Fuse
In electricity, a fuse is a device made up of a suitable support and a filament or sheet of a metal or alloy with a low melting point that is inserted at a certain point in an installation so that it melts (due to the Joule effect) when the current intensity exceeds (due to a short circuit or an excess load) a certain value that could endanger the integrity of the installation conductors with the consequent risk of fire or destruction of other elements.
General Information
The electric fuse, initially called an energy and protection device against electrical current overload by fusion, is the oldest protection device against possible failures in electrical circuits, appearing the first bibliographical citations in the year 1774, when which was used to protect capacitors from damage against discharge currents of excessive value. It was during the 1880s that its potential as a protective device for electrical systems, which were just beginning to spread, was recognized. From that moment to the present, the numerous developments and the appearance of new fuse designs have advanced in step with technology, and that is that, despite its apparent simplicity, this device currently has a very high technological level, both in terms of the materials used and the manufacturing methodologies. The fuse coexists with other protective devices, within a framework of very rapid technological changes that make it appear old-fashioned or obsolete, which it is not.
This concept is more easily understood when describing the current field of application, whose nominal parameters have very wide ranges. Working voltages range from a few volts up to 132 kV; rated currents from a few milliamps up to 6 kA, and breaking capacities in some cases as high as 200 kA.
The annual production of fuses exceeds 30 million units. A medium-sized industry may have a few hundred fuses installed and in a modern automobile between 40 and 60 fuses may be in use. Most electronic equipment has at least one fuse. Their sizes can be as small as the head of a wooden match, and at the other extreme, that is, for high-voltage applications with high short-circuit power, there are fuses whose weight is around 20 kilograms.
Worldwide production statistics indicate the constant growth of the market. For some types of fuses, the growth is very high, as is the case of devices for low power electronic circuits and elements for use in automobiles. On the other hand, for traditional fuses (low and medium voltage, and high breaking capacity) a slower growth is estimated, on the order of the growth of electrical systems, which is around 3% per year.
The principle of operation of the fuse is very simple: it is based on inserting a weaker element in the circuit, in such a way that when the current reaches levels that could damage its components, the fuse melts and interrupts the current circulation. The fact that the fuse element or weak link in the circuit melts does not necessarily imply that the current is interrupted, this difference being the key to understanding the technology involved in the apparently simple fuse.
Over the years, fuses have appeared for specific applications, such as protecting lines, motors, power transformers, voltage transformers, capacitors, power semiconductors, insulated conductors (cables), electronic components, printed circuits, integrated circuits etc These very diverse types of fuses have very different selection characteristics, which makes their correct selection complex.
This wide range requires that the user of fuses have a significant level of knowledge, which is not easy to acquire due to the lack of easily accessible information material.
Another important factor must be considered, which is the existence of fuses responding to the standards of various countries. When talking about electrical power distribution systems, high power fuses are used in our environment, basically responding to European standards, but for medium voltage and low power distribution, elements similar to North American standards are used.
European standardization has now practically been unified in the IEC (International Electrotechnical Commission) standards, but in our environment there are still an infinite number of devices installed whose origin comes from times prior to unification. The situation is much worse when reference is made to fuses installed in equipment, whether industrial, household or electronic, since the devices comply with the standards of the country of origin of the equipment.
The range of possibilities of fuses for low voltage equipment is practically unlimited, and it can be said that each country in the world is represented with a fuse. Faced with this situation, replacing the fuse is very difficult to achieve, so it must be replaced by a device with characteristics as similar as possible, which once again requires a good level of knowledge on the part of the user.
History
First stage
The fuse was the last protection device used in electrical systems for more than 210 years, whose development can be divided into seven stages for study. The history of fuses and the first stage of their development begins in the year 1774, at which time the results of extensive research carried out by Narne are published. These experiments consisted of studying the effect of electricity on plants, animals and human volunteers, for which high currents were produced by discharging capacitors (glass bottles covered internally and externally with metal plates), protecting the elements with a low section conductor. Subsequently, articles appeared describing many experiments and explaining some extremely simple applications, such as the protection of telegraph systems, reaching the 1880s.
