The AC circuit breaker can be derived as a DC circuit protection, but three changes must be noted:
Overload and short circuit protection
1 overload long delay protection. When the thermal type (bimetal element) is used for overload long delay protection, the action source is I2R, and the rms current of the AC is equal to the average value of the DC, so it can be used without any modification. However, for the high current specification, if the secondary side current of the current transformer is used, the transformer cannot be used because it cannot be used in the DC circuit.
If the overload long-delay trip unit is full electromagnetic (hydraulic type, ie oil cup type), the delay tripping characteristic should be changed, and the minimum operating current should be increased by 110%-140%. Therefore, the AC full electromagnetic type The trip unit cannot be used in DC circuits (redesigned if it is to be used).
2 short circuit protection. The short-circuit protection of the thermal-electromagnetic AC circuit breaker is based on a magnet system. It is used for the filtered rectifier circuit (DC), and the original AC current is multiplied by a factor of 1.3. The all-electromagnetic short-circuit protection is the same as the thermal electromagnetic type.
Circuit breaker accessories
Such as shunt release, undervoltage release, electric operating mechanism, etc.; shunt and undervoltage are voltage coils, as long as the voltage values ​​are the same, then used in the AC system, without any changes, can be used for DC system. Auxiliary, alarm contact, AC and DC universal. Electric operating mechanism to be redesigned for DC.
Other considerations
Since the direct current does not have the characteristics of zero crossing of the alternating current, the short-circuit current of the direct current (or even the fault current with a small multiple) is broken; the arc is extinguished, so the wiring should be connected by two or three poles. Fractures, causing each fracture to bear a portion of the arc energy.
In addition to the traditional thermomagnetic trip units, electronic trip units are also widely used. An important advantage of the electronic trip unit is that it can operate stably even in the event of a change in ambient temperature.
Note: Leakage protectors must be extremely sensitive, so be sure to use a big brand to be safe. For example, Siemens is good because they are very precise and sensitive to the line detection, in 0.1 seconds or less. It is possible to detect an abnormality and immediately trip before the current intensity and time have not reached the level of damage, cutting off the main circuit of the power supply, and fully ensuring personal safety. And if you use a quality brand that is not good enough, or old, even if it is only 1 second or even 0.5 seconds later, the damage to the human body is fatal. Life safety, must be vigilant!
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