circuit breakers

circuit breakers circuit breakers which can interrupt a circuit under normal and abnormal conditions. HIMERClassification and type

Low tension switchgears up to 1000V. High-tension switchgears above 1000V.

HIMERSF6 CIRCUIT BREAKERVACUUM CIRCUIT BREAKERAIR CIRCUIT BREAKERAIR BLAST CIRCUIT BREAKEROIL CIRCUIT BREAKER

SwitchgearsHigh tension switchgearsThe circuit breakers are automatic switches which can interrupt fault currents. In some applications like single-phase traction system, single pole circuit breakers are used. The part of the circuit-breakers connected in one phase is called the pole.HIMERSwitchgearsHigh tension switchgearsA circuit-breaker suitable for three phase system is called a triple-pole circuit-breakers.Each pole of the circuit-breaker comprises one or more interrupter or arc extinguishing chambers.HIMERSwitchgearsHigh tension switchgearsThe interrupters are mounted on support insulators. The interrupter encloses a set of fixed and moving contact. HIMERSwitchgearsHigh tension switchgearsThe moving contacts can be drawn apart by means of the operating links of the operating mechanism. The operating mechanism of the circuit-breakers gives the necessary energy for opening and closing of contacts of the circuit-breakers.HIMERSwitchgearsHigh tension switchgearsThe arc produced by the separation of current carrying contacts is interrupted by a suitable medium and by adopting suitable techniques for arc extinction. The circuit-breaker can be classified on the basis of the arc extinction medium.HIMERSwitchgearsTrip Circuit.HIMER

SwitchgearsHigh tension switchgearsTrip CircuitThe protected circuit x is shown by dashed line. When a fault occurs in the protected circuit, the relay (2) connected to the CT and PT actuates and closes its contacts (6). Current flows from the battery (5) in the trip circuit (4). HIMERSwitchgearsHigh tension switchgearsTrip Circuit.As the trip coil of the circuit breaker (3) is energised, the circuit-breaker operating mechanism is actuated and it operates for the opening operation. Auxiliary switch is an important item in the circuit.HIMERSwitchgearsArc extinctionHIMER

SwitchgearsArc examination in vacuumWhen the contact of vacuum interrupter are separated, the arc is drawn between them. The current leaves the electrodes from small, intensely hot spot (or spots).HIMERSwitchgearsArc extinction in vacuum...The metal vaporizes from the spots. The vapour stream constitutes the plasma in vacuum arc. The vacuum has high dielectric strength, hence the arc may not re-strike. Arc time constant of vacuum is lowest.HIMERSwitchgearsConstruction and working principleAir-break circuit-breakerCassette mounted horizontal draw out ACB (as in figure which follows)The air at atmosphere pressure is used as an arc extinguishing medium in air-break circuit-breakers. These circuit-breakers employ the high resistance interruption principle.HIMERSwitchgearsConstruction and working principleAir-break circuit-breakerCassette mounted horizontal draw out ACB (as in figure which follows).The arc is rapidly lengthened by means of the arc runners and arc chutes and the resistance of the arc is increased by cooling, lengthening and splitting the arc.HIMERSwitchgearsConstruction and working principleAir-break circuit-breakerCassette mounted horizontal draw out ACB (as in figure which follows).The arc resistance increases to such an extent that the voltage drops across the arc becomes more than the supply voltage and the arc extinguished.HIMERSwitchgearsContact opening sequence

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SwitchgearsIsolating contactsInsulating pushingCarriageArc runnerArc splittersContactsOperating solenoidOperating mechanismOperating leverCover with ventsLinkHIMERParts of shows truck-mounted air-break circuit-breaker in closed position (one pole)SwitchgearsVacuum interrupterHIMER

SwitchgearsVacuum interrupter.HIMER

SwitchgearsVacuum circuit-breakerThe vacuum circuit-breaker comprises one or more sealed vacuum-interrupter units per pole. The moving contact in the interrupter is connected to insulating operating rod linked with the operating-mechanism.HIMERSwitchgearsVacuum circuit-breaker.The contact travel is of the order of a few millimeters only. The movement of the contacts within the sealed interrupter unit is permitted by metal-bellows.The insulators (2,6) are made of metallized aluminium oxide ceramics, which permits them to be brazed to metal.HIMERSwitchgearsVacuum circuit-breaker.There are no replaceable seals and the interrupter has a permanently sealed construction.Vacuum tightness. All parts are either brazed or welded.HIMERSwitchgearsVacuum circuit-breaker.Joints made in this way are not subject to aging and the interrupter therefore remains vacuum tight throughout its working life.The arcing chamber (3) acts as a vapour shield. On opening, a metal vapour arc is drawn between the contact pieces (4,5) and is extinguished at current zero.HIMERSwitchgearsVacuum circuit-breaker.Vacuum interrupters rated 3.6/7.2/12/36 kV for indoor metalclad switchgear.Vacuum contactors rated 1.2/3.6/7.2 kV for indoor metal enclosed control gear.Vacuum interrupters rated 3.6/7.2/36 kV for outdoor porcelain housed, single interrupter per pole, circuit-breaker.HIMERSwitchgearsVacuum

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SwitchgearsContact travel HIMER

SwitchgearsMerits of VCBsVCB is self contained and does not need filling of gas or oil. They do not need auxiliary air system, oil handling system etc. No need of periodic refilling.No emission of gases, pollution free.HIMERSwitchgearsMerits of VCBs.Modest maintenance of the breaker, no maintenance of interrupters. Hence economical over long period.Breaker forms a unit which can be installed at any required orientation. Breaker unit is compact and self contained.HIMERSwitchgearsMerits of VCBs.Non-explosive.Silent operation.Large number of operations on load or short-circuit. Suitable for repeated operating duty. Long life.HIMERSwitchgearsDe-merits of VCBsThe vacuum interrupter is more expensive than the interrupting devices in other types of interrupters and its cost is affected by production volume. It is uneconomical to manufacture vacuum interrupters in small quantities.HIMERSwitchgearsDe-merits of VCBs.Rated voltage of single interrupter is limited to about 36/=20kV. Above 36kV, two interrupters are required to be connected in series. This makes the breaker uneconomical for rated voltages above 36 kV.HIMERMaintenance of SwitchgearsSafetyFollow the safety rules faithfully. Obtain work permit from authority concerned.Isolate the part from live parts during the period of maintenance. No switching on by mistake. Display caution notice board such as do not operate.HIMERMaintenance of SwitchgearsMaintenance of SwitchgearsMaintenance of SwitchgearsMaintenance of Switchgears

InterrupterContact gap

MinimumPractice

12 kV interrupter6 10 mm8 20 mm

3.6 kV interrupter2 3 mm3 5 mm

Insulator = metalized aluminium oxide ceramics

Vacuum pressure - 10-7 torr

Opening 0.5 to 0.8 mm / ms (10ms)

Closing 0.5 to 2 mm / ms