Module for exploration of installation guidelines
- 2. Content • Fuse • Miniature Circuit Breaker (MCB) • MCCB • Earth Leakage Circuit Breaker (ELCB) • Types of Wires and Cables • Earthing • Types of Batteries and its Characteristics
- 3. What is fuse? • Fuses are a type of over-current protection device. The essential component is a metal wire or strip that melts when too much current flows, which interrupts the circuit in which it is connected. Short circuits, overloads or device failures are often the reason for excessive current. • Fuses serve two main purposes: 1) To protect components and equipment from costly damage caused by over-currents. 2) To isolate sub-systems from the main system once a fault has occurred. • There are thousands of different styles of fuses available in the world. The primary way to group them is by Low Voltage (Voltage Rating less than or equal to 1500V)or Medium Voltage (Voltage Rating between 1500V and 40.5kV).
- 4. Working Principleof Fuse The working principle of the fuse is “heating consequence of the current”. It is fabricated with a lean strip or thread of metallic wire. The connection of the Fuse in an electrical circuit is always in series. When the too much current is produced due to the heavy flow of current in the electrical circuit, the fuse gets soften and it opens the circuit. The extreme flow of current may direct to the collapse of the wire and prevents the supply. The fuse can be changed by the new fuse with an appropriate rating. It can be designed with the elements like Cu (copper), Zn (zinc), Al (aluminum) and Ag (silver). They also perform like a circuit breaker for breaking the circuit while the abrupt fault happens in the circuit. This works like a safety measure or protector for humans from risks. Like this, the fuse works.
- 5. What is MCB? A Miniature Circuit Breaker (MCB) is an automatically operated electrical switch used to protect low voltage electrical circuits from damage caused by excess current from an overload or short circuit. MCBs are typically rated up to a current up to 125 A. Fuse vs MCB • MCB automatically switches off the electrical circuit during the abnormal conditions of the network (both overload and fault conditions). • As the switch operating knob comes at its off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of a fuse, the fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire. • Quick restoration of supply can not be possible in case of fuse, as fuses have to be rewirable or replaced for restoring the supply. But in the case of an MCB, quick restoration is possible by (literally) flipping a switch. • The handling of an MCB is more electrically safe than a fuse. • MCBs can be controlled remotely, whereas fuses can not.
- 6. Working & Operationof MCB • Under normal working conditions, MCB operates as a switch (manual one) to make the circuit ON or OFF. Under overload or short circuit condition, it automatically operates or trips so that current interruption takes place in the load circuit. The visual indication of this trip can be observed by automatic movement of the operating knob to OFF position. This automatic operation MCB can be obtained in two ways as we have seen in MCB construction; those are magnetic tripping and thermal tripping. • Under overload condition, the current through the bimetal causes to raise the temperature of it. The heat generated within the bimetal itself enough to cause deflection due to thermal expansion of metals. This deflection further releases the trip latch and hence contacts get separated. In some MCBs, magnetic field generated by the coil causes develop pull on bimetal such that it deflection activates the tripping mechanism.
- 7. Working & Operationof MCB • Under short circuit or heavy overload conditions, magnetic tripping arrangement comes into the picture. Under normal working condition, the slug is held in a position by light spring because magnetic field generated by the coil is not sufficient to attract the latch. When a fault current flows, the magnetic field generated by the coil is sufficient to overcome the spring force holding slug in position. And hence slug moves and then actuate the tripping mechanism. • A combination of both magnetic and thermal tripping mechanisms are implemented in most of MCBs. In both magnetic and thermal tripping operations, an arc is formed when the contacts start separating. This arc is then forced into arc splitter plates via arc runner. These arc splitter plates are also called arc chutes where arc is formed into a series of arcs and at the same time energy extracted and cools it. Hence this arrangement achieves the arc extinction.
- 8. Moulded CaseCircuit Breaker(MCCB) A moulded case circuit breaker (MCCB) is a type of electrical protection device that is used to protect the electrical circuit from excessive current, which can cause overload or short circuit. With a current rating of up to 2500A, MCCBs can be used for a wide range of voltages and frequencies with adjustable trip settings. These breakers are used instead of miniature circuit breakers (MCBs) in large scale PV systems for system isolation and protection purposes. • The MCCB uses a temperature sensitive device (the thermal element) with a current sensitive electromagnetic device (the magnetic element) to provide the trip mechanism for protection and isolation purposes. This enables the MCCB to provide: • Overload Protection, • Electrical Fault Protection against short circuit currents, and • Electrical Switch for disconnection.
- 9. Constructionof MCCB A Moulded case circuit breaker generally have a thermal element for overcurrent and a magnetic element for short circuit release which has to operate faster. Generallyconstructed of two pieces of heavy-duty electrically insulated plastic, these two halves are riveted together to form the whole. Inside the plastic shell is a series of thermal elements and a spring-loaded trigger. When the thermal element gets too warm, from an overcurrent situation, the spring trips, which in turn will shut off the electrical circuit. 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 current and trips 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.
- 10. Earth Leakage Circuit Breaker (ELCB) An ECLB is one kind of safety device used for installing an electrical device with high earth impedance to avoid shock. These devices identify small stray voltages of the electrical device on the metal enclosures and intrude the circuit if a dangerous voltage is identified. The main purpose of Earth leakage circuit breaker (ECLB) is to stop damage to humans & animals due to electric shock. For the protection of human body from the electric shock protective device like fuse or MCB are used. But generally this device are incapable of measuring small current flowing in human body, so requirement is to have a device which can sense small current and cut-off the supply instantly. The device used for this purpose is known as Earth Leakage Circuit Breaker (ELCB). There are two types of Earth Leakage Circuit Breaker (ELCB) • Voltage Operated ELCB • Current Operated ELCB
- 11. Workingof ELCB It is current operated device designed to operate when a leakage current exceeds the predefined value. It consists of a operating coil and a trip mechanism which operated the circuit when required. The coil is supplied through 1-Ф supply so current in phase & neutral wire will be same. This current will produce flux linkages same in magnitude but of opposite direction. This will result zero net flux in tripping coil of relay. When fault or leakage current exceeds the limit higher current will flow in phase conductor than neutral current. Resultant flux now is out of balance in tripping coil of relay. Difference of flux will induce emf in the coil which opens the contact of ELCB and isolate the circuit from the supply.
- 31. Electric battery A battery is a device consisting of one or more electrochemical cells with external connections for powering electrical devices such as flashlights, mobile phones, and electric cars. When a battery is supplying electric power, its positive terminal is the cathode and its negative terminal is the anode.
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