There are two fuses. Selection of fuses and current fuse links

A fuse is a single-use power electronics component that performs a protective function. The fuse is the weakest section of the protected electrical circuit, tripping in emergency mode, thereby breaking the circuit and preventing subsequent destruction of more valuable elements of the electrical circuit high temperature caused by excessive current values.

In an electrical circuit, a fuse is a weak section of the electrical circuit that burns in emergency mode, thereby breaking the circuit and preventing subsequent destruction by high temperature.

Fuses are divided into the following types:

1. low current inserts(to protect small electrical appliances up to 6 amperes)

• 3x15 (the first number means the outer diameter, the second - the length of the insert)
• 10x30

2. fork(to protect electrical circuits of cars)

• miniature
• regular fork

3. cork(found in residential areas, up to 63 amperes)

• DIAZED (most common in the USSR)
• NEOZED

4. knife(up to 1250 amperes)

• size 000 (up to 100 amperes)
• size 00 (up to 160 amperes)
• size 0 (up to 250 amperes)
• size 1 (up to 355 amperes)
• size 2 (up to 500 amperes)
• size 3 (up to 800 amperes)
• size 4a (up to 1250 amperes)

5. quartz

6. gas generating

Fuses also differ in their response characteristics relative to the rated current. Due to the inertia of fuses, in the professional environment of electricians they are often used as selective protection in conjunction with circuit breakers. Selectivity between the fuse links themselves is achieved with a ratio of 1:1.6 [ibid.], the time-current characteristic of the fuses is established by the dependence, respectively, I²t; The PUE regulates the protection of overhead conductive lines so that the fuse trips within 15 seconds (the short circuit current at the end of the line must be equal to three rated currents of the fuse). An essential value is the time during which the conductor is destroyed when the set current is exceeded. To reduce this time, some fuses contain a pretension spring. This spring also separates the ends of the broken conductor, preventing an arc from occurring.

40-amp fuses with a "gG" response characteristic, equivalent to the Soviet "PPN" characteristic

• fuse link - an element containing a discontinuous part of an electrical circuit (for example, a wire that burns out when a certain current level is exceeded)
• mechanism for attaching the fuse link to the contacts that ensure the fuse is turned on electrical circuit and installation of the fuse in general.

Fuse housings are usually made of high-strength grades of special ceramics (porcelain, soapstone or corundum-mullite ceramics). For fuse housings with low rated currents, special glass is used. The fuse body usually serves as a base part on which a fuse element with fuse contacts, an operation indicator, free contacts, devices for operating the fuse and a rating plate are mounted. At the same time, the housing performs the functions of an electric arc extinguishing chamber.

Fuse markings

The first letter means the protection range:

• a - partial range (short-circuit protection only)
• g - full range (protection from both short circuit currents and overload)
• h - high breaking ability (tubes are made of white or gray ceramics)

The second letter indicates the type of equipment being protected:

• G - universal fuse for protecting various types of equipment: cables, electric motors, transformers
• L - protection of cables and distribution devices
• B - protection of mining equipment
• F - protection of low-power circuits
• M - protection of electric motor circuits and disconnecting devices
• R - semiconductor protection
• S - fast combustion in case of short circuit and average combustion time in case of overload
• Tr - transformer protection

Fuses are used everywhere and everywhere - they are in technology, in a wide variety of electrical devices, cars, and industrial equipment. There are many types of these elements. Why are they needed and what are their features? Let's look at the main types of fuses.

Characteristic

Fuse is a general term that is used quite consistently in the electrical field. This part provides protection for wires, equipment and electrical networks.

The fuse is a switching product. What is its purpose? The fuse is designed to protect the electrical network from high currents and short circuits. The principle of operation of the part is very simple - in the event of the formation of overcurrents, an element specially designed for this purpose is destroyed. Often this is a fusible link. This is how all types of glass fuses are designed.

