Bulgaria's largest wind farm - the 156 MW Saint Nikola, operated by AES Geo Energy - has extended the duration of its unplanned outage to January 29 from January 21, the Independent Bulgarian Energy Exchange (IBEX) said.A problem with the distribution system left the plant with 56 MW of unavailable capacity on December 28, IBEX said in a notice.The Saint Nikola wind farm located near the town of Kavarna, on the Black Sea coast consists of 52 turbines of 3 MW each. It was built in 2009 and commenced operations in 2010.The total investment in the project was 270 million euro ($332.2 million), of which 198 million euro was provided by a bank consortium including the European Bank for Reconstruction and Development, the International Financial Corporation and UniCredit Market & Investment Banking.AES Geo Energy is a joint venture of New York-listed power corporation AES, which holds a majority stake, and the German Geo Power company.AES also operates the 600 MW coal-fired power plant AES Galabovo, located in southern Bulgaria.