The Energy Networks Association, which represents the power networks, said Monday's announcement showed the operators were "broadly improving engagement and services for connecting customers".
"DNOs will review these provisional findings and provide evidence on improved performance," it said, pledging to work with Ofgem.
UK Power Networks, which is made up of London, South-east and East operators, was snapped up by Li in £5.8 billion in 2010 from EDF.
It provides electricity networks for essential transport systems like the London Underground, Heathrow and Stansted airport and the Docklands Light Railway.
Li is worth an estimated $34 billion and owns UK assets including Northumbrian Water.