These inserts are required element, without which not a single type of safety element is possible. There is also a special arc extinguishing device inside it. Fuse inserts are made of porcelain or fiber casings and fixed into special parts that conduct electric current. Elements designed for low currents may not have a housing at all.

Melting

These are the most common types of fuses for household use. This is probably the only element that is easiest to diagnose for serviceability. To do this, you just need to look at the part in the light - you will see whether the insert melt is intact or not.

These parts are manufactured in a glass case.

Fusible Tubular Ceramic

This element is practically no different from a glass product. The only difference is the material from which the case is made. But these parts are not so comfortable to use - they can no longer be diagnosed “in the light”. To check, you must use testers or multimeters.

PVD fuse link

Fast acting fuses

These products are no different from the rest. The only difference is that when a short circuit occurs, the fusible part burns out very quickly.

SMD

These products can be found in electronic devices. They are very miniature. The principle of operation and purpose of fuses is to protect equipment from high currents, which they do an excellent job of.

Self-healing

These are quite interesting solutions. A self-resetting fuse is a part containing special plastic inside. As long as the plastic insert is cold, it can conduct electricity. As soon as the insert warms up to a certain temperature, its conductive properties are lost due to an increase in resistance.

After cooling, current will again be able to pass through the product. The advantage of these parts is that after a burnout there is no need to replace the element. The industry produces these products in various forms. They are suitable for soldering using surface or surface mount technology. These types of fuses are mainly used in low-power circuits.

Explosive

If everyone knows all of the above products, then the explosive fuse is a rare group. The process of burning out a part is ensured by a fairly impressive sound. A special one that is attached to a conductive part explodes. Special sensors are responsible for this. The latter monitor the current in the electrical circuit. These are very precise fuses, since they are practically independent of the characteristics of the metal on the conductive part. This element depends on the accuracy of the current sensor.

Other types of fuses

To work in circuits, special autogas, gas products, as well as liquid-type elements are used. There are even firing fuses. You cannot see them in everyday life - they are professional, powerful equipment.

Markings and symbols

Each manufacturer produces fuses under a specific code or article number. The fuse number allows you to find and clarify in catalogs specifications. Often these codes can be found on product bodies. The code can also be applied to the metal part. In addition to codes, basic data can also be indicated on the case - this is the rated current in A, rated voltage in V, disconnecting characteristics or design features. Using this data, you can determine the purpose of the fuses.

So, the rated current is the maximum permissible value at which the part can function normally for a long time.

Rated voltages are the maximum permissible voltage, in which the part safely breaks the circuit in the event of a short circuit or overload in the network.

The breaking capacity is called maximum currents. With them, the fuse will work, but its housing will not be destroyed.

Characteristics are the dependence of the time at which the fusible element collapses on the current that flows through the part. Different types of fuses according to their characteristics are grouped into groups according to their application features and response speed.

Typically these characteristics are indicated on power parts. Letters of the Latin alphabet are used for designation. The first is the breaking capacity. So, G is the full range, the part is capable of protecting the circuit from both overload and short circuit. A - the range is partial, and these types of fuses only protect against short circuits.

The second letter denotes the types of chain:

• G - general purpose circuit.
• L - protection of cables and distribution systems.
• M - protection of circuits in electric motors.
• Tr is a fuse capable of protecting a transformer network.

Items with the letter R are used in conjunction with power semiconductor equipment. And PV will be able to provide protection for solar panels.

So, we looked at what types of fuses there are and what markings they have.

–This is an element of an electrical circuit, the main purpose of which is to protect it from damage..

Operating principle

The fuse is designed in such a way that it burns out before other elements are damaged. After all, it is easier to insert a new fuse than to replace wires, microcircuits and other elements that can burn out when there is a surge in current in the circuit.

A fuse is called a fuse because it is based on a fuse link. This fuse link consists of an alloy that has low temperature melting and when a current dangerous for the circuit occurs, the amount of heat that is released when such a current flows through this insert is enough to melt it. When the insert melts - “burns out”, the circuit is open.

