasan(clearance) yang diperlukan untuk penebat.

ii)      Cross-blast air breaker

In this type of circuit breaker, an air-blast is directed at right angles to the arc. The cross-blast lengthness and forces the arc into a suitable chute for arc extinction. Figure below shows the essential parts of a typical cross-blast air circuit breaker.


Dalam pemutus litar jenis ini, letusan udara diarahkan pada sudut tepat ke arka. Panjangnya silang silang dan memaksa arka masuk ke chute yang sesuai untuk kepupusan arka. Rajah di bawah menunjukkan bahagian-bahagian penting dari pemutus litar udara serentak biasa.

When the moving contact is withdrawn, an arc is struck between the fixed and moving contacts. The high pressure cross-blast forces the arc into a chute consisting of arc splitter and baffles. The splitters serve to increase the length of the arc and baffles give improved cooling. The result is that arc is extinguished and flow of current is interrupted. Since blast pressure is same for all currents, the inefficiency at low currents is eliminated. The final gap for interruption is great enough to give normal insulation clearance so that a series isolating switch is necessary.

Apabila contact bergerak ditarik balik, arc dihasilkan ) antara contact tetap dan bergerak. Tekanan tinggi tekanan silang memaksa arc ke chute yang terdiri daripada splitter arc dan baffles. Splitter berfungsi untuk meningkatkan panjang arka dan baffle memberikan penyejukan yang lebih baik. Hasilnya ialah arc dipadamkan dan aliran arus terganggu. Oleh kerana tekanan letusan adalah sama untuk semua arus, ketidakcekapan pada arus rendah dihapuskan. Jurang terakhir untuk gangguan (final gap for interruption) adalah cukup besar untuk memberikan pelepasan(clearance) penebatan biasa supaya suis pengasingan(isolating switch) siri diperlukan.

Figure 15: Cross-blast air breakers

b. oil circuit breaker

Oil circuit breaker is such type of circuit breaker which used oil as a dielectric or insulating medium for arc extinction. In oil circuit breaker the contacts of the breaker are made to separate within an insulating oil. When the fault occurs in the system the contacts of the circuit breaker are open under the insulating oil, and an arc is developed between them and the heat of the arc is evaporated in the surrounding oil. The oil circuit breaker is divided into two categories:

Pemutus litar minyak adalah sejenis pemutus litar yang menggunakan minyak sebagai medium dielektrik atau penebat untuk kepupusan arka. Dalam pemutus litar minyak, Contact pemutus dibuat untuk memisahkan dalam minyak penebat. Apabila kesalahan berlaku dalam sistem, kenalan pemutus litar terbuka di bawah minyak penebat, dan sebuah arka dikembangkan di antara mereka dan haba arka diuapkan dalam minyak di sekitarnya. Pemutus litar minyak dibahagikan kepada dua kategori:

Bulk oil circuit breakers which are use a large quantity of oil. The oil has to serve two purposes. Firstly, it extinguishes the arc during opening of contacts and secondly, it insulates the current conducting parts from one another and from the earthed tank.

Pemutus litar minyak pukal yang menggunakan sejumlah besar minyak. Minyak itu harus digunakan untuk 2 tujuan. Pertama, ia memadamkan arka semasa pembukaan contact dan kedua, ia memisahkan bahagian-bahagian  yang mengoperasi arus dari satu sama lain dan dari tangki yang dibumikan.

Low oil circuit breakers which are use minimum amount of oil. In such circuit breakers, oil is used only for arc extinction. The current conducting parts are insulated by air or porcelain or organic insulating material.

                        

Pemutus litar minyak yang rendah yang menggunakan jumlah minimum minyak. Dalam pemutus litar tersebut, minyak digunakan hanya untuk kepupusan arka. Bahagian-bahagian-bahagian  yang mengoperasi arus diasingkan oleh udara atau porselin atau bahan penebat organik.

Bulk oil circuit breakers

In bulk oil circuit breaker, oil performs mainly two functions. Firstly, it acts as an arc extinguishing medium and secondly, it insulates the live parts of the breaker from earth. The quantity of oil requires for arc extinction is only about one-tenth of the total and the rest being used for the insulation.

Dalam pemutus litar minyak pukal, minyak melakukan terutamanya dua fungsi. Pertama, ia berfungsi sebagai pemadam arka sederhana dan kedua, ia memisahkan bahagian-bahagian hidup pemutus dari bumi. Kuantiti minyak memerlukan kepupusan arka hanya kira-kira sepersepuluh dari jumlah keseluruhan dan selebihnya digunakan untuk penebatan.

Figure 12: Oil circuit breaker

Firstly, the hydrogen gas has high heat conductivity and cools the arc, thus aiding the de-ionization of the medium between the contacts.

