SoCalEd seeks modification of order to underground Tehachapi project

The developer of the Tehachapi Renewable Transmission Project (TRTP) is asking California regulators to modify details of their July 11 decision directing how the utility should construct a stretch of the project to be placed underground through the city of Chino Hills, Calif. (Docket No. 07-06-031).

The design for the underground portion of the project submitted by developer Southern California Edison (SCE) included voltage control equipment, also referred to as reactive compensation, to mitigate the risk of flashover when one end of the transmission line is open. Specifically, SCE planned to implement shunt reactors for voltage control and to prevent electricity flashover in case one end of the Mira Loma-Vincent 500-kV line should be opened, while the other remained closed, the company said in its filing.

However, in its decision ordering the undergrounding of the 3.5 mile section of the 500-kV project, the California Public Utilities Commission (CPUC) determined that SCE had not justified the cost of, or need for, voltage control, and suggested that an increase in the basic insulation level (BIL) rating could be used instead of voltage control equipment to mitigate the same risk. The CPUC ultimately ordered the utility to study a potential BIL standard rather than authorize the use of voltage control.

SCE disagreed. In its Sept. 9 petition for modification, the company said studying a BIL standard would be an extensive process that “would be time-consuming and significantly delay the in-service date of the TRTP, perhaps as late as 2019.” The utility has repeatedly warned that even under the most favorable circumstances, there was “significant risk” the project would not meet the project’s planned 2015 in-service date if ordered to be placed underground. 

Further, the utility noted, “safety and reliability reasons make it important that the transmission system be operated within its rated voltage.” The highest-rated cross-linked polyethylene (XLPE) cable available is rated at 550-kV, SCE said. Undergrounding the transmission line will cause an increase in the transmission line charging current that could, in some cases, cause the voltage on the system to exceed its 550-kV rating.

“With that in mind, SCE designed [the underground segment] with voltage control equipment to control voltage conditions on the transmission system,” the utility said.

In its petition for modification, SCE asked that the commission remove the requirement for a study of the BIL standard, reinstate the installation of voltage control equipment as the utility had originally proposed, and clarify that the approved amount does not include the cost for voltage control and other necessary activities.

In addition, the utility acknowledged that the installation of voltage control equipment would cause the underground portion of the project to exceed the $224m cap authorized by the CPUC in its July order. However, the utility did not seek an increase in the cap in its petition for modification, asking instead that the commission agree not to make a specific finding of maximum cost for the underground portion of the overall project at this time, but instead to “address the issue when SCE seeks to amend the commission’s maximum prudent cost finding for the overall project.”

Requests seeking additional information from the CPUC regarding a timeline for a decision and next steps were not answered by press time Sept. 10.

SCE is a subsidiary of Edison International (NYSE:EIX).