Perlindungan Sistem kuasa-Basic Protection Equipment - Bahagian 7

the operation of circuit breakers:

a. Miniature Circuit Breaker (MCB)

The contact system comprises a fixed and a moving contact, and attached to each is a contact tip which provides a low-resilience contact junction to resist welding. Modern MCB are fitted with arc chutes consisting of metal plates which are held in position by insulating material. The arc chute does not necessarily surround the contact: in some designs arc runners are provided to pull the arc into the arc chute.

Sistem contact terdiri daripada contact tetap dan bergerak, dan dilampirkan kepada setiap adalah contact tip yang menyediakan a low-resilience contact junction to resist welding. MCB moden dilengkapi dengan pelongsor arka yang terdiri daripada plat logam yang dipegang oleh bahan penebat. Pelongsor arka tidak semestinya mengelilingi contact: dalam beberapa pelari arka rekaan disediakan untuk menarik arka ke dalam pelongsor arka.

The tripping mechanism usually consist of a thermal-magnetic arrangement. The thermal action is provided by a bimetal with, in some cases, a heater. The heat generated within the bimetal itself being sufficient to cause deflection. The deflection is then used to activate the tripping mechanism. The characteristics of the bimetal are chosen to provide particular delays under certain overload or fault current according to the required time-current characteristic.

Mekanisme 'tripping' biasanya terdiri daripada susunan terma magnetik. Tindakan haba disediakan oleh bimetal, dalam beberapa kes, pemanas. Haba yang dihasilkan di dalam bimetal itu sendiri cukup untuk menyebabkan deflection. Deflection kemudian digunakan untuk mengaktifkan mekanisme 'tripping'. Ciri-ciri bimetal dipilih untuk menyediakan 'delay' tertentu dalam keadaan 'certain overload or fault current' mengikut ciri 'required time-current'  yang diperlukan.

The magnetic tripping element usually consist of a coil which is wrapped around a tube, there being a spring-loaded slug within the tube. Movement of the slug operated the tripping mechanism to open the MCB. It can also be used to assist in opening the contacts by locating the coil close to the moving contact. When a fault current flows, the high magnetic field generated by the coil overcomes the spring force holding the slug in position: the slug then moves to actuate the tripping mechanism and forces the contact apart by striking the moving contact arm.

Elemen ' tripping' magnet biasanya terdiri daripada gegelung(coil) yang dibalut di sekeliling tiub, di mana terdapat sudu(slug) spring yang dimuatkan di dalam tiub. Gerakan slug mengendalikan 'tripping mechanism' untuk membuka MCB. Ia juga boleh digunakan untuk membantu membuka contact dengan mencari gegelung dekat dengan contact bergerak. Apabila 'fault current ' mengalir, medan magnet yang tinggi yang dijana oleh gegelung mengatasi daya pegas 'spring force' yang memegang kedudukan slug: slug kemudian bergerak untuk melancarkan 'tripping mechanism' dan memaksa contact itu dengan menarik'striking' lengan contact bergerak.

    b.    Moulded Case Circuit Breaker (MCCB)

The major components of MCCB include a mechanism which makes and breaks a contact through a toggle link mechanism having a spring which can store tripping force, an overcurrent trip device which reacts with overcurrent and short circuit cu r rent and t rip s MCCB, an Arc extinguishing device which extinguishes the arc generated upon current interruption, terminals for connecting wires and conductors, contacts which open and close the circuit and a moulded case in which these components are integrated and compactly contained.

Komponen utama MCCB termasuk mekanisme yang membuat dan 'breaks a contact ' melalui mekanisme pautan togol 'toggle link' yang mempunyai spring yang boleh menyimpan 'tripping force', 'an overcurrent trip device' yang bereaksi dengan 'overcurrent and short circuit current' dan 'trip' MCCB, Arka peranti pemadam 'Arc extinguishing device'yang memadamkan arka yang dijana semasa gangguan arus, terminal untuk menyambung wayar dan konduktor, contact yang membuka dan menutup litar dan 'a moulded case' di mana komponen-komponen ini bersepadu dan padat.

