① The type of molded case circuit breaker selected shall be determined according to the load nature, fault category and line protection requirements of low-voltage distribution system, and shall comply with the current relevant national standards.

②断路器的额定电压、额定频率应与所在回路的标称电压及标称频率相适应。

② The rated voltage and rated frequency of the circuit breaker shall adapt to the nominal voltage and nominal frequency of the circuit.

③断路器的额定电流不应小于所在回路的负载计算电流。

③ The rated current of the circuit breaker shall not be less than the load calculation current of the circuit.

④断路器应适应所在场所的环境条件。

④ The circuit breaker shall adapt to the environmental conditions of the site.

⑤断路器应满足短路条件下的动稳定和热稳定要求。用于断开短路电流时，应满足短路条件下的通断能力。

⑤ The circuit breaker shall meet the requirements of dynamic stability and thermal stability under short circuit conditions. When used to disconnect short-circuit current, it shall meet the on-off capacity under short-circuit conditions.

低压断路器应根据不同故障类别和具体工程要求，选择相适应的保护形式。其整定原则一般来说主要包括：

The low-voltage circuit breaker shall select appropriate protection forms according to different fault categories and specific engineering requirements. Generally speaking, the setting principles mainly include:

①断路器在正常使用中和用电设备正常起动时，所装设的保护不应动作。

① When the circuit breaker is in normal use and the electrical equipment is started normally, the installed protection shall not act.

②断路器的最根本任务就是起到保护作用，必须在规定的时间内能有效地切断故障电路，满足规范最基本的要求。

② The most fundamental task of the circuit breaker is to play a protective role. It must be able to effectively cut off the fault circuit within the specified time to meet the most basic requirements of the specification.

③低压配电系统各级断路器的保护动作特性应能彼此协调配合，要有选择性的动作，即发生故障时，应使靠近故障点的断路器保护首先切断，而其靠近电源侧的上一级保护不应动作，尽可能地缩小断电范围。

③ The protection action characteristics of circuit breakers at all levels of low-voltage distribution system shall be able to coordinate with each other and act selectively, that is, in case of fault, the circuit breaker protection close to the fault point shall be cut off first, while the upper level protection close to the power supply side shall not act, so as to reduce the power-off range as much as possible.

在低压配电系统中，主要设计任务就是合理地选择保护电器，根据断路器的整定原则要求，通过正确的整定其参数来实现各种保护功能，但这些整定原则又可能相互发生矛盾。

In the low-voltage distribution system, the main design task is to reasonably select the protection appliances. According to the setting principle requirements of the circuit breaker, various protection functions can be realized by correctly setting its parameters, but these setting principles may conflict with each other.

例如：断路器额定电流或整定电流大小受到整定原则第①和第②项的限定，而保护动作时间的快慢又受到整定原则第②和第③项的制约，所以必须经过准确的计算和认真的校验，协调相互之间的矛盾，实现对立的统一，以符合规范规定的动作特性、动作时间和有选择性保护的有关要求。

For example, the rated current or setting current of the circuit breaker is limited by items ① and ② of the setting principle, and the speed of the protection action time is restricted by items ② and ③ of the setting principle. Therefore, it is necessary to coordinate the contradictions between them through accurate calculation and careful verification, so as to achieve the unity of opposites, so as to meet the action characteristics specified in the specification Relevant requirements for action time and selective protection.

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Thank you for reading. The source of this article is ABB molded case circuit breaker agent. For more contents and questions, please click: http://www.jntongyu.com We will continue to work hard to provide you with services. Thank you for your support!