热脱扣器

热脱扣器是断路器和主隔离开关中的关键部件，旨在通过响应持续过电流提供过载保护。它基于电流的热效应工作，当电流超过额定阈值并持续预定时间时，经过校准的双金属片会受热弯曲。这种机械动作释放脱扣机构，断开触点以中断电路。与响应短路的磁脱扣器不同，热脱扣器保护免受渐进过载的影响，这些过载可能导致绝缘退化、过热或火灾。其特点是具有反时限特性，即过载越严重，脱扣时间越短。现代版本可与电子脱扣器集成，以增强协调和监控功能。

热脱扣器基于热膨胀原理工作。双金属片由两种热膨胀系数不同的金属组成，负载电流通过时使其受热。在正常条件下，双金属片保持平直。过载时，增加的电流产生过多热量，导致双金属片因金属膨胀不均而弯曲。这种弯曲动作触动锁扣或杠杆机构，释放弹簧加载的触点以断开电路。脱扣时间取决于过载的大小，遵循反时限特性：电流越高，脱扣越快。根据设计，该单元在冷却后自动复位或通过手动干预复位。

The thermal trip unit operates on the principle of thermal expansion. A bimetallic strip, composed of two metals with different coefficients of thermal expansion, is heated by the load current passing through it. Under normal conditions, the strip remains straight. During an overload, the increased current generates excess heat, causing the strip to bend due to unequal expansion of the metals. This bending actuates a latch or lever mechanism, which releases the spring-loaded contacts to open the circuit. The trip time depends on the magnitude of the overload, following an inverse-time characteristic: higher currents cause faster tripping. The unit resets automatically after cooling or via manual intervention, depending on the design.