The reasons for a blown fuse can be short circuit, overload and sudden surges in current.

Not only does the fuse protect the circuit from damage, but it also serves as protection against fires and fires, since the fuse link burns out in the fuse body, unlike the wire, which may come into contact with flammable materials during combustion.

It happens that people make the so-called bug. Usually this is an ordinary piece of wire that is inserted in place of the fuse. This is done because there is no fuse of the required rating at hand or to bypass the protection. Often, such bugs lead to fires, since it is not known at what current such a bug will burn out or whether it will burn out at all.

Fuse device

As mentioned above, the simplest fuse consists of its main part - a fuse link (wire) and a housing, which is intended to be connected to the electrical circuit and serves as a fastener for the insertion.

Advantages and disadvantages

The advantages of fuses include their relatively low cost.

The main disadvantage of a fuse is that it takes a relatively long time to operate compared to automatic fuses. During the time a fuse blows in high-voltage networks, equipment may fail. In addition, a fuse is a disposable element, that is, once it burns out, it cannot be used for further use, while automatic fuses can serve for quite a long time, since the principle of their operation is based on opening the circuit without damaging the structure of the fuse itself.

Main settings

The parameters that characterize a fuse are rated current, rated voltage, power, response speed.

Where U– network voltage, and Pmax– maximum load power with a margin of about 20%.

The speed at which fuses operate varies. For example, in circuits where there are semiconductor devices, it is better if the fuse burns out faster so as not to damage the devices, but if it is a powerful fuse that is used in the electric motor circuit, then it will be much more useful if it does not break the circuit every time at the moment of inrush currents.

A fuse is an electrical switching device that is used to disconnect a protected circuit. Its purpose is to protect the electrical network and electrical equipment from short circuits and significant overloads. The main parameters of the products are the rated and maximum switchable current, as well as the rated voltage. In this article we will take a detailed look at fuses: their purpose, types, design and principle of operation.

How does the device work?

The fuse operates in two modes, which differ significantly from each other.

1. Normal network mode. In this mode, the device heats up as a steady process. At the same time, it is completely heated to a certain temperature and releases the generated heat into environment. The so-called rated current strength is indicated on each element (as a rule, it is indicated highest value current of the structural element). The fuse can accommodate a fuse element of different rated current.
2. Short circuit mode and . The device is designed in such a way that if the current in the network increases, it could burn out in the shortest possible time. To do this, the fusible element in certain areas is made with a smaller cross-section, where more heat is released than in wide areas. When almost all or completely all narrowed areas burn out. When an element melts, an electric arc is created around it, which is extinguished in the mechanism’s socket.

The current strength must be indicated on the device body, and the maximum permitted voltage at which the device will not fail must also be taken into account.

The graph below shows the dependence of the burnout time of the fuse element on the current:

Where l10 is the current at which the element melts and is disconnected from the network in 10 s.

Varieties and types of elements

Fuses are divided into two types: low voltage and high voltage. This division is explained by the voltage value of the working electrical network in which the fuse is used.

Low-voltage devices are labeled as PN or PR and are designed for voltages up to 1000 V. In low-voltage PN devices, there is a fine-grained filler around the copper insert. Their use is designed up to 630 Amperes.

The PR device is simpler (pictured below) than the PN, but in the event of a short circuit, they are also capable of extinguishing an electric arc. Designed for currents from 15 to 60 Amps.

By design features fuses are divided into cartridge, plug, plastic and tubular. Depending on the type of execution, collapsible and non-dismountable products are produced. Collapsible ones have the ability to access the insert. The structure is disassembled and the burnt insert is replaced with a new one. Non-separable ones are constructed from a glass bulb, therefore they are considered disposable and the inserts cannot be replaced.

Design

A modern fuse consists of two parts:

• a base made of electrical insulating material with metal threads (necessary for connection to an electrical circuit);
• replaceable insert that melts.

