[Development of Small Circuit Breakers with Selective Protection]: Low Voltage Circuit Breakers are mainly used in power supply and distribution networks to distribute electricity and protect power lines and equipment from over-current (including overload and short circuit) hazards. The ideal mode of power supply is that once an overcurrent fault occurs in a certain part of the power supply and distribution network, the circuit breaker at that part trips quickly to remove the fault. And it does not bring harm into the .
Low-voltage circuit breakers are mainly used in power supply and distribution networks to distribute electricity and protect lines and power equipment from over-current (including overload and short circuit) hazards. The ideal mode of power supply is that once an overcurrent fault occurs in a certain part of the power supply and distribution network, the circuit breaker at that part trips quickly to remove the fault. However, it will neither further expand the hazards nor cause other circuit breakers connected in series in power supply lines to trip without reason, thus affecting the power supply.
In the early 1950s and 1960s, the distribution protection of domestic residences in China was mostly composed of simple knife-gate switch and fuse (porcelain plug RC1). When a short circuit occurs, the whole house is dark and it is inconvenient to replace the fuse. DZ5, DZ12 and DZ15 series bipolar plastic case circuit breakers were developed in China from the late 1960s to the 1970s. In the late 1970s, Beijing Switch Factory introduced German technology and transferred domestic manufacturers to produce S060 series miniature circuit breakers, but for various reasons, it failed to promote them on a large scale. In the mid and late 1980s, the large-scale production of C45N produced by Tianjin Meilan Rilan Company and DZ47 series miniature circuit breakers produced by many domestic manufacturers has brought our country's over-current protection circuit breakers to a new level.
Since the beginning of the new century, people's material life has been further improved, and the application of distribution system in the residential field requires higher and higher automation and high reliability. However, in the practical application of circuit protection, fault current often causes simultaneous tripping or even over-tripping of circuit breakers at the same stage. In order to ensure the reliability of power supply in distribution system and reduce its impact to the range of only fault points, we should not only improve its performance index, but also study how to improve the selective protection coordination mode between upper and lower circuit breakers connected in series in power supply and distribution network.
Selective protection of low-voltage circuit breakers is actually an over-current coordination between two or more over-current protection devices. Simply speaking, short circuit occurs in the protection scope of the next level of protective appliances. When the overcurrent fault occurs, the protective appliances should be operated by the protective appliances, while the upper level of protective appliances should not act. When the protective appliances refuse to operate, the upper level of protective appliances will only act, which should be divided into scope and sequence requirements.
According to GB14048.2-2008 "Low Voltage Switchgear and Control Equipment Part 2: Circuit Breakers" standard, it can be divided into the following two types:
Full selectivity: In the case of two series over-current protection devices, the over-current selectivity protection of the load side protection device does not lead to the operation of another protection device.
Local selectivity: In the case of two series overcurrent protection devices, the overcurrent selectivity protection of the load side protection device does not lead to the operation of another protection device when the overcurrent value and below are given.
The working principle of the product is as follows:
Under normal working conditions, the working principle of the main circuit bimetallic sheet of the selective protection circuit breaker is the same as that of the general MCB, which is used as overload protection. When a short-circuit fault occurs in a branch circuit, the core of the electromagnetic coil in the main circuit acts immediately on the active contacts of the main circuit to repulse and generate an arc, which quickly and effectively limits the short-circuit current. At the same time, the short-circuit current in the main circuit flows to the auxiliary circuit, while the auxiliary circuit is connected in series with a current-limiting resistance and selective bimetal sheet, which immediately limits the short-circuit current to only a few hundred amperes. If the short circuit current is cut off by the MCB of the fault branch at the load end, the main circuit moving contacts are closed again under the action of the spring to ensure that the other fault-free branches behind the main switch can work properly. If the short circuit occurs between or behind the main switch and MCB, and the MCB or other short circuit protection device can not cut off the fault circuit, the selective bimetal sheet can release the tripping mechanism within 10 ms to 300 ms, so that the contact can be disconnected and maintained at the disconnected position, and the fault circuit can be cut off at the same time.
Some foreign enterprises, such as ABB and Haig, are doing research and development in this field. They have also introduced some products to be applied in their domestic market. As the main switch of distribution system in family residence, the main idea is to emphasize the selective overcurrent release mode of the switch itself, rather than relying solely on the cooperation between the upper and lower switches to achieve the purpose of selective protection.
At present, Shanghai Institute of Electrical Appliance Science has successfully developed a new type of small circuit breaker with selective protection in cooperation with two other manufacturers, and has been put into the market. Among them, Jiangsu Kailong Electrical Appliance, as a holding subsidiary of Shanghai Institute of Electrical Appliance Science, is also rapidly developing the process of industrialization, and is expected to complete the development and market in November 2011.
As one of the main products of the fourth generation of low-voltage electrical appliances in China, the new type of small circuit breaker with selective protection is a technological achievement with completely independent intellectual property rights, which has been independently innovated and launched by the scientific researchers of low-voltage electrical appliances in China. Its technical and economic indicators have reached the international advanced level. The product effectively solves the problem of over-step tripping in the building distribution system, and greatly improves the stability and reliability of the terminal distribution system. Its main features are selective protection and interruption ability.
