Breakthrough in the technology of miniature circuit breakers

Selective fit and back-up

Selective fits and back-ups have been talked about in a variety of journal articles. Here are just a few ideas from an application perspective:

1) "Coordination" refers to the protection coordination between at least two upper and lower overcurrent protection devices, which does not exist without considering the cooperation of the other party.

2) The means of selective cooperation and backup protection are different. If only from the perspective of changing the characteristics of the upper-level overcurrent protection device (circuit breaker as an example):

A) Usually delay the action of the upper circuit breaker to wait for the action of the lower circuit breaker to obtain better selective cooperation

B) It is usually used to speed up the action of the upper circuit breaker to limit the short circuit energy, so as to provide backup protection for the lower circuit breaker.

Of course, the means to improve the upper and lower levels of selective cooperation is not limited to the action time coordination, but can also be based on current matching, energy coordination, logic

Control and other means. Of course, it is better that the circuit breaker itself can provide good selectivity and backup protection for other overcurrent protection devices.

3) The purpose of requiring selective cooperation is to reduce the scope of fault blackouts; the purpose of requiring backup coordination is to reduce investment costs.

4) From the perspective of two different purposes and different implementation methods, there is a conflict between the two types of cooperation.

Note: The low-voltage over-current protection device is mainly based on circuit breakers. If there is no description in the following, the circuit breaker refers to the over-current protection device.

Terminal power distribution continuity

According to the current status of terminal power distribution, the degree of specialization of cable laying and equipment installation is not high, but the distribution range of power equipment is wide, and the situation of chaos is relatively common; there are many non-professional users, overload phenomenon is common, overload or short-circuit fault The probability is high. Especially during peak load hours, the power supply department is busy dealing with all kinds of trip power outages. Because terminal power distribution seldom considers selective cooperation, a single short-circuit fault may cause power outage on the entire floor or building, which in turn makes the power supply department's fault location and restoration work even worse.

From an electrical design point of view, there is also a misunderstanding of the protection against electric shock within the general residential unit. Some designers only consider installing a residual current protection device at the main switch of the house, or the whole residential unit can only be powered by one loop. Or not taking into account the action time difference of the upper and lower circuit breakers, etc., all of which may result in the failure of the entire house due to a short circuit or ground fault, including failure of the security system power failure, power failure of the refrigerator and the living system (fish tank), and network interruption (router power loss) .

Outside of a typical residential unit, the designer may not consider the selective fit of the supply-side over-current protection device. On the user's home side, an incoming fuse or circuit breaker is installed, but it belongs to the jurisdiction of the power supply department. If these overcurrent protection devices malfunction due to poor selective cooperation (the lower circuit breaker has cut off the fault), it obviously also unnecessarily increases the attendance and overhaul workload of the power supply department, and greatly increases the time for failure.

Selective Coordination Research Approach

Due to the increasing importance of selective cooperation in terminal distribution, selective coordination is mainly discussed in this paper. In general, there are two research approaches to study selective fit, but they support each other and work together:

A) Find ways to increase selectivity by studying the cooperation between breakers on the upper and lower levels

B) Finding ways to improve selectivity by studying the improvement of the circuit breaker itself

The low-voltage side of the distribution transformer often has three or four layers of power distribution (common voltage 220/380V, IEC voltage standard 230/400V), at the first or second distribution layer, the designer will consider the optional cooperation according to user requirements, but The number of associated circuit breakers is small and the distribution is concentrated. Intelligent circuit breakers can often be selected to meet the requirements for selective coordination; however, the selective setting is complex and requires professional management. In these occasions, A) research approaches are often used.

The third or fourth tier is terminal power distribution, with little regard for selectivity or continuity of supply for cost reasons. The load of this layer is dispersed and the users are not professionals. There is a need for a cost-effective, simple-to-implement solution that guarantees ever-increasing power continuity requirements. In these occasions, we often use the B) research approach, which is to develop a new generation of circuit breakers to meet the selective requirements.

As early as 2004, at the “China Intelligent Building Qingdao Electric Salon” exchange organized by China Intelligent Building Technology Information Network, China Architecture Design and Research Institute and ABB China Co., Ltd., ABB Germany’s senior expert Mr. Mr. Bernd Siedelhofer introduced the structure, principle and application of the S700 with selective overcurrent protection circuit breaker. The participating experts positively affirmed the S700 SMCB, which is fully selective by ABB, and emphasized that the selective matching requirements should be improved in the domestic terminal distribution. The mature application of ABB's S700 SMCB is a good reference.

Terminal appliances improve the ability of selective fit

According to the IEC60898/GB10963 technical standard, MCBs for terminal distribution are generally required to operate quickly to cut short circuit faults as soon as possible. In other words, it does not need to withstand the "rated short-time withstand current Icw" according to IEC60947/GB14048, so the MCB volume of the same current level is much smaller than that of the MCCB.

If it is desired to increase the selectivity of the upper and lower MCBs, it is necessary to increase the time during which the upper MCB is subjected to the short-circuit current so that the lower MCB can quickly cut off the short-circuit current in the fault area; meanwhile, in order to ensure the “Grandfather” short-circuit protection device If the short-circuit current is too large and the time is too long to malfunction, it is also necessary to control the current-limiting characteristics and operation time of the upper MCB. In other words, the selective overcurrent protection circuit breaker SMCB should solve the problem of selectivity between multiple protection devices. The S700/S750 SMCB developed by ABB has achieved a breakthrough in technology and solved the problem that “bear and fish can not have both”.