Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 79

Based on the foregoing discussion, the plant distribution transformer selection will be as follows:

 Grid transformers (2): 230 to 13.8 kV, YNd1, 30/40 MVA, ONAN/ONAF, oil Immersed, solidly grounded.

 Process plant transformers (2): 13.2 to 4.16 kV, Dyn11, 12/15 MVA, ONAN/ONAF, oil immersed, 100 A grounding resistor.Figure 2.13 Plant phasing diagram.

 Plant transformers (2): 4.16 kV to 480 V, Dyn11, 2/3 MVA, ONAN/ ONAF, dry type, solidly grounded.

 Plant transformers (7): 13.2 kV to 480 V, Dyn11, 1/1.5 MVA,

ONAN/ONAF, dry type, solidly grounded.

Note Figure 2.13, we have selected lagging (−30°) winding configuration for the grid transformers and leading (30°) for the plant transformers. This will make the secondary voltage (4.16 kV) of the second‐level plant transformers in phase with the 230 kV grid voltage.

Furthermore, note that all the 480 V buses are not in phase. Those fed from the 13.8 kV buses are 30° apart from those fed from the 4.16 kV buses: for instance T41 and T31, respectively.

It is important to note that the 480 V buses from those transformers cannot be interconnected together. On our project in this book, this type of phasing may not be important, as the plant power distribution system is of radial nature without a need for synchronizing.

In other larger plants, where there is a requirement for synchronizing, it is essential to establish proper transformer winding configurations to suit. Engineers must learn how to assign correct transformer winding configuration and phasing orientation for the transformers on the electrical diagrams.