mcb, rccb, elcb

29
Fuse, RCB & ELCB Elements of Electrical Engineering

Upload: akash-ambaliya

Post on 06-Aug-2015

242 views

Category:

Engineering


16 download

TRANSCRIPT

Page 1: Mcb, rccb, elcb

Fuse, RCB & ELCBElements of Electrical Engineering

Page 2: Mcb, rccb, elcb

Fuse

Page 3: Mcb, rccb, elcb

About A fuse consists of a metal strip or wire fuse

element, of small cross-section compared to the circuit conductors, mounted between a pair of electrical terminals, and (usually) enclosed by a non-combustible housing.

The fuse is arranged in series to carry all the current passing through the protected circuit.

The resistance of the element generates heat due to the current flow.

Page 4: Mcb, rccb, elcb

About The size and construction of the element is (empirically)

determined so that the heat produced for a normal current does not cause the element to attain a high temperature.

If too high a current flows, the element rises to a higher temperature and either directly melts, or else melts a soldered joint within the fuse, opening the circuit.

The fuse element is made of zinc, copper, silver, aluminum, or alloys to provide stable and predictable characteristics.

The fuse element may be surrounded by air, or by materials intended to speed the quenching of the arc. Silica sand or non-conducting liquids may be used.

Page 5: Mcb, rccb, elcb

History in 1847, Breguet recommended use of reduced-

section conductors to protect telegraph stations from lightning strikes; by melting, the smaller wires would protect apparatus and wiring inside the building.  

A variety of wire or foil fusible elements were in use to protect telegraph cables and lighting installations as early as 1864.

A fuse was patented by Thomas Edison in 1890 as part of his electric distribution system.

Page 6: Mcb, rccb, elcb

Variations Fuses come in a vast array of sizes and styles to serve in

many applications, manufactured in standardized package layouts to make them easily interchangeable. Fuse bodies may be made of ceramic, glass, plastic, fiberglass, molded mica laminates, or molded compressed fiber depending on application and voltage class.

Cartridge (ferrule) fuses have a cylindrical body terminated with metal end caps.

Some cartridge fuses are manufactured with end caps of different sizes to prevent accidental insertion of the wrong fuse rating in a holder, giving them a bottle shape.

Page 7: Mcb, rccb, elcb
Page 8: Mcb, rccb, elcb

Fuse Fuses for low voltage power circuits

may have bolted blade or tag terminals which are secured by screws to a fuse holder.

Some blade-type terminals are held by spring clips. Blade type fuses often require the use of a special purpose extractor tool to remove them from the fuse holder.

Page 9: Mcb, rccb, elcb
Page 10: Mcb, rccb, elcb

RCB

Page 11: Mcb, rccb, elcb

About

RCDs are designed to disconnect the circuit if there is a leakage current.

By detecting small leakage currents (typically 5–30 mill amperes) and disconnecting quickly enough (<300 ms)

Page 12: Mcb, rccb, elcb

About

The device pictured is designed to be wired in-line in an appliance power cord.

It is rated to carry a maximum current of 13 amperes and is designed to trip on a leakage current of 30 mA.

This is an active RCD; that is, it latches electrically and therefore trips on power failure, a useful feature for equipment that could be dangerous on unexpected re-energisation.

Page 13: Mcb, rccb, elcb

About

Some early RCDs were entirely electromechanical and relied on finely balanced sprung over-centre mechanisms driven directly from the current transformer.

As these are hard to manufacture to the required accuracy, and prone to drift in sensitivity both from pivot wear and lubricant dry-out, the electronically amplified type with a more robust solenoid part as illustrated are now dominant.

Page 14: Mcb, rccb, elcb

Cross Section of RCB

Page 15: Mcb, rccb, elcb

Working Mechanism

The incoming supply and the neutral conductors are connected to the terminals at (1) and the outgoing load conductors are connected to the terminals at (2).

