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This arrangement provides a variation of providing future expansion as a full ring bus arrangement. The substation is laid out as 2 x 1.5 CB Diameters with "bus connected" transformers. Initial expansion is by adding the indicated equipment and yet further expansion is achieved with additional 1.5 CB Diameters as per the previous system, or making the ring bigger.
An issue for the expansion of this arrangement is the number TF Differential CT inputs available on the relay - the CTs cannot be paralleled as through currents between the CTs may cause one CT to saturate which would be seen as a false differential current causing TF Diff operation. The solution to this is to rearrange into a traditional 1.5 CB arrangement or a traditional ring bus connecting all feeds.
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