Standard MCCBs use single pivot-point mechanisms for the contacts, while current- limiting circuit breakers often use dual pivot mechanisms. See Figure 6. The magnetic fields around each of the contacts repel and rapidly force the contacts apart. As the short-circuit current flowing through them increases, the magnetic fields become stronger, and the contacts open faster.

Standard MCCBs menggunakan mekanisme pivot-point tunggal untuk contact, sementara pemutus litar (CB) arus yang terhad (current- limiting circuit breakers) menggunakan mekanisme pivot dua. Lihat Rajah 6. Medan magnet di sekeliling setiap contact menghalau dan memaksa contact terpisah dengan cepat. Apabila arus litar pintas mengalir melalui contact bertambah, medan magnet menjadi lebih kuat, dan contact terbuka dengan lebih cepat.

Figure 6: Standard MCCBs use single pivot-point mechanisms for the contacts, while current-limiting circuit breakers often use dual pivot mechanisms.

Arc chutes- An arc is a sustained discharge of electricity across a gap in a circuit or between electrodes, usually accompanied by the electrodes (contacts) being vaporized and/or melted by the extreme heat of the arc.

  

Pelekas Arc - Arka adalah pelepasan elektrik yang berterusan merentasi jurang dalam litar atau di antara elektrod, biasanya disertakan dengan elektroda (contact) yang diwapkan dan / atau dicairkan oleh haba arka yang melampau.

An arc chute, also known as arc extinguisher, is a structure that contains arc dividers. As the contacts part, the arc is drawn between the arcing contacts. The arc rises (due to its extreme temperature) and, as it does so, is stretched by the arc dividers. This cools the arc so it can be extinguished. MCCBs use arc chutes to stretch arcs, cool them down, and extinguish them, all in 1-1⁄2 to 2 cycles. See Figure 7.

Arc chute, juga dikenali sebagai pemadam arka, adalah struktur yang mengandungi pembahagi arka. Sebagai bahagian contact, arka terjadi di antara contact arcing. Arka naik (disebabkan oleh suhu yang melampau) dan, seperti yang dilakukannya, diregangkan oleh pembahagi arka. Ini menyejukkan arka supaya dapat dipadamkan. MCCB menggunakan pelongsor arka untuk menghulurkan arka, menyejukkan mereka, dan memadamkan mereka, semuanya dalam 1-1/2 hingga 2 kitaran. Lihat Rajah 7.

Figure 7 :MCCB Arc Chute

The operating mechanism of an MCCB opens and closes the contact assemblies and has three positions: open, closed, and trip. Branch circuit breakers of the type used for panel boards and lighting panels are of a fairly simple design. See Figure 8.

Mekanisme operasi MCCB membuka dan menutup himpunan contact dan mempunyai tiga kedudukan: terbuka, tertutup, dan 'trip'. Pemutus litar cawangan jenis yang digunakan untuk papan panel(panel board) dan panel pencahayaan adalah reka bentuk yang agak mudah. Lihat Rajah 8.

Figure 8: The operating mechanism of a molded-case circuit breaker opens and closes the contact assemblies. It has three positions: open, trip, and closed.

With the contacts closed, the trip latch is in the latched position (yellow circle). As the contacts are opened and closed, the trip latch position does not move. This type of trip latch is one of the major issues with MCCBs in that it, and other parts of the operating mechanism, is lubricated at the factory.

Dengan contact yang ditutup, selak perjalanan berada di kedudukan latched (lingkaran kuning). Apabila contact dibuka dan ditutup, posisi selak contact tidak bergerak. Jenis 'trip latch' ini adalah salah satu isu utama dengan MCCBs, dan bahagian lain dari mekanisme operasi, melincirkan di kilang.

Current flow through the contacts creates heat, which dries out the lubricant over time. As the factory-applied lubricant dries, it thickens and slows the circuit breaker performance. As it continues to dry, it begins to flake off, and metal-to-metal wear occurs. This metal-to-metal wear and the corrosion that can occur on the trip latch can easily cause the circuit breaker to fail to open as required. The only time the trip latch changes position is when the circuit breaker is tripped.

