HV Batteries and kAIC Calculation

[Kindle]

If I have 12 battery modules in series for 600VDC nominal and each module has a 4.8kAIC rating with a 147ms OCPD what is the rating for the stack? 57.6kAIC or do we use the 4.8kAIC since each unit has its own OCPD. I would assume that a 147ms trip rate would not interrupt a short circuit.

 

[jim dungar]

A module would not have an AIC rating, as these are reserved for devices that interrupt/clear faults, like breakers and fuses.

The modules could have an SCCR rating expressed in kA which is compared to a source's available short circuit current. Or, the modules are actually a source of short circuit current it is not clear from the OP

You, as a non-manufacturer, typically cannot use the opening time of a protective device to develop the SCCR of equipment.

Series connected circuits are usually additive in voltage, while paralleled circuits are additive in current.

 

[Kindle]

The modules have an SCCR rating of 4.8kA. I get the series parallel stuff for figuring out stringing. These are in series for high voltage but the question is whether the SCCR rating is additive for the 12 modules in series or if their internal OCPD should be considered good enough. I'm concerned about parallel stringing these in a combiner where the combiner has a kAIC rating of 10. I'm wondering how the math works for that rating and expect that it needs to be 65kAIC. Does that make sense? Thanks.

 

[Elect117]

I know the state of charge of the batteries will affect the available fault current, but The voltage of the series connection with the internal impedance summed with the wiring impedance should provide you with the available fault current.

I don't think you add them but it might be higher than 10kA.

Lets say your internal resistance is .002ohms, then the sum would be 12*.002= .024 which makes the fault current Voc / R but since I don't have your Voc, i will use the 600V DC,

600/.024 = 50kA

 

[wwhitney]

I know the state of charge of the batteries will affect the available fault current, but The voltage of the series connection with the internal impedance summed with the wiring impedance should provide you with the available fault current.

If one battery has a (maximum open circuit) voltage of V and an AFC of I, then its internal resistance is presumably R = V/I, yes?

Then if N batteries are in series, their voltage will be N*V, and the series resistance will be N*R. So the AFC would be N*V / N*R = I, i.e. the same as one battery.

Or is it not that simple?

Cheers, Wayne

 

[ron]

I like Wayne's formula. If the batteries are all in series, the resultant fault current will be 4.8kA. Many UPS battery strings have an output breaker rated at 10kAIC for that reason. The UPS itself may have a 65kA SCCR, but that is not related to the battery, it is due to the AC source

 

[winnie]

Or is it not that simple?

Cheers, Wayne

The original question is not clear.

OP asked about AIC rating, which @jim dungar pointed out only applies to the rating of OCPD.

The question changed to SCCR, which applies to the current tolerated by things such as bus bars when power is supplied by something external.

But we are taking batteries. Your answer is IMHO correct for the available short circuit current that a battery can supply.

But I still don't know if that is the original question!

 

[wwhitney]

But I still don't know if that is the original question!

My guess is that the original question is about battery AFC on the DC circuit, and all the instances of "AIC" in the OP should be AFC.

Cheers, Wayne

 

[Elect117]

If one battery has a (maximum open circuit) voltage of V and an AFC of I, then its internal resistance is presumably R = V/I, yes?

Then if N batteries are in series, their voltage will be N*V, and the series resistance will be N*R. So the AFC would be N*V / N*R = I, i.e. the same as one battery.

Or is it not that simple?

Cheers, Wayne

It should be.

I was reading through things online and they agreed that the AFC of one is the AFC for series connected batteries. There were some complicated answers online, but for worst case yes. The math should work out like that. I didn't have the Voc or resistance to verify that they were similar so I included how to calculate it just in case.