What are the questions about circuit breakers, fuse matching?

It is mainly to consider the relationship between the upper and lower levels, and the rated current of the upper level must be greater than the rated current of the lower level to prevent the action of skipping the level. Circuit breakers and fuses are generally not directly matched together, since there is a circuit breaker, do not use a fuse.

The fuse is activated for protection, and when there is an overload or short circuit, the fuse core in the fuse will burn out to protect the load at the rear end. The circuit breaker trips.

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to find the answer you want.

The fuse is used in conjunction with the circuit breaker, and the fuse is in front of the circuit breaker.

When the circuit breaker segmentation capacity is insufficient, a fuse needs to be added. Now most of the segmentation capacity can be satisfied, mainly considering the current limit, if there is an electronic load and need power switching, you can use the fuse plus circuit breaker scheme. However, at the same time, from a safety point of view, the front of the circuit breaker does need to be equipped with a fuse.

There must be an obvious visual disconnect point on the line for power outage maintenance to ensure the safety of maintenance personnel, and the circuit breaker cannot be used as an obvious disconnection point. Therefore, a fuse or knife switch should be installed in front of the circuit breaker to isolate the power supply during maintenance. At the same time, this can also be regarded as a problem of voltage level, whether it is 10kV or higher level substation or power plant in the general power sector, it is impossible to set a high-voltage fuse in the primary main circuit, and generally set a fuse in the voltage transformer of the protection and measurement circuit or the high-voltage primary circuit of the transformer.

Therefore, whether it is a high-voltage user or a low-voltage user, if it is set, it will increase unnecessary trouble (that is, there is one more point that causes failure), if there is still a poor phase contact, or a certain phase fuse will bring losses to the user (the motor of the lack of phase will burn out), the equipment of the first business provider of the circuit breaker can fully meet the protection action in the abnormal state such as short circuit, low voltage, overload - tripping! If it is a low-voltage user, it is not necessary to consider what main fuse to install on the low-voltage side of the transformer, because the fall insurance (actually a fuse) has been installed on the high-voltage side of the transformer.

The fuse and circuit breaker are both loop protection elements, one is fine, two are not necessary to use in series, and the two protections are also difficult to match. If it must be used in series, the fuse should be installed in the front, because most of the fuses have a certain breaking short-circuit current limiting function, which can protect the circuit breaker in the back from being hit by a large short-circuit current in the event of a fault.

The circuit breaker has the function of a fuse and is much better than the fuse, and only the circuit breaker is used to cancel the fuse.

The fuse should be called the fuse wire, and the circuit breaker should be the switch, and the switch is in front, otherwise the fuse wire can not be replaced.

The fuse is in the front and the circuit breaker is in the rear.

1. When the low-voltage circuit breaker is used with the fuse, the fuse should be installed on the power supply side.

2. Circuit breaker (English name: circuit-breaker, circuit breaker) refers to a switchgear that can close, carry and break the current under normal circuit conditions, and can close, carry and break the current under abnormal circuit conditions within a specified time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their scope of use, and the division of high and low voltage boundaries is relatively blurred, and generally more than 3kV is called high-voltage electrical appliances.

3. Fuse refers to an electrical appliance that melts and disconnects the circuit with the heat generated by itself when the current exceeds the specified value. The fuse melts the melt according to the heat generated by itself after the current exceeds the specified value for a period of time, so that the circuit is disconnected; A kind of current protector made by using this principle. Fuses are widely used in high and low voltage power distribution systems and control systems and electrical equipment, as a short-circuit and over-current protector, is one of the most widely used protection devices.

When a low-voltage circuit breaker is used in conjunction with a fuse, the fuse should be installed on the power supply side.

Low-voltage circuit breakers are used in conjunction with fuses? There is no need, because the circuit breaker already has a short-circuit protection function, and the fuse is equipped to deal with short-circuit faults, if the circuit breaker cannot meet the short-circuit protection, then the circuit breaker can be replaced with a larger capacity, if it is satisfied, there is one more protection to become double protection, I think it is okay, as long as you are not afraid of waste.

Twice the normal operating current.

1. Determine the type of fuse according to the conditions of use.

2. When selecting the fuse specification, select the fuse specification first, and then select the fuse specification according to the fuse specification.

3. The protection characteristics of the fuse should match the overload characteristics of the protected object.

4. In the power distribution system, the fuses at all levels should match each other, and the rated current of the upper melt is 2-3 times that of the lower melt.