The earth conductor (not shown) is connected through from supply to load uninterrupted. When the reset button (3) is pressed the contacts ((4) and hidden behind (5) close, allowing current to pass. The solenoid(5) keeps the contacts closed when the reset button is released.

The sense coil (6) is a differential current transformer which surrounds (but is not electrically connected to) the live and neutral conductors.

In normal operation, all the current down the live conductor returns up the neutral conductor.

Page 16: Mcb, rccb, elcb

Working Mechanism

This difference causes a current in the sense coil (6) which is picked up by the sense circuitry (7).

The sense circuitry then removes power from the solenoid (5) and the contacts (4) are forced apart by a spring, cutting off the electricity supply to the appliance.

The device is designed so that the current is interrupted in milliseconds, greatly reducing the chances of a dangerous electric shock being received.

The test button (8) allows the correct operation of the device to be verified by passing a small current through the orange test wire (9). This simulates a fault by creating an imbalance in the sense coil

Page 17: Mcb, rccb, elcb

Working Mechanism

The currents in the two conductors are therefore equal and opposite and cancel each other out.

Any fault to earth (for example caused by a person touching a live component in the attached appliance) causes some of the current to take a different return path which means there is an imbalance (difference) in the current in the two conductors (single phase case), or, more generally, a nonzero sum of currents from among various conductors (for example, three phase conductors and one neutral conductor).

Page 18: Mcb, rccb, elcb

Disadvantages

A residual-current circuit breaker cannot remove all risk of electric shock or fire. In particular, an RCD alone will not detect overload conditions, phase to neutral short circuits or phase-to-phase short circuits.

It cannot protect against electric shock where current flows through a person from phase to neutral or phase to phase. 

Page 19: Mcb, rccb, elcb

RCB

Residual-current and over current protection may be combined in one device for installation into the service panel; this device is known as a GFCI breaker (Ground Fault Circuit Interrupter) in the USA and Canada, and as an RCBO (residual-current circuit breaker with overload protection) in Europe. In the US, RCBOs are more expensive than RCD outlets.

Page 20: Mcb, rccb, elcb

ELCB

Page 21: Mcb, rccb, elcb

About

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.

Once widely used, more recent installations instead use residual current circuit breakers which instead detect leakage current directly.

The main purpose of earth leakage protectors is to prevent injury to humans and animals due to electric shock.

Page 22: Mcb, rccb, elcb

About

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.

Page 23: Mcb, rccb, elcb

ELCB

There are two types of ELCB:-voltage operated-current operated.

Page 24: Mcb, rccb, elcb
Page 25: Mcb, rccb, elcb
Page 26: Mcb, rccb, elcb

Advantages

ELCBs have one advantage over RCDs: they are less sensitive to fault conditions, and therefore have fewer nuisance trips. (This does not mean they always do, as practical performance depends on installation details and the discrimination enhancing filtering in the ELCB.)

Therefore by electrically separating cable armour from the cable circuit protective conductor, an ELCB can be arranged to protect against cable damage only, and not trip on faults in downline installations.

Page 27: Mcb, rccb, elcb

Disadvantages

They do not detect faults that don't pass current through the CPC to the earth rod.

They do not allow a single building system to be easily split into multiple sections with independent fault protection, because earthing systems are usually bonded to pipe work.

They may be tripped by external voltages from something connected to the earthing system such as metal pipes, a TN-S earth or a TN-C-S combined neutral and earth.

As with RCDs, electrically leaky appliances such as some water heaters, washing machines and cookers may cause the ELCB to trip.

ELCBs introduce additional resistance and an additional point of failure into the earthling system.

Page 28: Mcb, rccb, elcb

Prepared by …. Class FX students (Group No. - 5)

1. Akash Ambaliya2. Brijesh Daraniya3. Kaushik Dodiya4. Gopal Gol5. Neeldeepsinh Jadeja

Page 29: Mcb, rccb, elcb

Thank You…