A fuse rating ( to a voltage limit ) of blocking/ stopping power against over current flow.

Obviously, this is in reference to A/C systems with infinite bus character.

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kASC

kilo Amps Short Circuit

This is a metric related to the inverse impedance of a system.

It is calculated based upon what current can flow through from the Poco side into a shorted distribution system PLUS the instantaneous back EMF available from induction elements ( motors, chiefly ) and capacitive elements ( pf correction capacitor banks, chiefly ) when a 'bolted' short circuit occurs across a customer's main bus.

Because the system has a shifting impedance throughout and back-EMF changes with motor state the typical calculations are done WRT worst case fault energy thresholds.

A classic would be catastrophic transformer failure due to physical impact. Marc once related such a fiasco: a load shifted while on a massive forklift. Both load and lift tumbled into a rack of massive XFMRS. They went off like bombs. In a bolted short mode EMF from all associated systems drained into the short producing a plasma explosion, followed by a nasty fire.

Months later the rebuilt, redesigned system used COORDINATED fuses to protect against both Poco side energy and back-EMF coming back from all of the rotary loads.

They even threw in some bollards!

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For most situations rotating loads are trivial ( homes, small businesses ) but it gets interesting in industries that have the works.

Naturally, no electrician's calculations are going to satisfy: the insurance company will insist on an EE -- who carries a nice E & O Policy.

( E & O = Errors & Omissions = professional screw-up insurance )

This is a metric related to the inverse impedance of a system.

Say what????

I have been working with fault currents since 1974. Never in my life have I heard of kASC or the "inverse impedance of a system" with your description.

Available Short Circuit Amps (SCA) is always supposed to include the short circuit amps from all sources, utility, generators, motors etc.

Most likely someone has transposed some letters, and used a numeric suffix as a prefix.

The LOWER it goes the GREATER the instantaneous short circuit Amperage will flow.

Hence, an inverse relationship.

An infinite bus at a given voltage is dominated by the impedance of its elements from sources to the bolted fault.

QED

The term inverse is almost irrelevant to your description. Of course, for a given voltage, current and impedance have an inverse relationship. But that relationship has nothing to do with the phrase kASC.

Amps, Short Circuit is not a common expression.

In the 'power systems study' world, an infinite bus source is one that can deliver an unlimited amount of current into a fault. There is no need to add additional sources of fault currents to an infinite bus.

Re: kasc
[Re: JBD]
#197267 11/17/1005:39 AM11/17/1005:39 AM

In fault conditions the amps are coming up the line ( the Poco ) and back from loads ( back-EMF )

The expression 'infinite bus' is a term of art. Obviously, even the entire US grid is not infinite. However, for the purposes of the calculations infinite bus means that the delivered voltage is not considered to sag. Yeah, it's idealized.

Because of the interposition of magnetic circuits within our infinite bus THEIR impedance becomes huge in short circuit calculations.

Ditto for 'rotary transformers' ie 3-phase induction motors and the like.

In fault conditions the amps are coming up the line ( the Poco ) and back from loads ( back-EMF )

The expression 'infinite bus' is a term of art. Obviously, even the entire US grid is not infinite. However, for the purposes of the calculations infinite bus means that the delivered voltage is not considered to sag. Yeah, it's idealized.

Because of the interposition of magnetic circuits within our infinite bus THEIR impedance becomes huge in short circuit calculations.

Ditto for 'rotary transformers' ie 3-phase induction motors and the like.

Way to go. String together all sorts of fancy words, throw in enough minimum truth, and everyone will think you are an expert.

But what does this all have to do with the OP term of KASC? Do you have any references to show that this is a term used in our industry? After 35 years of doing short circuit studies in the US, maybe I am just out of touch the rest of the electrical world.