Evolution of 110 kV Substation Power Supply Side Bus Connection Configurations

Early 110 kV substations typically adopted the "internal bus connection" configuration on the power supply side, where the power source commonly used the "internal bridge connection" method. This was often observed in certain 220 kV substations supplying 110 kV buses from different transformers in a "same-direction dual-power" arrangement. This setup involved two transformers, with the 10 kV side using a single busbar with sectionalized connection.

Advantages included simple wiring, convenient operation, straightforward automatic transfer switching, and only three switches required on the power side for the two transformers. Additionally, the power-side busbar did not require separate protection—being covered within the transformer differential protection zone—and the overall investment was lower. However, limitations existed: each busbar could accommodate only one transformer, constraining the growth of the 10 kV load capacity. Moreover, when one transformer was in operation, half of the substation had to be de-energized, creating a risk of complete station blackout if the other half experienced equipment failure.

To enhance station capacity and improve supply reliability, an intermediate-stage solution for 110 kV substations adopted the "expanded internal bus connection" method, with the power side mainly using the "expanded bridge connection." This configuration involved three transformers. Power was supplied through two "side busbars" from the same-direction dual-power 110 kV buses of a single 220 kV substation, and one "middle busbar" from a different-direction single-power supply of another 220 kV substation.

The 10 kV side continued to use a single sectionalized busbar, ideally segmenting the middle transformer’s 10 kV output into sections A and B. This approach increased the number of 10 kV outgoing circuits and allowed load redistribution from the middle transformer to the other two in case of outage. However, it introduced greater complexity in operation and automatic switching, along with higher investment.

With urban expansion, increasing land scarcity, and surging electricity demand, there arose a pressing need to further boost substation capacity and reliability. The current design for 110 kV substations primarily employs a single sectionalized busbar on the power side, connecting four transformers—each linked to separate buses, with the two middle transformers cross-connected to the upstream power source. On the 10 kV side, an A/B segmented configuration is used, forming an eight-segment "ring connection" powered by the four transformers.

This design increases the number of 10 kV outgoing circuits and enhances supply reliability. The cross-connection of the two middle transformers to the upstream source ensures uninterrupted power supply to the eight-segment 10 kV busbar even if one 110 kV busbar is de-energized. Drawbacks include the need for dedicated protection on the 110 kV busbar, high initial investment, and increased operational complexity.