It must be remembered that at that time they only worked with direct current, so in addition to fusion, the rapid separation of the electrodes had to take place in order to extinguish the electric arc. The first fuse designs were of the open type, so that the conductive element, when it melted, was expelled in the form of drops, with more or less violence depending on the current energy that melted it. The risk of fire and personal injury was very high, so the fusible element began to be introduced in glass tubes with both ends open, reducing the aforementioned risks, without completely nullifying them. This type of fuse could not cover the ends of the tube, since the result when it operated at high currents was its explosion.
In the year 1880, more precisely on May 4, Edison files the first patent on fuses, with the number 227226, which takes place in the United States, in which it is indicated that the fuse is the element weak of the circuit, since the presence of dangerous overcurrents for the circuit would cause it to melt and cut off the circulation of current. At that time, the main application was in the protection of expensive electric lamps, which were damaged by overcurrent and surges that were generated in the poverty of the voltage regulators used at that time. The first closed fuse was patented by W. M. Mordey in England in the year 1890.
Following the first patents, countless designs can be found introducing extremely ingenious ideas, many of them in the direction of allowing the fuse to be reusable, that is, it should not be discarded after having operated.
At that time it was understood that one of the keys to using the fuse lay in its high reliability, an element that is seriously impaired with the necessary additions to allow the fuse to be reusable. From time to time, even today, new ideas arise to achieve this goal, but their applicability is low or non-existent, therefore, the fuse element is still disposable or single operation.
Second stage
It can be considered that the second stage begins in the year 1906, with the publication of the book by the German researcher Meyer, in which an analysis of the fusion process is presented, much more scientific than in previous articles. During this stage, the researchers dedicated their efforts mainly to the prediction of the relationship between the material and dimensions of the fusible element with the time taken for it to reach fusion. You begin to understand the thermal behavior of the fuse, axial and radial conduction, the effect of the terminals, etc. At that time, the main working parameter of the fuse was defined for that time, the minimum melting current. This publication presents the so-called Meyer constant, a value that allows determining the melting time of a fuse by the current density that passes through it and depending on the material used, under adiabatic conditions (without heat exchange). In analytical form, Meyer's constant is the value of the integral of the squared current density, which stores in the element a quantity of heat sufficient to cause fusion, an integral that received the name of specific energy.
The idea at that stage of development was that if the element reached fusion, it would eventually interrupt the overcurrent. Soon it was recognized that meeting the first requirement did not always mean meeting the second. At that stage, the energies released by the electrical systems in case of faults began to exceed the capacity of the fuse for its interruption, so the explosion of the fuse began to be common. The low level of knowledge at the time about the interruption process did not allow us to recognize where the problem lay. It was normal to find in the instruction manuals on the handling of fuses, indications that today seem ridiculous, such as that
"the operator had to approach the side fuse to reduce the profile exposed to the explosion, with the left arm covered with a leather sleeve, which had to move up to cover the eyes and just operate with the right hand enguantada", or that "the operator can only operate fusible when accompanied by another worker."
At this stage of development, the electrical systems began to migrate from direct current to alternating current, for which reason distribution lines of significant length are built and the working voltage begins to rise, already having systems with a few tens of kilovolts. At that stage of development, open fuses were available, capable of operating from a few volts to 70 kV, receiving the name expulsion fuse, possessing very little current interruption capacity.
High voltage devices were installed in solitary places and at high points on the pole, to reduce the risk of damage from ejected elements. This meant that fuses in those voltages could only be used for very low currents, relegating them to low power and rural distribution systems.
For the protection and operation of these higher voltage systems, there were switches based on oil extinction, giving rise to the idea of using a combination of switch in oil and fuse, called liquid or oil fuse. The fuse element, tensioned by a spring, is found inside the fuse, which is weakened by the temperature reached, the spring cuts it and moves it, lengthening the electric arc that goes out in oil. This device, in use for several years, allowed interrupting powers much higher than those of expulsion.
The wide variety of commercially available designs and the differences in design and application criteria led to the need to standardize, at which point work begins on specific standards in order to to ensure uniformity and interchangeability between manufacturers. Fuse standards are approved in North America, Germany and England, which were the countries that led the development.
The idea of placing the fuse element immersed in filler material was explored, testing the following substances: chalk, marble, ground brick, sand, mica, carborudurm and asbestos, without reaching conclusive results.
