Chancellor Angela Merkel has been sent to Christian Democrats (CDU), as she steps down as party leader.
"Our liberal values must be defended, internally and externally," she said.
Ms Kramp-Karrenbauer's chief rival in Friday's CDU vote is millionaire corporate lawyer Friedrich Merz.
Ms Kramp-Karrenbauer's chief rival is in Friday's CDU
Ms. Kramp-Karrenbauer's chief rival in Friday's CDU
The third candidate, health minister Jens Spahn, appears to have lost the chance of winning.
Ms. Merkel's speech was punctuated by applause and she got a standing ovation of more than six minutes at the end. CDU delegates at the congress in Hamburg so called "Thanks boss".
Then the conservative party paid tribute to Mrs. Merkel, 64, with a video showing highlights from her 1
In her speech she warned of tough challenges ahead, including climate change, maintaining European unity and coping with Brexit.
She reminded the CDU of other electoral successes last year, avoiding mention of this year's setbacks in state elections, which were heavy blows for her.
"I do not need to be party chairman to remain bound to this party And I'm still chancellor, "she said.
She stood for human dignity, and praised the late US President George Bush Senior and late Chancellor Helmut Kohl for reuniting Germany in 1990. She was at the funeral of George HW Bush on Tuesday.
Speaking of the end of the Cold War, they told the CDU that "at that deciding time he [Mr Bush] trusted Chancellor Kohl.
She expressed "overwhelming gratitude" for having had the role of CDU leader. Who wants Merkel's job?
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Annegret Kramp-Karrenbauer – known as AKK, the Merkel choice
The 56-year-old former prime minister of the state of Saarland was appointed CDU general secretary earlier this year and is the party favorite, polls suggest. Popular in Saarland and Berlin, she has an unpretentious style and reputation for calm analysis, as well as political acumen.
Her greatest strength is her greatest weakness; she is a Merkel loyalist, perceived as someone who wants to replicate much of Chancellor's style and policy.
Friedrich Merz – former top party figure, sidelined by Merkel
The millionaire businessman was a powerful player in the CDU in the early 2000s but left politics when he fell out with the chancellor.
Since then the 63- year-old lawyer – who has strong links to America – has built a career in the private sector and works for US investment firm Blackrock. Minister of Finance Minister Wolfgang Schäuble. He appeals to the more conservative and business-minded wing of the party.
Jens Spahn – young and energetic but unlikely to win
The health minister is ambitious and aged 38
A former banker, he was once described by Mr Schäuble as' one of the great hopes for the future of our party ".
But Mr Spahn has ruffled feathers at the party and in the cabinet. Sharply conservative, Catholic and gay, he is a divisive figure for many.