What is Oil-Circuit-Breaker?

What is Oil-Circuit-Breaker?how it works?

It is acknowledge that once a circuit carrying an outsizes current is broken, arc happens at the purpose wherever the contacts voltages square measure concerned and if short-circuit happens on a high voltage cable that is provided from massive power plant, the arc would be powerful to bridge the contacts of the switch and destroy it by burning. The device is used as AN oil circuit-breaker. AN oil circuit-breaker possesses the property of perpetually breaking AN electricity at its zero worth.

     These switches square measure appropriate for a most voltage of sixty six,000 volts and have most breaking capacities starting from seventy five,000 to 2,50,000 KVA.

          The contacts of those switches that break high tension circuits square measure immersed in oil to confirm fast and effective rupture of the circuit. once the arc happens, the oil in its path is volatilized and also the gas thereby generated exerts a pressure on the encompassing oil. This pressure is used in arc management devices to cause a movement of contemporary cool oil cross the trail of the arc, thereby with efficiency helping its interruption. Figure 27.1 shows a typical oil circuit-breaker with its contacts open.

 

 Central devices are:

1. Cross jet box: Simplest and utilized in low voltage up to six,600 potential unit circuit-breakers.

2. Cross jet pots : utilized in higher voltage circuit breakers.

(a) one among st the best arc management devices is that the cross it box. it'll be seen from the figure that the contacts square measure confined in an exceedingly special enclosure A that is house within the most oil tank. The enclosure is totally fitted with oil however incorporates a single-outlet or opening B that communicates with the chimney C.

(b) shows the position once the breaker opens and arcs square measure drawn out between the arcing contacts. The arc generates gas that sets up a pressure in arcing chamber and since the sole outlet for the oil is thru the orifices B (three for 3 phases), the oil is forced directly across the arc path through the opening and into the chimney, taking the gas product with C. during this manner the arc is initial of all weakened and so finally destroyed.

 

 

 

For larger and better voltage circuit-breakers crosier std and used as shown in Fig. 27.4. illustrates an outsizes circuit-breaker for AN or installation. it's used on 132000 potential unit service 3 such breakers square measure used to make a 3 part unit. The contacts square measure of the oil blast explosion pot kind. The e ceramic ware bushings projected on top of the oil tank vide the mandatory degree of insulation for such voltage.

I.E. Rule No. 54. Declared Voltage of offer to client to client

Ordinarily the declared voltage is 230 V just in case of low voltage, four hundred V just in case of medium voltage and eleven,000 V for prime voltage.

According to this rule and IS 538–1962;

For the 2-wire system, the quality voltage prescribed IS 240 volts. customary voltages for three-phase system square measure as

follows: The voltages shown in daring kind square measure the popular voltages.

                    415 V (voltage to neutral three.3 kV, 6.6kV, 11 kV, 22 kV, 33 kV,66 kV, one hundred ten kilovolt 132 kilovolt, 220 kV, 580 kV).

Notes:

1.These voltages ask the line-to-line voltage. in keeping with this rule variation of fifty within the case of low or medium voltage or y no more than twelve.5% within the case of high or additional high voltage.

2. 440-415-400 V. distinction of voltage worth is thanks to lupus distinction of generating finish voltage and receiving finish voltage.

 

OVER CURRENT protecting AND management EQUIPMENTS

Over current protecting and management equipments that square measure extensively utilized in transmission and distribution circuits, square measure referred to as switches, circuit breakers, reclosers, sectionalizers and fuses. they're used each for manual of the circuit and for automatic protection of the lines and instrumentality against overloads and short circuits. The principle of operation of those equipments square measure deals with as under:

SWITCHES

Switches is also divided into 2 general categories, i.e.,

1. Air switches

(a) Air break

(b) Disconnect

2. Oil switches

(a) fuse

(b) Reclose

Air switches, as their name imply, square measure switches whose contacts square measure opened in air whereas oil switches square measure switches whose contacts square measure opened beneath oil (Fig. 27.5). Air-break switches square measure nearly always operated by hand. Oil switches square measure nearly always designed for automatic operation, that's they're going to open mechanically on over load or tangency and might even be mean to reclose mechanically one or additional times.

 

Air Break Switch: The air-break switch has each blade and stationary contact equipped with arcing horns as shown in Fig. 27.6. These horns area unit items of metal between that they're forms once a circuit carrying current is opened. because the switch opens, these horns area unit unfold additional and additional apart, thereby protraction the arc till it finally breaks.

