Texas grid operator sees increased costs, benefits from 765-kV transmission

Incorporating 765-kV transmission in the Electric Reliability Council of Texas' existing grid by 2030 could added $2.2 billion to what would otherwise be a $30.8 billion transmission expansion plan, stakeholders were told Jan. 27, but 765-kV lines could enhance stability and cut annual costs by $257 million by 2039.

ERCOT's economic benefit analysis focused on the years 2034 and 2039 in comparing the 765-kV plan with the grid's existing 2024 Regional transmission Expansion Plan, which has transmission elements maximizing at 345 kV.

"The key takeaway from the economic study is the 765-kV plan has demonstrated a more consistent benefit through two years, 2034 and 2039, compared to this 345-kV plan," said Pengwei Du, ERCOT supervisor of economic analysis and long-term planning studies. "Basically, when we compare between the 345-kV and 765-kV plan, the 765-kV plan can produce $28 million more production cost savings and $229 million more savings for consumers. The congestion cost for the 765-kV plan is about $172 million less, compared to the $345-kV plan."

The 2024 Regional Transmission Expansion Plan identified needs for 345-kV transmission lines at the 2026-2030 time horizon as load is expected to jump from an existing unofficial peakload of 85.6 GW to about 150 GW, driven by large load interconnections for data centers, plus oil-and-gas exploration and production in West Texas' Permian Basin.

West Texas needs seen

But when the Public Utility Commission of Texas approved the Permian Basin Reliability Plan Sept. 26, it directed its staff to work with ERCOT on whether that plan should incorporate 765-kV transmission lines. The result was a report issued Jan. 24 comparing the 2024 RTP with a Texas 765-kV Strategic Expansion Plan, which was posted to the ERCOT Extra-High Voltage Workshop web page.

The comparison concludes that incorporating 765-kV lines could add $820 million to the Permian Basin Reliability Plan projects and $1.45 billion to the RTP projects outside the PBRP, but save about $50 million in reactive support system cost. Thus, the 765-kV STEP could cost almost $33 million, compared with the RTP's $30.8 billion.

The 765-kV plan would also require acquiring 3,441 miles of new right of way, compared with the 345-kV plan's 3,007 miles, ERCOT said.

Transfer, stability benefits seen

But ERCOT also compared the 765-kV STEP's relative system transfer capability and stability benefits relative to ERCOT's existing 345-kV RTP.

"Both 345-kV and 765 kV options improved the incremental transfer capability a lot," said Sun Wook Kang, manager of system dynamic studies. "However, we observed that the 765-kV option is a lot better compared to the 345k-kV option, particularly for transfers from the Far West to the major load centers. The 765-kV option provides an additional 600 to 3,000 megawatts more transfer capability than the 45-kV option."

Both plans enhance grid stability, Kang said.

"However, based on the result, we believe that the 765-kV option provides a lot better flexibility in terms of transfers and stability limits," he said. "In conclusion, the 765-kV option appears to better accommodate future load and generation."

Julia Wagner, an engineering specialist in the PUC's market analysis division, said the PUC plans a workshop on the 765-kV option for March 7.

ERCOT HV, EHV construction cost estimates
($ billion)	345-kV plan	765-kV plan
Permian Basin import paths	7.69	9.06
Permian Basin incremental local upgrades	1.23	0.69
Permian Basin common local upgrades	4.02	4.02
RTP 765-kV new lines, substations, transformers	-	8.09
RTP 345-kV new lines, upgrades	10.31	5.35
RTP 138-kV new lines, upgrades	4.04	3.01
RTP 69-to-138-kV line conversions	1.04	0.54
RTP dynamic reactive support	1.44	1.44
RTP static reactive support	0.14	0.09
RTP new 345/138-kV substations	0.12	0.10
RTP new 345/138-kV transformers	0.72	0.60
TOTAL	30.75	32.99
Notes:
HV is high voltage. EHV is extra high voltage.
RTP is regional transmission plan without the Permian Basin Reliability Plan.
Source: ERCOT