Secondly the gas sets up turbulence in the oil and forces it into space between contacts, thus eliminating the arcing products from the arc path. The result is that arc is extinguished and circuit current interrupted.

Pertama, gas hidrogen mempunyai kekonduksian haba yang tinggi dan menyejukkan arka, sekali gus membantu de-ionisasi medium antara contact.

Kedua, gas menimbulkan pergolakan dalam minyak dan memaksa ia ke ruang di antara contact, dengan itu menghapuskan arcing products dari laluan arc. Hasilnya ialah arka dipadamkan dan litar arus terganggu.

Low oil circuit breakers


Pemutus litar minyak rendah

In this type of circuit breaker minimum oil is used as an arc quenching medium and it is mounted on a porcelain insulator to insulate it from the earth. The arc chamber of such type of circuit breaker is enclosed in a bakelised paper. The lower portion of this breaker is supported by the porcelain and the upper porcelain enclosed the contacts.

Dalam minyak minimum pemutus litar jenis ini digunakan sebagai arc quenching medium dan ia dipasang pada penebat porselin untuk melindungi dari bumi.  Arc chamber jenis pemutus litar seperti ini dilitupi dalam kertas bakelis. Bahagian bawah pemutus ini disokong oleh porselin dan porselin atas disertakan contact.

This circuit breaker is of the single breaker type in which a moving contact tube moves in a vertical line to make or break contact with the upper fixed contacts mounted within the arc control devices.

Pemutus litar ini adalah jenis pemutus tunggal di mana tiub contact bergerak, bergerak dalam garis menegak untuk membuat atau memutuskan contact dengan contact tetap atas (upper fixed contacts) dipasang di dalam peranti kawalan arka.

A lower ring of fixed contacts is in permanent contact with the moving arm to provide the other terminal of the phase unit. Within the moving contact, the tube is a fixed piston. When the moving contact moves downwards, it forces the insulating oil to enter into the arc control devices . Thus, the arc gets extinguished.

Cincin bawah contact tetap berada dalam contact tetap dengan lengan bergerak untuk menyediakan terminal unit fasa lain. Dalam contact yang bergerak, tiub adalah piston tetap. Apabila contact bergerak, bergerak ke bawah, ia memaksa minyak penebat untuk masuk ke dalam peranti kawalan arka. Oleh itu, arka akan dipadamkan.

Minimum oil circuit breaker requires less space as compared to bulk oil circuit breaker which is an important feature in large installations. But it is less suitable in places where the frequent operation is required because the degree of carbonisation produced in the small volume of oil is far more dangerous than in the conventional bulk oil circuit breakers and this also decreases the dielectric strength of the material.

Pemutus litar minyak minima memerlukan kurang ruang berbanding pemutus litar minyak pukal yang merupakan ciri penting dalam pemasangan besar. Tetapi ia kurang sesuai di tempat-tempat di mana operasi kerap diperlukan kerana tahap karbonisasi yang dihasilkan dalam jumlah kecil minyak adalah lebih berbahaya daripada di pemutus litar minyak pukal konvensional dan ini juga mengurangkan kekuatan dielektrik bahan.

c. vacuum circuit breaker


c. pemutus litar vakum

In such breakers, vacuum is used as the arc quenching medium. Since vacuum offers the highest insulating strength, it has far superior arc quenching properties than any other medium. For example, when contacts of a breaker are opened in vacuum, the interruption occurs at first current zero with dielectric strength between the contacts building up at a rate thousands of times higher than that obtained with other circuit breakers.

Dalam pemutus tersebut, vakum digunakan sebagai medium pelindapkejutan. Oleh kerana vakum menawarkan kekuatan penebat tertinggi, ia mempunyai ciri-ciri penghapusan yang lebih tinggi daripada mana-mana medium lain. Sebagai contoh, apabila Contact pemutus dibuka dalam vakum, gangguan berlaku pada sifar semasa pertama dengan kekuatan dielektrik antara kenalan yang membina pada kadar ribuan kali lebih tinggi daripada yang diperoleh dengan pemutus litar lain.

Principle

The production of arc in a vacuum circuit breaker and its extinction can be explained as follows: When the contacts of the breaker are opened in vacuum, an arc is produced between the contacts by the ionization of metal vapours of contacts. However, the arc is quickly extinguished because the metallic vapours, electrons and ions produced during arc rapidly condense on the surface of the circuit breaker contacts, resulting in quickly recovery of dielectric strength.

Pengeluaran arka dalam pemutus litar vakum dan kepupusannya boleh dijelaskan seperti berikut: Apabila contact pemutus dibuka dalam vakum, arka dihasilkan antara contact dengan ionisasi wap logam contact. Walau bagaimanapun, arka itu cepat dimatikan kerana wap metalik(metallic vapours), elektron dan ion logam yang dihasilkan semasa arka dengan cepat mengembunkan pada permukaan contact pemutus litar, menyebabkan pemulihan cepat kekuatan dielektrik.

