Electronics > Beginners
Fuse Question
bostonman:
I'm having a work related problem regarding fuses.
It's regarding maximum A^2 * S
I'm given two columns, the first has the title Peak Current (A) and one of the values is 30. The second column has Maximum [indefinate integral] I^2 * t , A^2 * s and has a value of 90.
I understand the peak current being 30A, but don't understand the second column with regards to 90 being A^2 * s.
I looked on LittelFuse, but didn't find anything directly explaining this. Basically I don't understand the connection between the indefinate integral, A^2 * s, and what it means with the value of 90.
Can someone help end my confusion?
helius:
The main parameters that are relevant to fuses are current capacity, arc breaking or interrupting current, speed, and energy absorption.
The current capacity is the current that the fuse will pass without blowing over any amount of time. It's the intersection of the current diagram with t=∞ and is notated in amperes.
\$ \int I^2 dt \$ is the area under the curve represented by the current squared on the Y axis, with time on the X axis. The idea is that this function looks like a hump rising up from (near) zero at a certain point, and then decreasing back to zero since the circuit is broken. Power is proportional to current squared: \$ P = I^2 R \$ , so the area under the curve is power times time, or the energy the fuse is rated to absorb. I would expect this parameter to be in kilojoules.
SG-1:
I2t (Amperes Squared Seconds) This is a value obtained by multiplying an effective current squared by the time of flow of the current in seconds. It is not a heat energy value, but represents heat energy for comparison purposes. Some common uses are to determine fuse selectivity and to select current limiting fuses that will limit this value to be compatible with the withstandability of semi-conductors that have an I2t rating.
bostonman:
--- Quote ---∫I2dt is the area under the curve represented by the current squared on the Y axis, with time on the X axis
--- End quote ---
So to write it correctly, am I integrating I^2t dt or I^2 dt?
Also, if I integrate, I get I^3/3 * t +C. What value do I use for C?
bostonman:
--- Quote ---So to write it correctly, am I integrating I^2t dt or I^2 dt?
Also, if I integrate, I get I^3/3 * t +C. What value do I use for C?
--- End quote ---
Just realized, I didn't get clarification about this.
Navigation
[0] Message Index
[#] Next page
Go to full version