Third stage
The third stage is considered to begin with the birth of the device called Power fuse or fuse with filled outer material, which was introduced by German researchers during the 1940s. During that stage, extensive studies were carried out on the phenomenon of extinction of the electric arc and the influence of the filling, determining that the best extinguishing element was and still is today, quartz sand. The idea of using quartz sand stems from its already widespread use for putting out fires.
Fourth stage
This was followed by the fourth stage called the dark era of the fuse, which was the period in which World War II broke out. At this stage, there was a rapid increase in the fault energies of the already important electrical systems, which exceeded in a very short time the pending developments to supply the fuse with the breaking capacity to handle them. Furthermore, at the same time the magneto-thermal automatic switch was introduced, which as a competitor seriously threatened the at that time backward fuse. This situation continued until approximately 1945, that is, until the end of the Second World War, at which time new and ingenious fuse designs began to appear, with an important variety in different types and applications.
Fifth stage
The introduction of important innovations to improve the behavior of the fuse marked the beginning of the fifth stage. Such innovations are, fundamentally: the addition of the so-called effect, the use of a fusible element with distributed section reductions, the use of extinguishing material as filler, etc. Such features again put the fuse in a position to compete with the newcomer circuit breaker, surpassing the fuse in breaking capacity and reliability. The high breaking capacity fuse reached voltage levels of the order of 60 kV, thereby entering the field that until then was almost exclusively for switches. From that moment until today, the fuse is the device with the greatest volumetric capacity in fault energy management, which is achieved with rapid intervention, phenomena called limitation, which means that the fuse cancels the current without waiting for its natural passage through zero.
This period coincided with the great global expansion that followed the end of the war, growing the size and demand of electrical systems, giving rise to the birth of large fuse manufacturing companies, mainly in Europe and North America.
Sixth stage
The sixth stage originated with the introduction of the solid-state semiconductor, which took place in the early 1950s, although newly powerful semiconductors saw the light of day during the 1970s. Power semiconductors They have completely different operating characteristics from electrical systems. This difference is based, fundamentally, on its high energy density under nominal operating conditions and its reduced thermal capacity. In other words, power semiconductors handled high energy values in a very small volume, but had a very low capacity to withstand short-circuit overcurrents. These characteristics required a new type of protective devices.
The fuse is far superior to the other protective devices for this task, a function that is still leading today. The adaptation of the traditional fuse to fulfill this new function was not quickly achieved, since initially the pre-existing fuse manufacturers were not able to develop the appropriate fuse. Faced with this difficulty, power semiconductor factories created their own divisions to develop fuses specific to their semiconductors. However, in a short space of time, fuse manufacturers were able to understand the requirements of the semiconductor, harmonizing parameters and characteristics, taking charge of their manufacture. The fuse factories belonging to the semiconductor manufacturers were slowly disappearing, as the experts took the business back into their own hands.
From that time, until about the 1990s, the speed of fuse development slowed greatly, primarily due to the strong position of these devices in electrical systems. In that period, there was no outstanding innovation in fuse development, other than the ability to perform much more precise analytical studies using the power of computers and analysis techniques such as finite element, finite difference, Transmission Line Network, etc. Such analytical studies allowed a better understanding of the operation and facilitated the optimization of the dimensions and materials used in the devices. In addition, the extremely aggressive commercial policy and often with little technical foundation of the manufacturers of low voltage thermo-magnetic switches, which are presented as the panacea for protection devices, should not be forgotten.
