Incident Energy with CL Fuse Equations 1

[SJBatTCE]

Does anyone else have a problem with the IEEE 1584 incident energy equations for current limiting fuses?

Incident energy is based on the arcing fault current, not the bolted fault current. Arcing fault current is determined from the bolted fault calculation but takes several other variables into consideration, like system voltage, gap, etc. The CL fuse incident energy equations only use bolted fault values.

Why are the CL fuse equations based on bolted fault rather than arcing fault values?

For now, I am not using the equations in my analysis. Are my concerns unfounded?

Thanks.

 

[PHovnanian]

An interesting solution might be the combination of CL fuses and an arc quenching device. The quenching device would practically guarantee high current and fast operation of CL fuses.

I'm not sure what you are describing as "an arc quenching device". My understanding of the term is a device that, using an air blast, gas expulsion, magnetics, etc. "blows" an arc out by dissipating its plasma. But arc quenching doesn't adapt well to arcs at random fault locations. It is used in conjunction with devices that interrupt current.

It sounds like you are referring to a crowbar. With this, once a fault condition is detected, a low impedance path is provided downstream of the circuit protection (an intentional fault) to draw sufficient current to ensure its operation. The problem here is that typical CL fuses operate by interrupting fault current within a quarter of a cycle. Crowbars need to sense the initial fault condition, initiate the crowbar action and only then will the fuses operate. Its not likely that this can be done within a quarter cycle.

For a high energy, longer clearing time arcing fault, a crowbar could divert the available energy from the site of the exposure to the contained crowbar contactor. But this is all low speed stuff compared to CL fuse operation. You may as well just trip a standard breaker.

 

[Maak]

It sounds like you are referring to a crowbar. With this, once a fault condition is detected, a low impedance path is provided downstream of the circuit protection (an intentional fault) to draw sufficient current to ensure its operation. The problem here is that typical CL fuses operate by interrupting fault current within a quarter of a cycle. Crowbars need to sense the initial fault condition, initiate the crowbar action and only then will the fuses operate. Its not likely that this can be done within a quarter cycle.

For a high energy, longer clearing time arcing fault, a crowbar could divert the available energy from the site of the exposure to the contained crowbar contactor. But this is all low speed stuff compared to CL fuse operation. You may as well just trip a standard breaker.

Arc eliminators can detect (optical detection and very fast overcurrent detection) AND eliminate the arc within a few milliseconds. Manufacturers say that arc burning times of 2ms (LV) and 5ms (MV) can be reached. Thus a combination of a crowbar and a CL fuse would provide 1) very short arc burning time with minimal damage and 2) very short short-circuit current time, in case you are worried by the high current.

Light and overcurrent based arc detection is very fast. Optical sensors detect the arc light, and the overcurrent detection can be based on analog technology (I don't know the details) which does not require any algorithms for processing samples.