ABB has been in talks with Hitachi, Mitsubishi Electric Corp. and State Grid of China to sell all or part of the business, which makes power transformers and electricity substations, Reuters reported in November.
"ABB confirms that it is currently in discussions with Hitachi to expand and re-define the existing strategic power grid partnership between the two companies announced in December 2014," the Swiss company said in a statement.
Hitachi said in a statement it was discussing the power business with ABB but nothing had been decided.
ABB, which also makes industrial robots, wants to offload its least profitable division, allowing it to focus on areas such as automation, while Hitachi is keen to expand abroad.
"There can be no certainty that any transaction will occur, or as to the timing, structure or terms of any transaction," ABB said. Its shares rose as much as 4.3 percent and were up 4 percent at 1515 GMT.
One source familiar with the situation valued the power grid business — in which sources have said ABB could keep a stake via a joint venture — at between $10 billion and $12 billion.
Japan's Nikkei newspaper reported the companies were nearing a deal in which Hitachi would pay between 600 billion and 800 billion yen ($5.29 billion to $7.05 billion) for an initial 50 percent stake in the business.
One source said the main sticking points were valuation and the shares that ABB and Hitachi would take in a joint venture. ABB expected Hitachi to take a clear majority, while Hitachi would prefer a more balanced structure, this source said, adding a deal could still emerge by the December 25 Christmas holiday.
Hitachi's board confirmed a plan to go ahead with the deal, which would be the Japanese industrial conglomerate's largest-ever acquisition, the Nikkei reported.
ABB's power grid business employs 36,000 people and had sales of $10.4 billion last year. It had an operating profit margin of 10.0 percent in the third quarter, down 60 basis points from a year earlier.
The decision to sell it marks a U-turn for ABB Chief Executive Ulrich Spiesshofer, who decided to keep the business two years ago despite calls from some shareholders to sell.
Power Grids' weak performance has weighed on ABB's stock price, although the unit has fared better in the last two years.
ABB could return the sale proceeds to shareholders through a new share buyback program and also accelerate acquisitions in automation.