Results of optimal power flow

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Can someone help me understand the results of the optimal power flow, specifically the Summary Table for the Tap Changing Transformers?

The tap changing transformers are held at fixed position in the OPF settings but I'm not sure why the voltage at each bus changes

Summary Table for Tap Changing Transformers:

From Bus kV Area Zone Voltage Ratio Minimum MW Flow Sensitivity To Bus kV Area Zone Voltage Change Maximum MV Flow Tap Volt

652 BUS 652 1602 1.02675 1.02500 F 0.90000 -3.910 1.00817 659 BUS 659 699 0.99487 1.10000 0.724

655 BUS 652 1678 1.04511 1.00000 F 0.90000 1.870 -79.80223 700 BUS 652 1678 1.04999u 1.10000 -0.964 -76.70278