Aliran arus melalui contact menghasilkan haba, yang mengeringkan pelincir dari masa ke masa. Sebagai bahan pelincir yang digunakan kilang, ia menebal dan melambatkan prestasi pemutus litar/CB. Memandangkan ia terus kering, ia mula pecah, dan kerosakanlogam ke logam berlaku. Ini kerosakan/kakisan logam-ke-logam dan kakisan yang boleh berlaku di selak perjalanan dengan mudah boleh menyebabkan pemutus litar gagal untuk membuka seperti yang diperlukan. Satu-satunya masa trip latch changes position ialah apabila pemutus litar 'trip'.

 Note how the trip latch is stationary in the open and closed positions but is different in the trip position. Trip latch malfunction is one of the primary causes of MCCBs failing to operate in accordance with the OEM specifications. Modern large-frame MCCBs often include red mechanical trip buttons. The trip button operates the trip latch directly. The trip latch (yellow arrow in Figure 8) does not move when the circuit breaker is toggled from the open to the closed position. It does move, however, when the circuit breaker is tripped.

Perhatikan bagaimana  trip latch is stationary dalam kedudukan terbuka dan tertutup tetapi berbeza dalam kedudukan perjalanan. Kerosakan Trip latch adalah salah satu punca utama MCCBs yang gagal untuk beroperasi mengikut spesifikasi OEM. Modern large-frame MCCBs sering kali memasukkan red mechanical trip buttons. 'Trip button' mengendalikan 'trip latch' secara langsung. 'Trip latch' (anak panah kuning dalam Rajah 8) tidak bergerak apabila pemutus litar(CB) ditukar daripada terbuka ke kedudukan tertutup. Ia bergerak, bagaimanapun, apabila pemutus litar 'trip'.

Figure 9: A modern, large-frame MCCB often includes a red mechanical trip button, which operates the trip latch directly (mechanically).

MCCB Trip elements

Trip elements trip the operating mechanism of a circuit breaker during either a prolonged overload or a short circuit current. Some moulded case circuit breakers have a screwdriver slot located on the front of the trip unit used for adjusting sensitivity.

Elemen trip-''trip" mekanisme operasi pemutus litar semasa sama ada  arus 'overload' yang berpanjangan atau litar pintas. Beberapa pemutus litar kes dibentuk mempunyai slot pemutar skru yang terletak di hadapan unit 'trip' yang digunakan untuk mengubah-suaikan kepekaan.

Figure 10:Thermal magnetic circuit breakers employ a bi-metallic strip to sense overload conditions.

Instantaneous Magnetic Trip

Magnetic trips work by using an electromagnet in series with the load current. When the current reaches the set point, the electromagnet instantaneously trips. This type of trip is commonly found in low voltage breakers (e.g., household circuit breakers).

'Trip' magnetik seketika

'Trip'  magnet berfungsi dengan menggunakan elektromagnet secara siri dengan arus beban. Apabila arus mencapai titik set, 'trip' elektromagnet dengan segera. Jenis 'trip' ini biasanya terdapat di pemutus voltan rendah (cth. Pemutus litar rumah).

Thermal Trip

Considered the industry standard, these trip elements work using a bimetal heated by the load current. When overheated, indicating an overload, the bimetal will detect, which causes the operating mechanism to trip.

'Trip' haba

Mengambilkira piawai industri, elemen 'trip' ini berfungsi menggunakan bimetal yang dipanaskan oleh arus beban. Apabila terlalu panas, menunjukkan 'overload', bimetal akan mengesan, yang menyebabkan mekanisme operasi berjalan.

Electronic Trip

Current transformers and solid-state circuits are used to monitor the current. When an overload or short circuit is detected, the monitors initiate a trip. Electronic trip elements can include trip features and exibility not present in other types of trip elements (e.g. , adjustable pickup, time delays, instantaneous pickup, selective interlocking). Solid-state components have replaced electromechanical-magnetic and thermal magnetic trip elements in some molded-case breakers.

