Precautions for using AC circuit breakers

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AC circuit breakers can be adapted for protecting DC circuits, but three changes must be taken into account: overload and short-circuit protection. ① Overload with long delay protection. When a thermodynamic type (bimetallic element) is used for long-delay overload protection, the triggering mechanism is based on I2R; since the effective value of alternating current is equal to the average value of direct current, no modifications are required for its use. However, for high-current specifications, those that use the current on the secondary side of a current transformer for heating cannot be used, as transformers cannot be applied in DC circuits. 　　If the overload long-delay trip device is of the fully electromagnetic type (hydraulic type, i.e., oil cup type), the delay tripping characteristics will change, and the minimum operating current will increase by 110%–140%. Therefore, AC fully electromagnetic trip devices cannot be used in DC circuits (if they are to be used, they must be redesigned). ②Short-circuit protection. The short-circuit protection of thermoelectromagnetic AC circuit breakers relies on a magnet system; it is used in filtered rectifier circuits (DC), and the rated current value for the original AC supply must be multiplied by a factor of 1.3. The short-circuit protection in the all-electromagnetic type is the same as that in the thermoelectromagnetic type. Attachments of circuit breakers such as release relays, under-voltage release relays, electric operating mechanisms, etc ； Both shunt and under-voltage types are voltage coils; as long as the voltage value remains the same, those designed for AC systems can be used in DC systems without any modifications. Auxiliary and alarm contacts, suitable for AC and DC. The electric operating mechanism needs to be redesigned for use with direct current. Other considerations: Since direct current does not have the zero-crossing characteristic that alternating current does, breaking the short-circuit current in direct current (even fault currents that are not significantly higher in magnitude) ； It is difficult to extinguish the arc; therefore, the wiring should be arranged in a two-or three-pole series configuration to increase the number of break points, so that each break point can handle part of the arc energy. 　　 In addition to traditional thermal-magnetic circuit breakers, electronic circuit breakers are also widely used. An important advantage of electronic trip units is that they can operate stably even when the ambient temperature changes. 　　 Note: Circuit breakers for leakage protection must have extremely high sensitivity; therefore, it is essential to choose products from reputable brands to ensure safety. Brands such as Siemens are excellent, as they offer very precise and sensitive detection of electrical faults. They can detect abnormalities within 0.1 seconds or even less, and will immediately cut off the power supply before the current level and duration reach dangerous levels, thus ensuring personal safety. Conversely, if inferior generic brands or outdated models are used, even a delay of just 1 second or even 0.5 seconds can be fatal to the human body. Be vigilant for life safety!