Construction

Figure 17 below shows the parts of typical vacuum circuit breaker. It is consists of fixed contact, moving contact and arc shield mounted inside a vacuum chamber. The moveable member is connected to the control mechanism by stainless steel bellows. This enables the permanent sealing of the vacuum chamber so as to eliminate the possibility of leak. A glass vessel or ceramic vessel is used as the outer insulating body. The arc shield prevents the deterioration of the internal dielectric strength by preventing metallic vapours falling on the inside surface of the outer insulating cover.

Rajah 17 di bawah menunjukkan bahagian pemutus litar vakum biasa. Ia terdiri daripada hubungan tetap, sentuhan bergerak dan perisai arka yang dipasang di dalam ruang vakum. Ahli yang boleh dipindahkan disambungkan ke mekanisme kawalan oleh belos keluli tahan karat. Ini membolehkan pengedap kekal ruang kebuk supaya dapat menghapuskan kebocoran. Sebuah kapal kaca atau kapal seramik digunakan sebagai badan penebat luar. Perisai arka menghalang kemerosotan kekuatan dielektrik dalaman dengan menghalang wap metalik yang jatuh pada permukaan dalam penutup luar penebat.

Figure 17: Vacuum circuit breakers

Working

When the breaker operates, the moving contact separates from the fixed contact and an arc is struck between the contacts. The production of arc is due to the ionization of metal ions and depends very much upon the material of contact. The arc is quickly extinguished because the metallic vapours, electrons and ions produced during arc are diffused in a short time and seized by the surfaces of moving and fixed members and shields. Since vacuum has very fast rate or recovery of dielectric strength, the arc extinction in a vacuum breaker occurs with a short contact separation.

Apabila pemutus beroperasi,contact bergerak berpisah dari  contact tetap dan arka dipukdihasilkan antara contact . Pengeluaran arka adalah disebabkan pengionan ion logam dan sangat bergantung pada bahan contact . Arka itu cepat dipadamkan kerana wap, elektron dan ion logam yang dihasilkan semasa arka disebarkan dalam masa yang singkat dan dirampas oleh permukaan anggota bergerak dan tetap dan perisai. Oleh kerana vakum mempunyai kadar yang sangat laju atau pemulihan kekuatan dielektrik, kepupusan arka dalam penghancur vakum berlaku dengan pemisahan contact pendek.

d. gas circuit breaker

In such circuit breakers, sulphur hexafluoride (SF₆) gas is used as the arc quenching medium. The SF6 is an electro-negative gas and has a strong tendency to absorb free electrons. The contacts of the breaker are opened in a high pressure flow of SF₆ gas and an arc is struck between them. The conducting free electrons in the arc rapidly captured by the gas to from relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds up enough insulations strength to extinguish the arc. The SF₆ circuit breakers have been found to be very effective for high power and high voltage service.

Dalam pemutus litar tersebut, gas sulfur hexafluoride (SF6) digunakan sebagai medium penghapusan. SF6 adalah gas elektro-negatif dan mempunyai kecenderungan kuat untuk menyerap elektron bebas. Contact pemutus dibuka dalam aliran tekanan tinggi SF6 gas dan arka dihasil  di antara mereka. Mengendalikan elektron bebas dalam arka dengan cepat ditangkap oleh gas dari ion negatif yang tidak bergerak. Kehilangan penyelenggaraan elektron dalam arka dengan cepat membina kekuatan penebat yang cukup untuk memadamkan arka. Pemutus litar SF6 telah didapati sangat berkesan untuk kuasa tinggi dan perkhidmatan voltan tinggi.

Construction

Figure 16 shows the parts of typical SF6 circuit breaker. It consists of fixed and moving contacts enclosed in chamber which is called arc interruption chamber containing SF6 gas. This chamber is connected to SF6 gas reservoir. When the contacts of breaker are opened, the valve mechanism permits a high pressure SF6 gas from the reservoir to flow towards the arc interruption chamber. The fixed contacts are hollow cylindrical current carrying contact fitted with an arc horn. The moving contact is also a hollow cylinder with rectangular holes in the sides to permit the SF6 gas to let out through these holes after flowing along and across the arc. The tips of fixed contact, moving contact and arcing horn are coated with copper-tungsten arc resistant material. Since SF6 gas is costly, it is reconditioned and reclaimed by suitable auxiliary system after each operation of the breaker.

