Substation Battery Diodes

[captainsubstation]

I've got a substation with two battery systems. The client wants to use a battery diode box to prevent backfeeding one battery from the other. The systems are connected via breakers on two separate dc panels. The systems are 125VDC, 150AH. 225A panels. How much would are the diode's and where can I buy them?

 

[ScottyUK]

Diodes in that current range are commodity items from the likes of Westcode, IXYS, Semikron, Powerex, IR, Eupec to name a few. You need to look at the energy let-through of the fuse or breaker protecting the installation because that will determine the diode size, not the current rating. Don't be surprised if you end up with a 1000A diode or bigger if you have a 200A fuse.

You will need to heatsink the diodes because they will dissipate quite a bit of heat, i.e. about 130W at 200A.

 

[catserveng]

I have used the packaged BBS units from SENS with good results,

http://www.sens-usa.com/upload/fmproduct_right_menub/111050_BBS_datasheet_Rev_C.pdf

They also have a nice paper on the subject,

http://www.sens-usa.com/upload/fmproduct_right_menua/Appn_Note_111028A_397.pdf

I have not personally used these but LaMarche has been around a long time and have seen these in some substations recently,

http://www.lamarchemfg.com/userfiles/file/Product_Datasheets/ARBS P25-DSARBS-1.pdf

Hope that helps,

Mike L.

 

[submonkey]

Hi Captain,

Are the two battery systems supposed to be independent
(e.g. for supply to 'A' and 'B' protection systems)?

If so, connecting the batteries together with diodes
is a terrible idea. The diode box will form a common
point of failure.

If your client does insist, be careful of failure due
to reverse transient voltages. Even diodes with high
current ratings can be easily destroyed by fast reverse
transients. Where I work, equipment connected to a station
battery is expected to survive 0.5J (energy limited) fast
impulses of 5 kV peak between isolated circuits as a type
test. Impulse and disturbance testing used to be listed
in the IEC60255 suite. You may want to consider connecting
a transient suppression diode across the high current device.
Transient suppression diodes go by various names 'tranzorb',
'transil diode' etc.

Thanks,
Submonkey.