Fuse out of glass and ceramics

Fuses

It is a protection measure of the electrical circuits. The active part of the fuse is a special alloy wire which, placed in an electrical circuit, shuts off the current while melting if the intensity reaches a certain limit.
Symbol
There are two families of fuses, the rapids which found continuation and delayed or temporised which is a little slower.
Differences to recognise them :
  Fast fuse Delayed fuse
Wire Simple wire Simple or spiral wire
Symbol F T or D
Standard dimensions
For electronics For the house For the car
Generally out of glass Generally out of ceramics FKS
5 X 20 mm 0,1 to 10 have
6,35 X 32 mm 0,5 to 12 have
8,5 X 23 mm 4 to 16 have
8,5 X 31,5 mm 4 to 20 have
10,3 X 25,8 mm 10 to 16 have
10,3 X 38 mm 10 to 32 have
3 to 30 has
Microfuse TR5 Fuse CMS  
 

Alternatives

Automatic thermal fuses by thermal switches : this type of fuse contains a thermal switch which becomes deformed at a temperature given at the time of the passage of a too high current. When the temperature goes down again the contact restored if this fuse is car réarmable, if not a small button is allowed to rearm it manually.


Thermal fuses: these fuses found at a temperature given.

PolySwitch

PolySwitch is a plastic compound charged with carbonaceous particles which, under L ? effect of a fault current, undergoes an increase in temperature involving a separation of these particles and thus increasing the internal resistance of PolySwitch to L ? ’ infinite. It can thus be comparable with a fuse réarmable.

Uses

As it is a protection measure have finds it upstream circuits, afterwards on the level of the transformer on the primary to avoid making trip the line if that is at fault or to protect the transformer if a shortcircuit occurs in the circuit.
If the electronic circuit is fed in 220v with triacs or thyristors which control outputs it is to advise to rather place fuses on each outputs than on the general feeding thus if one of the outputs of power dissolves a fuse have knows continuation of or comes the problem.
To carry out a coherent electric wiring it is necessary that the fuse on the basis of the table principal is of the most important value for then decreasing towards the apparatuses and can support the sum of all the intensities maximum of all the apparatuses which can be connected simultaneously.

Circuit breaker and protection

Classify electric protection

There exist 4 classes of protection:
Classify 0: the apparatus has a functional insulation without earth electrode. The sockets of this equipment do not have a ground pin. The carcass could be put at a dangerous potential for the Man (by a defect of insulation for example) without the defect not being detected before the contact.
Classify 1: the apparatus has a functional insulation with a ground terminal and an equipotential connexion. This equipment has sockets having an earth electrode on which the parts are connected metal.
Classify 2: the apparatus has an insulation reinforced without accessible metal parts. The sockets of the equipment of class 2 do not have a ground pin.
Classify 3: the apparatus functions in very low working stress (TBTS) of 50 volts maximum. The lowering of tension must be carried out using a transformer of security, carrying out a sure galvanic insulation between the primary and the secondary.
symbol of protection classifies 2
symbol of protection classifies 3
The electric class of protection of the equipment must be indicated above using the corresponding symbol.

circuit breaker

A circuit breaker (a circuit breaker is a body electromechanical, even electronic, of protection, whose function is to stop it) is an electromechanical body (electromechanics is the association of technologies of electricity and mechanics.), even electronics, of protection, whose function is to stop the electric current (an electric current is an overall displacement of electric charge carriers (electrons).) in the event of incident on an electrical circuit (an electrical circuit is a simple or complex unit conductors and components electric or electronic). It is able to stop a current of overload or a current 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 fuse is that it is rezettable (it is designed not to undergo any damages during its operation).

Various techniques used by the circuit breakers

Thermics

Thermics is a circuit breaker where whorls of wire heat by Joule effect, if the heating becomes sufficiently important, the thermal switch starts thus stopping the current.
This electromechanical system is rather simple and robust.
On the other hand, it is not very precise and its response time is relatively slow
Thermal protection (thermal protection, in the field of astronautics, is the whole of the devices used to prevent that one) for principal function the protection of the conductors has against the heating due to the prolonged overloads of the installation.

Magnetic

A winding detects the electromagnetic field generated by the current crossing the circuit breaker, when it detects an current surge superior with the instruction, the interruption is "instantaneous" in the case of a reel fast or "controlled" by a fluid in the reel which allows delayed releases. It is generally associated with a switch (a switch (derivative of rupture) is a device or body, physics or virtual, making it possible to stop or) of very high-quality which authorises thousands of operations.
This operation can replace the fuse on short-circuit
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, switch ⁄ circuit breaker for assembly front face, compatible Bi-tension 100 ⁄ 220 Volts, winds under voltage, 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 fuse amndt (protection of the engines). 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 greater accuracy very.

