Dc Breaker Sizing To Meet Iec 61660 Standard

IEC standard 61660 develops a methodology for the calculation of DC short circuit waveform. The waveform is characterized by peak current and quasi current.

DC breakers, designed for IEC are characterized by ultimate breaking capacity Icu, which I presume is similar to the interrupt rating used in North America.

When sizing the DC breaker, should the Icu be compared to the peak or the quasi current?

I2t Calculation For Semiconductor Fuses

Vendors for Semiconductor fuses normally may supply let-through charts as well as melting and clearing I2t figures. When used for dc application where the short circiut waveform is known to have the following equation I(t)=Isc(1-exp(-at)), what method will be more accurate:



Method 1: Use the Let-thru chart, with Iprospective= Isc to determine the let through current, Ic, and then use the equation above to find the melting time. Note in this method the published melting I2t is not used.



Methopd 2: Use the melting I2t data and equate it the square of the above equation and solve iteratively for the melting time, and the let-thru current Ic. note this method does not use the let-through charts



Both of the above methods provide significantly different answers.