Currently, there are no relays in the global DIgSILENT Library that support large number of CT inputs out of the box, needed for the busbar differential protection.

The user can adapt one of the available relay types to accommodate for the desired number of CT inputs, by following the steps in this FAQ. The relay chosen for the base here is the Generic 87L relay.

Open the relay and click on the Show Diagram button, then right click on the empty space in the newly opened window and select Show Type Diagram. Here you can copy and paste the CT blocks to suit your needs for inputs. After that you need to create a new block, name it Addition block for example, Class Name is RelLogdip. For input signals you need to write Irct1_A;Iict1_A,Irct1_B;Iict1_B,Irct1_C;Iict1_C,Irct2_A;Iict2_A,Irct2_B;Iict2_B,Irct2_C;Iict2_C... (this was for 2 additional CTs, for more just follow the numbering).
For the output it is I2r_A;I2i_A,I2r_B;I2i_B,I2r_C;I2i_C.
You need to then connect this block to the Measurement block.

Now you need to go back to the previous Diagram page (the one with green background) and double click on the Addition Block, click on the arrow next to the Type. In the Input signals simply copy all the signals you just wrote previously, same as for the output signals (use only commas here, not semicolons).
Go to the Logic page on the left and write the addition logic, where you need to add currents for each phase and each phase's real and imaginary part. Also, make sure you take care of possibility of having differently sized CTs. Something like following:

I2r_A = ct1Invf * 1/rat1 * Irct1_A + ct2Invf * 1/rat2 * Irct2_A,

• ct1Invf is the inversion factor of the first remote CT (takes care of the CT directionality),
• rat1 is the turn ratio of the first remote CT in relation to the Local CT (if the local CT is 1200/1 and the first remote CT is 400/1, then this factor is 3)

Currently, there is a limit of 64 signal inputs to the logic block, which means that a maximum of 10 CTs can be connected to a single logic block. This means that if more than 10 CTs are needed, additional Addition logic blocks are needed. This is also illustrated in the example in the attachment. Special attention needs to be paid to the type definition of the Addition logic blocks, to learn how the addition of signals work.

After that refresh the diagram pages and update Slots from within the relay.