In the low-voltage power distribution system, when a current fault occurs in the lower-level distribution circuit, the upper-level protection device cannot be effectively prevented and controlled, resulting in the occurrence of large-scale power outages, and even major economic losses and casualties. The problem is the most studied topic in low-voltage power distribution systems, and it is also an old problem that has been unsolved for a long time. Therefore, in the current low-voltage power distribution system design work, in order to improve and ensure the safety and reliability of electrical equipment and avoid fire or electric shock accidents during operation of electrical equipment, staff have put forward many solutions and strategies. , especially in the selection of protective electrical appliances, it has invested a lot of energy to research and summarize, so that the quality of the entire project has been guaranteed to a certain extent.

1. Analysis of low-voltage protection appliances

Low-voltage protection appliances occupy an important position in the current low-voltage power distribution system and play an irreplaceable role, especially the main protection device for power distribution line failures, and it is also the primary link to avoid fault expansion and deterioration. As of the current social development, low-voltage protection appliances have become the focus of research in the work of industry insiders. It can be mainly divided into two categories: fuses and circuit breakers.

(1) Fuse

The fuse is a primary measure for safety protection in low-voltage power distribution systems, and it is also the most common electrical equipment in low-voltage power distribution systems. It is widely used in power grid protection and electrical equipment protection in current work. . Generally speaking, low-voltage fuses are usually installed on electrical lines or on the electrical circuit of electrical equipment. When a fault occurs in the power grid or the operation of electrical equipment, the fuse can cut off the fault in time and effectively. circuit, thus effectively avoiding and preventing the spread and expansion of faults.

(2) Circuit breaker

A circuit breaker mainly refers to a switchgear that can switch on and segment normal load current, overload current, and overvoltage current. It can ensure the stability and safety of electrical equipment by switching on and segmenting short-circuit current during operation. run. In the current work, the common circuit breakers mainly include open circuit breakers and molded case circuit breakers. Among them, open circuit breakers refer to circuit breakers that are in the air of atmospheric pressure or a circuit breaker structure that is closed. , This circuit breaker structure has the advantages of convenient installation and obvious fault inspection in application, while the molded case circuit breaker is mainly made of a molded insulating material into a corresponding casing to protect the integral part of the circuit breaker. In the application of low-voltage circuit breakers, it is mainly used on the basis of the clear specification of the rated voltage, in which the voltage value of the AC voltage is below 1000V or the DC voltage is below 1500V. Only in this power system, it can Play the role and efficiency of the application, and effectively protect and control the circuit.

(3) The advantages and disadvantages between the two

In short, from the functional analysis, there is no obvious difference between circuit breakers and fuses, and there is not much difference in their applications. They are all devices that are mainly used for circuit protection. However, when the fuse is used, it is a one-time device. After it is used, it needs to be replaced and handled by the staff in time. It is a cheap and widely used control device. The circuit breaker has the electric remote control function, the protection function is relatively complete, and the adjustment is convenient, and it can continue to be used when the fault is disconnected.

Second, the choice of low-voltage protection appliances

In the current newly-built civil buildings and industrial installations, few workers start to use fuses as low-voltage protection appliances, and at present, fuses are mainly used in some old production installations and early residential quarters. With the continuous development of electrical automation technology in recent years, building construction technology has also been significantly improved, and its construction requirements have also been greatly improved. In the selection work of low-voltage protection appliances today, according to the current fault characteristics of existing distribution lines and the advantages and disadvantages of low-voltage protection appliances, the appropriate selection is made according to local conditions. The recommended options are as follows:

(1) A new type of circuit breaker should be used for the protection appliances in the low-voltage main switch cabinet.

(2) For general equipment, fuses should be used to protect electrical appliances in general power distribution cabinets. Because the fuse has good current-limiting characteristics and is cheap, it is easy to meet the selectivity requirements. However, when there are not many power supply and electrical equipment, and the impact of occasional power failure is not too great, a non-selective circuit breaker can also be selected.

(3) Non-selective circuit breakers or leakage protectors are usually used to protect electrical appliances in terminal distribution boxes to improve the sensitivity of protective electrical appliances.

(4) For important equipment, intelligent circuit breakers should be used at all levels and ZSI technology should be used to ensure selective coordination between levels. Improve the reliability of power supply.

Third, the selectivity of distribution line protection

The selectivity of distribution line protection means that when an overcurrent fault occurs at a certain point in the distribution network, the distribution protection appliances selectively act according to the predetermined sequence of actions. . The action of the upper and lower protection electrical appliances used in the distribution line should be selective. There should be coordination and cooperation at all levels. There are two types of protective appliances currently used: circuit breakers and fuses. The former can be divided into selective and non-selective circuit breakers from the perspective of protection characteristics.

(1) Requirements of distribution lines for protective appliances

There are usually two types of distribution lines, trunk type and radial type, as well as hybrid systems of the two. Low-voltage protection appliances are divided into three levels according to their installation position and importance in the distribution line: protection appliances in low-voltage main switch cabinets, protection appliances in general distribution switch cabinets, and protection appliances in terminal distribution boxes. The requirements of distribution lines for low-voltage protection appliances at all levels are as follows:

1) Protect the electrical appliances in the low-voltage main switch cabinet

The protection appliances in the low-voltage main switch cabinet should place the reliability of the power supply in the main position to ensure continuous power supply. Since the low-voltage protection appliances are close to the power transformer, the capacity of the distributed busbar is particularly large, so it is required that it should not only be connected with the primary side of the power transformer. The protection characteristics of high-voltage fuses should be coordinated with the lower-level protection appliances to achieve full selective protection as much as possible.

2) Protect the electrical appliances in the terminal distribution box

The terminal distribution box is directly connected to the electrical equipment, and the circuit is required to be cut off as soon as possible or even instantaneously in the event of a short circuit or ground fault, and there is no selective requirement. The low-voltage protection appliances in the terminal distribution box should be provided with short-circuit and ground-fault protection, while the end of the line does not need to be provided with short-circuits, but should be equipped with control appliances or overload protection appliances for electrical equipment according to the needs of the connected electrical equipment.

(2) Selective coordination technology between low-voltage protection electrical appliances

Only according to the characteristics of the low-voltage power distribution protection appliances, properly select the protection appliances, and correctly set the rated current, operating current and operation time of the protection appliances, can the selective cooperation between the low-voltage protection appliance stages be realized, and the protection of the circuit can be ensured as far as possible when there is a fault. Reduce outages.