Connecticut regulators are making Eversource resubmit its homework on an application for a new natural gas pipeline to a proposed power plant — one Gov. Ned Lamont has complained is an unnecessary addition to the region’s grid. NTE Energy wants to build a 650-megawatt plant in Killingly that would provide power for the equivalent of 500,000 homes, at a projected cost of $500 million. While the Connecticut Siting Council approved the plant’s construction several years ago, the pipeline still requires a thumbs up from the state Public Utilities Regulatory Authority. On Wednesday, PURA denied that request on grounds Eversource filed incomplete information, leaving the door open for the company to fill in the blanks. An NTE spokesperson indicated Friday that the company remains confident that it will get the few remaining approvals required to begin construction, and that the Killingly Energy Center will help fill the gap from the 2024 retirement of a power plant outside Boston.