5. The fuse to protect the motor, the influence of the starting current of the motor should be noted, the fuse is only used as the short-circuit protection of the motor, and the thermal relay is used for overload protection.

6. The rated current of the fuse should not be less than the rated current of the fuse, and the rated short-circuit capacity should be greater than the maximum short-circuit current that may occur in the circuit.

1. Determine the type of fuse according to the use conditions.

2. When selecting the specification of the fuse, the specification of the melt should be selected first, and then the specification of the fuse should be selected according to the melt.

3. The protection characteristics of the fuse should be well matched with the overload characteristics of the protected object.

5. For the fuse to protect the motor, attention should be paid to the influence of the starting current of the motor, the fuse is generally only used as the short-circuit protection of the motor, and the thermal relay should be used for overload protection.

6. The rated current of the fuse should not be less than the rated current of the melt; The rated breaking capacity should be greater than the maximum short-circuit current that may occur in the circuit.

The fuse should be connected in series in the circuit in the circuit. It is generally installed behind the power supply.

Fuses are used to protect electrical equipment. It can be strung directly into the power cord of the device. If it's three-phase electricity, string one on each item.

If it is 220V, only one in series on the live wire is fine. It is located below the power supply, in front of the device.

The fuse is generally strung in the circuit, and is generally connected to the live wire (or positive pole), and the neutral line does not need to be connected to the fuse!

Whichever part you want to protect, connect the fuse in series on its power input side.

Principles for the selection of fuses.

1. Select the appropriate type of fuse according to the use environment and load nature.

When selecting a fuse, attention should be paid to its protection form to meet the requirements of the production environment. For example, for the simple protection of lighting lines or motors with small capacity, RC1A series semi-enclosed fuses can be used; RM series non-packing enclosed fuses can be used in switch cabinets or power distribution panels; For places where the short-circuit current is quite large or there is flammable gas, the RTO series enclosed fuse with packing should be used;

In the control circuit of the machine tool, the RL1 series screw fuse should be used; For silicon rectifier components and transistor protection, RLS or RS series fast fuses should be used.

2. The rated voltage of the fuse must be greater than or equal to the rated voltage of the line.

3. The rated current of the fuse must be equal to or greater than the rated current of the line. The rated current of the fuse must be equal to or greater than the rated current of the installed melt.

In general, the rated current of the fuse should be selected according to the above, but sometimes the rated current of the fuse can be a larger or smaller one. For example: 60A melt, both 60A fuse can be selected, 100A fuse can also be selected, at this time, it can be determined according to whether the circuit often has a small multiple overload current, if there is often a small multiple overload, a larger fuse should be selected, so as not to rise too high.

4. The breaking capacity of the fuse should be greater than the maximum short-circuit current that may occur in the circuit.

5. The coordination of the upper and lower levels of the fuse in the circuit should be conducive to the realization of selective protection.

6. In the place of multi-level protection, in order to achieve selective protection, the error of the fuse protection characteristics should be taken into account, and the fusing time of the upper fuse of the circuit should be more than 3 times that of the next fuse when passing through the same current. When the upper and lower stages adopt the same type of fuse, the current level should be two levels apart. If different types of fuses are used, the fusing time selection should be given according to the protection characteristic curve.

Precautions for the use of fuses:

1. The protection characteristics of the fuse should be adapted to the overload characteristics of the protected object, and the fuse with the corresponding breaking capacity should be selected considering the possible short-circuit current;

2. The rated voltage of the fuse should be adapted to the line voltage level, and the rated current of the fuse should be greater than or equal to the rated current of the melt;

3. The rated current of the melt of the fuses at all levels in the line should be matched accordingly, and the rated current of the previous melt must be greater than the rated current of the next melt;

4. The melt of the fuse should be matched according to the requirements, and it is not allowed to increase the melt at will or replace the melt with other conductors.

Fuse patrol inspection:

1. Check whether the rated value of the fuse and melt is compatible with the protected equipment;

2. Check whether the appearance of the fuse is damaged or deformed, and whether there are traces of flicker discharge in the porcelain insulation part;

3. Check whether the contact points of the fuse are intact, the contact is tight, and whether there is overheating;

4. Whether the fuse signal indicator of the fuse is normal.

1. Select according to wire protection (GG GL characteristics).

The overload current and short-circuit current in the line will cause the temperature of the wire and cable to be too high, resulting in the insulation damage or even the breakage of the cable. The fuse can be arranged at the inlet or outlet end of the wire and cable for wire and cable overload protection, and the rated current of the fuse is about times of the line current; When the fuse is used for short-circuit protection, it must be installed at the inlet end of the wire and cable, and the rated current of the fuse is about several times of the tripping current.

