electrical protective equipment
TRANSCRIPT
Vishwakarma government engineering college
Topic : Electrical Protective Equipment
• In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit.
2VGEC
Fuse
The power consumed in an electrical circuit is reflected as the heat generated.
Fuse is nothing but a thin wire made up usually of lead. Resistance of the wire is constant. If current in the circuit
exceeds more than the rated current, then the heat generated also exceeds and which causes the meltdown of fuse wire.
Fuse is connected in series in a circuit, due to the rupturing it halts the current flow and thus protecting the devices (connected to the voltage source) from overcurrent damage.
3VGEC
Fuse Working Principle:
• Electric fuses : consists of a metal strip or wire fuse element, of small cross-section compared to the circuit conductors
• Thermal fuses : A thermal fuse is a cutoff which uses a one-time fusible link. Unlike the thermal switch which automatically resets itself when the temperature drops.
• Water fuses : A water fuse is an active component in a household or industrial plumbing system that detects abnormal flow or pressure drops, and stops the water flow to ensure that water damage does not occur, in a manner analogous to an electrical fuse.
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Fuse Types:
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Applications:
Fuse
A fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit.
Its 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 circuit, overloading, mismatched loads or device failure are the prime reasons for excessive current.
A fuse interrupts excessive current (blows) so that further damage by overheating or fire is prevented.
The limitation of fuse is that you have to change it after whenever it gets blew.
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Ratings:Fuse Wiring regulations often define a maximum fuse current rating for particular
circuits. Fuses are manufactured in a wide range of current and voltage ratings to
protect wiring systems and electrical equipment. The fuse ideally would carry its rated current indefinitely, and melt quickly on a
small excess. Voltage rating of the fuse must be greater than or equal to what would become
the open circuit voltage. For example, a glass tube fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 or 230 V. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result.
Rated voltage should be larger than the maximum voltage source it would have to disconnect. Rated voltage remains same for any one fuse, even when similar fuses are connected in series. Connecting fuses in series does not increase the rated voltage of the combination.
MCB(miniature circuit breaker) A MCB is a manually or
automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit.
Its basic function is to detect a fault condition and interrupt current flow.
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Working principle• An MCB functions by interrupting the continuity of
electrical flow through the circuit once a fault is detected. • There are two contacts one is fixed and the other
moveable. When the current exceeds the predefined limit a solenoid forces the moveable contact to open (i.e., disconnect from the fixed contact) and the MCB turns off thereby stopping the current to flow in the circuit. In order to restart the flow of current the MCB is manually turned on. This mechanism is used to protect from the faults arising due to over current or over load.
8VGEC
MCB
Types:• There are 3 MCB types, Type B, Type C and Type D• All 3 MCB types use a magnetic fault protection,
which trips the MCB within one tenth of a second when the overload reaches a set level.
1. Type B trips between 3 and 5 time full load current;2. Type C trips between 5 and 10 times full load
current; and3. Type D trips between 10 and 20 times full load
current.
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MCB
Applications• A miniature circuit breaker is used in new constructions instead
of the older types of fuses.• The miniature circuit breaker is designed to protect the house
from circuit overload.• Miniature circuit breaker can be used with ground fault, or arc
fault mechanisms, because the breakers consist of a system that opens the contacts if a line to ground fault occurs.
• Using miniature circuit breakers in the lighting system of the house, because they can deal with the amount of power needed to light a house, especially if using specific types of lamps, such as fluorescent lights.
10VGEC
MCB
Difference between MCB and MCCB• “MCB” stands for “Miniature Circuit Breakers” while “MCCB”
is “Molded Case Circuit Breaker.”• The main difference between the two is their capacity with
the MCB rated under 100 amps with an interrupting rating of under 18,000 amps. Consequently, their trip characteristics may not be adjusted since they basically cater to low circuits.
• On the other hand, an MCCB comes with an adjustable trip characteristic for the higher models. Usually, this type of circuit breaker would provide amps as high as 2,500 or as low as 10 depending on what is necessary. Their interrupting rating can be around 10,000 amps to 200,000 amps.
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MCB
ELCB• An Earth Leakage Circuit
Breaker (ELCB) is a safety device used in electrical installations with high earth impedance to prevent shock.
• It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected.
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ELCBWorking principle• An ELCB is a specialized type of latching relay that has a
building's incoming mains power connected through its switching contacts so that the ELCB disconnects the power in an earth leakage (unsafe) condition.
• The ELCB detects fault currents from live to the earth (ground) wire within the installation it protects.
• If sufficient voltage appears across the ELCB's sense coil, it will switch off the power, and remain off until manually reset.
• A voltage-sensing ELCB does not sense fault currents from live to any other earthed body.
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Types• There are two types of ELCB:1. voltage operated 2. current operated.• A voltage-operated ELCB detects a rise in potential
between the protected interconnected metalwork (equipment frames, conduits, enclosures) and a distant isolated earth reference electrode.
• They operate at a detected potential of around 50 volts to open a main breaker and isolate the supply from the protected premises.
14VGEC
ELCB
• Residual-current devices (RCD)s protect against earth leakage using a different method of detection.
• Both circuit conductors (supply and return) are run through a sensing coil; any imbalance of the currents means the magnetic field does not perfectly cancel.
• The device detects the imbalance and trips the contact.• When the term ELCB is used it usually means a voltage-
operated device. Similar devices that are current operated are called residual-current devices. However, some companies use the term ELCB to distinguish high sensitivity current operated 3 phase devices
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ELCB
Applications• An Earth Leakage Circuit Breaker (ELCB) is a safety device used in electrical installations with high earth impedance to prevent shock.
• Once widely used, more recent installations instead use residual current circuit breakers (RCCB) which instead detect leakage current directly.
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ELCB
Thank you !
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