[Milsurplus] Brouhaha over Navy ROTHR radar

[Richard]

Interesting problems!  It "almost" makes wish I were still working.  
You've noticed that standard fuses and circuit breakers have a much 
lower rating for DC interruption, if indeed they have a DC rating.  AC 
interruption is greatly aided by the current zeros that occur every 
cycle.  Fuses and circuit breakers are suicide type devices; exceed 
their ratings too much and "kabang."

Richard, AA1P


On 03/30/2017 09:58 PM, Peter Gottlieb wrote:
> I did a lot with lithium ion and now I work with vanadium redox flow 
> batteries.  Depending on the system the voltage range will most 
> commonly be in the 400 to 1100 volt DC range.  4 kV strings are being 
> discussed for larger systems but not much so far.  Short circuit on a 
> string is at least 3 kA and on a system can easily be over 100 kA.  
> When testing we sometimes related a 1 MW fault to a stick of 
> dynamite.  You remember being nearby when it happens.  Most big DC 
> fuses have a max interrupting current of 100 kA and they can explode 
> violently if you exceed that, so yes, the big systems have some 
> challenging protection problems (then there's arc flash).  Oh yes 
> there's design calculations you have to do on busbars because the 
> mutual magnetic field on a fault could break them from their 
> supports.  There are load break contactors to react to less severe 
> problems and the overload "relay" function is programmed into a 
> controller and the current is monitored with current transformers. 
> Also voltage taps so any number of current and voltage vs time 
> parameters can operate that circuit breaker.  So yes a lot of thought 
> goes into over-current and short circuit protection.
>
>
>
> On 3/30/2017 8:15 PM, Richard wrote:
>> Large battery systems are interesting. What kind of batteries are you 
>> using, how many and what voltage?  I see interesting problems with 
>> over-current and short-circuit protection.
>>
>> Richard, AA1P
>>
>>
>> On 03/30/2017 06:31 PM, Peter Gottlieb wrote:
>>> I work in that industry. Wind and solar are both economically wins 
>>> even without any subsidies. Some companies actually don't even file 
>>> for the subsidies as the paperwork is quite onerous. I make large 
>>> battery systems which solve the intermittency problem and yes those 
>>> are now economically feasible as well.  My batteries are made in 1 
>>> MW chunks and run 4-10 hours depending on how much electrolyte is 
>>> used. Typical real systems are 4 to 35 MW.  Investors buy the 
>>> battery systems and sell the services to utilities and there is no 
>>> subsidy from anyone. Ratepayers save money and both utilities and 
>>> investors make their desired returns.
>>>
>>> As with all things electrical and electronic the price keeps 
>>> decreasing and asymptotically approaches material costs.
>>>
>>>
>>