Seventh stage
In the 1990s, the seventh stage of fuse development began, which can be considered as generated by the so-called Slim Fuse. One of the most difficult fields of application for fuses is for currents low nominal currents, from the order of fractions of amperes to no more than 10 A. To operate adequately with these nominal currents, the fuse element must have such small dimensions that it becomes unmanageable in assembly, from a mechanical point of view. Thus, the so-called Substrate Fuse appears, which consists of the conductive material deposited on an insulating plate, similar to the printed circuits widely developed for the assembly of electronic devices. Various deposition techniques for conductive material are used, such as photographic and acid etching used in printed circuits, vacuum deposition used in plating non-conductive materials, permeable mask applied in labeling, etc. Alumina, silicon, mica, etc. are used as substrate. Currently, fuses of even smaller dimensions are being developed, called lithographic fuses, since they are obtained by the well-known offset method, using a very thin and flexible substrate. The need for low-size fuses is increasing, due to the miniaturization of electronics, being able to affirm that each modern electronic equipment currently has one or more fuses, such as mobile phones, digital cameras, camcorders, etc.. Another field of very high current development is automotive fuses, due to the increasing addition of electronics and electricity in the automobile. This one, fully electric or simply hybrid, contains many electrical circuits and with them a large number of fuses. The next development that is expected of fuses, which would give rise to the next stage, is the addition of capacity or ability to make decisions or adapt, which would cause its operation to be modified by working conditions regardless of the magnitude of the current.. Thus giving rise to the so-called smart fuse, of which some still incipient advances are already being produced and highly protected due to their possibilities of being patented.
Definitions
- Characteristics: General terms to designate each of the characteristic quantities that define the operating conditions for which the device has been designed and from which the testing conditions are determined.
- Suspected current of a circuit: Current that would flow in a circuit if the cutter was replaced by a despicable impedance foil, without any other way or in the circuit or in the source.
- Suspected current of rupture: The alleged current corresponding to the moment of initiation of the arc during the rupture operation.
- Breaking capacity: An alleged current of rupture that a fuse is capable of interrupting under the prescribed conditions.
- Limit rupture current The instant maximum value reached by the current during the operation of the fuse rupture, when it operates in the form of preventing the current from reaching the maximum value to which it would arrive in the absence of the circuit.
- Pre-arc time: Lapso between the beginning of the circulation of a sufficient current to melt the fuse elements and the moment the arch begins.
- Operating time: Add the pre-arc time and the arc time.
- Integral de Joule (I2 t): The integral of the square of the alleged current of rupture.
- Virtual time: I2 t divided by the square of the alleged current of rupture.
- Restoration voltage: Tension that appears between terminals of a short circuit after the rupture of the current.
- Breakdown voltage: Maximum value of the tension, expressed in crest value, which appears between the terminals of the circuit during the operation of the fuse.
Classification
The fuses can be classified using various construction or operating characteristics, and there are numerous antecedents with different criteria. For example, if they are divided on the basis of their property of being reusable, they can be classified as:
- Dismissable, It is not possible to reuse them once they act, they must be replaced.
- Renewable, can be reused more than once without the need to replace them (e.g. TE Connectivity reset fuses: PolySwitch).
- Smart, only unused portion is reused.
Types of fuses
They can be classified according to their size and according to their class of service.
Depending on the format
- Cylindrical cartridges:
- Type CI00, 8.5 × 31.5 mm, for fuse from 1 to 25 A.
- Type CI0, 10 × 38 mm, for fuse from 2 to 32 A.
- Type CI1, 14 × 51 mm, for fuse from 4 to 40 A.
- Type CI2, of 22 × 58 mm, for fuse from 10 to 100 A.
- Fusible type D:
- Size of 25 A, for fuse from 2 to 25 A.
- Size 63 A, for fuse 35 and 50 A.
- Size of 100 A, for fuse of 80 and 100 A.
- Fusible type D0:
- Type D01, for fuse from 2 to 16 A.
- Type D02, for fuse from 2 to 63 A.
- Type D03, for fuse of 80 and 100 A.
- Fusible D02, 63 A.
- Fusible type of blades or also called high rupture NH (APR):
- Type CU0, for fuse from 50 to 1250 A.
- Type CU1, for fuses from 160 to 250 A.
- Type CU2, for fuses from 250 to 400 A.
- Type CU3, for fuses from 500 and 630 A.
- Type CU4, for fuse from 800 to 1250 A.
Another name of the blade fuse or NH:
- Size 00 (000), 35 to 100 A
- Size 0 (00), 35 to 160 A
- Size 1, 80 to 250 A
- Size 2, 125 to 400 A
- Size 3, 315 to 630 A
- Size 4, 500 to 1000 A
- Size 4a, 500 to 1250 A
According to the class of service
Regarding the class of service, the fuses are designated by two letters; the first tells us the function it is going to perform, the second the object to be protected:
First letter. Function.
- Category “g” (general purpose) fuses of general use.
