Circuit breaker

A circuit breaker is a electromechanical Organe , even electronic, of protection, whose function is to stop the Electric current in the event of incident on a Electrical circuit. It is able to stop a current of overload or a Courant of short-circuit in an installation. According to its design, it can supervise one or more parameters of an electric line. Its main feature compared to the fusible is that it is réarmable (it is designed not to undergo any damage during its operation).

This article treats only circuit breakers low tension, the circuit breakers high voltage are the specific article object: Circuit breakers with high voltage.

Various techniques used by the circuit breakers

Thermics

The running crosses the circuit breaker where whorls of wire heat by Joule effect a Bilame, at a certain temperature the thermal switch starts opening the contact and thus stopping the current.
  • This system electromechanical is rather simple and robust.
  • On the other hand, it is not very precise and its reaction time is relatively slow (it is the goal).

It one of the functions is classically filled by a fusible gG (in the past gl - general use)

Thermal protection has for principal function the protection of the drivers against the heating due to the prolonged overloads of the installation.

Magnetic

The protection of the installation against shorts-circuit is ensured by magnetic circuit breakers.

We point out here that a short-circuit produced an abrupt increase in current. That occurs when two elements having different potentials enter in direct contact

La strong variation of intensity passes through the whorls of a reel ( reference mark 7 on photography “ Eclaté of a circuit breaker” ). It produces, according to the rules of electromagnetism, a strong variation of the magnetic fields. The fields thus created starts the displacement of a soft iron core which mechanically will open the circuit and thus will remove the defect. -- B.Parisse November 16th, 2007 with 17:37 (THIS)

The interruption is " instantanée" in the case of a fast reel or " contrôlée" by a fluid in the reel which allows delayed releases. It is generally associated with a switch of very high-quality which authorizes thousands of operations.
  • This operation can replace the fuse on the short-circuits.
  • According to the type of circuit breaker, the value of intensity of instruction goes from 3 to 15 times the nominal intensity (for the standard models).
  • many other possibilities exist, release by reel tension (instruction coming from sensors), switch/circuit breaker for assembly front face, compatible bitension 100/220  volts, winds under voltage (circuit breaker maintained starting from an instruction tension), remote release, remote rearmament.
  • Many curves of release for DC, CA 50/60  Hz and 400  Hz.
  • a tight option is generally available, either tight version front face, or entirely IP67.
It is the function filled by a fusible amndt (protection of the Moteur S). Magnetic protection has for principal function the protection of the equipment against the defects (overload of the equipment, short-circuit, breakdown,…). It is chosen by the engineer who has the concern of protecting his equipment with very high degree of accuracy.

Differential

A differential circuit breaker is a interruptory differential also carrying out a protection while running of Court-circuit (overload).

The principle of a differential device with residual current (GDR) is to compare the intensities on the various drivers which cross it. For example, in single-phase current, it compares the intensity circulating in the driver of phase, and that of the driver of neutral. It is an apparatus of protection of the people and detection of the leakage currents to the ground of electrical installation.

The differential device is based on the following principle: in a normal installation, the electric current which arrives by a driver must arise by another. In a single-phase installation, if the current in the driver of phase at the beginning of a Electrical circuit is different from that of the neutral driver , it is that there is a escape. The difference in intensity of the current to which a circuit breaker reacts is called the " differential sensitivity of the disjoncteur" (obligatorily 30  my on the home terminal circuits), noted IΔn (" I delta n").

Its operation is very simple: each driver passes in a magnetic Tore, thus forming electromagnetic fields of identical force and in opposition which are cancelled. In the event of difference, from where its differential name of , the electromagnetic Champ resulting actuates a device which shuts off the current immediately.

There exist several classes of differential devices:

  • devices of class " AC"
  • devices of class " A" , are planned for the dedicated circuits, cookers, hotplates to induction, washing machine, whose operation produces residual currents comprising a continuous component. The safety of the people remains assured, the risk of unjustified release remains limited. Sometimes the differential devices of class AC do not start on this type of fault current. In the tertiary sector, this type of device (interruptory differential or differential circuit breaker) is obligatory on the circuits or the materials of class 1 which are likely to produce the type of phenomenon describes above.
  • devices of class " HI" (also called Hpi or So according to the manufacturers). This type of differential device profits from a complementary immunization against inopportune releases. They are also recommended for the circuits requiring a continuity of the service, such as the data-processing freezers or circuits (generally in the tertiary sector).

