Busbar protection - CT core rule

[Ivan_Puškaš_EC]

Hi everyone,

I have a question regarding the busbar protection in general, but with main focus on SE products Micom P740 and P746.

@HenriGRASSET maybe you can help on this.

I will make a simple question but if someone need to elaborate please do it.

Can we connect busbar protection relay current inputs in series current circuits with main protection relay (using only one CT core for main protection relay and busbar protection relay)? Or we need a separate protection CT core that will be just for busbar relay? Is there any rule about this?

BR

[HenriGRASSET · Accepted solution]

Hello Ivan,

This is one of the benefits of low power protection schemes.

As the relays' CT input burden is very low, we can connect them in series to the same CT secondary output.

Of course, the CT requirements must be met for all applications using this CT.

Regards

[HenriGRASSET]

Hello,

As written below, you can connect in series low impedance relays to the same CTs.

MiCOM relays, as well as, P3 and P5 are low impedance IEDs.

Thus, because P746 and P740 are from the MiCOM range they can be connected in series with any other low impedance relay to the same CTs.

Regards

[Jefferson_Leite]

You can connect tho relays in series using the same secondary, but this is not recommended. 

To get more protection system reliability, is recommended to use different CT cores.

Regards,

Jefferson Leite