- Category (a)accompanied fuses) accompaniment fuse.
Second letter. object to protect
- Object “I”: Cables and drivers.
- Object “M”: Connection fittings.
- Object “R”: Semiconductors.
- Object “B”: Mining facilities.
- “Tr” Object: Transformers.
The combination of both letters gives us multiple types of fuses, but I will only put the most common or used:
- Type gF: Quick fusion fuse. Protects against overloads and short circuits.
- Type gT: Slow fusion fuse. Protects against sustained overloads and short circuits.
- Type gB: Fuses for the protection of very long lines.
- AD type: Fuses accompaniment of disjunctor.
- Type gG/gL: Standard CEI 269-1, 2, 2-1. It is a limiting cartridge of the current used mainly in the protection of circuits without important current tips, such as lighting circuits, heating, etc.
- Type gI: Fusible for general use. It protects against overloads and short circuits, usually used for the protection of lines although it could be used in the protection of motors.
- Type gR: Semiconductors.
- Type gII: General use fuse with delayed melting time.
- Type aM: Engine accompaniment fuses, that is, for protection of motors against short circuits and therefore the engine against overloads should be protected with a device such as the thermal relay.
In general, when a fuse blows for whatever reason, the rest of the fuses that have not blown have very possibly lost their factory characteristics when they are crossed by currents and voltages that are not nominal, that is why in In a three-phase system, when one fuse blows, the correct thing to do is to change all three, as in a single-phase system, the correct thing to do is to change both fuses when one of them has blown.
NH fuse with its extraction handle.
When changing NH fuses, always use the handle and DO NOT use universal pliers to remove these fuses, especially with voltage.
The blade or cartridge fuses can have a striker and/or fuse indicator, the striker is a mechanical device that works when the fuse melts, it moves a striker that generally actuates a contact that signals the melting of the fuse and /or trigger an alarm.
Fuse used in railway installations. The red dot seen above is the striker that would protrude if it melted. The contact that activates the blown fuse signal would be located on top of this striker. Photo traveler.
The fuse indicator is a kind of circle that jumps when the fuse has blown, the color indicates the amperage according to the following table:
- Rose = 2 A
- Brown = 4 A
- Green = 6 A
- Red = 10 A
- Black = 13 A
- Grey = 16 A
- Blue = 20 A
- Yellow = 25 A
- Black = 32, 35 or 40 A
- White = 50 A
- Copper = 63 A
- Silver = 80 A
- Red = 100 A
There are many types of fuses, let's review the most important ones:
- Glass cylindrical fuses that are usually used as protectors in receptors such as appliances, radios, power supplies, fire detectors, etc.
- Fusible glass. When these fuses are changed they should be replaced by another of the same characteristics, not only should you look at the tension and amperage that you support should also take into account the letter that you carry before the amperage because according to the letter (F, FF, T, etc.) the fuse is more or less rapid in its merger. Example: if we replace a T or TT-type fuse with an equal but faster opening (F or FF), the result will normally be the immediate fusion at the time of the energizing of the equipment that incorporates the fuse, without any leakage.
Table glass fuses. Letters indicating the melting behavior of the fuse.
The IEC 60127 norm or standard indicates five types of fuses, depending on the time/current characteristic, defining each type according to the time required to cut ten times the rated current:
FF = (Fast, fast) very fast. Action time less than 1 mS
F = (Fast) fast. Actuation time between 1 and 10 mS
M= average delay
T= retarded (Slow Blow). Actuation time between 10 and 100 mS
TT= ultra retarded or very slow. Actuation time between 100 mS and 1 second
- Fuel for vehicles. In the vehicle fuses is usually indicated in the car's entertainment manual which are the amperages that should go on each circuit despite the amperage is indicated by a color code:
- Brown = 5 A
- Red = 10 A
- Blue = 15 A
- Yellow = 20 A
- Colorless = 25 A
- Green = 30 A
- Fuses for semiconductors.
- Exhaustion fuse for high voltage.
- Different representations of fuse according to various rules.
- HH fuses high rupture power (APR) for high voltage.
- Fusible 10 A plane for Metrópoli model, although still installed it tends to replace it. Photo viatger.
- Various types of fuse used in railway facilities. Photo viatger.