Air break switches area unit sometimes mounted on station structures or on poles and area unit operated from the bottom. they're operated by suggests that of a rod mounted on the structure (See Fig. 27.6). Ina 3-phase circuit all three switches, one in every part, area unit opened and closed along as a "gang" because the system is called.

 

A additional recently developed version of the air-break switch is that the load break that breaks the arc within a fibre tube. As within the expulsion lightening constraint the fibre tube produces a gas that helps to confine the arc and blow it out. there's an opening that the unconfined arc related to the horn-type switch would possibly communicate itself to adjacent conductors or structures, inflicting injury and doable injury. however the load-break switch eliminates this hazard.

The vital component of the load-break switch is that the device unit shown here. Naturally, the center of the unit is that the arc-extinguishing section that consists of a try of arcing contacts (one stationary and one movable) and a trailer operative at intervals a fibre bore. The trailer that is formed of synthetic resin, follows the contact through the bore, confining the arc between the fibre wall and itself. The arc is destroyed by deionizing gases coming back from each the fibre and therefore the synthetic resin.

Disconnect Switch : The disconnect switch isn't ped with arc-quenching devices and so, ought to accustomed open circuits carrying current. This disconnect hisolates one portion of the circuit from another and isn't supposed to be opened whereas current is flowing. Airbreak switches is also opened beneath load, however disconnect swatches should not be opened till the circuit is interrupted another suggests that .

 

Oil Circuit Recloser: associate degree oil circuit recloser could be a form of cilswitch designed to interrupt associate degreed reclose an alternatingcurrent circuit mechanically (Fig. 27.10). It is created to repeat this cycle many times. Reclosers area unit designed to be used on single-phase circuits or on three-phase circuits.

Redosers area unit sometimes connected to safeguard parts of primary circuits and should take the place of line fuses. The switch or breaker is organized to reclose once a brief interval of your time and re-open against ought to the fault or overload that caused the surplus current flow persist. additionally just like the repeater fuse cutout, the recloser is set for three or four Operations before it locks itself open for manual operation. It Otters from the repeater fuse cutout therein its action is wstantaneous. in an exceedingly recloser, there's associate degree operative rod Suited by a magnet plunger that opens and closes the contacts, whereas the repeater fuse works only the metal has been liquified by overheat.

 A recloser is magnetically operated by a magnet connected asynchronous with the road. Minimum trip current is typically doubly the traditional load current rating of the recloser coil. The operations area unit performed by a hydraulic mechanism and a mechanical linkage system. once the fault current reaches doubly traditional line current, the raised force field pulls plunger down into the coil. because the advertizer moves downward, the lower finish visits the contact assembly to open the contacts and breaks the circuit. As presently because the contacts area unit open, there's no additional current within the coil to carry them open, therefore a spring shut the mechanism and reenergises the road.

The Oil-Blast Circuit Breaker

Oil Switches or sectionalizer

The oil switch has each the blade and therefore the contact mounted in an exceedingly tank full of oil. The switch is typically operated from a handle on the surface of the case. because the switch opens, the arc shaped between the blade and phone is quenched by the oil.

 

 

Oil switches is also unmanned  still as operated by hand. they're used for capacitance change, street lighting management and automatic disconnect just in case of breakdown.

 

 

 

When a fault happens behind the switch, the recloser can operate. If the fault is of a permanent nature, the switch can count variety|the amount|the quantity} of operations of the recloser and trip and lock itself out once a preset number sometimes 3, of recloser operations. The recloser continues on its forth operation and restores service up to the sentionalizer. A switch should so, forever be secured by a recloser of correct size.

SIMPLIFIED change

The tape recloser by pass switch consists of a switch unit and an influence fuse unit, integrally mounted on one base. This single unit simplifies the change needed on recloser maintenance, and permits the operator to see quickly the condition of each the disconnect and by-pass circuits before playacting any change operation.

CUT OUT FUSES

 Fuses area unit protecting devices connected into circuits to safeguard the circuit and any connected equipment from injury because of over load or short. A fuse is associate degree on purpose weakened sport than circuit. it always consists of a brief piece of metal wire which is able to soften at coldness. once the present flowing through such a metal becomes develops enough heat to soften the metal thereby gap the circuit before the abnormal current will injury the circuit or any connected equipment.

 

 

Fuses area unit sometimes fogbound to stop the liquefied metal from flying and doing injury or inflicting a hearth. fogbound fuse additionally acts in enchaining the arc.

Image for oil circuit breaker