Transmission lines are necessary to allow energy to flow from power plants to major substations. UniSource is committed to strengthening the transmission system, which is the backbone of our electrical grid, and allows customers to power their homes and businesses.

How does UniSource determine where it needs to build new transmission lines?

UniSource analyzes forecasted customer energy needs, energy efficiency programs, distributed generation and other factors to prepare its 10-Year Transmission Plan, which describes how UniSource expects to maintain and improve transmission and other facilities over the next decade to meet the forecasted conditions and third-party interconnection requests.

To prepare the plan, UniSource conducts a review of its existing Bulk Electric System as defined by the standards of the North American Electric Reliability Corporation (NERC). The review helps ensure UniSource can plan for the system's maintenance and improvement in accordance with NERC standards.

The plan describes:

  • Prospective transmission line projects above 115 kilovolts that UniSource intends to initiate over the next decade to maintain reliability and meet customers’ future energy needs.
  • Upgrades necessary to maintain reliable service.
  • System locations where new transmission facilities may be required.

The plan is filed annually with the Arizona Corporation Commission, which must review and approve individual transmission line projects before construction can begin.