2. Select according to motor protection (AM GM characteristics).

A simple set of motor circuits usually consists of a fuse, contactor, thermal relay, motor, etc. As a rule of thumb, in this line, the rated current of the selected fuse is about a multiple of the rated current of the motor.

3. Select according to the capacitor switchgear.

In capacitor switchgear, the fuse is stored for short-circuit protection, and the rated current of the selected fuse shall not be less than multiple times of the rated current of the capacitor.

(1) Selection of fuse type.

The type of fuse is selected based on the protection characteristics of the load and the magnitude of the expected short-circuit current.

2) Selection of fuse rated voltage.

The rated voltage of the selected fuse should not be lower than the rated working voltage of the line, but when the fuse is used in the DC circuit, the DC circuit data provided by the manufacturer should be paid attention to or negotiated with the manufacturer, otherwise the voltage should be reduced.

3) Selection of melt rated current.

For fuses used to protect lighting or electrical heating equipment and general control circuits, the rated current of the selected melt should be equal to or slightly greater than the rated current of the load.

The fuse used to protect the motor should be considered according to the multiple of the starting current of the motor, and the influence of the starting current of the motor should be avoided.

4) Selection of fast fuse.

The choice of fast fuse is related to the way it is connected to the circuit, taking the three-phase silicon rectifier or three-phase thyristor circuit as an example, the common ways of the fast fuse to access the circuit are to access the AC side and access to the rectifier bridge arm (that is, to connect with the silicon element in series).

Selection of melt current rating. When selecting the rated current of the melt, it should be noted that the rated current of the melt of the fast fuse is expressed in terms of the effective value, while the rated current of the silicon rectifier element and thyristor is expressed as the average value.

Selection of the rated voltage of the fast fuse. At the moment when the fast fuse breaks the current, the maximum arc voltage can reach multiple times the power supply voltage. Therefore, the reverse peak voltage of the silicon rectifier element or thyristor must be greater than this voltage value in order to operate safely, i.e

where UF – the reverse peak voltage of the silicon rectifier element or thyristor;

un - the rated voltage of the selected fast fuse;

k2 - safety factor, the value of which is generally.

A fuse is a current protector that melts the melt with the heat generated by itself when the current exceeds the specified value for a period of time, so that the circuit is disconnected. Fuses are widely used in high and low voltage power distribution systems and control systems, as well as electrical equipment, as a protector for short circuit and overcurrent.

Classification of fuses.

Plug-in fuse: It is often used at the end of the line at the voltage level of 380V and below, as a distribution branch line or electrical equipment for short circuit protection.

Spiral fuse: The upper end of the melt is covered with a fuse indicator, once the melt is blown, the indicator will pop out immediately, which can be observed through the glass hole on the porcelain cap, it is often used in the electrical control equipment of machine tools. Spiral fuse.

The breaking current is large, and it can be used for short-circuit protection in circuits with voltage level 500V and below and current level below 200A.

Enclosed fuse: enclosed fuse is divided into two types: packing fuse and non-packing fuse, the packing fuse is generally used square porcelain tube, filled with quartz sand and melt, strong breaking capacity, used in the circuit below the voltage level of 500V and the current level of 1KA below. The fillerless closed fuse loads the melt into a closed cylinder with a slightly smaller breaking capacity, and is used in power grids or power distribution equipment below 500V and below 600A.

Fast fuse: Fast fuse is mainly used for short-circuit protection of semiconductor rectifier components or rectifier devices. The structure of the fast fuse is basically the same as that of the packed closed fuse, but the melt material and shape are different, and it is a V-shaped deep groove variable cross-section melt made of silver sheets.

Self-resetting fuse: Sodium metal is used as the melt, which has high conductivity at room temperature. When a short-circuit fault occurs in the circuit, the short-circuit current generates a high temperature that causes the sodium to vaporize rapidly, and the vapor sodium presents a high-resistance state, thus limiting the short-circuit current.

When the short-circuit current disappears, the temperature drops, and the sodium metal regains its original good conductivity.

The resettable fuse can only limit the short-circuit current, but cannot really break the circuit. The advantage is that the melt does not have to be replaced, and it can be reused.