'Trip' Elektronik

Transformer arus dan litar solid-state digunakan untuk memantau(monitor) arus. Apabila 'overload' atau litar pintas dikesan, pemantau (monitor) memulakan trip. Unsur trip elektronik boleh merangkumi ciri trip dan kebolehlihatan yang tidak terdapat dalam unsur-unsur trip lain (contohnya, pickup boleh-laras, lengah masa, pikap segera, saling selektif(selective interlocking)). Komponen solid-state telah menggantikan unsur-unsur trip elektromekanik magnetik dan termal dalam beberapa pemutus kes dibentuk (molded-case breakers).

Shunt Trips

A shunt trip relay completes the circuit between the control-power source and the solenoid coil. Shunt trips are used to trip a  circuit breaker electrically from a remote location and consist of a momentary-rated solenoid tripping device mounted inside a molded case.

The shunt trip can remotely trip the breaker, but cannot remotely reclose the breaker. To reclose the breaker, the breaker handle must first be moved to the reset position and then to the “on” position.

'Trip' Shunt

Relay trip shunt melengkapkan litar antara sumber kuasa kawalan dan gegelung solenoid. Trip shunt digunakan untuk trip pemutus litar secara elektrik dari lokasi jauh dan terdiri daripada peranti tersendiri solenoid 'a momentary-rated solenoid tripping device' yang dipasang di dalam 'a molded case'.

'Trip' shunt jauh dari trip pemutus, tetapi tidak dapat dari jarak jauh 'reclose' pemutus. Untuk ' reclose', handle pemutus mesti terlebih dahulu dipindahkan ke kedudukan 'reset' dan kemudian ke kedudukan "ON".

At its core, the protection mechanism employed by MCCBs is based on the same physical principles used by all types of thermal-magnetic circuit breakers.

Pada terasnya, mekanisme perlindungan yang digunakan oleh MCCBs adalah berdasarkan prinsip fizikal yang sama yang digunakan oleh semua jenis pemutus litar thermal-magnetic.

• Overload protection is accomplished by means of a thermal mechanism. MCCBs have a bimetallic contact what expands and contracts in response to changes in temperature. Under normal operating conditions, the contact allows electric current through the MCCB. However, as soon as the current exceeds the adjusted trip value, the contact will start to heat and expand until the circuit is interrupted. The thermal protection against overload is designed with a time delay to allow short duration overcurrent, which is a normal part of operation for many devices. However, any overcurrent conditions that last more than what is normally expected represent an overload, and the MCCB is tripped to protect the equipment and personnel.

• Perlindungan beban lebih dicapai melalui mekanisme termal. MCCB mempunyai contact bimetallic yang mengembang dan kontrak sebagai tindak balas terhadap perubahan suhu. Di bawah keadaan operasi normal, contact itu membenarkan arus elektrik melalui MCCB. Bagaimanapun, sebaik sahaja arus melebihi nilai trip yang dilaraskan, contact akan mula panas dan berkembang sehingga litar terganggu. Perlindungan termal terhadap 'overload' dibina dengan lengah masa untuk membolehkan jangka masa lampau yang pendek, yang merupakan bahagian operasi biasa untuk banyak peranti. Bagaimanapun, keadaan overcurrent yang lebih tinggi daripada apa yang dijangka biasanya mewakili overload, dan MCCB di'trip' untuk melindungi peralatan dan kakitangan.

• On the other hand, fault protection is accomplished with electromagnetic induction, and the response is instant. Fault currents should be interrupted immediately, no matter if their duration is short or long. Whenever a fault occurs, the extremely high current induces a magnetic field in a solenoid coil located inside the breaker – this magnetic induction trips a contact and current is interrupted. As a complement to the magnetic protection mechanism, MCCBs have internal arc dissipation measures to facilitate interruption.