The basis of the device is an insert that burns or melts during a short circuit. In order to extinguish the arc that is formed as a result of the burnout of the replaceable insert, arc extinguishing devices are installed.

The terminals of the insert are connected to the terminals in such a way that the fuse is connected to the electrical circuit line. For this purpose, special reliable fastening terminals (holders) are used, which must ensure good contact. If it is not there, then heating may occur in this place.

A design feature of fuses is that the device burns out before other parts of the mechanism are damaged. After all, it is easier to replace than a microcircuit or other hardware component. Therefore, such a part is selected so that its melting rate is greater than in the line wires. Their temperature should not reach dangerous levels, as this will lead to equipment failure.

The design of the plug-type mechanism has the form of a cartridge into which a fuse with a base is screwed. When an emergency occurs, the plug burns out. Today this plug looks like a button, similar to a regular switch. This button returns the device to working condition after an accident.

In addition to the fact that the fusible component protects the electrical circuit from damage, it also protects against fires and fires. After all, an ordinary wire can come into contact with flammable materials at the moment of fire, and the part burns inside the device body.

The device ratings are selected based on the lowest calculated currents of the electrical network or a separate part of the electrical circuit. The table of denominations is provided below:

If it is necessary to replace such a component with AB (circuit breakers), then their rating should be one step greater than the component part. For example:

We talked about this in the corresponding article.

A fuse is an electrical element that performs a protective function. Unlike a circuit breaker, after each operation it needs to replace the circuit-breaking part. Fuse link that burns out when exceeded permissible value rated current must be selected taking into account the load on the network.

Operating principle and purpose of fuses

Inside the fuse insert there is a conductor made of pure metal (copper, zinc, etc.) or alloy (steel). Circuit protection is based on physical property metals heat up when current passes. Many alloys also have a positive coefficient of thermal resistance. Its effect is as follows:

• when the current is below the rated value provided for the conductor, the metal heats up evenly, managing to dissipate heat, and does not overheat;
• too much current leads to strong heating, and an increase in the temperature of the metal causes an increase in its resistance;
• Due to the increased resistance, the conductor heats up even more intensely, and when the melting point is exceeded, it is destroyed.

The fusing of the insert placed in the electrical fuse is based on this property. Depending on the scope of application, the shape and cross-section of the conductor can be different: from thin wire to household and automotive devices up to thick plates designed for a current of several thousand amperes (A).

The compact part protects the electrical circuit from overload and short circuit. If the permissible current for the network (i.e., rated) current is exceeded, the insert is destroyed and the circuit breaks. Its operation can be restored only after replacing the element. When there is a defect in the connected equipment, the fuses will blow immediately after the faulty device is turned on, allowing the cause to be determined. If it happened on the network short circuit, the protective device operates in the same way.

Conventional graphic symbol on the diagram

According to Unified system design documentation of Russia, on graphic diagrams In electrical circuits, fuses are designated by a rectangle with a straight line running inside it. Its ends are connected to 2 parts of the circuit before and after the protective device.

In the documentation for imported devices you can find other designations:

• rectangle with separated parts at the ends (IEC standard);
• wavy line (IEEE/ANSI).

Types and types of fuses

For use in electrical circuits use different types and varieties of PP. Products manufactured in Russia differ in type of design:

The concept of fullness is associated with the presence inside certain types of inserts of a substance that extinguishes the electric arc that occurs at the moment the conductor burns out. The circuit will be opened only after it disappears. Therefore, flasks filled with PP contain quartz sand. Unfilled ones can release gases that extinguish the arc. This occurs when the material of the insert body is heated.