(standard NF C 15-100)

Magnetothermal

Principle

Two of the techniques previously described are associated in order to take care on several parameters:
  • Overload, heating effect , the answer to the dysfunction is then slow (the cut of the circuit can take few tenths of a second to several minutes, according to the importance of the overload).
  • Short-circuit (intensity being able to go up to several thousands of amps), magnetic effect , the answer is then very fast (about the millisecond).

Components

  1. Lever being used to cut or rearm the circuit breaker manually. It also indicates the state of the circuit breaker (opened or closed). The majority of the circuit breakers are conceived to be able to trip even if the lever is maintained manually in closed position
  2. Mécanisme related to the lever, separates or approaches the contacts
  3. Contacts making it possible the current to pass when they touch
  4. Connecteurs
  5. Bilame
  6. Vis of calibration, makes it possible to the manufacturer to adjust the instruction of current with precision after assembly
  7. Solénoïde (winds)
  8. Réducteur of arc.

Use

These models are intended to replace the fusible gG (in particular used as a servant), by offering the advantage of being réarmables (a lever to be actuated, no cartridge to be replaced) and by cumulating in the same case a thermal against the overloads prolonged and magnetic detection against the fast increases in current.

Time-constants

Certain circuit breakers are equipped with mechanical systems , electric or electronic , adjustable in duration, intensity or of sensitivity, making it possible to prohibit the operation of the one of the 3 functions above (thermal, magnetic, differential) during a certain amount of time. This delay with release makes it possible to authorize certain negligible transitory phenomena from the point of view of the protection of the people, the circuits and the equipment, but which could differently start the opening of protection (powering of transformer S or Alimentation at cutting for example). They can also be regulated in order to leave the possibility to another protection located in downstream to fulfill its role, thus allowing the selectivity of protections.

Capacity breaking

The breaking capacity of a circuit breaker corresponds to its aptitude to cut a circuit without destruction and undoubtedly in the presence of a current of Court-circuit.

The cut of a load circuit implies the systematic formation of an electric arc between the contacts. This arc makes it possible the current to continue to circulate, it thus tends to be opposed to the cut. More the current is important plus the arc is powerful. In the presence of a fort running, the Electric arc which develops between the contacts of the circuit breaker subjects the latter to violent electrodynamic forces, which tend to " lutter" against the opening. If the movement is not fast enough and if the disappearance of the arc is not ensured in a sufficiently short time, the fusion of the contacts is likely to involve their welding, and thus to prevent the final opening of the circuit breaker. The circuit breaker is then not able to take up its duty.

A circuit breaker must thus be dimensioned to be able to carry the current of short-circuit potentially present at its insertion point in a circuit, under the tension potentially present at this same insertion point. The intensity and the tension of this current depend on several factors:

  • capacity of the feeding circuit required a maximum current under a certain tension;
  • the possibility for the circuit (wire, tracks) and supplied equipment, to generate a more or less important current;
  • faculty that with equipment as well as the circuit of feeding with being the seat of a more or less important tension (normal or accidental).
In the contrary case, it will have to be itself protected either by a fuse, or by another circuit breaker presenting a sufficient breaking capacity.

Aptitude for the cutting

In order to carry out the physical separation of the circuits, at the time of intervention or work on the circuit concerned, the circuit breaker must have an aptitude for the cutting. In this case, he will meet the standard NF C 61-410 or chapter 437.2 of the standard NF C 15-100.

A device of judgment (Lock and labels judgment) then allows the blocking of the contacts in open position in order to comply with the rules concerning electric enabling (UTE C 18-510, 520,540).

See too

External bonds

  • ''' Circuit breakers: ''' releases, curves of release, selectivity, filiation
  • differential Devices
  • ''' Fusible and circuit breakers ''' by the site CultureSciences-Physics of the ENS Lyon

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