Settings calculation BB protection HV network

[buskos]

Please can you inform based on experience settings Id and Istab of BB protection of type relay siprotec Low impedance numerical protection 7SS/
In the substation when there are different ratio of CT from the smalest 200/1A and bigest ratio 2000/1 in bus coupler there will be problem of saturation in these case for external short circuit

 

[slavag]

Hi.
You must read recommendation of mnf.
Possible few option of calculation.
This difference ie not so important 2000:200A 10:1 , nothing for this protection. You can choice setting about 80% of max load current on the station, or used 2000A, as max load current and put setting on the 1600A. Istab is angel in this protection, if I remember right.

Saturation is not problem, 7SS5 have all algorithms, problem is second SC, in the same time, at zone of BB.

Best Regards.
Slava

 

[buskos]

yes right Istab is angle. The differential current Id>kIstab, k=0.10-0.80. The question is wich factor "k" used for differential current/

 

[slavag]

I will check with guys from Siemens and will back to you.