In addition to types, there are different types of PP:

1. Low-current ones are used in low-power household appliances with a current consumption of up to 6 A. These are cylindrical inserts with contacts at the ends.
2. Fork-mounted PCBs are often installed in cars. The name is due appearance: The contacts are on one side of the housing and are inserted into the connectors, like a plug into a socket.
3. Plug plugs are common electrical plugs for the meter in single-phase networks. The rated current of such inserts is 63 A; they are designed for simultaneous activation of several household appliances. The blown insert in such a fuse is located inside a ceramic housing with a cartridge; 1 contact remains outside, and the other is connected to the contacts of the plug. If the load is exceeded, the part burns out, completely cutting off power to the apartment. The power supply can be restored by replacing the insert with a new one.
4. The structure of the tubular PP resembles an insert for plugs, but its fastening is made between 2 contacts. The type of such fuse is unfilled, and the body is made of fiber, which releases gas when heated strongly.
5. Blade fuses are designed for a current value of 100-1250 A and are used in networks where a high load is needed (for example, when connecting a device with a powerful motor).
6. Quartz, filled with quartz sand, are used in networks with voltages up to 36 kV.
7. Gas-generating, collapsible and non-dismountable. When varieties of PSN and PVT are burned, a powerful release of gas occurs, accompanied by popping. PP is used for networks with voltage 35-110 kV. The rated current of such a PP is up to 100A.

Depending on the total load on the network, set different types PP - more powerful ones are installed in special transformer booths; they can withstand the current that meets the needs of a residential area or enterprise. Low-power ones are installed in meters: they protect individual apartments. Old household appliances can also have a PP (low-current) installed, but modern appliances rarely contain these elements.

Selecting a fuse link

The selection of fuses is made taking into account their ratings, time-current characteristics and the total load on the network (the total power of all operating elements). The rated current of a PP is the one that the fuse link can withstand before destruction. This value is indicated on its body (for example, marking 63 A for cork household fuses).

Time-current characteristics are calculated using special graphs. They must be taken into account only when connecting an electric motor to the network, the starting current of which exceeds the operating voltage several times. When using several such devices (in an enterprise), the starting torque of the most powerful engine is calculated.

The total (maximum) load power of the network is the sum of all operating currents of the devices (indicated in the instructions and on the case). If an electric motor is connected to the network, then its starting torque is also taken into account, divided by the coefficient k = 2.5 (for easy starting and squirrel-cage rotors) or 2-1.6 (for hard-starting or phase-wound rotors).

In order not to waste time on calculations, select the rated current of the fuse link according to the table.

Calculation of fuse wire diameter

Complex calculations are made in order to temporarily repair a burnt insert if it is not possible to replace it. In order for the network to be protected from overload, the thickness of the wire used to install the “bug” must correspond to the rating of the destroyed insert. For the network of a city apartment, where a 63 A PP is installed, you can use copper wire with a diameter of 0.9 mm.

If repair of another protective device is required, then you need to determine the rating of the PP (indicated on the housing), and then determine the compliance of the existing copper wire:

• measure its diameter;
• cube this number and take the square root of the value;
• multiply the resulting figure by 80.

The result should be approximately equal to the PP rating indicated on the case.

During repairs, the selected wire is wound around the contacts of the burnt insert, connecting them. The bug is inserted into the socket on the fuse body.

If the wire melts again, it means that the fault is in the protected device or in the apartment’s network, and they must be repaired. You cannot use thicker wire, as this may cause a fire.

Functionality check

Modern car fuses sometimes have a built-in blown indicator. He tells the owner that the part needs to be replaced. In low-current PCBs, the wire is visible through the transparent body. But part of the software is opaque and has no indicators.

If it is impossible to visually determine a conductor break inside the PCB, then its performance can be determined with a multimeter. Before checking the fuse with a tester, you need to select the minimum resistance value (Ohm). Apply the tester probes to the contacts of the PP and determine the readings of the device:

• when the resistance value is zero or close to 0, a conclusion is drawn about the operability of the insert;
• if the tester shows 1 or an infinity sign, then the PP has burned out.

If the tester has a sound device, you can simply ring the fuse by applying probes to the contacts. The squeak of the tester indicates the serviceability of the element.