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.
