RICHFIELD — Rocky Mountain Power began construction Wednesday on a new high-voltage transmission line to serve customers throughout six Western states.

Gov. Gary Herbert joined company officials for the groundbreaking on the 160-mile Sigurd to Red Butte transmission line, just as the company announced completion of its 100-mile Mona to Oquirrh transmission line that will begin serving customers May 17. Both projects are located in Utah.

Investment in new transmission lines is essential in the West for the reliability and security of the electric system and to improve access to both conventional and renewable generation resources, said Natalie Hocken, senior vice president of transmission and system operations for PacifiCorp, which owns Rocky Mountain Power.

The first segment of the company’s Energy Gateway transmission expansion project, a 135-mile segment from Idaho to Utah, has been serving customers since 2010. Other segments continue in varied stages of siting and permitting and will be completed in a phased approach to respond to customers’ needs.

The 345-kilovolt Sigurd to Red Butte transmission line will stretch from the Sigurd substation near Richfield to the expanded Red Butte substation in Washington County. It is expected to begin serving customers in summer 2015.

The recently completed Mona to Oquirrh transmission line includes a new single-circuit 500/345-kilovolt line from the Clover substation in Juab County to the site of the future Limber substation in Tooele County. From there, it continues as a double-circuit, 345-kilovolt line to the existing Oquirrh substation in West Jordan.