Battery Sizing for Disconnect Switches

[kvramesh]

Hi, I am working on a battery sizing for a substation. I have a whole lot of outdoor SF6 breakers and gang operated disconnect switches. The control power for breakers and switches is 125VDC. I consider the breaker sequence operation for peak load calcuations and all the relays associated with breakers for continuous and peak operation (i.e. 1 minute operation per IEEE485)

My question is with regards to the switches, these switches are killers, I mean they take about 15amp to operate. Infact I do not need them to operate on fault, they will be operated for maintnenace as required. So, considering their use should I include them either in my continuous or peak load calculations? Either way my battery size will go up...

any advise or discussion is really appreciated

thanks

 

[rcwilson]

I would include the disconnects' motor operators in a load profile, but not the maximum "first minute" peak load calculation. The first minute and the last minute loading usually determine the battery bank size.

The first minute is when all of the breakers and lockout relays trip and the breaker's springs are recharged while the continuous loads still operate. The last minute is the critical time when the battery has to have enough power left to operate the relays and controls and close the breakers to return station service power. (Per IEEE standard sizing criteria, all currents are assumed to last 1 minute.)

Usually the disconnect switches will not operate at the beginning and end of the outage but will probably operate sometime during the outage.

Automatic controls might use the disconnects to isolate or reconfigure the substation during the outage or during the critical first or last minute. If that is the case, size the battery accordingly.

 

[brian john]

IEEE has a Standard for sizing batteries in Substations, I cannot quote the Standard number off the top of my head, but can post on Friday when I get in my shop.

Might be IEEE 485