• Sebaliknya, perlindungan kerosakan dicapai dengan induksi elektromagnetik, dan tindak balasnya segera. Fault current harus di'interrupt' dengan serta-merta, tidak kira jika tempohnya pendek atau panjang. Apabila berlaku fault, arus yang sangat tinggi menginduksi medan magnet dalam gegelung solenoid yang terletak di dalam pemutus - ' induksi magnet ini trip' contact dan arus terganggu. Sebagai pelengkap kepada mekanisme perlindungan magnet, MCCBs mempunyai langkah-langkah pelencongan arka dalaman untuk memudahkan interruption.

As with all types of circuit breakers, the MCCB includes a disconnection switch which is used to trip the breaker manually. It is used whenever the electric supply must be disconnected to carry out field work such as maintenance or equipment upgrades.

Seperti semua jenis pemutus litar, MCCB mengandungi suis pemotongan(disconnection switch) yang digunakan untuk trip pemutus secara manual. Ia digunakan apabila bekalan elektrik mesti diputuskan untuk menjalankan kerja lapangan seperti peningkatan penyelenggaraan atau peralatan.

c. Low voltage Air Circuit Breaker (LV-ACB)

Air Break Circuit Breaker Construction

Construction of air circuit breaker (arc-chute type) used for low and medium voltage is shown in the figure 11.

Figure 11: air circuit breaker 

There are two sets of contacts in such breakers named as main contacts and arcing contacts. Main contacts are usually made of copper and carry the current in the closed position of the circuit breaker. They are silver coated to make low contact resistance.

Terdapat dua set contact dalam pemutus tersebut yang dinamakan sebagai contact utama dan contact 'arcing'. Contact utama biasanya diperbuat daripada tembaga dan membawa arus dalam kedudukan tertutup pemutus litar. Mereka bersalut perak untuk membuat rintangan contact rendah.

The arcing contacts are hard, heat resistant and usually made of a copper alloy. Arcing contacts are used to reduce the damage of main contacts due to arcing. These contacts can be replaced easily. The arcing contacts close before and open after main contacts. Here blow-outs consist of steel inserts in the arcing chutes.

Arcing contacts adalah keras, tahan panas dan biasanya dibuat daripada aloi tembaga. Arcing contacts digunakan untuk mengurangkan kerosakan contact utama akibat 'arcing'. Contact ini boleh digantikan dengan mudah. Arcing contacts ditutup sebelum dan dibuka selepas contact utama. Di sini blow-outs terdiri daripada sisipan keluli dalam arcing chutes.

These are so arranged that the magnetic field induced in them by the current in the arc moves it upward faster. When the arc comes into contact with the cool surfaces of the steel plates made in arc chute, it gets rapidly cooled. Thus the arc is quenched by lengthening and excessive power loss. The main problem in this type of circuit breakers is inefficiency at low currents where the electromagnetic fields are weak.

Ini diatur sebegitu rupa supaya medan magnet yang diinduksi di dalamnya oleh arus dalam arka bergerak ke atas dengan lebih cepat. Apabila arka bersentuhan dengan permukaan sejuk plat keluli yang dibuat di arc chute, ia akan didinginkan dengan cepat. Oleh itu, arka dipadamkan dengan memperpanjang dan kehilangan kuasa yang berlebihan. Masalah utama dalam pemutus litar jenis ini adalah ketidakcekapan pada arus rendah di mana medan elektromagnet lemah.

Operation

On the occurrence of a fault, main contacts separate first and the current is shifted to the 'arcing contacts'. Now the arcing contacts separate and the arc is struck between them. This arc is pushed upwards by the electromagnetic forces and thermal action. The arc ends travel along the arc runners. The arc is split by arc splitter plates. The arc is quenched by lengthening, cooling and splitting.

Apabila terjadinya fault, contact utama dipisahkan terlebih dahulu dan arus dipindah ke 'arcing contacts'. Kini 'arcing contacts' itu terpisah dan 'arka'nya tersentak di antara mereka. Arka ini ditekan ke atas oleh daya elektromagnetik dan tindakan haba. Arka itu bergerak di sepanjang pelari arka. Arka itu dipisahkan oleh plat pembahagi arka. Arka dipadamkan dengan memanjangkan, menyejukkan dan splitting.