Differential

A differential circuit breaker is a differential switch also carrying out a protection while running of short-circuit (overload).
The principle of a differential device with residual current (GDR) is to compare the intensities on the various conductors which cross it. For example, in single-phase current, it compares the intensity circulating in the conductor of phase and that of the conductor 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 conductor must arise by another. In a single-phase installation, if the current in the conductor of phase at the beginning of an electrical circuit is different from that of the neutral conductor, it is that there is an escape. The difference in intensity of the current to which a circuit breaker reacts is called the "differential sensitivity of the circuit breaker" (obligatorily 30 my on the home terminal circuits), noted I N ("I delta N").
Its operation is very simple: each conductor passes in a magnetic core, thus forming electromagnetic fields of identical force and in opposition which are cancelled. In the event of difference, from where its name of differential, the resulting electromagnetic field actuates a device which shuts off the current immediately.
There exist several classes of differential devices:
Devices of class "AC"
The devices of class "has", are planned for the dedicated circuits, cookers, hotplates to induction, washing machine, whose operation produces residual currents comprising a continuous component. the security 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 are obligatory on the circuits or the hardware of class 1 which is likely to produce the type of phenomenon describes above.
Devices of class "HI". This differential type of 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).

Magnetothermal

Two of the techniques previously described are associated in order to take care on several parameters:
Overload, heating effect, the answer to the abnormal operation 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).
Burst of a circuit breaker
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 manually maintained in closed position
Mechanism related to the lever, separates or approaches the contacts
Contacts allowing the current to pass when they are touched
Connectors
Thermal switch
Screw of calibration, makes it possible to the manufacturer to adjust the instruction of current with precision after assembly
Solenoid
Reducer of arc.

Use

These models are intended to replace the fuses gG (in particular used as a servant), by offering the advantage of being rezettable (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 systems mechanical, 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 authorise 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 transformers or feed at cutting for example). They can also be regulated in order to leave the possibility to another protection located downstream from fulfilling 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 short-circuit.
The cut of a load circuit implies the formation systematically electric arc. 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 fight" 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 feeding it 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.

Electronics

An electronic release can fulfill the functions of the thermal and ⁄ or magnetic releases, that is to say to detect according to the case the currents of overload or the currents of short-circuit to cause the opening of the contacts.
It is always composed of a device of measurement of the current (shunt, or generally transformer of current with iron or air), of a device of electronic processing of measurement (comparison of the current measured with a definite value), and of a device of release (an electromagnet which releases the mechanism of opening).
The advantage of an electronic release is to be able to have a broad range of tuning (of the level of release, time of release), to if required include sophisticated algorithms of detection of fault current, for example by taking of account the derivative of the current, to allow the transmission of the state of the circuit breaker, the measurement of the current, etc. towards an automatism of monitoring of the network.
Its disadvantage is to require a feeding by taking energy necessary:
on the current (apparatus called to "clean running") : a time is necessary after the powering so that the feeding accumulated a sufficient energy to be able to start the opening. These releases can react only one magnetic also quickly.
On the network: a device must prevent the closing of the circuit breaker as long as the feeding by the tension of the network is not assured.
On a separate network which must be protected.
Indeed, a circuit breaker must be able to start as of the appearance of a short-circuit, including that resulting from its own closing

Hydraulics

The trip used in the case of a circuit breaker Magneto-hydraulics or Hydromagnetic is double. On the one hand the already explained magnetic part Ci above, and on the other hand, the hydraulic device. This one replaces the "thermal" part. It thus will make it possible to detect the light overcurrents but long life.
Its advantages are the following :
No thermal inertia: After a release, réeclenchement is immediately possible
Not shift of protection with the ambient temperature: The thermal trips see their gauge varying according to the ambient temperature, contrary to hydraulic technology.
Its principal disadvantage remains its price with respect to thermal technology

Capacity breaking

The breaking capacity of a circuit breaker corresponds to its aptitude to stop a current of short-circuit without destruction and undoubtedly. It is characterised by the maximum intensity of the current which would pass if no circuit breaker stopped it.
The cut of a load circuit implies the systematic formation of an electric arc between the contacts. The current circulates through the arc, which delays the cut, but which generates between the contacts a tension, known as tension of arc, which is opposed to the tension of the network which created it. The current decreases, until cutting itself, as soon as the tension of arc is higher than that of the network, consequence of the equation of the circuit: .
L * (dI ⁄ dt) = Er - Uarc - R * I
A fort running subjects all the conductors to violent electrodynamic forces, which according to the architecture of the apparatus can help it or not to open quickly, to also help the electric arc to lengthen and to join a zone, known as chamber of extinction, where its energy will be well absorbed.
The more important the current is, the more the arc is powerful (produced intensity by tension of arc), the more accumulated energy can be destroying. If the disappearance of the arc is not ensured in a sufficiently short time, the case of the apparatus can not withstand the pressure of overheated gases more, the fusion of the contacts is likely to prevent the rearmament of the apparatus. The circuit breaker would not be then able any more 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 feeding it 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.
classify    
B magnetic threshold of release between 3 and 5 times nominal intensity resistive load
C magnetic threshold of release between 5 and 10 times nominal intensity indictive load
D magnetic threshold of release between 10 and 14 times nominal intensity strongly inductive load
MY magnetic threshold of fixed release has 12 (20% of tolerance)  
K magnetic threshold of release between 10 and 14 times nominal intensity electronic protection of the circuits
S current of command selective delays via a hystétrésis
Z magnetic threshold of release between 2,4 and 3,6 times nominal intensity protection of the semiconductor

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