Rajah 16 menunjukkan bahagian pemutus litar SF6 biasa. Ia terdiri daripada contact tetap dan bergerak yang tertutup di ruang yang dipanggil ruang gangguan arka yang mengandungi gas SF6. Ruang ini dihubungkan dengan reservoir gas SF6. Apabila contact pemutus dibuka, mekanisme injap membenarkan gas SF6 tekanan tinggi dari takungan mengalir ke arah ruang gangguan arka. Contact tetap adalah silinder gegelung arus membawa contact  dipasang dengan tanduk arka (arc horn). Contact  bergerak juga merupakan silinder berongga dengan lubang segi empat tepat di sisi untuk membolehkan gas SF6 melepasi lubang-lubang ini setelah mengalir sepanjang dan melintasi arka. Petua contact tetap, contact bergerak dan arcing horn dilapisi dengan bahan tahan arc tembaga-tungsten. Oleh kerana gas SF6 mahal, ia dibaikpulih semula dan direkabentuk oleh sistem tambahan yang sesuai selepas setiap operasi pemutus.

Figure 16: Sulphur Hexafluoride (SF₆) circuit breakers

Working

In the closed position of the breaker, the contacts remain surrounded by SF6 gas at a pressure of about 2.8kg/cm2. When the breaker operates, the moving contact is pulled apart and arc is struck between the contacts. The movement of the moving contact is synchronized with the opening of a valve which permits SF6 gas at 14 kg/cm2 pressure from the reservoir to the arc interruption chamber. The high pressure flow of SF6 rapidly absorbs the free electrons in the arc path to form immobile negative ions which are ineffective as charge carriers. The result is that the medium between the contacts quickly builds up high dielectric strength and causes the extinction of the arc. After the breaker operation i.e. after arc extinction, the valve is closed by the action of a set of springs

Dalam kedudukan tertutup pemutus, contact tetap dikelilingi oleh gas SF6 pada tekanan kira-kira 2.8kg / cm2. Apabila pemutus beroperasi, contact  bergerak ditarik dan arka dipukul antara contact . Pergerakan contact  bergerak disegerakkan dengan pembukaan injap yang membolehkan gas SF6 pada tekanan 14 kg / cm2 dari takungan ke ruang gangguan arka. Aliran tekanan tinggi SF6 dengan cepat menyerap elektron bebas di laluan arka untuk membentuk ion negatif yang tidak bergerak yang tidak berkesan sebagai pembawa caj. Hasilnya adalah bahawa medium antara contact  dengan cepat membina kekuatan dielektrik tinggi dan menyebabkan kepupusan arka. Selepas operasi pemutus i.e selepas kepupusan arka, injap ditutup oleh tindakan set spring.

Show the operation of the circuit breakers as mentioned above

Write the advantages and disadvantages of the circuit breakers as mentioned above

a. air circuit breaker

Advantages	Disadvantages
High speed operation as compared to OCB	Little moisture content prolongs arching time
Ability to withstand frequent switching	Pressure should be checked frequently for frequent operation
Facility for high speed reclosure	Risk of fire hazards due to over voltage
Less maintenance as compared to OCB	It can’t be used for high voltage operation due to prolonged arc quenching
Due to lesser arc energy, air blast CB are very suitable for conditions where frequent operation is required	The air has relatively inferior arc extinguishing properties

b. oil circuit breaker

Advantages	Disadvantages
Oil has good dielectric strength	Slower operation, takes about 20 cycles quenching
Low cost	It is highly inflammable. So high risk of fire
Oil is easily available	High maintenance cost.
It has wide range of breaking capability

c. vacuum circuit breaker

Advantages	Disadvantages
Free from arc and fire hazards	High initial cost due to creation of vacuum
Low cost for maintenance & simpler mechanism	Surface of contacts are depleted due to metal vapours
Low arching time & high contact life	High cost & size required for high voltage breakers
Silent and less vibrational operational
Due to vacuum contacts remain free from corrosion
They are compact, reliable and have longer life

d. gas circuit breaker

Advantages	Disadvantages
Very short arcing period due to superior arc quenching property of SF6	SF6 breakers are costly due to high cost of SF6
Can interrupt much larger currents as compared to other breakers	SF6 gas has to be reconditioned after every operation of the breaker, additional equipment is required for this purpose.
No risk of fire
Low maintenance, light foundation
No over voltage problem
There are no carbon deposits

Comparison of Circuit Breakers

Factor	OCB	ACB	VCB/ SF6
Safety	Risk of explosion and fire due to increase in pressure during multiple operations	Emission of hot air and ionized gas to the surroundings	No risk of explosion
Size	Quite large	Medium	Smaller
Maintenance	Regular oil replacement	Replacement of arching contacts	Minimum lubrication for control devices
Environmental Factors	Humidity and dust in the atmosphere can change the internal properties and affect the dielectric		Since sealed, no effect due to environment
Endurance	Below average	Average	Excellent