Battery Sizing profile/philosophy question

[Sn00ze]

While checking a colleague's DC study for batt sizing. We've come to a disagreement.

When it comes to the final duty of the battery – ie: restoration of station service.
Assuming no one can get to the station within the time the batteries run out. so remote restoration.
2 issues:

1) for this particular station through SS1, there is “back feed” from one of the feeders (L4). When considering restoration my sr engineer is considering restoring that feeder's breaker and that’s it. My question here is, is this reliable enough? Should we consider this source to be the path towards restoration? That to me seems unreliable since I would assume there is a transfer trip or maybe anti-islanding scheme going on downstream on the remote end. Maybe the IPP (client) is not producing that day or something unforeseen. My point is, we are depending on a second, or third party to restore our power since we own the upstream line substation/system. That, logically, does not make sense to me. Which brings me to point 2

2) looking at the PDF, the second way to restore the Station service is simply to close the 25Kv tie breaker. to the other TX. but if there was an A/B before or after the Tie breaker, he is saying we don't consider the A/B just the breaker. This does not sound right to me. why would we not consider the Airbreak?

I am just trying to make it make sense to me. If anyone can weigh in on this. I would appreciate it.

thanks

 

[crshears]

Hmmm...my utility would not typically install a scheme like that, because upon loss of normal supply the clock is immediately ticking on the batteries going dead.

With all station service load supplied from one bus as in your drawing, we would typically install an auto transfer scheme that, upon loss of the normal supply, would promptly transfer the station service to the healthy supply; provided the ATS works, end of immediate problem, more or less. [Yeah, yeah, I know, until the normal supply is restored there's a loss of redundancy in the event of the next contingency...]

Alternatively, if using a manual AC transfer scheme is preferred, we would have the station service loads divided onto two busses, each having its own battery and charger, with a DC ATS to provide extended black-out coverage.

Having SS restoration from an LT feeder is nice third option to have in your back pocket just in case, but I agree that for any number of reasons this capability could prove to be unavailable just when you need it most, and my utility would never put its eggs into someone else's basket like that, at least not as the only ready source for SS restoration.

Hope this helps.



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Sn00ze]

Thanks Crshears,

Yeah, our system is not 100% redundant as there is only 1 set of batteries. And it is a manual Transfer Switch so i assume they mean that if no one can get there within 8 hours on the last minute they want to remotely open a breaker that will restore SS.

You have any thoughts as to why they would not consider the A/B for restoring SS? only breaker?S

 

[crshears]

...open a breaker that will restore SS

Now I'm confused; did you mean close?

And so what if nobody can get to the station within eight hours? If I could promptly restore station service by remotely operating some devices while the battery voltage is presumably still somewhat healthy, why would I wait for it to decay until such operations might become problematic?

As to the air break switch, because I am not familiar with the symbol conventions you are using, I cannot tell from your diagram whether or not it is motorized and capable of remote operation...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]