Adds deal size benchmark in paragraph 3, German government comment in paragraph 13, details on talks with Germany in paragraph 14, advising banks in paragraph 18

By Bart H. Meijer, Andres Gonzalez and Christoph Steitz

THE HAGUE/LONDON/FRANKFURT, Sept 24 (Reuters) - The Dutch government is selling 46% of power grid operator TenneT's German unit to an investor consortium for up to 9.5 billion euros ($11.3 billion), it said, kicking off the separation from a business it has long been trying to divest.

The sale to a consortium of Dutch pension fund manager APG, Singapore's sovereign wealth fund GIC and Norges Bank Investment Management (NBIM) NOCB.UL, operator of the world's No. 1 sovereign wealth fund, comes as funding needs for power lines soar across the continent, forcing owners to seek new capital.

Under the agreement, the consortium will take a stake of 46% in TenneT Germany via a private placement of new shares by the Dutch government, in what marks Europe's third-largest deal this year according to LSEG data.

The deal follows an unsuccessful attempt to sell TenneT Germany to the German government last year.

With more than 14,000 kilometres (8,699 miles) of power lines, TenneT Germany is the country's biggest operator of high-voltage transmission grids. Parent TenneT <IPO-TTH.A> is also the sole grid operator in the Netherlands.

APG'S STAKE IN TENNET GERMANY TO BE 11%

The consortium's investment will provide TenneT Germany with 8.5 billion euros it needs to sustain its credit rating and an extra buffer to limit risks for the Dutch state, the Dutch finance ministry said.

APG said it would acquire about an 11% stake in TenneT Germany, while NBIM said it has a 21.8% stake, which would leave GIC with the balance of 46%.

APG CEO Ronald Wuijster told Reuters it had been working on the deal for more than a year and many investments were needed in European infrastructure.

"We need to work very hard to make our infrastructure better and energy transition is a very important element of that," he said.

"This asset offers us a relatively secure, stable cash flow that is also of great interest for the members of the pension fund," he said, adding that APG sees Germany as a stable and reliable country.

Wuijster said the fund was looking to get a board position.

GERMANY EXPECTED TO BUY MINORITY STAKE

Germany continues to consider a minority stake in TenneT Germany, Dutch finance minister Eelco Heinen said, after such plans fell apart last year under the previous government.

A spokesperson for Germany's economy ministry confirmed this.

TenneT said it intended to enter talks with German state-owned lender KfW KFW.UL over the matter, with more clarity on possible German investments expected before the end of the year.

Germany, which already holds minority participation in high-voltage power grids TransnetBW EBKG.DE and 50Hertz ELI.BR, has previously expressed interest in buying a 25% stake in TenneT Germany.

Sources told Reuters in May that a sale of new shares in TenneT Germany could raise up to 12 billion euros, either via a private placement or an initial public offering in what could become one of Europe's biggest deals this year.

In a sign of how big funding needs for grid expansion are, TenneT Germany's smaller peer Amprion this month secured 3.2 billion euros from Apollo Global Management APO.N in a deal with RWE RWEG.DE.

ABN Amro, Lazard and Deutsche Bank served as advisors to TenneT, while the investor consortium was advised by RBC Capital Markets.

($1 = 0.8494 euros)

(Reporting by Bart Meijer, Andres Gonzalez and Christoph Steitz; Additional reporting by Anousha Sakoui, Holger Hansen and Tom Kaeckenhoff; Editing by Bernadette Baum and Ed Osmond)

((christoph.steitz@thomsonreuters.com; +49 30 220 133 647;))