If you have more than two Plant, you can used quota arrangement to distribute the percentage of internal purchasing accordingly.

Plant A purchase from Plant B   Plant C
MM02 - Procurement type           F
               Special procurement      Blank
               Quota arr.usage              3

Plant B and Plant C
MM02 - Procurement type           F
              Special procurement      Blank
               Quota arr.usage             Blank

OMD9 - Maintain Special Procurement

Plnt      SP Type   Special Procurement type description
Plant A   Plant B   Procure from Plant B
Plant A   Plant C   Procure from Plant C

MEQ1 - Quota Arrangement for Plant A

If you press Enter, the start date comes automatically.  Multiple period can be maintained.

Click Item Overview for Overview of Quota items

P    S     PPl.       Quota
F    U    Plant B      30
F    U    Plant C      70

P - Procurement type
S - Special Procurement

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