Ac circuit breaker for direct current circuit

Update date:2018-01-03 Source:MAXGE

Ac circuit breakers can be derived as direct current protection, but three changes must be noted:


1. Overload and short circuit protection.   

1) overload long delay protection. Using thermal type (double) metal components for overload long time delay protection, its action source is I2R, both dc and ac current of effective value equal to the average, so don't need any restructuring can be used. However, for the large current specification, the secondary current heating of the current transformer can not be used because the transformer can't be used in direct current.   


If overload long time delay tripping device is to use the whole electromagnetic (hydraulic, namely oil cup type), the time delay tripping characteristics to change, the minimum operating current 110% 140% to be big, therefore, ac electromagnetic all tripping device cannot be used in dc (e.g., want to use to redesign).   

2) short circuit protection.   

Thermal - type electromagnetic ac breaker short circuit protection is to use the magnet system, it is used in the filter after the rectifier circuit (dc), the original setting of the communication must be current value multiplied on a factor of 1.3. All electromagnetic type short circuit protection is the same as thermal electromagnetic type.


2. Accessories for circuit breakers, such as shunt tripping, undervoltage tripping device, electric operating mechanism, etc. The shunt and undervoltage are all voltage coils. As long as the voltage value is consistent, the ac system can be used for the dc system without any changes. Auxiliary, alarm contact, ac - dc universal. Electric operating mechanism, for direct current design.   


3. Because the dc current is not like ac has the characteristics of zero point, the short circuit current of dc (or even a small number of failure current) is broken; It is difficult to extinguish the arc, so the wiring should be in series of two or three poles, increasing the fracture and taking part of the arc energy of each fracture.   

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