The chargesheet accuses former minister and CPI-M state secretary Pinarayi Vijayan and 10 others, including some officials, of receiving kickbacks for allotting a contract to a Canadian firm in 1997.
The charges are expected to be filed in the Kerala High Court after the CBI gets a nod from state governor, a CBI official said on Wednesday.
"The rules are very clear. The CBI has to get a sanction of the governor if the accused is or was a minister and likewise if there are government officials involved, the chief secretary has to be informed," said the official, who wished not to be named.
The investigating agency on Wednesday submitted in the high court a progress report about the case. A report was also filed in a CBI court in Kochi.
The court had in September last year given four months to the CBI to complete the probe.
The Comptroller and Auditor General of India (CAG) had found irregularities in the contract with SNC Lavalin of Canada for the renovation and modernisation of the Pallivassal, Chengulam and Panniyar hydro-electric projects in Idukki district.
CPI-M state secretary Pinarayi Vijayan, as electricity minister in 1997, had awarded the contract to SNC Lavlin.
The high court in January 2007 ordered a CBI probe into the case.
The CBI had questioned Vijayan early this year and a team had visited Canada to get more details into the case.