SWITCHGEAR&PROTECTION

FuseSemi-enclosed rewirable fuse• The detachable fuse carrier permits the replacement

of fuse element without any danger of coming in contact with live parts.

• The cost of replacement is negligible.

High-Rupturing capacity (H.R.C.) cartridge fuse• They are capable of clearing high as well as low fault

currents.• They do not deteriorate with age.• They have high speed of operation.

Isolator

Arc

Circuit BreakerElectrical circuit breaker is a switching device which can be operated both manually and automatically for controlling and protection of any electrical power system.During interruption of huge current, there would be large arcing in between switching contacts, so care should be taken to quench these arcs in circuit breaker in safe manner.The dielectric strength of the media in between contacts can be increased in numbers of ways, like by compressing the ionized arcing media since compressing accelerates the deionization process of the media, by cooling the arcing media since cooling increase the resistance of arcing path or by replacing the ionized arcing media by fresh gasses.

Classification (H.T.)Oil circuit breakers which employ some insulating oil (e.g., transformer oil) for arc extinction.

Bulk oil circuit breaker.Minimum oil circuit breaker.

Air-blast circuit breakers in which high pressure air-blast is used for extinguishing the arc.Sulphur hexafluoride circuit breakers in which sulphur hexafluoride (SF6) gas is used for arc extinction.Vacuum circuit breakers in which vacuum is used for arc extinction.

Classification (L.T.)Air Circuit breakerMiniature circuit breakerMoulded case circuit breakerEarth leakage circuit breaker

Bulk Oil Circuit BreakerIn oil circuit breaker the fixed contact and moving contact are immerged inside the insulating oil.Whenever there is a separation of current carrying contacts in the oil, the arc in circuit breaker is initialized.Due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately creates a hydrogen bubble around the arc.This highly compressed gas bubble around the arc prevents re-striking of the arc after current reaches zero crossing of the cycle.

Bulk Oil Circuit Breaker The construction is simple and it consists of

fixed and moving contacts enclosed in a strong weather tight earthed tank containing oil up to a certain level and an air cushion above the oil level.

These breakers are used up to 11 KV with an interrupting capacity of 250MVA.

Minimum Oil Circuit BreakerThese types of circuit breakers utilize oil as the interrupting media.The insulating oil is available only in interrupting chamber.The features of designing MOCB is to reduce requirement of oil, and hence these breaker are called minimum oil circuit breaker.

Minimum oil circuit breaker Constructional featuresSupporting chamberIt is a porcelain chamber mounted on a metal chamber.

Circuit breaking chamberIt is a porcelain enclosure mounted on the top of the

supporting compartment. It contains the main circuit breaking components.

Top chamberIt is a metal chamber and is mounted on the circuit-

breaking chamber. It provides expansion space for the oil in the circuit breaking compartment.

Sulphur Hexafluoride Circuit BreakerA circuit breaker in which the current carrying contacts operate in sulphur hexafluoride or SF6 gas is known as an SF6 circuit breaker.SF6 has high electro-negativity. That means it has high affinity of absorbing free electron.The movement of the moving contact is synchronised with the opening of a valve which permits SF6 gas at 14 kg/cm2 pressure from the reservoir to the arc interruption chamber.

Sulphur Hexafluoride Circuit BreakerDue to the superior arc quenching property

of SF6, such circuit breakers have very short arcing time.

Dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt much larger currents.

The SF6 circuit breaker gives noiseless operation due to its closed gas circuit and no exhaust to atmosphere unlike the air blast circuit breaker.

There is no risk of fire in such breakers because SF6 gas is non-inflammable.

Vacuum Circuit Breaker The dielectric strength of vacuum is eight times

greater than that of air and four times greater than that of SF6 gas.

The high dielectric strength makes it possible to quench a vacuum arc within very small contact gap.

As it is vacuum, the metal on the contact surface is easily vaporized due to that hot spot and create a conducting media for arc path.

At current zero this vacuum arc is extinguished and the conducting metal vapour is re-condensed on the contact surface.

Air Circuit Breaker

Miniature Circuit Breaker

Moulded Case Circuit Breaker

Earth Leakage Circuit Breaker

Attracted Armature Type Relay

Solenoid Type Relay

Balanced Beam Type Relay

Shaded Pole Type Relay

Watthour Meter Type Relay

Static Relay

Microprocessor Based Relay

Definite Distance Relay

Time Distance Relay

MHO Relay

Directional Relay

Current Differential Relay

Voltage Differential Relay